© TROUL - USNEE REPORT © «NOsum55 PROBLEM NEL 2A5 Dre 7 JULY i948 if :; | DOCUMENT | \ COLLECTION yy oe SRW ee a : final report some oceanographic observations on operation HIGHJUMP ROBERT S. DIETZ RESEARCH DEPARTMENT acknowledgments The data for this report were collected by Robert S. Dietz, of the Oceanography Section of the U. S. Navy Electronics Laboratory, with the assistance of Herbert J. Mann, of the Scripps Institution of Oceanography, both of whom, as Navy Electronics Laboratory representatives, accompanied ships of the Western Task Group of Task Force 68 on Operation HIGHJUMP. Personnel of the USS HENDERSON and the USS CACOPAN furnished assistance in the collection of the oceanographic data. The report was prepared by R.S. Dietz with assistance from and supervision by E. C. LaFond and with assistance from D. W. Pritchard. The work of Luis Capurro, who made a study of the heat content and temperature distribution in antarctic water, and the work of Estil Hamill, who investigated internal waves, are adapted for and included in this report. The bathythermograph records were processed by the Bathythermograph Pro- cessing Section at the Scripps Institution of Oceanography. Salinity determinations and the analysis of a lake water sample from Antarctica were made under the direction of N. M. Rakestraw of Scripps Institution of Oceanography. D. M. Updegraff and Brian Boden of the same Institution furnished, respectively, bacteriological analyses of sea floor sediments and information on the antarctic phytoplankton. MBL/WHO! IMM 0 0301 O0?236b 2 MONA abstract Two civilian representatives of the U.S. Navy Electronics Laboratory accompanied the Western Task Group of the U.S. Navy Antarctic Development Project of 1947 to obtain oceanographic data. Data were necessarily collected more or less at random and the areas surveyed were not always critical; even so, much useful information was obtained about regions that heretofore have been little known. This report concerns some of the results as of 31 December 1947. The geological and biological, as well as oceanographic, observa- tions made on Operation HIGHJUMP are discussed. Much of the data are being worked up separately and will be reported elsewhere. Oceanographic observations included temperature, salini- ty, and transparency measurements. The temperature data provided information concerning the thermal structure and depth of the surface layers in the antarctic, the sea surface temperatures, the Antarctic Convergence, and internal waves. The temperature and salinity data were used to determine the temperature-salinity relation in the antarctic. The geo- logical observations included data concerning the antarctic sea floor sediments, the sea floor features, and the ice-free areas in Antarctica. The biological observations included data concerning marine growth, natural slicks, and the deep scattering layers, in the Pacific and the Antarctic Oceans. table of contents INTRODUCTION .... PHYSICAL OCEANOGRAPHIC OBSERVATIONS IN THE ANTARCTIC... Thermal Structure of the Surface Layers. ... SealSurfaces@lemperatune sii) ls)tel cliell Cp = OM where: Q, = Radiation absorbed in the ocean from the sun and sky. This term represents both the radiation from the sun incident on a unit horizontal surface and the diffuse radiation from the sky, less the percentage of the two that is reflected. This term is a function of the altitude of the sun, the cloudi- ness, and the transparency of the atmosphere. 17 18 Q, = Back radiation from the sea surface. This term represents the long-wave radiation returned to the atmosphere from the surface of the ocean and is a function of the tempera- ture of sea surface, the cloudiness, and the humidity of the air over the ocean. Q; = Amount of heat used locally to melt any ice that may be present. This term may be negative and hence repre- sent the heat given off when sea water is frozen. Q, = Heat lost by evaporation from the sea surface. This term may also include the heat gained by condensation of water on the sea surface, though this effect is usually small. Q, = Convection of sensible heat from the sea to the atmosphere. Q,, = Net amount of heat which by currents or processes of mixing is brought into the region. Q, = Amount of heat used locally to increase the tempera- ture of the sea water. The bathythermograms provide the necessary data for the computation of the term Q>. Since this term represents the heat used in changing the temperature of the water, it is necessary to determine the change in the relative heat content of the surface layers. The evaluation of this term Q, involves the averaging of the temperatures from bathythermograms for each month for depths down to 450 feet. The resulting average temperature-depth curve for each month is shown in figure 11. —— Se FIGURE 11. Average vertical temperature structure observed during December (A), January (B), and February (C), between 66.5° and 68.0°S and 105.0° and 112.0° W (see plot of area). The average monthly curves, since they are combinations of a large number of bathythermograms taken at different times and at slightly different geographical positions, will be somewhat smoothed. This results in the minimizing of certain characteristic features such as the sharpness of the thermocline. However, these curves give a reasonable re- presentation of the relative heat content in the surface layers. Qualitative investigations lead to the conclusion that within the antarctic region the heating of the surface layers does not extend below 200 feet. Changes in the thermal struc- ture below this depth must be related to advection. In view of this fact the relative heat contents of each of the average thermal structures have been computed only for the upper 200 feet, using the temperature at 200 feet as the reference temperature. The computation of the relative heat content involved the numerical integration of the equation: 200 Hoo0 F % Pp x Bt dz 2 = conversion factor involving conversion of feet to cm. and of °F to °C. p = average density of the column of sea water. fo) tt specific heat of sea water. At, = ty-to00; i.e., the temperature at the depth, d, minus the temperature at 200 feet. z = the vertical variable, positive downwards. The resulting relative heat content for each of the three months is shown in table 2. Table 2. Relative heat content. * Relative Heat Content to 200 Feet (gm.-cal./cm.?) December January February 19 20 The difference between these quantities represents the amount of heat that has gone into increasing the temperature. Since the terms in the heat budget are usually expressed in gram-calories per square centimeter per minute, 0g may be found by dividing the differences between two values of heat content by the number of minutes between the middle of each of the two periods over which the heat content was deter- mined. The amount of heat which has been used to increase the temperature in the interval from 25 to 31 December and 1 to 31 January and in the interval between this latter period and 1 to 6 February, are presented in table 3, together with the corresponding values ofQ,. The central day in each period is used to represent the period. Table 3. Heat used to raise the temperature in the surface layers. Time Interval Change in Heat Content Qa j (gm.-cal./cm.7) (gm.-cal./cm.?/min.) December 28 to January 16 January 16 to February 3 The equation for the heat budget may be simplified some- what since considerations of the processes which maintain evaporation and heat conduction lead to the development of an expression for the ratio of the convection of sensible heat to the heat lost by evaporation. This ratio, R = Q,/0. , is called the Bowen ratio and may be determined from the ob- servations of the moisture and temperature gradients over the sea. In this case the equation becomes: CON reat GMO oO 03), During the period from 28 December to 16 January the term 0-0, is of the order of magnitude of 0.2 gm.-cal./cm.4 per minute. During this same period the Bowen ratio was calculated to have a value close to minus one.* This means that the heat lost by evaporation is nearly balanced by the heat gained through conduction and hence the termo,(1 + R) is very small. It is thus seen that the term Q,-0; must ac- count for the excess of incoming radiation, since, as seen from table 3, Q,is equal to 0.028 gm.-cal./em.“ per minute and hence is only about 1/7 as large as the EOmnIanAQ. — Oj, The term Q,is very difficult to estimate and in most cases in the ocean even impossible. It is generally con- sidered small; however, in the Antarctic Ocean, this assump- tion may not be valid since the shifting of the Antarctic Con- vergence, as described elsewhere in this report, may displace the surface waters by water of very different character. However, since the melting of ice is known to be important during the December-January period, it may be assumed that a considerable portion of the excess radiation goes into melting the ice. During the period from 16 January to 3 February, the heat balance is much more difficult to explain. During this period the incoming radiation decreases Be tas and the terms Q-0,, and 0, (0.195 gm.-cal./cm.@ per minute) are of the same order of magnitude. Investigation of the Bowen ratio indicates that during this period more heat was lost by evapo- ration than was gained by conduction; in fact, during the last part of the interval, the conduction term also led to a loss of heat from the surface layers. Since the term Q, may be neg- lected during this period, it appears that the advection term, 0,» must have brought sufficient heat into the area to balance the heat budget. These considerations may be applied to a discussion of the seasonal change in the thermal structure as indicated by the average curves shown in figure 11, During winter the entire area must be covered by a layer of cold isothermal water. The average curve for late December shows onlya *For details on the computation of the term Q,-Q,% and the Bowen ratio, see SIO Oceanographic Report No. 10, 1947. 21 22 slight negative gradient in the upper 100 feet, below which nearly isothermal conditions are found to nearly 450 feet. Thus only a small amount of heat has been used to raise the temperature of the surface layers. During January the surface temperature has increased and consequently the negative gradient is stronger. Heating does not extend below 125 feet; however it is sufficiently strong to resist the formation of an isothermal layer. Between mid-January and early February, considerable change has taken place. By February the surface has been warmed nearly 1 degree C. and the processes leading to mixing (wind stirring and evaporation) have resulted ina nearly isothermal layer to 200 feet. Below this a negative gradient extends to the cold, winter-cooled layer at 400 feet. The changes in the thermal structure below 200 feet may be related to rising of the antarctic circumpolar water nearer the surface, thus bringing the transition layer of positive gradient between 400 and 700 feet, as shown in the average curve for February. SEA SURFACE TEMPERATURES General. Sea surface temperature observations were available in sufficient number to construct isotherms com- pletely around the Antarctic Continent. However, it was necessary to make interpolations in some regions. Surface temperature data analyzed in this report comprise obser- vations made by all three task groups on Operation HIGHJUMP. Although a few of the temperatures were obtained as far south as 78°52'S , by far the greater number of the obser- vations were taken between 60°S and 70°S. Observations extended over the period from December to March. The majority of the observations, however, were made during the months of January and February (see table 4). Table 4. Monthly distribution of sea surface temperature observations. - Number of Observations Per. Cent of Total December 1946 January 1947 February 1947 March 1947 FIGURE 12. Sea surface isotherms. Analysis of Data. The available sea surface temperatures were, for the most part, averaged for each l-degree quad- rangle of latitude and longitude. In the areas where the hori- zontal temperature gradients were small, the sea surface temperatures were averaged for 5-degree quadrangles. The main objectives were to determine the geographical dis- tribution of surface temperature and to locate the Antarctic Convergence. Therefore, in areas where the gradients were large, the sea surface temperatures were not averaged, as the averaging process might have eliminated the large gradi- ents indicative of the convergence. The average values were then plotted on a chart showing the bottom configuration so the influence of the topography on the distribution of the isotherms could be studied. Whole-degree isotherms were drawn, using the above- described temperature plots. Sufficient data were available to construct isotherms from only -1 degree C. to 3 degrees C. (see fig. 12). In areas where data were lacking from Operation HIGHJUMP (see fig. 2),the location of the isotherms was determined by using data from the Discovery Reports! and then considering the probable effect of the bottom topography on the pattern of the isotherms. 50° ) iy Ca Tl 60° LW atl Ae ‘IW Sar Ti iy ASK ean 5 z if, i: As 70 80° 90° 100° : NG \ My se Dai: 110° i S My eas Ss 120° xz <2 2 ZEEE = i Ts /- zz = 2 KA f= iN} \y ox He TTI INN i as (is Is IY \ \ ( UCL OC ae 140° 150° 160° 170° 180 170 160° 150° FE ES 24 The general trend of the sea surface isotherms obtained from Operation HIGHJUMP data is similar to the trend of those previously obtained from the Discovery Expedition. However, the HIGHJUMP data indicate an over-all southward displacement of the isotherms. This southward displacement is shown in table 5 where the position of the zero-degree C. isotherm on Operation HIGHJUMP (1946-47) is compared to its position as shown in the Discovery Reports. Table 5. Comparison of position of the zero-degree Centigrade iso- therm as observed on the Discovery and HIGHJUMP cruises. Longitude Latitude Latitude Difference (Discovery) (HIGHJUMP) (miles) 67° S The remaining isotherms (-1 to 3 degrees C.) are displaced much the same.as the zero-degree C. isotherm in both di- rection and amount. As can be seen from the table there is a large variation in the location of the zero-degree C. iso- therm except at the zero-degree meridian. This general southern displacement of isotherms might be explained if, in the year of the HIGHJUMP observations, there was an unusually strong thermohaline circulation toward the south, associated with a weak wind circulation in the antarctic region which did not offset the south-flowing thermo- haline current. Thermohaline circulations are related to the heating in low latitudes and cooling in high latitudes. Thus the greater abundance of ice encountered on HIGHJUMP than in previous years indicated excessive cooling in the region and suggests a stronger thermohaline circulation. As stated previously, the sea surface temperature chart (see fig. 12) is based on observations made during four differ- ent months. In some regions, observations were repeated so that the seasonal change could be investigated. A summary of the month-to-month changes observed are shown in table 6. “Table 6. Average sea surface temperature changes. Time Interval Temperature Change Number of Observations : (degrees C.) December to January January to February February to March December to February ANTARCTIC CONVERGENCE General. Proceeding southward from the region of warm surface water in the low latitudes, one first encounters gradual decreasing temperatures. However, ina region between 55°S and 65°9S, the temperature decreases markedly within a short distance. Beyond this region of strong horizontal temperature gradients, the surface temperatures remain rather constant and near the freezing point. This boundary is a region where part of the cold antarctic surface water, brought northward by the transverse circulation created by the westerly wind system, sinks below the warmer water transported southward by the thermohaline circulation which dominates in the subantarctic region. This area of sinking is called the Antarctic Convergence. As indicated in the section, ‘Icebergs and Sea Ice,’’ the convergence was quite apparent as an abrupt water-mass 25 26 FIGURE 13. sea surface temperature section across Schematic representation of boundary. Soon after crossing it, observers on the HENDER- SON encountered their first group of icebergs. As the con- vergence was crossed, the water changed in color from blue to gray, new types of birds appeared, and the sky cleared. These changes closely followed the drop in temperature which was over 2.5 degrees C. in about 20 miles. Location of the Convergence. As an aid in locating the Antarctic Convergence, as well as presenting the complexities of the antarctic thermal structure, horizontal temperature plots and vertical cross sections of temperature versus depth have been constructed for five locations as shown on the chart in figure 12. They are numbered A, B, C-1, C-2Z, and C-3 for reference. Both the plots and cross sections are based ona series of bathythermograph observations taken by individual ships on nearly straight runs across the convergence. Three of the sections, C-1, C-2, and C-3 were taken in the same lo- cality and serve to indicate the seasonal trends in the location of the convergence. These features are discussed more fully below. Horizontal Surface Temperature Sections. Ideally, if the surface temperatures were plotted against latitude, with temperature as the vertical coordinate and latitude as the horizontal coordinate, the Antarctic Convergence should appear on sucha plot as a sharp break in the slope of the surface temperature curve. A schematic presentation of such a graph under ideal conditions is shown in figure 13. 55°S Latitude 70°S 7 ANTARCTIC CONVERGENCE Surface Temperature (degrees Centigrade) the Antarctic Convergence. | NN ce : Sf 6° L | <4), 3S Nl! / \ Meee, 7, eee SECTION C-3 | i —— )) \ a i 2 Venn Zan 5p | \ eS | a a Bae | SECTION C-1 ~~ i \ grr yal x NV \ \ = SECTION C2 Pate er Pi \ \ eS, aN sa Mha.c. & A\ Sas YN [\, es, Sai \ SECTION B — NG) Na “ se = \ iy ap fk wie =) WOGLAC AV] \ B ‘ \ ~ : Wy 4 1 S u s EN pelle |; AC Py hee x it [* ny Yi Ye seh Ka Vy — ‘\ : ees \Dieo" \ 5 | asi E INGE oo ae \f Sania iv Mes ro 4 Ea “ “ Ninshtunty eg) Verte i yer a, VI [ \ ag we WINE ON X \ iN We, ly a oot sl | / bellies wie V/ \ ‘ 1 \ 1? ( f { l -=i - ! Se When actual observed values of surface temperatures are plotted in the above fashion, erratic variations of the surface temperature complicate the picture considerably (see fig. 14). The more observations available, the more complex the surface temperature fluctuations appear. They are related to the variations in the meteorological conditions, currents, and melting ice, as well as to the convergence circulation. However, in each section the characteristic break in temperature is easily discernible. Cross section A was taken during late December along a north-south line which closely followed the 100°W meridian. The sharp break in slope of the surface temperature plot is apparent at about 61°947’S with a mean temperature of 3.2 de- grees C. on the steepest part of the slope (see table 7). This is a higher temperature than was observed at the convergence on any of the other sections. The surface temperature de- creases about 2.2 degrees C. in a distance of 20 miles. 57° 58° 59° 60° 61° 62° 63° 64° 65 Go » @F 68 FIGURE 14. Surface temperature sections across the Antarctic Convergence. All 28 Table 7. Section Location of temperature sections across the Antarctic Convergence. at Lotitude ie eave } Latitude | Temperature (degrees C.) 17) 23-25 Dec - 100°30’—102°30’ W| 61°47’S 25-28 Dec -| — 131i? 156° Ba Vey ee 2.0 21-23 Dec ~176° 62°46" 1.8 13-16 Feb ~176° 63°50’ 27 27 Feb-1Mar ~176° | 63°20’ 2.8 In section B, which lies 40 degrees to the west of section A, the large temperature gradient indicative of the convergence was found much farther north at 60924’S. The observations are more closely spaced in this section and consequently give a more variable temperature structure. The tempera- ture gradient at the convergence on this section is about 2) Clegrees G5 iia 1S wailes Sections C-1, C-2, and C-3, which are all in one locality, give indications of seasonal changes in the surface tempera- tures at the convergence. In section C-1 the convergence was found early in the season at 62°946’S with a mean temperature of about 1.8 degrees C. This is the most striking break in temperature found. The decrease is 2.5 degrees C. ina distance of 10 miles. Section C-2 taken 54 days later shows the convergence at 63°950’S with a mean temperature of 2.7 de- grees C. This indicates that the convergence had moved south about 64 miles and the temperature at the convergence in- creased by 0.9 degree C. The temperature gradient de- creased to 1.8 degrees C. in 30 miles. The third section in the same longitude shows that the convergence again moved north to about 63°920’S with a mean temperature of 2.8 degrees C. This northerly displacement amounts to 30 miles ina period of 14 days. The surface temperature gradient here is 2.8 degrees C. in approximately 80 miles. A summary of the surface temperature characteristics at the convergence is contained in table 7. Vertical Temperature Section. The convergence should be marked at subsurface depths by a continuation of the sharp gradients found at the surface. Another important indication of the northern limit of the antarctic region, hence of the location of the Antarctic Convergence, is the position of the northern boundary of the subsurface temperature minimum which develops in summer. The development of this typical summer thermal structure in the antarctic region was dis- cussed earlier. North of the Antarctic Convergence the tem- perature continuously decreases with depth, and the typical minimum at 200 to 500 feet is not developed. This subsurface temperature structure characteristic of the Antarctic Con- vergence is demonstrated by vertical cross section plots of the five crossings (see figs. 15 and 16). On these cross sections all areas below zero degrees C. have been shaded in order to indicate the location of the subsurface minimum. In vertical section, figure 15A, the temperature gradient between 2 and 3.5 degrees C. continues to mark the con- vergence as it slopes downward to the north below the warmer subantarctic surface water. Taking the 3-degree C. isotherm as indicative of the location of the boundary between the two water masses at the convergence Zone, it is seen that this boundary has a slope downward toward the north of 3 x 1073 in the upper 400 feet; that is the cold antarctic intermediate water sinks below the warmer subantarctic surface water at the rate of eighteen feet for each mile to the north. South of the Antarctic Convergence the typical area of subsurface minimum temperature does not appear well-developed. The vertical temperature cross section shown in figure 15B is particularly interesting since bathythermographs were taken at very short intervals in the southward progress of the USS NORTHWIND. The detail shown here points out that the usual cross section drawn from stations spread in much larger intervals presents a very smoothed picture of the vertical thermal structure. The apparent thermal structure is very complicated indeed, appearing more and more com- plicated the greater the detail of the observations. Internal waves, which are discussed later, may contribute greatly to the complicated thermal structure shown here. The boundary zone in this vertical temperature section (fig. 15B) is fairly well marked at subsurface depths between the 1-degree C. and the 3-degree C. isotherms. This zone has an average slope of about 4 x 1074 in the upper 300 feet. The region of subsurface temperature minimum, shown by 29 55° 56° Sa 58° 59° 60° Depth (meters) “NI a a 1253) 150 ANTARCTIC CONVERGENCE 58° 59° 60° ] 25 50 100 Depth (meters) 125 200 es | | | Ie FIGURE 15. Vertical temperature sections across the Antarctic Convergence. 30 61° ANTARCTIC CONVERGENCE 61° ; 62° 63° 63° 64° 64° 100 200 300 400 500 100 200 300 400 500 600 700 Depth (feet) Depth (feet) Ma. the shaded area of temperatures less than zero degrees C., is well marked in this section. The northern limit of this area occurs just south of the convergence, and serves asa further indication of the location of the boundary Zone. The three vertical sections in figure 16, sections C-l, C-Z, and C-3, all show a fairly well-defined boundary zone at subsurface depths as indicated by the temperature gradients. These sections were all taken approximately along the same north-south line and serve not only to demonstrate the fluctu- ations with time in the location of the convergence but also show the seasonal development of the subsurface temperature minimum. On vertical section C-1 the structure a short distance south of the convergence shows a nearly isothermal surface layer with temperatures below zero degrees C. The increase in temperature in the transition layer at greater depths does not appear here because of the shallowness of the section. Section C-2, taken 54 days later, indicates that the surface heating has produced an area with a well-marked subsurface minimum. The data in this section extended deep enough to penetrate the region of positive gradient. Section C-3 also shows this subsurface minimum and its northern boundary, serving as an indication of the location of the bound- ary zone. The southward displacement of the convergence in the 54-day period between section C-1 and C-Z2 may be related to an increase in the thermohaline circulation in the sub- antarctic region, coupled with a decrease in the intensity of the transverse circulation related to the prevailing westerlies in the antarctic region. This displacement appears to bea seasonal phenomenon with the convergence occurring farther south in summer than in the colder months. In winter the cold antarctic water extends farther north along the surface before sinking to form the antarctic intermediate water at the convergence. The northward displacement of the con- vergence between sections C-2 and C-3 may indicate that the southward seasonal trend has been reversed by late February when section C-3 was obtained. oll Depth (meters) ANTARCTIC CONVERGENCE 56° 57° 58° 59° 60° 61° 62° 763° 64° 65°S 0 T T rps rene praneriaeccerttses is 0° ey t : 6° ; 25 | 100 50 |- 4200 = ao 2 Aa 5° 2 o 1300 0 100 }- i Aon 400 125 wh 150 E Jl. | 500 C-] SIZ ANTARCTIC CONVERGENCE ——— 60° 61° 62° 63° 64° 65° 66° T 75 |- Depth (meters) 100 ANTARCTIC CONVERGENCE ° ° 60° 61° 62° 63° 64° 65 66 | T I 25) |= 64 5 Oe Depth (meters) N a ae ae ——a 100 | 4° 4° 125) = C-3 sob FIGURE 16. Vertical temperature sections across the Antarctic Convergence. + 100 + 200 — 300 — 400 500 Depth (feet) 200 | 300 4 400 500 Depth (feet) DEPTH OF THE SURFACE LAYER AS AN INDICATION OF SURFACE CURRENTS. General. The usual procedure in determining the current distribution is to determine the relative mass field from the vertical temperature and salinity distribution. In the absence of sufficient salinity data, it is often possible to obtain an indication of the relative mass field from the depth of the lighter warm surface layer. This results from the fact that in the southern hemisphere the mass field and current field are related in such a manner that the lighter water must occur on the left of the current and the heavier water must occur on the right of the current (observer facing downstream). Hence, in the antarctic the slope of the semidiscontinuity surface at the bottom of the surface layer (top of the thermocline) is associ- ated with a relative current that flows in such a direction that the deeper layer (hence lighter water) is on the left and the shallower layer (hence heavier water) is on the right. This current-mass field is shown schematically in figure 17 which presents a vertical section taken across a current which is shown as though flowing into the paper. The boundary between the relatively warm surface water and the heavier cold water below the thermocline is shown as sloping upward to the right. Since column A has a greater percentage of light surface water than column B, column B will weigh more than column A. The conditions requiring the lighter water on the left-hand side of a current in the southern hemisphere are thus satisfied; hence the current flow is at right angles to the section and the direction of flow is into the paper. Surface Currents from the Observed Temperature Struc- ture. The layer depth was taken as the depth from the surface to the top of the main seasonal thermocline. This depth was averaged for each degree of latitude and longitude, and for some regions, where the number of observations were few, averages were taken over larger areas. The averaging tended to smooth the data and hence to diminish the effect of the small-scale, short-period changes in factors that alter the layer depth (wind force, local heating and cooling, internal waves, etc.), and to emphasize the more widespread, longer- period trends. 33 WATER WATER Z = =} J {e) 8) COLUMN COO OOO9SOOCOVCOOOVO CVO UDO OOO OOOO 4 2 WY atsalats neat coctstsalatntetstonateranstenansonntctonetets! IN COMMA a THERMAL STRUCTURE <— Z = =) = fe) 1o) SEA SURFACE a INTO PAPER LIGHT SURFACE WATER PTH —— aan COLD HEAVIER WATER BELOW THE THERMOCLINE CURRENT DIRECTION = THERMAL STRUCTURE N re M%A%e a %eMA MEMO TAPAVOPOOCTOOON q VE \\ RRR Ere REFERENCE LEVEL FIGURE 17. Schematic representation of mass field in the sea. 34 FIGURE 18. Contours of layer depth as un indication of surface currents. The final averaged values of the layer depth were contoured as shown in figure 18. On the basis of the theory outlined above, arrows have been entered on the figure paralleling the contour lines and indicating the direction of the flow. The surface current field as thus indicated agrees well with the current field presented in other studies of the antarctic. The trend of the lines of equal layer depth is practically the same as that of the isotherms, indicating that there is little flow across the isotherms. This procedure of deriving surface currents assumes that the salinity effect in the surface layer is small and that the major flow is above the thermocline. In this region these assumptions are sufficiently accurate to give the direction of the surface flow, but uncertainty remains as to the use of this method to obtain current speed. The location of the boundary between currents which flow in. opposite directions should be the location of the mini- mum layer depth. From figure 18, showing the topography of the layer depth, it is thus seen that there should be a general easterly setting flow north of the area of 30 meters layer depth and a westerly setting flow south of it. The slope of the discontinuity surface for the easterly flowing current is on the average 0.058 meter per kilometer. This means that the boundary surface sinks 0.058 meter with each kilometer toward the north. For the westward current, the boundary surface sinks on the average 0.055 meter with each kilometer toward the south. 36 INTERNAL WAVES Bathythermograms obtained from the USS CACOPAN on Operation HIGHJUMP in the antarctic were used to study internal waves. The first series (fig. 19A) was taken at a stationary location (68°16'S, 174°53'W) which was occupied on 28 and 29 January 1947. Repeated lowerings at this location were made every 10 minutes for the five-hour period, 2135Z to 0230Z. Another series (fig. 19B) was made in the area 67°47°S, 176°54'W to 67°40°S, 176°10°W. Measurements here were made for 2 hours and 20 minutes at five-minute intervals from 0045Z to 0305Z on 28 January 1947. Whenever repeated bathythermograph observations are made in one locality, the vertical fluctuations of any isotherm is considered to result from internal waves. In order to study them in the antarctic, depths of isotherms were plotted against time. An examination of the bathythermograms revealed that the most suitable temperature was the 30-degree F. (1.1l-degree C.) isotherm because it was continuously in the thermocline. Many of the bathythermograms showed a double trace in the thermocline. This double trace may be due to hysteresis of the instrument or to the presence of internal waves of very short periods. Only the shoaler trace is used here. Figure 19A shows variation in the depth of the 30-degree F. isotherm at each observation made at 10-minute intervals. The maximum variation in any 10 minutes was 15 feet. In this 5-hour period, the maximum difference between crest and trough for the series was 40 feet. Figure 19B (the second series of repeated lowerings) shows similar fluctuations due to internal waves for the first 80 minutes at an average depth of 50 feet. Then there is a very sharp drop in the depth of the isotherm to about 140 feet. However, these observations were made while the ship was moving at about 3 knots so it is likely that a boundary between two water masses was crossed. Thus, this increase in the depth of the isotherm is probably not related to internal waves. Because each station was occupied for only a short time, it is impossible to make any analysis involving the long-period waves such as those related to tidal periods. For the same reason, it would not be profitable to perform a harmonic analysis to determine the dominant periods. The bathythermograms collected from the USS CACOPAN prove quite convincingly that internal waves exist in the antarctic region. Long-period waves attained a height of as much as 40 feet in a period of 90 minutes. Many short- period waves of about 10, 20, and 30 minutes and with a height of about 10 feet were found to be superimposed on the longer waves. AN I \\ \ FIGURE 19. Internal waves — vertical fluctuations in the depth of the 30-degree isotherm; data from repeated bathythermo- graph observations on 28 and 29 January 1947 at two locations. TEMPERATURE AND SALINITY ; General. During Operation HIGHJUMP, the USS HENDER- : SON and the USS CACOPAN of the Western Task Group made a a number of simultaneous sea temperature and salinity obser- a, vations to determine the density and buoyancy of the antarctic ‘y water. The following is a discussion of these data. The observations consist of (1) six hydrographic stations 4 taken from the surface to depths of 150 to 250 meters, (2) one : station at which observations were made at the surface and at 4 300 meters only, (3) one station at which observations were & made at the surface and at 50 meters only, (4) one station at 2 which a salinity sample was obtained from the water trapped ; in a coring device at a depth of 2700 meters, and (5) thirty-one .. surface observations of temperature and salinity from bucket samples. Only those temperature observations made at the ; same time that salinity samples were taken are included. The positions where the hydrographic stations were occupied are shown in figure 20. Methods of Collection. The method used in taking these stations differed markedly from the standard procedure. j Consideration of this fact should be made when comparing 4 these data to other hydrographic stations where reversing thermometers were used. Reversing thermometers were not used for the stations discussed here. Instead, a bathy- thermograph and a Nansen bottle were attached to the bathy- thermograph wires. The temperatures listed in table 8 were then obtained from the temperature-depth trace made by the i + a 40° 30° 20° 10° 0° 10° 20° 30° 40° 5 rae — 100 FIGURE 20. Location of hydrographic stations. Table 8. Temperature — salinity data. - ; ~ OBSERVED VALUES INTERPOLATED VALUES STATION Depth Temperature. Salinity Depth Temperature Salinity | (meters) (degrees C.) (°F o0) (meters) (degrees C.) (°7 00) Station C-1 : ; Y 30 January 1947 0200 GCT 68°43’ S 174°55' W Station C-2 11 February 1947 0730 GCT 59°55°S 96°45".E tation C-3 13 February 1947 1000 GCT 65°55" S:-85°55;E tation C-4 . 19 February 1947 0630 GCT 59°57’S 40°30'E Station C-5 4 January 1947 0300 GCT moe 61°13’ S 149°20' E- Station C-6 5 January 1947 0500 GCT 59°55’S 148°50’E tation C-7* 13 January 1948 0730 GCT ‘ 60°15’ S 147°50’E | 1650 fathoms ) tation H-1 6 January 1947 0300 GCT 63°49’ S 146°43’E 1750 fathoms . Station H-2 16 January 1947 0730 GCT : 64°38’ S 135°55’E 1300 fathoms * Salinity sample obtained from bottom sampler. 40 900-foot bathythermograph and the salinity samples were obtained from the Nansen bottle. The depths of the samples are the length of wire payed out according to the counter on the bathythermograph winch. Accuracy of Observations. The temperature cannot be tead from bathythermograms to a greater accuracy than 40.1 degree F.; the instrumental error is estimated at 40.1 de- gree F. There may also be some difference between the actual depth at which the water sample was taken and the depth at which the bathythermogram was read. It is thus probable that the temperatures corresponding to salinities given here are accurate to about 0.1 degree C. The depths at which the water samples were obtained from the counter of the bathythermo- graph winch are fairly accurate at shallow depths. The water samples were titrated with silver nitrate by the Knudsen method@ to determine chlorinity and salinity. The salinities are expressed in parts per thousand (o/oo) and are accurate to 0.02 o/oo. The density of the water was calculated from the tempera- ture and the salinity by means of Knudsen’s Tables.? In discussing density in this report the common notation, ¢ will be used. This density is defined by the relation: t’ ex = HOOD (Bag a — 1) wherefsg,s,ois the density of a parcel of water of salinity s, temperature ¢@, and pressure 0 (one atmosphere). Because of the low temperature range encountered, the 0.l-degree C. error does not introduce a serious error in the computed density. Within the temperature and salinity range encoun- tered, the probable error in temperature corresponds to an error of less than 0.01 ino,. Results. Earlier in this report, there is a discussion of the results of temperature observations made with bathy- thermograms. The general conclusions which apply to the over-all temperature structure (as given in the bathythermo- gram discussion) apply also to the temperature distributions that are presented here. The temperature-depth structure for the six hydrographic stations is shown in figure 21. In general, these temperature traces show certain charac- teristic trends. At all stations, except station C-1, a minimum temperature layer appears between 50 and 100 meters. The temperatures both above and below this layer are from 1 to 2 degrees C. warmer than in the cold layer (referred to earlier as type S-l thermal structure). At stations C-2, C-3, and C-4, the warming of the upper layer is especially well-marked. An explanation of the processes leading to this type of temperature distribution has been discussed in the section: ‘‘Thermal Structure of the Surface Layers in the Antarctic Ocean.”’ Temperature (degrees Centigrade) 0 —2.00 —1.00 0.00 1.00 2.00 3.00 Depth (meters) FIGURE 21. Vertical thermal structure at hydrographic stations. 41 42 In winter, intense cooling results in a virtually homo- geneous layer of water about 100 meters (300 feet) thick. On the basis of winter observations in this region, this layer has a temperature that is near freezing. Below this mixed layer, increasing salinity allows for an increase in temperature without resulting in instability. According to Sverdrup, Johnson, and Fleming,* antarctic circumpolar water, which occurs a short distance below the surface water, is charac- terized by a temperature maximum at a depth of 500 to 600 meters. In summer, the radiation surplus is first used to melt the ice and next to increase the temperature of the surface layers. Station C-1, which was occupied in the Ross Sea fairly close to the ice pack, shows a temperature minimum at a depth of only 35 meters, compared to approximately 75 meters for the other stations. The increase of temperature above 35 meters is much less than in the other cases, indi- cating that in this region the radiation surplus had apparently been used mainly for melting the ice. The relatively high temperature of the surface layer above 45 meters (150 feet) in the five hydrographic stations other than C-1 must be largely the result of actual heating of the surface layers. There is some indication that stations C-2, C-3, and C-4 were taken near the Antarctic Convergence, hence the high temperatures found on the surface at these stations may be partly due to the southward intrusion ofa thin surface layer of warm water from north of the conver- gence. The stability which is associated with the strong negative gradients thus developed aids in restricting this warm layer to the upper 150 feet. The minimum temperatures found at all stations from 60 to 100 meters (200 to 300 feet) must therefore be the re- mainder of the winter-cooled surface layer mentioned above. The increase in temperature that occurs below 100 meters at the different stations evidently corresponds to the transition layer between surface water and antarctic circumpolar water, which has a maximum temperature of between 2.0 and 2.5 de- grees C. at depths from 500 to 600 meters. Figure 22 gives the salinity-depth curves for all stations. These curves also show certain characteristics which tend to support the conclusions gained from the thermal structures. The melting of ice results in lowered salinities very near the surface. This low salinity layer is shown best at station C-l, FIGURE 22. Vertical salinity structure at hydrographic stations. which was taken near the ice pack. The surface salinity at this station was 32.90, as compared with an average surface salinity of 33.80 for the other five stations. The salinity distribution in the summer thus aids in establishing stability in the upper layers. This stability restricts the heating in the ice-free areas to the upper 45 meters (150 feet) and leaves the winter-cooled layer just below this depth at temperatures near freezing. At all stations the salinity at 300 feet lies between 34.0 and 34.5 o/oo which corresponds to the types of water found in the cooled layer in winter. Salinity (°/oo) 32.80 33.40 34.00 34.60 0 a Depth (meters) 43 44 The temperature-salinity diagrams in figure 23 further substantiate the conditions described above. The characteristic temperature minimum is evident on all the T-S curves. This minimum, which occurs very close to -1.0 degree C. and between 34.1 and 34.2 o/oo, corresponds to the layer of winter- cooled water. Surface heating and low salinity are indicated by the sharp rise in the curves at the left of the temperature minimum. At station C-1 the elongation of the T-S curve on the left shows the effect of dilution caused by the melting of ice. The approximate T-S value of antarctic circumpolar water at 600 meters for the region within which the stations were occupied is plotted as a large dot labeled ‘“‘A.C.P.W.”’ It can be seen that the increase of temperature and salinity with depth below 100 meters tends to bring the T-S curves toward this point. The density structure, as represented by the curves of figure 24, indicates instability or indifferent equilibrium in the upper 30 meters except at stations C-1 and H-1. Station H-1 shows slight stability, while station C-1 shows marked stability, in this layer. There is generally a moderate in- crease in density in the 30- to 60-meter layer, the increase leading to moderate stability at these depths. Below 60 meters there is only slight stability. The effect of this density structure on submarine diving operations is indicated in figure 25. The amount of buoyancy change required in diving from a depth of 50 feet to any depth down to 300 feet has been computed for a 2400-ton submarine using the diving rule of 1400 pounds per 100.feet. These figures were computed on the basis of a 5400 pound change in buoyancy for each unit change inz,, At stations C-1 and C-4, the computed buoyancies indicate that flooding is necessary to go from 50 feet to 150 feet. At station C-1, a submarine at 50 feet would be in the center of a sharp density layer. At station C-4 there is a fairly sharp density layer, approximately 2000 pounds per 100 feet between 125 and 175 feet. At the other four stations no appreciable density layer is indicated. These data indicate that relatively little flooding or pumping is needed for diving operations in the antarctic. FIGURE 24. Vertical distribution of g; at hydrographic stations. (RO \) \ \ \ {\ A AN NN ANY 25 50 75 100 125 Depth (meters) 150 175 FIGURE 23. Temperature-salinity graphic 26.80 27.40 relation at 200 225 250 hydro- 45 Depth (feet) The data described above are presented in table 8, which includes all stations at which salinity samples were taken at subsurface depths. Table 9 summarizes all simultaneous surface temperature and salinity observations as well as the time and location and the computed?7;+. Twenty-five of these surface samples were taken in the antarctic; the other fourteen observations were taken en route to the equatorial region. A salinity of 32.90, the lowest surface salinity experienced within the antarctic region, was found to exist very close to the pack ice. The maximum salinity found in the antarctic re- gion was 34.07. The increase in surface salinity in mid- latitudes is shown by the observations made on the voyage northward to the equatorial region. Pump (pounds) 1500 2500 3500 4500 FIGURE 25. Buoyancy change between 50 feet and depths to 500 feet. 46 Table 9. Surface temperatures, salinities, and temperature values. Serial No. Date Time Latitude Longitude Tecinoratee Salinity (GCT) (degrees C.) (°/00) : 62°12’S | 162°15’E 63°40’ | 162°11’ 62°23"|, 159°R2" 61°46’ 158°14’ 59°20’ | 152°03’ 61°13’ | 149°20’ 59°55’ | 148°50’ 63°49’ | -146°43/ 64°38’ | 135°55’ 61°03’ | 140°00’ 60°58’ | 135°17’ 65°43’ | 141°35’ 64°30’ | 156°00’ 65°27’ | 176°08’ 66°55’ | 173°48’ W 174°40’ 174°55’ 121°50’ 96°45" 88°55’ 40°30’ 29°45’ 82°20’ 115°40’ 117°35’ 124°40’ 135°33’ 136°30’ 143°05". 144°12’ 32°67’ | 165°00’ 29°54’ | 170°03’ 26°17! |. 1752357 D2E36t.2 1179° 40" 18924".7| 174°55’ W420" “|. 170°20'° 09°57’ | 165°55’ 03°28’ | 159°32’ 01°37’N | 154°54’ rn peas : ‘ —|}O O MAN AaAIOa FB WN 48 SEA WATER TRANSPARENCY MEASUREMENTS Water transparency measurements were made from the USS CACOPAN at fifteen different stations in the antarctic. The transparency measurements were made with the aid ofa Secchi disk (a white disk 30 centimeters in diameter). The Secchi disk was lowered into the water in a horizontal position and the maximum depth at which the disk was still visible was noted. This depth was taken as a measure of the trans- parency. In the Antarctic Ocean the Secchi disk readings (table 10) vary from 23 to 90 feet with an average of 50 feet. Most of the measurements are Similar to the average transparencies for open-sea conditions. But the readings between 23 and 32 feet at four of the stations are very low transparencies for open-sea conditions. The low transparency is probably related to high phytoplankton production. Both the color of the sea and the surface temperature were noted at the same time that the transparency measure- ment was made (see table 10). Antarctic water is typically blue-gray, blue-green, or green. Near the pack ice the water is usually green and of low transparency owing to high organic content. On 19 February a tongue of bright blue water was encountered which appeared to be a tongue of Indian Ocean water that extended into the antarctic. ANTARCTIC ‘‘SEEING’’ Especially impressive during Operation HIGHJUMP was the crystal clearness of some of the antarctic days, the stellar brilliance of some of the nights, and the consequent fitness of these regions for making celestial observations even from sea-level elevation. Polar regions are noted for many curious optical phenom- ena, most of which are related to excellent visibility rather than to optical distortion. It is well known that, because of atmospheric clarity, the mariner and the explorer in high latitudes frequently underestimate distances by as much as 50 miles and occasionally by as much as 200 or 300 miles when superior mirages or loomings are involved. Regarding celestial observations, Byrd® states that observers at Little America noted as many as 60 meteors per minute. He attri- butes such exceptionally high counts to the clarity of the sky which permitted the sighting of faint trails that would be invisible in other parts of the world. Table 10. Antarctié Ocean transparency (Secchi Disk) measurements. Time Date Latitude | Longitude Surface | Water Color © |Transparenc Zone Water ; (feet) . Temperature | (degrees F.) : anes 2 3 4 5 6 7 8 9 0) 64°12 S| 62°15 E ‘ Green — 64°09’ 162°15’ Ny Blue-Green 622.13 W595 117 : Blue-Gray | 59°06’ | 150°17’ ; Blue-Gray | 60°24’ | 150°45’ ; Blue 59°55’ | 148°50’ : Blue-Gray 68°43’ | 174°55’ Blue-Gray 59°55’ | 96°45’ : Blue-Gray 60°55’ 88°55’ : Blue-Gray 60°52’ | 84°30’ . : Green 59°57’ | 40°30’ | 36. Bright Blue 61°14’ | 37°40’ 5 - Blue 60°45’ 29°45’ : Blue-Gray 60°18’ | 47°45’ 63°55’ | 82°20" Green (at edge of ice pack) On clear days, icebergs stand out with such definition that one feels he might reach out and touch them although they are obviously many miles away. The topmost portion of large bergs can still be seen when the base is so distant that curvature of the earth causes it to appear well below the horizon. The sun, which sets with little distortion or change in color, is so brilliant that one cannot look directly at it until it has almost entirely disappeared below the horizon. Even more impressive than the clarity of some of the antarctic days, is the atmospheric transparency of many of the antarctic nights. A strong beam of light is invisible because of the absence of the Tyndall effect as there are no solid particles in the air to scatter light. Stars shine brilliant- ly and can be seen down almost as far as the horizon. Most surprising is the fact that the stars shine with a bright steady light and do not twinkle. All of this adds up to excellent ““seeing’’ -- probably unsurpassed anywhere in the world. This excellent ‘‘seeing’’ in the antarctic region is largely understandable. As these regions are uninhabited areas of water and ice, there is practically no source for inorganic or organic dust particles, or for pollution by smoke. A permanent high pressure area lies over Antarctica, so that cold, dry, and consequently haze-free air flows radially outward from the continent. Strong temperature inversions cause the air to be stable and the airflow to be laminar. a9) FIGURE 26. Portion of a typical “youthful” tabular antarctic iceberg. Recent formation of this berg by break- ing off from shelf ice is indicated since there are, as yet, no sea caves or other evidence of sea weathering devel- oped along the waterline. FIGURE 27. View of a typical pyramidy iceberg. This has the form of a moderately weathered ‘‘mature” berg. Note the tilted and uplifted shoreline produced by a calving which changed the center of gravity. Observations from aboard ship show a low percentage of clear days but aircraft pilots usually reported good weather over the continent and their aerial photographs show high atmospheric transparency. Thus it seems that astronomers should take an active interest in investigating portions of the Antarctic Continent for possible use in making astronomical observations. Perhaps the ice-free ‘‘oases’’ recently dis- covered by the Navy. near the Antarctic Circle would furnish satisfactory bases. Along with excellent “‘seeing,’’ the long winter night permits uninterrupted observations and long photographic exposures, ICEBERGS AND SEA IGE On 23 December 1946 the HENDERSON crossed the Ant- arctic Convergence and entered the polar water mass. The well-marked boundary of this water mass was very apparent. While running about 20 miles, the surface water bucket tem- peratures dropped abruptly from 39 to 33 degrees F. A similar abrupt temperature drop when crossing this boundary was revealed when the injection temperatures of both the CURRITUCK and the CACOPAN were checked. The change from blue to gray in the color of the water, the appearance of new types of birds, the clearing of the sky, and the quieting of the sea were other striking observations that were noted. The HENDERSON left the convergence and had traveled about 25 miles in a southerly direction when the ship encoun- tered the first iceberg; this berg was one ofa large field of bergs that extended to the south. Throughout the entire antarctic passage, the bergs were seldom observed to be isolated; they appeared rather to be collected into fields. The northernmost limit of bergs as noted by the CACOPAN was roughly 60°S. Distribution of both bergs and pack ice as noted by the HENDERSON is shown in figure 1. As antarctic bergs are formed largely by the calving of shelf ice, they are typically tabular in shape (fig. 26). How- ever, melting and wave erosion result in the formation of an ice foot and of sea caves along the waterline and, after much weathering, the bergs begin to lose their original tabular form. They become pyramidy (fig. 27) and often are gro- tesquely carved. Pyramidy bergs frequently display uplifted and tilted waterlines formed by calving which results ina sudden change in the center of mass. 51 bye FIGURE 28. Newly formed pads of pancake sea ice a few feet across as viewed from the deck of the USS CURRITUCK after a few days of below-freezing weather. When the ship was lying to near the pack, icebergs some=- times appeared to be plowing through the sea ice because, as is well known, bergs are usually current driven while sea ice is wind driven. For this reason the bergs may move at a different rate from that of the sea ice and often move in a different direction. This is related to the deep draft of the bergs and especially to their great mass because, relative to sea ice, bergs have a small surface area for the wind to act on aS compared to their mass. During the last few days of February, the temperature, which had been continuously above freezing, dropped to a little below freezing and pancake ice formed. This presaged the growth of the ice pack and the coming of winter. The freezing of sea water is markedly different from that of fresh water. Fine needles of ice form slightly below the surface and then float to the surface producing a slush. After slight surface buffeting and further freezing, this slush is trans- formed into ‘‘lily pads’’ of pancake ice (see fig. 28). geological observations ANTARCTIC SEA FLOOR SEDIMENTS* Three core samples (see table 11) were obtained in the antarctic by means of a gravity, coring device of the type described by Emery and Dietz. Because the small wire size limited the weight of the sampler, however, and because the oceanographic winch did not permit the wire to be lowered rapidly, only a small impact force could be obtained. Conse- quently, the three cores collected were of short length. Two earlier attempts had been made to secure bottom cores; however, these attempts were both unsuccessful. The bottom could not be reached largely because the makeshift oceanographic winch was unsatisfactory. It consisted ofa spool which was welded to a large warping winch of the CACOPAN and which held 4500 meters of 5/32-inch, 7x7 strand wire. The very slow speed at which the wire could be lowered and the rapid drift of the ship resulted in large wire angles and excessive wire strain. After the two unsuccessful at- tempts, bottom was finally reached on the top of a deep ridge by intermittently backing down the ship at one-third speed to reduce the wire angle. The four or five hours necessary to obtain a core sample in deep water was excesSive, so there were few opportunities to attempt abyssal bottom sampling. And, unfortunately, the entire Antarctic track of the CACOPAN was in deep water. *The samples are only briefly described here since a detailed mineralogical study is being made separately by J. L. Hough, presently of the University of Illinois; in addition, an investi- gation of the foraminiferal fauna is being made separately by Miss M. Bradley at the University of Southern California. Table 11. Sediment samples obtained from the USS CACOPAN on Operation HIGHJUMP. Date Sample | Sonic Depth Sampling Remarks (1947) No. Latitude teaciudes (fathoms) . Device NEL 394 60°13’ S 147°45’ E : Diatomaceous globigerina ooze; 19 in. "core; from top of submarine ridge (Indian-Antarctic Swell). NEL 395 60°55’ 84°30" aia 4G Diatomaceous globigerina ooze; top of Gaussberg-Kerguelen Ridge; small sample as most of core washed out. NEL 396 63°55’ 82°20’ ( : Green glacial mud and sand; at base of e 4 Antarctic Continent slope; about 42 in. long. NEL 397 39°30’ 144°10' | Scoopfish | Coarse shell sand, Bass Strait, Australia NEL. 398 39°30’ 144°14’ Were Scoopfish | Coarse shell sand, Bass Strait, Australia 3 NEL 399 | 39°20’ : 145°00’ - 2 Scoopfish Coarse shell sand, Bass Sven Australia NEL 400 | 11 ef 39°20’ 145°30". aay j Scoopfish Coarse shell sand, Bass Strait, Australia} 54 The first two core samples (NEL 394 and NEL 395), obtained from the top of deep oceanic ridges, are similar in that they both consist of diatomaceous globigerina ooze. Also a flood of G. pachyderma, a pelagic polar species, is present in both of the samples. A fresh granite chip found in NEL 395 from Kerguelen-Gaussberg Ridge suggests that this structure may be, in part, granitic; however, this cannot be definitely established because such chips might reach their present location by ice rafting in this part of the world. The finding of globigerina ooze in a zone previously considered to be covered by diatomaceous o00ze may be due to the topo- graphically high position at which the samples were taken. In this case, the light diatomaceous material would have been largely winnowed out by current action and then transported into the surrounding basins. This is in line with recent observations elsewhere which have shown that topographic highs on the sea floor, regardless of depth, are covered with coarse sediment. Bottom currents at great depths are generally considered to be weak but currents associated with eddies with vertical axes or with internal waves are probably strong enough to stir up the finer bottom material. Thus a mechanism probably exists that sweeps the finest sediment from topographic highs. Core sample NEL 396 was obtained from a depth of 2000 fathoms at the base of the continental slope of Antarctica in the vicinity of the Shackleton Ice Shelf. It consists of green mud and sand, and the poor sorting suggests that here the deposition of material rafted by ice was important. The presence of two cleanly washed sand layers is noteworthy in that it shows that effective currents must have existed even at this great depth. The four bottom samples, NEL 397, 398, 399, 400, (see table 11) were obtained with an underway sampler, the ‘‘scoop- fish,’’ in the shallow waters of Bass Strait, Australia. All of the samples are similar in that they consist of a coarse shell sand. The performance of this new device which permits underway sampling was entirely satisfactory. It was used on the bathythermograph winch at speeds up to approximately 8 knots. Core samples NEL 394 and 396 were subjected to bac- teriological analyses by D. M. Updegraff of the Scripps Institution of Oceanography. Various selective media were inoculated with about 0.5 gram of sediment. The bacteria present are listed in table 12. Since the samples had been stored for a long period in unsterile containers before analy- sis, it is not certain that the results represent the conditions in the original sediment. However, every effort was made to avoid contamination by aseptically sampling the center of the cores. E Table 12. Bacteriological. analyses. CORE NUMBER Distance from surface of core (inches) - |Methane-oxidizing bacteria Aerobic heterotrophic bacteria Anaerobic heterotrophic bacteria — . |Phenol-producing bacteria (produce phenol from L-tyrosine) Aerobic hydrocarbon-ozidizing bacteria _ [Anaerobic hydrocarbon-oxidizing, sulfate-reducing bacteria _ -{ present — absent 55 na 4 will Peat Ze ior isk A v Sree oor Fe s B f A ee, | 5 | Bea eas Re F jacks 4 ca ate nea uw | | | ithe aaa ido esa PO sh 2087 16K joov # +3 A ss f fouTcoIn® sieNaL ‘ = zi6r 7k D jono\r te 5, 6 t i n ‘000 FIGURE 29. Fathometer bottom trace (fathogram) of four Pacific seamounts. fd sical S* IN Nene eitie bes 4 H t 2 2000 2n00 238 240 Di cate ee ce ae a eat * oo = 09ST TK f foror heey i wa pron eri pecs ea 2 FIGURE 31. 56 Fathograms of two antarctic sea-floor escarpments. bi ele, ae es i Ge BOAT TWAT wives 3 ASLO Se : A [ms Be is ist 2 } | Vi 2000 FIGURE 30. Fathograms” showing a southwest Pacific sea- mount, the Easter Island Swell, and the continental slope of south Australia. nensys fe-z08 5Eo 387 aeeace ; fesliciet ms 9220S gym i pe ir RON, >» 2060" \5K 2 per ons 2 EE) 8 IS ne ee sue a SvTSMORICe Scrat D ai = eee ‘i ro PaeMAAS aK Pe ae ae Mara cae } ourcofic ~= 225°C 13.Nb B pasemaonrensnn ni eeaaeR OMe oP eds Widat SiIWHdWOuaLSV MN ON) ON) CNNNINT SNV9313 SNIVHdWOUs1SV ema e naan a 13400 SNIVHdWOUSLSV WNYONVOVaAd VYOHdWV SANVf SNIDADONILIV SNOUIIB SNIDADONILIV SNWINIW SNOSIGONIDSOD TT va Uh VR = very rare. = rare; R C = common; abundant; A No diatoms detected No diatoms detected No diatoms detected eve SEL SWOLVIG 40 JDNVGNN8Y OULU BS 1884, Do be Dactyliosolen antarcticus, Castracane,!6 1886, jo UBe According to Hendy, 1937, p. 323, this species exhibits three phases -- ‘‘Antarcticus,’’ ‘“‘borealis,’’ and ‘“‘laevis.”’ The epithet used above designates only the “‘antarcticus”’ phase. The other two forms were not encountered in the collection. E.ucampia balaustium, Castracane,!6 1886, p. 97. This form appeared frequently in the plankton but never in great numbers. Its extreme variability has been noted before (Hendy,? 1937, p. 286 and J. Hart, personal comm.) and at times it is rather difficult to identify on this account. Eucampia cornuta (Cleve), Grunow ex van Heurck,2© 1880-5, jalls QHD, tio Be Fragilariopsis antarctica (Castracane), Hustedt in Schmidt,*3 UGS. yally Zs asi6 Wo ls. Fragilariopsis antarctica f. bouvet, Karsten,!! 1905, p. 123. Hendy,? 1937, p. 332, states that antarctica is probably oceanic and the ‘““bouvet’’ phase is probably neritic. The two forms are frequently associated and, in the HIGHJUMP col- lection, they are usually found together. Grammatophora marina (Lyngbye), Kutzing,2? 1844, p. 128. Guinardia flaccida (Castracane), H. Peragallo,@® 1892, p. 107. Navicula trompii Cleve var. major, Heiden and Kolbe,29 OZ Shpeozoe Nitzschia closterium (Ehrenberg), Wm. Smith,39 1853, p. 42. Hendy? gives the apical axis of this form as ‘“‘up to 80u."" Numerous, longer cells, in the neighborhood of 100\1in length, were encountered in the HIGHJUMP collection. These forms are easily confused with N. longissima (Brebisson) Ralfs, in Pritchard,!5 1861, p. 783. The length of N. longissima, according to Cupp,3! 1943, p. 200, is 125-250. 75 76 Nitzschia seriata, Cleve,3% 1883, p. 478. Pinnularia lanceolata, Heiden and Kolbe ,29 1928, p. 598. Pleurosigma directum, Grunow, 33 1880, p. 53. Occurs seldom in the plankton. Rhizosolenia alata, Brightwell,3* 1858, p. 96. Rhizosolenia alata f. indica (Peragallo), Hustedt,35 1929, p. 602. Rhizosolenia alata f. inermis (Castracane), Hustedt,2° 1929, p. 602. Rhizosolenia antarctica, Karsten,!! 1905, p. 95. Rhizosolenia bidens, Karsten,!1 1905, p. 98. This form has markings similar to R. styliformis, but possesses a bifurcate spine. Heiden and Kolbe, 1928, p. 517, have made it a form of R. styliformis. The diatom does not occur very frequently in the HIGHJUMP collection and the author has not been able to form any opinion as to its status. Rhizosolenia delicatula, Cleve,>© 1900, p. 28. Rhizosolenia hebetata f. semispina (Hensen), Gran,?/ 1905, io DDo A very variable form especially regarding size. Rhizosolenia styliformis, Brightwell,34 1858, p. 95. Rhizosolenia styliformis var. longispina, Hustedt in Schmidt, 23 1914, plate 316, figs. 5-7, 12. Schimperiella antarctica, Karsten, !1 1905, p. 88. The genus Schimperiella is confined to the Antarctica. Synedra pelagica, Hendy,” UE Thp joe Shai be This form is synonymous with S. spathulata, Schimper ex Karsten,!! 1905, p. 124 but not S. spathulata, O’Meara, 1875, p. 310. It is not uncommon in the plankton and often occurs with S. longissima. Thalassiosira antarctica, Comber,2” 1896, p. 491. This variable species is usually very common in antarctic waters but was comparatively rare in the HIGHJUMP collection. Thalassiosira decipiens (Grunow ex van Heurck), Jorgensen, 9 1905, p. 96. Reported formerly from the Pacific, as occurring in the Peru Current, by Hendy,” 1937, p. 239. Thalassiotrix longissima (Cleve and Grunow)>? (Schimper ex Karsten) Cleve and Moller. The taxonomy of this form is extraordinarily confused. Hendy, ? 1937, p. 335 refers to it as T. antarctica Karsten. Karsten, however, 1905, p. 124, designates it T. antarctica Schimper, referring apparently to Schimper’s Mss. notebook. Hendy, therefore, should have accorded the authority to Schimper ex Karsten. In a personal communication from Prof. Ruth Patrick, the form is referred to as T. longissima var. antarctica, with the authority quoted as Cleve and Moller Type-slide No. 125. The author is constrained to agree with Prof. Patrick that this form does not warrant specific rank, but is merely a variety of T. longissima. Although the author has been able to trace no published authority for this variety, he accords it to Cleve and Moller on the basis of Prof. Pa- trick’s comments. This is one case where the Rules of Taxonomy should be suspended to obviate the ridiculous nomenclature given above. The diatom is extremely common in the plankton and is frequently one of the dominant forms. var. antarctica, Tropidoneis antarctica, (Grunow), Cleve,*! 1894, p. 24. Tropidoneis glacialis var. constricta, Heiden and Kolbe ,*? USVA35 jos OSG 77 78 NATURAL SLICKS IN THE PACIFIC AND ANTARCTIC OCEANS Natural slicks are glassy patches or streaks upon the surface of the ocean that give it a heterogeneous aspect insofar as the reflection of light is concerned. Prior to departure on Operation HIGHJUMP, it was decided to observe the distri- bution of these features. They have apparently received little previous attention, for there is little information about natural slicks in oceanographic literature. It is known that the natural slicks are commonly referred to by fishermen and mariners as streaks where the wind is not striking the sea surface. Also, sailboats frequently avoid these areas of supposed calm. Yet, a few simple observations, such as watching the slicks drifting slowly with the current, show that the theory that they are produced by the wind is untenable, They are discussed in the biological section of this report in the belief that they are thin films of natural oil from organisms, especially diatoms; thus in a sense they are presumably a biological phenomenon. The fact that diatoms synthesize droplets of oil in their cells to provide a food reserve and also to assist them in keeping afloat is well known (Sverdrup, Johnson, and Fleming ;4+ Cupp?!), Upon their destruction, it is probable that these droplets of oil rise to the surface and that they then tend to spread into a monomolecular layer, thus producing slicks. Of course other marine animals may also contribute oil to form natural slicks but they are probably quantitatively unimportant as compared to diatoms. In any case, much of their oil results from grazing upon the diatoms. If slicks are films of natural oils, one would expect them to be the most prominently developed in regions of high organic production, as in coastal waters and near islands where upwelling occurs. With this in mind, daily observations were made during Operation HIGHJUMP and such a distribution was found actually to exist. Upon the departure of the ships from California on 2 De- cember 1946, it was noted that slicks were developed rather prominently in the green coastal waters but that when the blue oceanic waters were reached the slicks had disappeared altogether. When the ships passed the Marquesas Islands, the only landfall en route to the antarctic, a slight develop- ment of slicks was noted. Although as a general rule slicks were not noted in oceanic water, on 15 December in the South Pacific (latitude 30°48'S, longitude 152°924'W), with smooth sea conditions prevailing, some slicks were found that were just faintly discernible. Upon reaching the green antarctic waters, where organic production is notably high in the summer, prominent well- developed slicks were frequently observed, especially near the pack (fig. 38A). Aerial observers who were questioned reported generally good development of slicks in the antarctic coastal waters. Frequently slick-like areas were noted in the lee of melting ice. These areas appeared to nave been caused by the spreading of fresh water over salt water (fig. 38B). FIGURE 38 Top: Slick-like patches developed in the lee of melting brash ice. Such patches are often especially prominent in the lee of melting ice bergs. They are probably formed by relatively fresh water from the sea ice floating on sea water of greater density. Middle: A typical development of slick patches during quiet sea conditions in the antarctic. These slicks are probably largely films of phytoplankton oil and thus show the high productivity of these waters. U9) Bottom: Slicks in San Diego harbor probably resulting from both natural (diatom oil) sources and artificial (ship’s oil and refuse) sources. 80 Slicks were noted but once on the high seas during the homeward passage. These slicks, found in a subtropical area (latitude 20°S, longitude 75°W) under unusually calm conditions, were only faintly discernible. However, well- developed slicks were found in Australian coastal waters, and especially striking slicks were seen in the insular waters of American Samoa. And, when the coastal waters of Cali- fornia were reached, prominent slicks were again found. Thus it would appear that, under favorable conditions, slicks that are just faintly discernible may be found in oceanic water, but that the most prominently developed slicks are to be found in coastal and insular waters that typically have high organic production. This further suggests that slicks are produced from natural oil of organisms and, conversely, that slicks may have a practical use as indicators of high organic productivity. During Operation HIGHJUMP, it was noted that during calm conditions slicks have a patchy distribution but, under windy conditions, they drift with, or slightly faster than, the surface water and tend to line up in elongated streaks parallel to the wind. Probably the streaks are developed by the slick material collecting along small convergences associated with helical circulating cells of water in the homogeneous layer above the thermocline .42543 High winds and attendant rough seas result in the complete disappearance of the slick patterns. A critical velocity of only a few miles per hour and no fetch at all is normally required to form capillary ripples, but a considerably higher wind velocity is needed to produce ripples in a slick area. Slicks appear as glassy streaks largely because they damp out the small ripples and thus produce a calm area in the midst of rough water. This calming effect appears to be mainly caused by the molecules of the slick film forming a cohesive and nonmiscible blanket over the water so that the slick particles do not take part in the vertically circular motion described by the water molecules when ripples are present. In addition to the damping effect that slicks have upon the water ripples entering a slick patch, the slick sub- stance itself probably resists the formation of capillary ripples because of certain physical properties such asa relatively high viscosity. Also, there must be a considerable frictional drag along the slick-water boundary, and the film is so thin that the vertical circulation necessary to produce capillary ripples with the slick substance cannot be set up. Thus, even a fresh water film such as from melting ice floating on top of cold and saline salt water can produce a slick. But, the fact that slicks are generally surface films of a foreign substance has been demonstrated by the unpub- lished work of E. C. LaFond and of D. E.. Root, both of whom have shown that the surface tension of water collected from slicks is less than that of other sea water. Also, surface bubbles produced on slicks tend to persist while those in other water disappear rapidly. Artificial slicks produced by ship’s oil and other refuse are present in harbors (fig. 38C), where they frequently constitute a fire hazard. They have often been artificially produced on the high seas by ships in distress to damp the roughness of storm waves to keep them from breaking. Artificial slicks can be readily produced by almost any fluid which is nonmiscible and lighter than water. Fluids of low surface tension are especially good slick producers because of their rapid spreading ability.*4 Newly formed artificial slicks commonly display high-order interference colors whereas natural slicks display no color other than possibly a first-order gray, but this difference is obviously related to the relatively large thickness of the newly formed film of an artificial slick. In general, a similar type of origin for natural slicks and for artificial slicks is suggested by their similar appearance. Petroleum released from oil seeps on the sea floor may be responsible for some local slicks, but diatom oil must largely account for the widespread development of slicks in coastal and insular waters. DEEP SCATTERING LAYER IN THE PACIFIC AND ANTARCTIC OCEANS* Introduction. During Operation HIGHJUMP (U.S. Navy Antarctic Development Project, 1947), the writer frequently noted the presence of a layer of deep scatterers on the fatho- gram of the USS HENDERSON. This layer partially scatters the outgoing sound signal of the recording echo sounder during daylight hours so that a reflection is recorded which shows a false bottom at various depths between 150 and 450 fathoms. *The writer is indebted to C. Eckart and R. W. Raitt of the University of California Marine Physical Laboratory, to M. W. Johnson of the Scripps Institution of Oceanography, and to R. J. Christensen, E. C. LaFond, and D. W. Pritchard of the U.S. Navy Electronics Laboratory for critically reading this manuscript. The fathograms from which the data are taken were obtained by the personnel of the USS HENDERSON and the USS NEREUS. In connection with obtaining the fatho- grams, the assistance of Captain C. F. Bailey of the USS HENDERSON and of E. C. LaFond, who supervised the ob- taining of the arctic fathograms of the USS NEREUS, is especially appreciated. 82 Subsequent examination of a fathogram across the Pacific and one from Hawaii to the arctic also revealed the frequent display of this phenomenon. As these records greatly increase the present knowledge of the geographic distribution and as other new information was observed regarding this phenome- non, the results of an examination of these three fathograms is presented in this paper. Previous Investigations. Previous investigations+5~49 made with sonar gear since 1942 by workers at the University of California Division of War Research and later at the U.S. Navy Electronics Laboratory, the Scripps Institution of Ocea- nography, and the University of California Marine Physical Laboratory revealed that sound scatterers are not uniformly distributed in the ocean but that they exhibit a striking vari- ation with depth. Frequently, at about 175 fathoms, an ex- ceptionally well-defined layer of scatterers was found that had at least ten times the scattering power of scatterers at shoaler depths. It was noted that this deep scattering layer* is principally a daytime phenomenon. In the morning, scatterers descended from near the surface to form the deep scattering layer and in the evening they ascended toward the surface. Such a diurnal cycle strongly suggested that this phenomenon was caused by migrating marine organisms rather than by a physical dis- continuity in the water (e.g., a temperature change). Also, a temperature-change boundary could not account for the in- tensity of the scattered sound. It is well known from net hauls that offshore zooplankton in general (such as the cope- pods Calanus finmarchicus and Metridia lucens, pelagic prawns, euphausiids, and many others) exhibit negative phototropism and that they make daily vertical migrations from the surface to depths as great as 2500 feet. Presumably, many types of zooplankton migrate to the surface at night to feed in the phytoplankton-rich surface layers and in the morning they descend to regions of darkness at great depth, SS *It has also been suggested that this layer of deep scatterers be called the ECR layer in recognition of the joint discovery by C. F. Eyring, R. J. Christensen, and R. W. Raitt, in con- nection with underwater sound work at the University of California Division of War Research. Other workers who have made important contributions to the study of this phe- nomenon include C. Eckart, G. E. Duvall, R. Ely, and M. W. Johnson. M. W. Johnson first showed the apparently biological nature of the scattering layer. Most of the studies by these workers are in anonymous wartime reports. possibly for safety from their predators. However, many marine zooplankton forms may be too small to scatter 18-kc. sound effectively. For this reason it has been suggested that the sound scatterers are nekton such as fish or squid which follow and feed upon the zooplankton. In any case it is probable that migrating zooplankton are at least indirectly responsible for the deep scattering layer. There is comparatively little previous information re= garding the geographical distribution of the deep scattering layer. It is known to be frequently present off the California and Baja California coasts, especially during the day. It has been occasionally reported from various spots in the Pacific. Recently, workers at Woods Hole Oceanographic Institution have reported (personal communication) the presence of this phenomenon in the Atlantic Ocean. Also it is probable that some of the uncharted shoals reported by ships at sea are false bottoms ascribable to the deep scattering layer. Deep Scattering Layer on the USS HENDERSON and USS NEREUS Fathograms. Prior to a discussion of the HENDERSON and NEREUS types, it should be pointed out that the absence of a record of the deep scattering layer on the fathogram does not necessarily preclude its presence, because such absence may be due to mistuning or to other causes. A low gain setting will fail to bring in the deep scattering layer; on the other hand, a gain setting which is too high may mask the layer. Such changes in sensitivity undoubtedly account for its alternate disappearance and re- appearance throughout certain days. The layer may also be masked by background noise produced by the ship when underway or by operation of ship’s equipment of various kinds. However when it does not show up throughout a long period of time, it may be assumed that it is absent or at least that it is very poorly developed. Throughout these cruises, the echo sounders were primarily operated to obtain depth information and the recording of the deep scattering layer was incidental. The length of the outgoing sound signal ‘masked any echoes from the layer when it ascended to depths of less than about 100 fathoms on the HENDERSON record and less than about 60 fathoms on the NEREUS tape. The time used throughout this paper is the standard time for the zone in which the ship was located. The NMC fathometer of the HENDERSON and the NMC-1 fathometer of the NEREUS utilized 18-kce. sound pulses. { 83 FIGURE 39. Map of the Pacific Ocean showing the distribution of the deep scattering layer along the tracks of the USS HENDERSON and the USS NEREUS. Solid lines indicate the continuous or almost continuous day- time development of the layer. Dotted lines show the intervals during which indications of the layer were rare of entirely absent from the fathogram. © #2 8 @ © © BB BER OO ®@ ve @ @©se © € © 8 8 8 He HH 8B 8 8 HT RT 7FrmUDDOmUUDDDCUO WA YOU O8SE-iW LevHS VSO NI 3G¥W TN NSOWYS ONL GO SNIGNLSVANNYW vou 9638 IW LdvHO VSO NI 30¥W e me i eae nee 3 5: Farge a OC ee aya ye = y Tosan: erie ie z } § red fs HOUSE ieee seis : i Z z: a : Deep Scattering Layer jt ae Quigoing Signal ie : - ee: ee ot NO ae EN rbd a "Sunrise at 0545 | ae Se | sf : teciean i, nate ENE ipa ie a $ & | 3 0600 se FIGURE 40. A. Fathogram showing the daytime development of the deep scattering layer at 200 to 225 fathoms on 8 December 1946 in the vicinity of latitude 03° N and longitude 131° W. Note formation of the scatterers into a layer at about 0615 hours or shortly after sunrise. Earlier downward descent of the scatterers is not apparent on this type of fathogram because of the long length of the outgoing sound signal and general extension of this signal caused by near-surface scattering. #*eeoeeoeeo @ BEEBE IDA BA Bs Occ Tae z : PEN ek Yoiae Topmek Ne Wiction- Serum, eal: fesyed seid Leal / 0898-1 LHVYHS ON N3GWYD SNI OD SNIEoisvan hes Ti ro ? CRO Raa TE we er As ering aaa 3 Ls. “T7 Beep Scat were 4 ped. en B. Fathogram showing daytime development of the deep scattering layer at 275 fathoms on 28 January 1947 in the antarctic in the vicinity of latitude 62° S and longitude 117° W. This was one of the few instances in which the layer was well-developed in the antarctic. 84 The distribution of the deep scattering layer during Operation HIGHJUMP and other cruises is shown in figure 39; its general appearance is shown in figure 40. With the ex- ception of two days in the vicinity of the Marquesas Islands, the layer was recorded the greater part of each day during the daylight hours throughout the passage from San Diego to the antarctic from 2 December to 23 December 1946. Con- trolled by the length of daylight, the layer was detected at least discontinuously for as short as a 10-hour period and as long as a 19-hour period. Except in the early morning or in the late evening at times when the layer was actively mi- grating, it was developed at depths that ranged from 150 to 450 fathoms. Near San Diego a depth of about 150 to 200 fa- thoms were characteristic whereas, in the tropical and southern waters, a depth of 200 to 350 fathoms was more typical. The ascent and the descent of the layer were closely correlated with sunset and sunrise. With the exception of one or two questionable sporadic displays of the deep scattering layer, it was completely absent from the fathogram during hours of darkness. The phenomenon of a double layer was frequently displayed. The Antarctic Convergence was crossed at noon on 23 De- cember in the vicinity of latitude 62°S. This water-mass boundary was clearly indicated by the abrupt drop in tempera- ture from 39 to 33 degrees F. It is noteworthy that the deep scattering layer disappeared completely for three days after the ship crossed this boundary and that it was seldom observed to be well-developed in antarctic waters. During the period from 25 December to 2 March, the HENDERSON navigated slowly westward along the western Pacific and Indian Ocean sectors of Antarctica. Only a few indications of layers of deep scatterers were recorded for short intervals from 27 December to 21 January, a period of permanent or of almost permanent daylight. From 21 to 29 January, the deep scattering layer was again well-developed and during this interval displayed the typical diurnal cycle (fig. 40). This display might be correlated with the return of a day-and-night cycle because by this date there were a few hours of complete darkness. However, after 2 February, the deep scattering layer was seldom observed either during the remainder of the antarctic cruise or en route to Australia. During the return passage from Australia to the United States, the deep scattering layer was detected on the third day out of Sidney. The typical diurnal cycle was recorded each day until the echo sounder went out of operation (at about latitude 20°S) because of mechanical failure. 85 ; : x He Sos ; ; ; ) % es sap oas: r 50 SUNRISE _ ke es 3 5 OF \C "Say a a Nos 06 60, 07 é : Nos : : ZOIULY 47% fH 20) 0 EE Be 4 oe | 14OG6 RR ae PAS 2) =10) é 10 $ an 16 7 0 18 Sat RASEEY. 21 22 DEEP SCATTERING LAYER COO se 4 x : aml ‘| @23 00:00 va) Fy OL Ls O2 03 21 JULY 47 Sf may 9 FIGURE 41. Development of the deep scattering layer in the North Pacific on 20 and 21 July 1947 at 150 to 175 fathoms indicated depth scale would be in- creased by a factor of 5). Note descent of the scatterers beginning before sunrise to form the layer and ascent beginning shortly before sunset but not reach- ing the 60-fathom line until well after sunset. Note, also, the development of double layers at 0700 and 1300 hours. Although most of the scatterers rise with nightfall, this fathogram shows the unusual development of a layer throughout the night. 86 During the period between 15 July and 10 August 1947, the USS NEREUS made acontinuous fathogram from Pearl Harbor to the arctic with an NMC-1 fathometer using 18-kc. sound pulses. The itinerary was via Adak and the Bering Sea. This fathogram shows indications of the development of the deep scattering layer each day throughout the cruise whenever the vessel was in deep oceanic water. The shoal depth of the Bering Sea precluded the development of a deep layer of scatterers and the fathogram shows no evidence of any layers of scatterers in these areas. The NEREUS fathogram displays especially well the morning descent and the evening ascent of scatterers. They appear to migrate as a layer rather than diffused but the movement of scatterers in depths less than 60 fathoms cannot be determined beéause of masking by the qutgoing ping. Although the diurnal vertical migration is well displayed, the scatterers descended to a depth so great that, throughout most days, they were beyond the range of good detection by the echo sounder; therefore it was only sporadically recorded. On 20 July at noon position of latitude 44°49'N, longitude 175°19'W, the layer was prominently developed throughout the entire day (fig. 41). This comparatively strong develop- ment of the layer may have been caused by a higher concentra- tion of scattering organisms in the productive waters of the Aleutian (Subarctic) Current which lies between latitude 42°N and the Aleutian Islands. The development of the deep scattering layer from 175 to 225 fathoms was in agreement with depths observed elsewhere. Twice during this day, a double layer appeared. Especially surprising was that, although a portion of the scatterers rise at sunset, the rest remained at a depth of 175 fathoms throughout the night. Al- though the other tapes examined occasionally show sporadic indications of a scattering layer at night, this was the only record of a prominent and continuous layer throughout the most of the night. Another interesting phenomenon noted only on the NEREUS fathogram was the presence of a double layer descending each morning during the period from 15 July to 18 July. These double descending layers were separated by a time interval of about 20 minutes and apparently were the result of the downward migrations of two types of organisms that are negatively phototropic to markedly different degrees. Yet, at sunset of these same days, only a single ascending layer was noted. 87 88 The vertical migrations were so clearly defined on the NEREUS tape that it was possible to measure roughly the rate of ascent and descent. In the morning the scatterers appear to descend at a rate of about 10 to 15 feet per minute. The evening ascent was slightly more rapid and was accom- plished at a rate of about 15 to 18 feet per minute. In agreement with all other observations, the deep scat- tering layer was almost entirely a daytime phenomenon and the vertical migrations were closely correlated with sunrise and sunset or, more exactly, with the beginning and end ofa certain, but unknown, amount of twilight. The descent, deeper than 50 fathoms, began about one hour before sunrise and the layer attained its maximum depth shortly after sunrise. The layer varied only slightly from this depth throughout the day. The evening ascent began shortly before sunset but did not reach the 50-fathom depth until about one hour after sunset. Just what became of the layer at depth shoaler than 50 fathoms is not known because any further rise of the layer was masked by the outgoing signal. However, prominent extension of the outgoing signal during hours of darkness indicated the abundance of scatterers in the upper 50 fathoms of water. During the period from 11 August to 1 September 1947, the USS HENDERSON obtained a fathogram across the Pacific Ocean with a recording NMC fathometer from San Diego, California, to Yokosuka, Japan, via Pearl Harbor, Hawaii. Although the fathometer was operating erratically most of the time so that the fathogram is poor, the deep scattering layer can be at least sporadically detected almost every day at various times during daylight hours. From the fathogram it appears probable that a properly working and sufficiently sensitive echo sounder would have recorded a daytime de- velopment of the deep scattering layer essentially continu- ously across the Pacific. When the vertical migration of the layer was clearly recorded, it invariably began to descend about one-half hour or more before sunrise and to rise shortly before sunset; however the upward migration was not completed until after sunset. Multiple layers were occasionally present and the scatterers were located at a depth between 150 and 250 fa- thoms. During the first half of the San Diego to Pearl Harbor passage, the layer was present during portions of each day at a depth from 175 to 250 fathoms. Because of mechanical failure, the echo sounder was not in operation during the last half of this passage. After leaving Pearl Harbor, the layer was fairly well- developed the first day out of port. During the next two days, it was not detected. Yet from the fourth day out of port until arriving in the shallow water off Japan, five days later, the layer was recorded every day and it appeared to become more strongly developed with westward penetration. Discussion and Conclusions. Examination of three fa- thograms, which cross the Pacific in both a North-South and an East-West direction and cover a sector of the Antarctic Ocean, shows a wide development of the deep scattering layer. It appears to be an oceanic phenomenon which is Pacific-wide and probably world-wide. All of these records further substantiate the diurnal cycle by which the scatterers descend in the morning and ascend to near the surface at night. On the NEREUS fatho- gram, the scatterers begin their descent about one hour before sunrise and they do not complete their ascent until about one hour after sunset, so the scatterers are in the surface waters only during rather complete darkness. Ap- parently the scatterers are motivated by a small amount of light, so the migrations are actually correlated with a certain amount of twilight rather than sunrise and sunset. No infor- mation: was obtained on the distribution of scatterers in the surface water at night because of masking by the outgoing ping. Because of the diurnal cycle, it is evident that the deep scattering layer is a biological phenomenon, so the scattering agents must be zooplankton, nekton, or bubbles associated with some organisms. Yet, from these records, no definite conclusion can be drawn as to whether zooplankton or fish cause the scattering. It will be necessary to make numerous laboratory experiments on the scattering characteristics of the various forms and to correlate underwater sound data with net hauls before the nature of the scatterers can be established. However, the extensive distribution of the deep scattering layer is suggestive of zooplankton. The compara- tively slow speed and the migration of the scatterers asa layer is, perhaps, more suggestive of the general zooplankton than of faster swimming fish. The occasional development of night layers, of double descending layers, and of multiple deep layers of scatterers show that the phenomenon is com- plicated and probably involves many kinds of organisms and different stages of development of a single species. The amount of scattering is dependent in part on the sum of the cross-sections of all of the objects present. The total 89 90 mass of zooplankton in the ocean is many times the mass of fish. Also, since the mass of a body varies as the cube of any linear dimension, whereas the surface varies as the square, a given mass of small organism such as Zooplankton present a much greater surface from which scattering might take place than an equal mass of fish. Thus the extensive and frequently continuous distribution of the deep scattering layer suggests that pelagic zooplankton may be the basic cause of the phenomenon. Yet, if zooplankton scatter sound like solid or liquid particles, most of them are too small to be effective scatterers of 18-kc. sound, which has a wave length of about 3 inches in water, because the scattering efficiency of an object smaller than the wave length is pro- portional to(d/\)*,where ) is the wavelength of the sound Signal, and d is the circumfexence of the scattering object. Therefore, solid or liquid particles are inefficient scatterers if less than about one inch, so an unreasonably high concen- tration of such organisms is required to produce the observed scattering. Also the intensity of the scattering from small organisms is highly dependent upon the frequency of the sound but, in work off California, such frequency dependence has been shown not to exist. Thus, although the small zoo- plankton such as the copepods are probably not the scatterers, larger. forms such as the euphausiids, which often reach the length of about one inch, may possibly cause the scattering. Very small air bubbles in water are known to be excellent scatterers of sound because a gas has a markedly different density and compressibility than water. For this reason, gas bubbles have an ‘‘effective diameter’’ for scattering sound of many times their actual physical diameter. Scattering is especially great if the bubble is of a certain critical size so that it is resonant. The diameter of a resonant air bubble in water for 18-kc. sound is about 1.5 millimeters at 150 fathoms, about 2.0 millimeters at 265 fathoms, and 2.5 milli- meters at 415 fathoms. The size of a resonant gas bubble enclosed in a marine organism would vary somewhat from these figures because it would depend upon the elastic proper- ties of the organism and the type of gas. In any event, if minute bubbles are enclosed in the migrating organisms or if they are excreted by these organisms and exist for a short interval before being dissolved, they would probably adequately account for the phenomenon of deep scattering. However there is no record of the presence of such bubbles in vertically migrating types of pelagic organisms. As might be expected, there appears to be some correlation between the depth of the deep scattering layer and factors which control the depth penetration of light. For example previous observations*® in coastal water off California showed the characteristic depth to be about 150 to 200 fathoms. A similar depth was observed off California on the HENDER- SON records. However in the oceanic tropical and subtropical Pacific under conditions of highly transparent water and an overhead sun, the deep scattering layer was typically ata depth from 250 to 350 fathoms. No good correlation was detected between the amount of cloud cover and the depth of the layer. An interesting question to consider is what effect the continuous daylight of polar midsummer has upon the diurnal cycle of the scatterers. From the HENDERSON fathogram it appears that the layer generally does not form under condi- tions of permanent or almost permanent daylight. Yet, weakly developed and questionable layers of deep scatterers were sporadically present. In this connection, net haul studies of plankton by Bogorov29 are noteworthy. According to his studies, zooplankton in the Barents Sea (latitude 75°N), under conditions of permanent daylight, do not perform the regular vertical migrations that are characteristic of zoo- plankton of lower latitudes but rather they maintain an almost unchanged vertical distribution throughout a 24-hour period. Further south in the White Sea (latitude 65°S) Bogorov noted the presence of a mixture of both the usual migrating types and the polar nonmigrating types of zooplankton. Correlated with the return of a day-night cycle in the antarctic toward the end of January, the diurnal migrating of the scatterers and the development of a deep scattering layer was once again detected. However, in this connection, the almost complete absence of the layer during both February and the first part of March is puzzling and without a reasonable explanation. Investigation of the deep scattering layer is a fertile field for research. This phenomenon is of importance in connection with the transmission of underwater sound. If the scatterers are, even in part, fish, a study of the layer is of obvious direct commercial value. If the scatterers are zooplankton, much can be learned about these organisms, their habits, and distribution. Also, if measurements are made under controlled conditions so a scattering coefficient can be ob- tained, roughly quantitative data concerning the populations of the scatterers might be obtained. A study of the variation of the amount of scattering with sound pulses of various fre- quency would yield information on the size of the scatterers. 91 92 bibliography 1, Deacon, G.E.R., ‘‘The Hydrology of the Southern Ocean,”’ Discovery Reports, vol. 15, pp. 1-124, 1937. 2. Oxner, M., ‘‘Chloruration par la methods de Knudsen,’ Bulletin de la Commission Internationale pour 1’Exploration Scientifique de la Mer Mediterranee, No. 3, 1920. (Translated by Deevy, G., ‘‘The Determination of Chlorinity by the Knudsen Method,’’ Woods Hole Oceanographic Institution, Woods Hole, Mass., 1946.) 9 3. Knudsen, M., Hydrographical Tables, 1901. 4. Sverdrup, H.U., M.W. Johnson and R.H. Fleming, The Oceans: Their Physics, Chemistry, and General Biology, Prentice-Hall Inc., New York, 1942. 5. Byrd, R.E., ‘‘Exploring the Ice Age in Antarctica,” National Geographic Magazine, vol. 68, No. 4, p. 430, 1935. 6. Emery, K.O. and R.S. Dietz, ‘Gravity Coring Instrument and Mechanics of Sediment Coring,’’ Bulletin of Geological Society of America, vol. 53, pp. 1685-1714, 1941. 7. Hess, H.H., ‘‘Drowned Ancient Islands of the Pacific Basin,’’ American Journal of Science, vol. 244, pp. 772-791, 1946, 8. Shepard, F.P., ‘‘Submarine Topography off the California Coast,’’ Geological Society of America, Special Papers, No. 31, pp. 35-41, 1941. 9. Hendy, N.I., “‘The Plankton Diatoms of the Southern Seas,’’ Discovery Reports, vol. 16, pp. 151-364, 1937. 10. Hart, T.J., ‘‘On the Phytoplankton of the Southwest Atlantic and the Bellingshausen Sea,’’ Discovery Reports, vol. 8, pp. 1-268, 1934. 11. Karsten, G., “‘Das Phytoplankton des Anarktischen Meeres nach dem Material der Deutschen Tiefsee-Exxpedition 1898-9,”’ Deutsche Tiefsee-Expedition, vol. 2, pt. 2, pp. 1-136, 1905; pp. 137-219, 1906; pp. 223-544, 1907. 12. van Heurck, H., ‘‘Diatomees. Resultats du Voyage duS.Y. *“Belgica’’ en 1897-9,’’ Expedition Antarctique Belge, vol. 6, Botany, pp. 1-126, 1909. 13. Bailey, J.W., ‘‘Notice of Microscopic Forms Found in the Soundings of the Sea of Kamtschatka,’’ American Journal of Science, vol. 22, ser. 2, 1856. 14. Greville, R.K., ‘‘Descriptions of Diatomaceae Observed in California Guano,’’ Quarterly Journal Microscopical Science, vol. 7, pp. 156-66, 1859. 15. Pritchard, A., A History of the Infusoria, London, 1861. 16. Castracane, A.F., Report on the Scientific Results of the Voyage of H.M.S. ‘‘Challenger’’ During the Years 1873-6, Botany, vol. 2, 1886. 17. Ehrenberg, C.G., Resultate Untersuchungen der ihm Sud Polreise des Capt. Rofs in den Jahren 1841-3, Bericht Berlin Akademie, pp. 182-207, 1844. 18. Ehrenberg, C.G., Neve Untersuchungen uber das Kleinste eben als Geologisches Moment, Bericht Berlin Akademie, pp. 53-88, 1845. 98 94 19. Cleve, P.T., ‘‘On Diatoms from the Arctic Sea,’’ Bihang Svenska Vetenskopsakemien Akademie Handlingar, vol. l, No. 13, 1873. 20. Brightwell, T., “On Filamentous, Long-Horned Diatoma- ceae with a Description of Two New Species,’ Quarterl Journal Microscopical Science, vol. 4, pp. 105-9, 1856. 21. Peragallo, M., Diatomees c’Eau Douce et Diatomees d’Fau Salee, Deuxieme Expedition Antarctique Francaise TIOS— NORM oZile 22. Ehrenberg, C.G., Uber Noch Zahlreich Jetzt Lebende Thierarten der Kreidebildung und den Organismus der Poly- thalamien, Berlin, 1840 and in Abhandlingar Akademie, Wissenschaften, Berlin, 1839, 1841. 23. Schmidt, A., Atlas der Diatomaceen=Kunde, 1874-1913. 24. Ehrenberg, C.G., Uber die Bildung der Kreidefelsen und des Kreide-mergels durch Unsichtbare Organismen, Abhand- lingar Akademie Wissenschaften, Berlin, 1838, pp. 59-147, 1839. 25. Grunow, A., Diatomeen von Franz Josephs Land, Denk- schriften der Akademie der Wissenschaften, Mathematische- Naturwissenschaftliche, pp. 53-112, 1884. 26. van Heurck, H., Synopsis des Diatomees de Belgique, atlas, 1, 2 (1880-1), text (1885). 27. Kutzing, F.T., Die Kieselschaligen Bacillarien oder Diatomeen, 1844, Nondhausen, 1865. 28. Peragallo, H., *‘Monographie due genre Rhizosolenia et des quelques genres voisins,'’ Le Diatomiste, vol. ly. Dida UY—G45 Gout, ita). 29. Heiden, H., and R.W. Kolbe, ‘‘Die Marinen Diatomeen der Deutschen Sudpolar-Expedition, 1901-3,’’ Deutsche Sudpolar Expedition, vol. 8, No. 5, pp. 450-714, 1928. 30. Smith, Wm., A Synopsis of the British Diatomaceae, vol. 1, 1853; vol. 2, 1856. 31. Cupp, E.E., ‘‘Marine Plankton Diatoms of the West Coast of North America,’’ Bulletin, Scripps Institution of Oceanogra- phy, University of California, vol. 5, No. 1, p. 26, 1943. 32. Cleve, P.T., Diatoms Collected during the Expedition of the ‘‘Vega’’, Ur Vega-Expeditionens Vetenskapliga Iakt- tagelser, vol. 3, 1883. 33. Cleve, P.T., and A. Grunow, ‘‘Beitrage zur Kenntniss der Arctischen Diatomeen,’’ Svenska Vetenskopsakademien Akademie Handlingar, vol. 17, No. 2, 1880. 34. Brightwell, T., ‘‘Remarks on the Genus ‘Rhizosolenia of Ehrenberg,’’ Quarterly Journal Microscopical Science, vol. 4, pp. 93-5, 1858. oD 96 35. Hustedt, F., Die Kieselalgen Deutschlands, Osterreichs und der Schweiz, Rabenhorst’s Kryptogammen-flora, Parts 1 and 2, 1927-33. 36. Cleve, P.T., ‘‘The Plankton of the North Sea, the English Channel, and the Skagerak in 1898,’’ Svenska Vetenskopsakad- emien Akademie Handlingar, vol. 32, No. 8, 1900. 37. Gran, H.H., Diatomeen in Nordisches Plankton (Brandt, K. und C. Apstein), Lief. 3, 19, pp. 1-146, 1905. 38. O'Meara, E., ‘‘Report on the Irish Diatomaceae,’’ Royal Irish Acadamy Procedure (ser. 2), vol. 2, Science, pp. 235-425, 1875-77. 39. Comber, T., *‘On the Occurrence of Endocysts in the Genus Thalassiosira,’’ Transactions Royal Microscopical Society, pp. 489-91, 1896. 40. Jorgensen, E., *‘Protisplankton. The Protisplankton and the Diatoms in Bottom Samples. Hydrographical and Biological Investigations in Norwegian Fjords,’’ Bergens Museum Skrifter, vol. 7, pp. 49-148, 1905. 41. Cleve, P.T., *‘Plankton Undersokningar, Cilioflagellates og Diatomaceer,’’ Bihang Svenska, Vetenskopsakademien Akademie Handlingar, vol. 20, No. 2, 1894. 42. Woodcock, A.H., ‘‘A Theory of Surface Water Motion Deduced from the Wind-Induced Motion of the ‘Physalia,’ ”’ Journal of Marine Research, vol. 5, No. 3, pp. 196-205, 1944. 43. Langmuir, I., ‘‘Surface Motion of Water Induced by Wind,’’ Science, vol. 87, No. 2250, pp. 119-123, 1938. 44. Use of Oil to Calm the Sea, Reprint of Hydrographic Office Information, No. 3, 1909. 45. Reverberation Studies at 24 Kilocycles, Reverberation Group of the University of California Division of War Re- search, Report No. U7, 1942. 46. Volume Reverberation: Scattering and Frequency Attenu- ation vs. Frequency, Reverberation Group of the University of California Division of War Research, Report No. U50, 1943. 47. Forward Scattering from the Deep Scattering Layer, Sonar Data Division of the University of California Division of War Research, Report No. M398, 1946. 48. Stratification of Sound Scatterers in the Ocean, Sonar Data Division of the University of California Division of War Research, Report No. M397, 1946. 49. Studies of the Deep Scattering Layer, Sonar Data Division of the University of California Division of War Research, Report No. M445, 1946. 50. Bogorov, B.G., ‘‘Peculiarities of Diurnal Vertical Mi- grations of Zooplankton in Polar Seas,’'’ Journal of Marine Research, vol. 6, No. 1, pp. 25-32, 1946. NEL San Diego 10-48 175 OG