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RESULTS OF
THE COAST GUARD'S
TARBALL SAMPLING PROGRAM

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RESULTS OF THE COAST GUARD’S TARBALL SAMPLING PROGRAM

BY

CADET 1/c CARL K. ANDERSON

U.S. COAST GUARD ACADEMY

GROTON, CONNECTICUT 06320
AND

J. L. SHUHY
U.S. COAST GUARD OCEANOGRAPHIC UNIT
WASHINGTON, D.C. 20590

MAY 1979

U.S. COAST GUARD TECHNICAL REPORT

The reports in this series are given limited distribution within agencies, universities,
and institutions engaging in cooperative projects with the U.S. Coast Guard. Therefore,
citing of this report should be in accordance with the accepted bibliographic practice
of following the reference with the phrase UNPUBLISHED MANUSCRIPT. Reproduc-

tion of this report in whole or in part is permitted for any purpose of the U.S. Govern-
ment.

ABSTRACT

The U.S. Coast Guard has been conducting a tarball sampling program since
December 1971 and to date over 1000 tows have been made. These tows have
been made in the North Atlantic Ocean, the Labrador Sea, Gulf of Mexico, North
Pacific Ocean, Bering Sea and the Gulf of Alaska. In general, low tar concentra-
tions are found in the polar areas, the average concentration being less than 0.038
mg/m?, and can probably be attributed to the small number of natural seeps and
limited amount of man’s activities in these areas. High average concentrations
(> 1.65 mg/m?) were found in the North Atlantic and North Pacific Oceans and
the Gulf of Mexico where man’s activities in the form of both drilling and ship-
ping are greater.

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Table of Contents

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TByoyoryoyeaveroe eral TARO NNUNE
North Pacific Ocean and Adjacent Areas__.-_-_-_
(Gualltqote ext eo Miata si Minnie Tl aN Re ee a eae
North Atlantic Ocean and Adjacent Areas__.-__
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Figure 1.
Figure 2.
Figure 3.
Figure 4.

List of Illustrations

Tarball Tow Apparatus used by the U.S. Coast Guard___.-_
Distribution of Tarballs in the North Pacific Ocean and Adjacent Areas_
Distribution of Tarballs in the Gulf of Mexico____-_._-_-_-
Distribution of Tarballs in the North Atlantic Ocean and Adjacent Areas

vi

INTRODUCTION

Tarballs are lumps of weathered petroleum pro-
ducts which are found floating on the sea surface.
The origin of tarballs have been attributed to both
man-made oil spills and natural crude seepage.
General reviews of the subject include those by
Butler, Morris and Sass (1973), Butler (1975), and
National Academy of Sciences (1975). For several
years the U.S. Coast Guard has been involved with
collecting samples of this oil residue. The goal of
this program was to learn something about the
distribution of tarballs and obtain baseline data on
their concentration in the ocean so that long term
trends could be observed. This monitoring of long
term changes would provide an evaluation of the
effectiveness of control measures in oil trans-
portation (by water) and offshore drilling.

EQUIPMENT AND PROCEDURES

Data for the tarball program were collected by
tarball tows conducted from Coast Guard cutters.
The program was started in December 1971, and
over 1000 tows have been made. The tows were
made daily when a ship occupied an Ocean Station
or when on fisheries patrol, on a not-to-interfere
with primary mission basis. In addition, tows were
taken on special cruises as directed by Area Com-
manders. The equipment utilized consisted of a
Neuston net (Fig. 1) attached to a towing frame
developed at the Coast Guard Research and
Development Center, Groton, Connecticut. The
net and frame were attached to a boom aboard the
ship by a wire harness. A propeller-type, digital
flow meter was hung in the mouth of the net to
measure the horizontal distance of the tow.

Tows were generally made at 3 knots or less for
a duration of between 45 to 60 minutes. Tarballs
were separated by hand from any other material
collected during the tow. Then they were sent to
the Coast Guard Oceanographic Unit where they
are presently in storage. Additional measurements
made while conducting the tow were sea surface
and air tempertures, wave/swell height and direc-
tion, and wind speed and direction. The tarballs
were weighed at the Oceanographic Unit, and the
concentration of tarballs on the sea surface (in

mg/m?) was calculated. These measurements were
entered in a data log along with the ship’s name
and cruise designation, the location and time of the
tow, and other environmental information and
were submitted to the National Oceanographic
Data Center (NODC).

The data have been separated into four
geographic locations: 1) The North Pacific Ocean
and adjacent areas, 2) The Gulf of Mexico, 3) The
North Atlantic Ocean and adjacent areas, and 4)
Ocean Weather Station Hotel. The data for the
North Atlantic and Pacific Oceans was further
broken down by location. A 5° x 5° grid was utilized
as the division of each locale. For the Gulf of Mex-
ico a 2° x5° grid was used due to the much smaller
area of the Gulf. The concentration of tarballs
(mg/m?) was found in each grid giving some indica-
tion of the quantity of petroleum residue present.

Due to the large number of tows made at OWS
Hotel and their continuity, it provided an ideal
location to observe variations in tarball concentra-
tion. Both seasonal change and those due to differ-
ing water masses and sea currents were examined.
The data were grouped into four three-month
seasons. Winter spanned December through
February; Spring, March through May; Summer,
June to August; and Fall, September through
November. Again the concentrations in each
season were averaged.

NORTH PACIFIC OCEAN AND ADJACENT
AREAS

Several observations can be made and others
deduced from the data thus far collected by the
Coast Guard in the tarball program.

It was found that the concentration of tarballs in
the Gulf of Alaska was very low. With nearly two
hundred tows made in the Gulf of Alaska, the tar-
ball concentration averaged less than 0.03 mg/m?
of sea surface area (Fig. 2). There are numerous
natural seeps along the coast of Alaska which may
account for a substantial amount of these tarballs.
With the opening of the Alaska Pipeline, and the
resultant increase in tanker traffic through these

waters, the Gulf of Alaska can serve as an ideal
laboratory to accurately monitor the effect of oil
transport through this region.

The Bering Sea had an even lower concentration
of tarballs than did the Gulf of Alaska. This may be
attributed to the few natural oil seeps along its
coastline and to the fact that ship traffic is nearly
nonexistent in this region. Twenty-three tows
were made in the Bering Sea and of these only one
tow recovered any tarballs. The concentration of
tarballs on that tow was .009 mg/m?.

Throughout the North Pacific Ocean tarball con-
centrations in the various grid areas fluctuated
widely (Fig. 2) from 0.0 to 3.8 mg/m?. Few of the
areas, however, had more than five tows made
within their boundries. Those areas with high con-
centrations generally had one or two tows with
much larger values than the rest, and thus their
high averages may be due to anomalies. The
average concentration for the North Pacific Ocean
was about 1.25 mg/m?. Typically there were high
concentrations between the Hawaiian Islands and
the west coast of the United States which may be a
result of commercial traffic through this area.

GULF OF MEXICO

In the summer of 1975 and winter of 1976 the
USCGC ACUSHNET made oceanographic cruises
in the U.S. coastal waters of the Gulf of Mexico.
During each of these cruises, tarball surveys were
conducted at 44 and 45 locations respectively. This
gave a reasonably synoptic picture of the tarball
concentrations in these waters.

The Gulf of Mexico was also found to have a
fairly high overall tarball concentration, about 1.45
mg/m? (Fig. 3). It was not constant throughout the
Gulf but increased from east to west. Charles W.
Morgan (personal communication) showed that
this may have some correlation with offshore oil
drilling. Morgan also described how the currents of
the Gulf will tend to sweep material rapidly into
the area along the Texas coast and then let it
accumulate as the water slows down. Koons and
Monaghan (1976) indicate that the shelf area of the
southwestern area of the Gulf is a region of high
seepage potential which may account for many of
the tarballs throughout the Gulf.

NORTH ATLANTIC OCEAN AND ADJACENT
AREAS

The Labrador Sea is another region of very low
tarball concentration. The area along the north-
eastern coast of Newfoundland was sampled by 3

tows with an average tarball concentration of
<0.01 mg/m? indicating a fairly stable condition.
Any increase in tarball concentration in this region
would tend to indicate that man-made oil spills or
dumping was responsible since this area is becom-
ing increasingly important in the search for oil.

The North Atlantic Ocean was an area of
extreme fluctuation in tarball concentration from
one grid area to another (Fig. 4). Although some
areas were sampled very heavily, there was a large
area at midocean that was never sampled. From
the data which was taken, it may be concluded that
along the northern half of the U.S.’s eastern
seaboard the tarball concentration is higher than in
other observed areas of the North Atlantic perhaps
due to the tremendous amount of commercial traf-
fic, including tankers, through the area. The cur-
rents in this area tend to bring tarballs from other
regions to this area resulting in higher tarball con-
centrations. The average concentration for the
North Atlantic Ocean was about 1.65 mg/m?
although some grid areas had concentrations of
greater than 8 mg/m.

OCEAN WEATHER STATION HOTEL

The data for OWS Hotel, as previously mentioned,
were grouped by season. It was found that the tarball
concentration can vary tremendously over a 24 hour
span, even if two successive tows were made in the
same water mass. In one instance during November
1975, the observed tarball concentration went from
0.0 mg/m? on the 25th to 320.7 mg/m? on the 26th!
Sea state conditions, water temperature, etc.,
remained constant over the period.

One particular three week span, November 19th
to December 12th, 1975, had an average tarball
concentration three orders of magnitude over the
usual November/December average. A system of
two warm-core eddies entered the region during
the time and may have carried the tarballs respon-
sible for this anomaly from the Sargasso area but
positive correlation is not possible.

The relatively high average concentration of
7.996 mg/m? and large standard deviation of
+45.475 may be a biased number due to the nature
of the operations on OWS Hotel. Basically the ship
remained in the area of a circle with a 15 nautical
mile radius while occupying OWS Hotel which
meant the ship was often drifting. It therefore may
well have been that the personnel conducting the
tows were looking for tarballs and made a con-
scious effort to collect tarballs. One tow had a con-
centration of 639.351 mg/m? which in it self is

enough to raise the average weight by almost 2
mg/m?. The large standard deviation is indicative
of the large spread in observed valves. By contrast,
the average concentration for the 5° x 5° grid that
OWS Hotel is located in was only 1.172 mg/? with
a standard deviation of +0.235. These latter
numbers were arrived at by excluding the OWS
Hotel data.

A final observation to be made at OWS Hotel
was that the tarball concentration did vary
seasonally. It was lowest in the winter season and
generally highest in the summer, although the tar-
ball concentration can be large in the fall or spring
as well. The winter season at OWS Hotel was
usually the period with highest sea state and the
greatest winds which would induce mixing of the
surface waters to greater depths. This would tend
to make values from samples collected during this
period lower than in periods of smaller seas and
lesser winds.

CONCLUSIONS AND RECOMMENDATIONS

In general, low tarball concentrations were
found in the polar regions. This can probably be
attributed to the limited amount of man’s activities
and fewer number of natural seeps in these areas.
Certainly these would be areas that would require
watching over the next several years.

Areas of the heaviest tarball concentration
appear to be in areas of high commercial traffic,
although high traffic areas generally coincide with
areas where extensive drilling is taking place, so
caution must be used when drawing conclusions.
Areas along both the east coast and west coast of
the United States fall into this category.

Due to the crude nature of sampling for tarballs,
the data presented is only representative of the
tarball concentration in the region. The more tows
that are taken, the more confidence that can be put
on the numbers associated with the concentration.

There are improvements which might be made
with the sampling techniques. High tarball concen-
trations have been found in wind rows (Langmuir
cells) and if the sampling happens to be done
between wind rows as opposed to along or across
wind rows, the results would be expected to differ
considerably. One- possible solution to help
eliminate this bias would be to sample in a trackline
perpendicular to the wind. This would tend to cut
across wind rows giving a more representative
sample.

More emphasis should also be given to describing
the hardness, texture, color, and sizes of the tar-
balls collected. When stored in jars, the tarballs
tend to lose their identity. These better descrip-
tions would give some insight into the age and
possibly source of the tarballs.

There are still areas in the middle of the Gulf of
Mexico that have not been sampled under this pro-
gram. Special attention would have to be given to
the water mass being sampled during the tow to
determine whether the collected samples
originated in the Gulf of Mexico or are being
carried through by the Loop Current.

There have been a fair number of tows taken in
the Gulf of Alaska, an area that bears future
watching. An increase in the tarball concentration
in this area could be indicative of the increase in
petroleum transportation and the need for stricter
guidelines and/or enforcement of pollution regula-
tions. Similarly, continued monitoring of the polar
regions in the western North Atlantic Ocean is
necessary to evaluate the fate of that region.

Finally, emphasis should be put on sampling in
those areas where there is little or no information
now available. The chemical analysis of tarballs
would give some insight into the origins and
possibly age of the tarballs by looking at the
hydrocarbon fractions and trace elements.
However, due to the large number of samples
collected and the expense involved in the analysis,
only selected samples could be analyzed. Only
through diligence can changes in concentration be
detected and this is necessary if we are to deter-
mine whether the control measures presently
employed are adequate.

REFERENCES

Butler, J. N., B. F. Morris, and J. Sass (1973). Pelagic Tar from
Bermuda and the Sargasso Sea, Bermuda Biological Station
for Research, Special Report No. 10, 346 pp.

Butler, J. N. (1975). Pelagic Tar, Scientific American, 232,
No. 6, 90-97.

Koons, C. B. and P. H. Monaghan (1976). Input of Hydrocar-
bons from Seeps and Recent Biogenic Sources. Sources,
Effects, and Sinks of Hydrocarbons in the Aquatic Environ-
ment, American Institute of Biological Sciences, pp. 84-107.
National Academy of Sciences (1975).

National Academy of Sciences (1975). Petroleum in the Marine
Environment, National Academy of Sciences, 107 pp.

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U.S. DEPARTMENT OF TRANSPORTATION
UNITED STATES COAST GUARD
Washington, D.C. 20590

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