HELDIANA
Botany
NEW SERIES, NO. 43
El Nino in Peru:
Biology and Culture Over 10,000 Years
Jonathan Haas and Michael O. Dillon, Editors
July 31, 2003
Publication 1524
PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY
EL NINO IN PERU:
BIOLOGY AND CULTURE
OVER 10,000 YEARS
Papers from the VIII Annual
A. WATSON ARMOUR III SPRING SYMPOSIUM
MAY 28-29, 1 999 CHICAGO
FIELDIANA
Botany
NEW SERIES, NO 43 NATURAL \ F5TC&Y SURVEY
AUG 8 2003
LIB&AIN
El Nino in Peru:
Biology and Culture Over 10,000 Years
Jonathan Haas and Michael O. Dillon, Editors
Field Museum of Natural History
1400 South Lake Shore Drive
Chicago, Illinois 60605-2496
U.S. A.
Published July 31, 2003
Publication 1524
PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY
2003 Field Museum of Natural History
ISSN 0015-0746
PRINTED IN THE UNITED STATES OF AMERICA
CONTENTS
Contributors vii
Introduction ix
1 The Lomas Formations of Coastal Peru: Composition and
Biogeographic History 1
Michael O. Dillon, Miyuki Nakazawa, and Segundo Leiva Gonzdles
2 Response of a Land Snail Species (Bostryx conspersus) in the
Peruvian Central Coast Lomas Ecosystem to the 1982-1983 and
1997-1998 El Nino Events 10
Rina Ramirez, Saida Cordova, Katia Caro, and Janine Dudrez
3 Debris-Flow Deposits and El Nino Impacts Along the Hyperarid
Southern Peru Coast 24
Luc Ortlieb and Gabriel Vargas
4 Paleoenvironment at Almejas: Early Exploitation of Estuarine
Fauna on the North Coast of Peru 52
Shelia Pozorski and Thomas Pozorski
5 The Impact of the El Nino Phenomenon on Prehistoric Chimu
Irrigation Systems of the Peruvian Coast 7 1
Thomas Pozorski and Shelia Pozorski
6 El Nino, Early Peruvian Civilizations, and Human Agency:
Some Thoughts from the Lurin Valley 90
Richard L. Burger
Contributors
Editors
Jonathan Haas
Anthropology Department
Field Museum
1400 So. Lake Shore Drive
Chicago, Illinois 60605-2496
U.S.A.
(jhaas@fmnh.org)
Michael O. Dillon
Botany Department
Field Museum
1400 So. Lake Shore Drive
Chicago, Illinois 60605-2496
U.S.A.
(dillon @ sacha.org)
Contributors
Richard L. Burger
Peabody Museum of Natural History
Yale University
170 Whitney Avenue
New Haven, Connecticut 06520
U.S.A.
(Richard.Burger@yale.edu)
Katia Caro
Museo de Historia Natural
Universidad Nacional Mayor de San Marcos
Apartado 14-0434
Lima- 14, Peru
Saida Cordova
Museo de Historia Natural
Universidad Nacional Mayor de San Marcos
Apartado 14-0434
Lima- 14, Peru
Janine Duarez
Museo de Historia Natural
Universidad Nacional Mayor de San Marcos
Apartado 14-0434
Lima- 14, Peru
Segundo Leiva Gonzales
Museo de Historia Natural
Universidad Privada Antenor Orrego
Trujillo, Peru
Miyuki Nakazawa
Department of Biology
Kyushu University
6-10-1 Hakozaki, Higashi-ku
Fukuoka 812-8581, Japan
(chn52010@par.odn.ne.jp)
Luc Ortlieb
Institut de Recherche pour le Developpement
UR Paleotropique
32 Avenue Henri-Varagnat
F-93143 Bondy-Cedex, France
(Luc.Ortlieb@bondy.ird.fr)
Shelia Pozorski
Department of Psychology and Anthropology
University of Texas-Pan American
Edinburgh, Texas 78539
U.S.A.
(spozorski@panam.edu)
Thomas Pozorski
Department of Psychology and Anthropology
University of Texas-Pan American
Edinburgh, Texas 78539
U.S.A.
(tpozorski @ panam.edu)
Rina Ramirez
Museo de Historia Natural
Universidad Nacional Mayor de San Marcos
Apartado 14-0434
Lima- 14, Peru
(rinarm@pucrs.br)
Gabriel Vargas
Institut de Recherche pour le Developpement
UR Paleotropique
32 Avenue Henri-Varagnat
F-93143 Bondy-Cedex, France
(Gabriel.Vargas@bondy.ird.fr)
Departamento de Geologia
Universidad de Chile
Plaza Ercilla 803
Santiago, Chile
(gvargas@ing.uchile.cl)
vn
Title-page illustration: Moche fineline painting from northern Peru
showing a naturalistic figure in an animated reed boat. The draw-
ing is by Donna McClelland and is reproduced from Moche Fine-
line Painting: Its Evolution and Its Artists (UCLA Fowler Museum
of Cultural History, 1 999) courtesy of the artist, the authors, Chris-
topher Donnan and Donna McClelland, and the publisher. The ves-
sel from which the drawing was made is in the collections of the
Art Institute of Chicago.
Introduction
On May 28-29, 1999, a group of sixteen scientists met at the Field
Museum in conjunction with the VIII Annual A. Watson Armour
III Spring Symposium to discuss the impacts of the El Nino phe-
nomenon on the biology and cultural history of coastal Peru over
the last 10,000 years. The meeting brought together anthropolo-
gists, archaeologists, and biologists with a shared interest in the
effects of this potent global weather disturbance. The one-day
workshop and subsequent symposium presented research results
documenting the impact of this phenomenon from a wide range of
perspectives. The papers published here represent the results of
research from these various fields and differing points of view.
The impact of El Nino on terrestrial and marine ecosystems has
been well documented over the last 20 years, but the interpretation
of these results remains controversial. The common thread linking
most of these efforts is an attempt to date the onset of the El Nino
phenomenon using various types of proxy data. Estimates range
from a few thousand to tens of thousands of years. Whatever its
age, it is obvious that El Nino had and continues to have a pro-
found impact on the coastal environments of Peru, and more gen-
erally of western South America.
Michael O. Dillon
IX
The Lomas Formations of Coastal Peru:
Composition and Biogeographic History
Michael O. Dillon, Miyuki Nakazawa, and Segundo Leiva Gonzdles
For nearly 3,500 km along the western coast of
South America (5-30S latitude), the Atacama
and Peruvian deserts form a continuous hyper-
arid belt, broken only by occasional river val-
leys from the Andean Cordillera. Native vege-
tation of the deserts is largely restricted to a
series of fog-dependent communities termed lo-
mas formations, meaning small mountains. This
chapter provides a backdrop for the subsequent
discussions in this volume of human occupation
in coastal Peru over the last 10,000 years. This
requires a synthesis of the present-day coastal
vegetation, analysis of the origins of the mod-
ern flora, and reconstruction of past climates,
including the onset of El Nino conditions, using
proxy data from a variety of sources. Paleocli-
matic data suggest that arid conditions existed
along the coast prior to 100,000 years ago, well
before the arrival of the first humans in western
South America. Distributional patterns and re-
lationships within specific members of the flora
are discussed to help explain current conditions.
Specifically, we have examined relationships in
the flowering plant genus Nolana (Solanaceae),
a group of over 80 species distributed predom-
inantly in the lomas formations of Peru and
Chile. The reconstructed phylogeny of Nolana
provides a framework for examining the coastal
lomas formations and the processes important
in their evolution, including the effects of gla-
cial cycles, sea level changes, and the historical
development of the El Nino-Southern Oscilla-
tion weather phenomenon.
Introduction
Much of the western coast of South America
(5-30S latitude) is occupied by deserts, form-
ing a continuous belt that extends for more than
3,500 km along the western escarpment of the
Andean Cordillera, from northern Peru to north-
ernmost Chile. The climate and geomorphology
of this region have been discussed in detail
elsewhere (Dillon 1997; Ferreyra 1953; Rundel
et al. 1991), and only a brief sketch is provided
here for discussion purposes. The Peruvian de-
sert is a narrow coastal band at the base of the
Andean Cordillera that extends nearly 2,000 km
in length but is only 50-100 km wide. The de-
sert is interrupted only by occasional rivers that
reach the coast, and their borders support ripar-
ian vegetation common to the inland river val-
leys. The factors responsible for the develop-
ment of the hyperarid conditions include isola-
tion from eastern weather patterns by the An-
dean Cordillera, and temperature homogeneity
resulting from the influence of cool sea-surface
temperatures associated with the south-to-north
flow of the Humboldt (Peruvian) Current. This,
combined with a positionally stable subtropical
anticyclone, results in a mild, uniform coastal
climate with the regular formation of thick fogs
below 1 000 m elevation from September to De-
cember.
Where the coastal topography is low and flat,
this stratus layer dissipates inward with little bi-
ological impact (Figs. 1 and 2A), but where iso-
lated mountains or steep coastal slopes intercept
M. O. Dillon et al
o vegetation
Tillandsia spp. 4-800
fv" woody plants
o:6-. o: ./ herbaceous perennials
:<.<-
no vegetation
Tillandsia spp.
Figure 1. Vegetation zonation in the fog zone or lomas formation of coastal Peru.
the clouds, a fog zone develops with a stratus
layer concentrated against the hillsides (Fig.
2B). This fog, termed garua in Peru, is key to
the floristic diversity of the unusual desert plant
communities, termed lomas formations. In
Peru, we estimate there are nearly 70 discrete
localities supporting lomas vegetation (Fig. 3),
including several offshore islands (e.g., Islas de
Las Viejas, San Gallan, San Lorenzo). The ac-
tual area covered by vegetation, even during pe-
riods of maximum development, is probably
less than 8,000 hectares. The vegetation of the
lomas formations of Peru is unique and com-
posed of many species that occur only in these
small desert oases.
Lomas Vegetation
Lomas communities occur as islands of vege-
tation separated by varying distances of hyper-
arid habitat devoid of plant life. Since plant
growth is dependent on available moisture and
the drought tolerance of individual species, a
combination of climate, physical topology, and
the ecophysiology of each species of plant ul-
timately determines community composition.
The individual formations are highly variable
and consist of mixtures of annuals, short-lived
perennials, and woody vegetation. Current es-
timates of the flora of the Peruvian lomas in-
clude over 815 species distributed in 357 genera
and 85 families of flowering plants. The distri-
bution patterns of these species can be roughly
grouped into broad categories, including (1)
pan-tropical or weedy species, (2) long-distance
disjunctions from the Sonora Desert or Baja
California, (3) species disjunct from the adja-
cent Andean Cordillera, and (4) plants restricted
to the coastal deserts, sometimes in a single lo-
cality. Endemism at the level of species often
exceeds 40% in individual lomas communities.
The greatest number of endemics are found in
southern Peru between 15S and 18S latitude
and include both endemic genera, such as Is-
laya (Cactaceae), Weberbaueriella (Fabaceae),
Mathewsia, and Dictyophragmus (both Brassi-
caceae), and endemic species within genera,
such as Ambrosia (Asteraceae), Argylia (Big-
noniaceae), Astragalus (Fabaceae), Cristaria
and Palaua (both Malvaceae), Calceolaria
Figure 2. Atacama and Peruvian desert communities. A. Flat inland desert region devoid of plants. B. Stratus
clouds impacting the headlands where lomas formations develop. C. Rainstorm above Cerro Campana in the northern
Peruvian coastal desert during the 1997-1998 El Nino event, February 1998. D. Cerro Cabezon during the 1997-
1998 event. E. Corn cultivated within the lomas formations of Cerro Cabezon in northern Peru, January 1998. F.
Goats grazing on the abundant vegetation at Mejfa during the El Nino event, October 1983. G. A carpet of Nolana
humifusa on the upper slopes of Cerro Cabezon, January 1998. H. Flowering individual of Nolana humifusa at Cerro
Cabezon.
The Lomas Formations of Coastal Peru
M. O. Dillon et al.
ACHENOO
MEJIA '.
-^ V3AMA GRANDE
200\ 400 690 \800km
Figure 3. Geographic features, including lomas formation localities, in the Atacama and Peruvian deserts.
(Scrophulariaceae), Tiquilia (Boraginaceae),
Jaltomata, Leptoglossis, and Nolana (all Sola-
naceae), and Eremocharis (Apiaceae).
We have examined patterns of similarity
within the overall flora of the lomas formations
and have found that the coastal deserts of west-
ern South America are not uniform (Duncan
and Dillon 1991; Rundel and Dillon 1998; Run-
del et al. 1991). Our analysis supports three flo-
ristic segments that appear to have independent
histories: (1) a northern Peruvian unit from
755'S to 12S latitude, (2) a southern Peruvian
The Lomas Formations of Coastal Peru
unit from 12S to 18S latitude, and (3) a north-
ern Chilean unit from 20S to 28S. The area
between 1 8S and 20S is nearly devoid of veg-
etation (Rundel et al. 1991) and is suggested to
have been a barrier to coastal dispersal for an
extended period (Alpers and Brimhall 1988).
Only 1 15 species, or ca. 12% of the total desert
flora of 1,350 vascular plant species, are re-
corded from both sides of 18S (roughly the
Peru-Chile border). When widespread weeds
are eliminated from that total, less than 6% of
the native species are known from either side.
Although the richness of the marine environ-
ment would have provided early man with a
primary source of sustenance (Keefer et al.
1998), the lomas formations could also have
acted as an important source of fresh water,
food, and construction materials for early coast-
al visitors and inhabitants (Lanning 1965). The
presence of vegetation, often forageable, would
have attracted the native camelids, for example,
guanaco, and deer, both of which were game
for early man. Supplies of seeds and insects
would have made lomas sites havens for native
bird species. The native flora does contain some
edible fruits; for example, Jaltomata and Ly-
copersicon, both members of the Solanaceae
family, have tomato-like, edible berries. Edible
roots from diverse plant families might also
have provided some nourishment that could
have been utilized periodically, for example,
Argylia radiata (Bignoniaceae), Begonia octo-
petala (Begoniaceae), Oxalis dombeii (Oxali-
daceae), Solarium montanum (Solanaceae), and
Tropaeolum peltophorum (Tropaeolaceae). Ag-
riculture may also have been practiced at some
locations, especially during exceptional years
associated with El Nino events. Today, crops
are cultivated in the lomas formations when op-
portunities are provided by increased available
moisture. Corn was planted at Cerro Cabezon
(Fig. 2E) in northern Peru during an El Nino
event in March 1998, and both corn and wheat
were cultivated in the lomas between Moque-
gua and Tacna in 1983.
The influence of man on the lomas forma-
tions, especially over the last 1500 years,
should not be underestimated. Many native
woody species have been severely depleted for
firewood and construction. It may be assumed
that native tree species, such as Caesalpinia
spinosa (tara), Carica candicans (mito), or
Myrcianthes ferreyrae, had wider distributions
and larger populations prior to the arrival of
man. The removal of woody vegetation almost
certainly would have changed the extent of her-
baceous plants. Building in many coastal areas
has replaced lomas habitat with homes and fac-
tories. Movement of livestock between the in-
terior and the coast has led to the introduction
of many Andean weeds (Sagastegui and Leiva
1993). The historical introduction of alien or
exotic species, such as Australian trees (Euca-
lyptus and Casuarina), has changed the char-
acter of the landscape. Perhaps the worst plague
that man has set upon the lomas formations
since the arrival of Europeans was the intro-
duction of herbivores such as goats (Fig. 2F),
which are very destructive to the native com-
munities.
El Nino Events
In our search for the forces that act on the
coastal regions, we identified short-term cli-
matic fluctuations of El Nino events (5- to 50-
year cycles) as important seasonal influences on
the coastal region. The physics behind the El
Nino-Southern Oscillation (ENSO) phenome-
non is complex and represents a worldwide
weather perturbation. El Nino conditions pre-
vail when the normally cold waters of the coast
of western South America are displaced by a
warmer, western Pacific surface and subsurface
body of water that stimulates brief periods of
heavy rainfall (Fig. 2C) and relatively high tem-
peratures. This influx of available moisture has
profound effects within the lomas formations
(Fig. 2D) and has undoubtedly helped shape
their composition and structure. Primarily, this
moisture stimulates massive germination of
seeds, leading to large blooming events that re-
plenish seed banks for annual and perennial
plants. These events also provide opportunities
for seed dispersal and establishment, which
would expand distributions under favorable
conditions (Fig. 2G). The impact of El Ninos
on these communities is obvious (Dillon and
Rundel 1990), and one can only wonder what
the coastal vegetation would resemble in the ab-
sence of these conditions. Potentially, levels of
floristic diversity would be much lower and mi-
gration and establishment more difficult. In the
western Pacific, the reverse effects of recurrent
droughts and rainfall variability have been im-
M. O. Dillon et al.
plicated in the evolution of vegetation patterns
in Australia (Nicholls 1991).
El Nino events have been recorded in both
historical (Quinn and Neal 1987) and Holocene
periods (DeVries 1987; Fontugne et al. 1999;
Magilligan and Goldstein 2001; Rodbell et al.
1999; Sandweiss et al. 1996, 1999, 2001). Lon-
ger-term records of El Nino events are more
difficult to detect and interpret (Moseley 1987).
Recently, Hughen et al. (1999) detected vari-
ability in growth patterns in fossil coral which
they interpreted as representing El Nino-like
conditions that may have existed for at least
124,000 years. Our studies of modern vegeta-
tion do not allow for estimations of the onset
of El Nino conditions, but regardless of their
age, they have undoubtedly played an important
role in shaping the present coastal communities.
Glacial Cycles and Sea Level
Changes
Longer-term climatic change associated with gla-
cial cycles (13,000- to 200,000-year cycles) pre-
dates the arrival of man and the first El Nino and
would have been active throughout the Pleisto-
cene (1.8 million years ago). It is estimated that
there have been at least 20 glacial events during
the Pleistocene, each with cycles of approximate-
ly 200,000 years. The formation of glaciers on
mountains and poles has caused sea levels to fluc-
tuate dramatically (Matthews 1990). Estimates of
sea level fluctuation range between 400 and 750
feet (120-230 m), and this lowering would have
significantly changed the position of the seashore
in relation to that of today. This drop would have
exposed a considerable area of the continental
shelf and displaced lomas plant communities, es-
pecially between 5S to 15S latitude (Fig. 4).
This would have resulted in species shifting their
ranges in relation to the near-ocean environments,
adapting to changing conditions in situ, or under-
going range reductions and extinction. Glacial cy-
cles would also have had a profound influence on
the flora and fauna of the coastal deserts by pro-
viding geographic isolation at certain times, and
at other times, opportunities for merging species,
thereby allowing for gene exchange. The last gla-
cial cycle ended ca. 13,000 years ago, and post-
glacial vegetation patterns are comparable to
those we find today (Dillon et al. 1995).
Nolana Studies
Within the lomas formations, the genus Nolana
(Solanaceae-Nolaneae) stands out as one of the
most wide-ranging and conspicuous elements of
the flora (Tago-Nakazawa and Dillon 1999).
Nolana is a genus of ca. 85 species that is large-
ly confined to coastal Andean South America
from central Chile to northern Peru, with one
species endemic to the Galapagos Islands. It is
the only genus to be encountered in nearly all
lomas formations. Nolana species are often im-
portant members of their respective communi-
ties and dominate in the numbers of individuals
present. Their showy flowers are beautiful, and
species display various types of habits annu-
als, perennials, or shrubs and variable corolla
sizes and shapes (Fig. 2H). Ecologically, No-
lana species prefer arid and semi-arid habitats,
with their greatest concentration in near-ocean
habitats within a few kilometers of the shoreline
(Fig. 2G). The establishment of a phylogeny for
Nolana has provided a framework for testing
hypotheses of isolation events in desert com-
munities. The species distribution pattern in No-
lana is similar to that in the overall flora and
displays three distinctive units: northern Peru,
southern Peru, and northern Chile. Only four
species have distributions that span the 18-
20S gap. The presence of two major groups
(clades) in the genus Nolana, one Peruvian and
the other Chilean, points to long-term isolation
of the genus above and below 18S latitude.
Reliable data on speciation rates for desert
plants are largely lacking. However, the devel-
opment of endemic genera and species, and the
morphological and physiological adaptations
they manifest, support the hypothesis of long-
term aridity along the coast of Peru, at least
from 12S to 28S latitude (Rundel and Dillon
1998). The timing of vicariant events (separa-
tion) can be estimated with molecular diver-
gence data to establish a molecular clock (Tago
1999). For the genes investigated, all estimates
for the first appearance of Nolana are late Ter-
tiary (Miocene, 10.6-11.6 mya). These data
also suggest that TV. galapagensis potentially
reached the Galapagos Islands sometime be-
tween 4 and 8 mya (late Miocene to early Pli-
ocene). Because of character evolution in the
mainland members of Nolana, it appears that
N. galapagensis was pre-adapted to arid habi-
tats prior to its dispersal to the island chain
(Tago-Nakazawa and Dillon 1999). The geo-
The Lomas Formations of Coastal Peru
10
12
13
78
77
76 C
Figure 4. Bathometric diagram illustrating the continental shelf of Peru between 5S and 14S latitude. Stippled
area indicates the land exposed should there be a 100-meter drop in sea level. Between 14S latitude (Pisco, Peru)
and 28S latitude (northern Chile), the continental margin is very narrow.
graphic origin of this remote island endemic re-
mains a mystery, but comparative morphology
points to Chilean ancestors (Dillon, unpubl.).
Recent archeological findings from the north-
ern Atacama Desert have recorded Nolana
fruits (technically mericarps containing seeds)
in rodent middens dating to 35,000 years B.P.
(Betancourt et al. 2000). These mericarps are
comparable to those we find in this desert lo-
cality today. Therefore, the divergence data
from molecular studies and the presence of No-
lana in desert habitats for no less than 35,000
years suggest that 10,000 years ago, the overall
character of the coastal flora was similar to that
found today. The frequency of strong El Ninos
and demonstrated sea level changes suggest that
these phenomena have played a role in stimu-
lating evolution in the plants of the lomas for-
mations.
Conclusions
The vegetation of coastal Peru is largely re-
stricted to the lomas formations, a series of iso-
8
M. O. Dillon et al.
lated, fog-dependent plant and animal commu-
nities that are diverse and highly endemic. In-
dividual lomas localities have unique species
compositions and display disharmonic patterns
found in "true" insular communities. While the
aridity along the Peruvian coast is essentially
constant, with negligible rainfall, the topogra-
phy and geologic history combine to divide
coastal Peru into a northern unit, 755'S to 12S
latitude, and a southern unit, from 12S to 18S
latitude.
Given available paleoclimatic data and di-
vergence times suggested by molecular clock
calculations on gene sequences, it appears that
Nolana occupied coastal desert environments in
both Peru and Chile prior to the Pleistocene gla-
cial events. Further investigations will be nec-
essary to test hypotheses of the age for the de-
sert, but our preliminary studies point to west-
ern South America as an arid region of great
antiquity well over 35,000 years ago. It appears
that the flora of the lomas formations have been
shaped by the effects of short- and long-term
climatic changes and by the influence of man
and introduced animals. Our data suggest sta-
bilized aridity for coastal Peru since before the
arrival of its first inhabitants (10,000 years
ago), but with dynamic periods with much
greater available moisture (Sandweiss et al.
2001). Early man would have found an envi-
ronment with more trees and much denser veg-
etation, which could have provided valuable re-
sources in the inhospitable coastal desert.
Acknowledgments. M.O.D. acknowledges the
support of the National Science Foundation and
National Geographic Society for field studies
associated with El Nino events. S.L.G. thanks
the Field Museum Scholarship Committee for
financial support to visit the Field Museum. F.
Barrie, W. Burger, and P. Rundel provided con-
structive reviews that improved the manuscript.
Literature Cited
ALPERS, C. N., AND G. H. BRIMHALL. 1988. Middle
Miocene climatic change in the Atacama Desert,
northern Chile: Evidence from supergene mineral-
ization at La Escondida. Geological Society of
America Bulletin, 100: 1640-1656.
BETANCOURT, J. L., C. LATORRE, J. A. RECH, J. QUADE,
AND K. A. RYLANDER. 2000. A 22,000-year record
of monsoonal precipitation from northern Chile's
Atacama Desert. Science, 289: 1542-1546.
DEVRIES, T. J. 1987. A review of geological evidence
for ancient El Nino activity in Peru. Journal of Geo-
physical Research, 92(C13): 14471-14479.
DILLON, M. O. 1997. Lomas Formations Peru, pp.
519-527. In Davis, S. D., V. H. Hey wood, O. Her-
rera-McBryde, J. Villa-Lobos, and A. C. Hamilton,
eds., Centres of Plant Diversity: A Guide and Strat-
egy for their Conservation. World Wide Fund for
Nature, Information Press, Oxford, United King-
dom.
DILLON, M. O., AND P. W. RUNDEL. 1990. The botan-
ical response of the Atacama and Peruvian desert
flora to the 1982-83 El Nino event, pp. 487-504.
In Glynn, P. W., ed., Global Ecological Conse-
quences of the 1982-83 El Nino-Southern Oscil-
lation. Elsevier, New York.
DILLON, M. O., A. SAGASTEGUI A., I. SANCHEZ V., S.
LLATAS Q., AND N. C. HENSOLD. 1995. Floristic in-
ventory and biogeographic analysis of montane for-
ests in northwestern Peru, pp. 251-270. In Chur-
chill, S. P., H. Balslev, E. Forero, and J. L. Luteyn,
eds., Biodiversity and Conservation of Neotropical
Montane Forests. The New York Botanical Garden,
Bronx, New York.
DUNCAN, T, AND M. O. DILLON. 1991. Numerical
analysis of the floristic relationships of the lomas
of Peru and Chile, abstract. American Journal of
Botany, 78: 183.
FERREYRA, R. 1953. Comunidades des vegetales de
algunas lomas costaneras del Peru. Estacion Exper-
imental Agricola "La Molina," Boletin, 53: 1-88.
FONTUGE, M., P. USSELMANN, D. LAVALLEE, M. JULIEN,
AND C. HATTE. 1999. El Nino variability in the
coastal desert of southern Peru during the Mid-Ho-
locene. Quaternary Research, 52: 171-179.
HUGHEN, K. A., D. P. SCHRAG, S. B. JACOBSEN, AND
W. HANTORO. 1999. El Nino during the last inter-
glacial period recorded by a fossil coral from In-
donesia. Geophysical Research Letters, 26: 3129.
KEEPER, D. K., S. D. DE FRANCE, M. E. MOSELEY, J.
B. RICHARDSON III, D. R. SATTERLEE, AND A. DAY-
LEWIS. 1998. Early maritime economy and El Nino
events at Quebrada Tacahuay, Peru. Science, 281:
1833-1835.
LANNING, E. P. 1965. Early man in Peru. Scientific
American, 213: 68-76.
MAGILLIGAN, F. J., AND P. S. GOLDSTEIN. 2001 . El Nino
floods and culture change: A late Holocene flood
history for the Rio Moquegua, southern Peru. Ge-
ology, 29: 431-434.
MATTHEWS, R. K. 1 990. Quaternary sea-level change,
pp. 88-103. In Sea-Level Change. National Acad-
emy Press, Washington, D.C.
MOSELEY, M. E. 1987. Punctuated equilibrium:
Searching the ancient record for El Nino. Quarterly
Review of Archaeology, 8: 7-10.
NICHOLLS, N. 1991. The El Nino/Southern Oscillation
and Australian vegetation. Vegetatio, 91: 23-36.
QUINN, W. H., AND V. T. NEAL. 1987. El Nino occur-
rences over the past four and a half centuries. Jour-
nal of Geophysical Research, 92(C13): 14449-
14461.
RODBELL, D. T, G. O. SELTZER, D. M. ANDERSON, M.
The Lomas Formations of Coastal Peru
B. ABBOTT, D. B. ENFIELD, AND J. H. NEWMAN.
1999. A ~ 15,000-year record of El Nino-driven al-
luviation in southwestern Ecuador. Science, 283:
516-520.
RUNDEL, P. W., AND M. O. DILLON. 1998. Ecological
patterns in the Bromeliaceae of the lomas forma-
tions of coastal Chile and Peru. Plant Systematics
and Evolution, 212: 261-278.
RUNDEL. P. W., M. O. DILLON, H. A. MOONEY, S. L.
GULMON, AND J. R. EHLERiNGER. 1991. The phyto-
geography and ecology of the coastal Atacama and
Peruvian deserts. Aliso, 13(1): 1-50.
SAGASTEGUI-A., A., AND S. LEIVA G. 1993. Flora In-
vasora de Los Cultivos del Peru. Editorial Libertad,
Trujillo. 539 pp.
SANDWEISS, D. H., K. A. MAASCH, AND D. G. ANDER-
SON. 1999. Transitions in the Mid-Holocene. Sci-
ence, 283: 499-500.
SANDWEISS, D. H., K. A. MAASCH, R. L. BURGER, J.
B. RICHARDSON III, H. B. ROLLINS, AND A. CLEM-
ENT. 2001. Variation in Holocene El Nino frequen-
cies: Climate records and cultural consequences in
ancient Peru: Geology, 29: 603-606.
SANDWEISS, D. H., J. B. RICHARDSON HI, E. J. REITZ,
H. B. ROLLINS, AND K. A. MAASCH. 1996. Geoar-
chaeological evidence from Peru for a 5000 years
B.P. onset of El Nino. Science, 273: 1531-1533.
TAGO, M. 1999. The Evolution of Nolana L. (Sola-
naceae) at lomas in South America. Ph.D. diss., To-
kyo Metropolitan University, Tokyo, Japan.
TAGO-NAKAZAWA, M., AND M. O. DILLON. 1999. Bio-
geograffa y evolucion en el clado Nolana (Sola-
neae-Solanaceae). Arnaldoa, 6(2): 81-116.
Response of a Land Snail Species (Bostryx conspersus} in the
Peruvian Central Coast Lomas Ecosystem to the
1982-1983 and 1997-1998 El Nino Events
Rina Ramirez, Saida Cordova, Katia Caro, and Janine Dudrez
Land snails are conspicuous inhabitants of the
lomas ecosystems, which are islands of vege-
tation in the Pacific coastal desert of South
America. The mollusks are adapted to survive
the extreme summer conditions of the lomas,
when the highest temperatures and the lowest
humidities are reached. Bostryx conspersus
(Sowerby, 1833; Mollusca, Bulimulidae) is the
most common species from the lomas of the
Peruvian central coast. In a year without an El
Nino event, individuals of B. conspersus aesti-
vate during the dry season (December-April)
buried in the ground, mainly next to perennial
plants. During the wet season the snails become
active again. We present our observations of
changes in snails' seasonal activity during the
1982-1983 and 1997-1998 El Nino events, oc-
curring within the lomas of Iguanil and Lachay
(Lima, Peru), respectively. The activity of B.
conspersus during the summer of those years
was unusual. The snails behaved as if it were a
wet season. They had successful recruitment
that led to a remarkable population explosion,
mainly due to the high humidity and increased
shelter. However, the response of B. conspersus
showed differences between the two El Nino
events, reflecting dissimilarities between the
starting time and duration of the sea-surface
temperature anomalies and the concomitant
weather variation in the lomas of the central
coast of Peru. The response of B. conspersus to
the seasonal changes during 1995 and the cold
year of 1 996 are contrasted with those of the El
Nino years.
Introduction
The coast of Peru is a desert. The terrestrial
biodiversity, mollusks in particular, is concen-
trated mainly in the lomas. The desert land-
scape changes drastically during El Nino
events, the oceanographic component of El
Nino-Southern Oscillation (ENSO), which has
affected the Pacific coast of South America
since 5800 B.P. (Sandweiss et al. 1999). The
lomas are spectacular ecosystems, islands of
vegetation that endure the harsh conditions of
dry summers and enjoy the humidity of the ad-
vective fogs coming from the ocean during the
winter. The resident fauna of the lomas is also
adapted to its seasonality (Aguilar 1954, 1985).
Similarly, the biota must be adapted to climatic
changes in the mid- and long term produced by
recurrent El Nino events or the species would
have become extinct. However, almost nothing
is known about the responses of terrestrial spe-
cies to El Nino events, compared to what is
known about the marine biota (Arntz et al.
1985; Arntz and Fahrbach 1996; Vegas 1985).
Among the fauna, land snails are conspicuous
inhabitants of the lomas, and because of their
low vagility, they are good animals in which to
study responses to El Nino events. Following
10
Response of a Land Snail Species (Bostryx conspersus)
\ 1
Figure 1. Map showing location of the study sites, Lachay and Iguanil, Peru.
an El Nino event (a phase with warm tropical
water), there is a phase with cold tropical water
called La Nina (Sandweiss et al. 1999), produc-
ing changes in the lomas weather as well. Our
study deals with the response of Bostryx con-
spersus (Sowerby, 1833) to the last two major
El Nino events (1982-1983 and 1997-1998)
and the 1996 La Nina event in the lomas of the
central coastal desert of Peru.
Materials and Methods
Study Site
Location. The two study sites are located in
the Department of Lima, Peru (Fig. 1 ). The lo-
mas of Lachay (1119'S, 7722'W), a national
reserve, are 105 km north of Lima City and 7
km from the seashore. The altitude is between
150 and 750 m. The lomas of Iguanil (1 123'S,
7714'W) are located southeast of Lachay and
103 km from Lima, 15 km from the seashore.
The altitude is between 250 and 750 m.
Climate. The climate of the lomas is season-
al, characterized by a dry season (December-
April) and a wet one, also called the "lomas
season" (late July-September). The other
months are transitional between seasons. Usu-
ally the highest temperatures (monthly mean:
20C) and the lowest humidities (79%-82%)
are reached during summer, contrary to what
happens during the wet season, when the mean
monthly air temperature is 15C, with very high
air humidity (Ordonez and Faustino 1983; Saito
1976; Torres 1985). The El Nino events change
this seasonal picture because of an increase in
precipitation as drizzle or summer precipitation
(Pinche 1994; Torres 1985).
During an El Nino event, the sea-surface
temperature increases abnormally above the
mean (Fig. 2). In the continental area, air tem-
peratures in the lomas also change, showing the
same tendency (Fig. 3). The same tendency was
also noticed in Lima City (Obregon et al. 1985).
Sea-surface temperature data corresponded to
mean monthly values from Puerto Chicama
(0742'S, 7927'W).
12
R. Ramirez et al.
Ja r M Ap My Jn J ASONDJaFMApMyJnJ A 3 O N D
---*--- 1982-83
1995-96
1997-98
Figure 2. Sea-surface temperature anomalies at the Puerto Chicama station, Peru (0742'S, 7927'W). The char-
acterization of years follows Aguilar (1990): El Nino events: >2.7 (extraordinary), 1.7-2.7 (strong), 0.8-1.6 (mod-
erate), 0.5-0.7 (weak). A normal year is 0.6 to 0.4. La Nina events: 0.9 (cold year), 1.8 (very cold year).
Lomas of Iguanil During 1982-1983. The
micrometeorologic data were recorded by CIZA
(Arid Zones Research Center, Agrarian Univer-
sity, La Molina, Peru). Observations were taken
during 10 hours of 1 day a month, at altitudes
of 300 and 500 m. We used the mean values of
the day for air temperature, relative humidity,
and soil humidity. Precipitation values are from
Torres (1985) (Table 1). The climatogram is
shown in Figure 4.
Lomas of Lachay During 1995-1998. The
data were acquired from SENAMHI (Servicio
Nacional de Meteorologfa e Hidrografia del
Peru). The data for both air temperature and
relative humidity are mean monthly values; pre-
SST (1982-83) SST (1995-96)
* SST (1 997-98) - - - *- - - AT (Iguanil 1 982-83)
- - o_ . AT (Lachay 1 995-96) - - A - - AT (Lachay 1 997-98)
Figure 3. Comparison of sea-surface temperatures at the Puerto Chicama station and air temperatures at two
lamas along the central coast of Peru.
Response of a Land Snail Species (Bostryx conspersus)
13
TABLE 1. The lomas of Iguanil: Meteorologic and biologic data (1982-1983).
Month, year
Air temp.
(C)
Relative
humidity (%)
Soil humidity
(%)
Precipitation
(mm)*
Ground cover
(%)*
B. conspersus
(no. snails/
9400 m 2 )
Jan. '82 (Ja2)
23.99
77.49
1.18
0.81
Mar. '82 (M2)
1.05
May '82 (My2)
22.6
72.15
0.85
2.55
July '82 (J2)
16.05
85.08
0.82
5.025
15
Aug. '82 (A2)
17.89
86.62
5.09
3.3
23
Sept. '82 (S2)
38
Oct. '82 (O2)
18.42
80.12
3.27
38.65
43
Nov. '82 (N2)
12.5
Dec. '82 (D2)
24.88
73.76
1.895
30
7
Jan. '83 (Ja3)
26.13
76.34
2.49
7
44.15
Feb. '83 (F3)
24.72
80.4
2.815
8
64.3
Mar. '83 (M3)
27.57
65.07
0.915
45.8
6
Apr. '83 (Ap3)
23.59
93.44
6.83
6
94
May '83 (My3)
21.59
94.14
3.2
5
47.9
24
June '83 (Jn3)
20.93
96.06
9
75.65
July '83 (J3)
16.09
93.65
8.5
5
94
118
Sept. '83 (S3)
16.66
97.17
6
54.5
* After Torres (1985).
cipitation is the cumulative monthly value (Ta-
ble 2). The climatogram is shown in Figure 5.
Vegetation. The lomas vegetation consists of
herbaceous species that are green mainly during
the wet season, and also perennial species
(shrubs and trees) that adapt to the seasonality
of the lomas (Dillon and Rundel 1989; Ferreyra
1993; Ono 1986). In general, changes in climate
conditions during the year modify the landscape
I
X
100
95
90
85
80
75
70
65
60
ap3
14
19 24
Temperature (C)
29
Figure 4. Climatogram of the lomas of Iguanil, Peru, 1982-1983.
14
R. Ramirez et al.
TABLE 2. The lomas of Lachay: Meteorologic and biologic data (1995-1998).
Month, year
Air temp. Relative humidity Precipitation
(C) (%) (mm)
RGC* B. conspersus
(%) (no. snails/400 m 2 )
Jan. '95 (Ja5)
21.2
89
3.5
Feb. '95 (F5)
22.1
85
0.5
Mar. '95 (M5)
21.2
84
1.4
Apr. '95 (Ap5)
19.9
86
May '95 (My5)
18.4
86
0.7
June '95 (Jn5)
16
92
2
July '95 (J5)
13.5
97
19.9
72
Aug. '95 (A5)
13.2
98
4.7
1271
3
Sept. '95 (S5)
14
97
17.2
1492
69
Oct. '95 (O5)
14.5
96
10.5
456
85
Nov. '95 (N5)
15.8
92
1.6
681
54
Dec. '95 (D5)
16.5
89
1.4
207
Jan. '96 (Ja6)
18.4
88
1.1
21
Feb. '96 (F6)
22.5
82
20
Mar. '96 (M6)
22.1
79
7
Apr. '96 (Ap6)
19.3
81
0.4
7
May '96 (My6)
16.4
88
31
June '96 (Jn6)
13.2
98
278
43
July '96 (J6)
14.2
97
Aug. '96 (A6)
368
89
Sept. '96 (S6)
147
60
Oct. '96 (O6)
39
12
Nov. '96 (N6)
15.7
91
2
25
Dec. '96 (D6)
18.2
89
10
Jan. '97 (Ja7)
21
95
Feb. '97 (F7)
22.2
93
Mar. '97 (M7)
22.6
97
May '97 (My7)
July '97 (J7)
19.1
96
10.7
3
Aug. '97 (A7)
18.1
95
31.7
211
8
Sept. '97 (S7)
18.1
93
40.4
1345
6
Oct. '97 (O7)
17.4
92
28.4
927
13
Nov. '97 (N7)
18.9
93
20.4
373
2
Dec. '97 (D7)
21.2
94
65.2
237
5
Jan. '98 (Ja8)
23
96
103.1
476
220
Feb. '98 (F8)
23.6
95
47.5
980
552
Mar. '98 (M8)
23.7
91
6
724
637
Apr. '98 (Ap8)
22.3
88
2.5
321
146
May '98 (My8)
18.9
93
16.5
325
897
June '98 (Jn8)
16.4
98
34.5
529
1587
July '98 (J8)
15.4
97
16.4
907
1473
Aug. '98 (A8)
14
99
46.4
763
5448
Sept. '98 (S8)
14.1
99
28.2
806
9369
* Reiterated ground cover.
from a brown color (almost zero ground cover)
during summer to a vivid green color during
winter, when the annual species provide a large
amount of ground cover. However, during El
Nino events, the timing of these changes is very
different, as was observed during the 1982-
1983 El Nino event in Iguanil (Torres 1985) and
in 1997-1998 in Lachay (Arana et al. 1998).
Ground cover data for Iguanil are from Torres
(1985). We used the mean values for each
month (Table 1). For Lachay, we used the "re-
iterated ground cover" figure obtained by the
botanical team from the Museum of Natural
History of the University of San Marcos (Table
2).
Mollusks. Bostryx conspersus (Sowerby,
1833; Gastropoda, Bulimulidae) has a globose
and rather thin shell of about 15 mm height
(Fig. 6c). It has been recorded in the lomas of
central and southern Peru (Departments of
Lima and Arequipa) (Aguilar and Arrarte 1974;
Response of a Land Snail Species (Bostryx conspersus)
15
E
3
I
100
95
90
85
SL 80
75
12
16
20
24
Air Temperature (C)
Figure 5. Climatogram of the lomas of Lachay, Peru, 1995-1998.
Figure 6. Some lands snails from Lachay: a, Succinea peruviana; b, Bostryx modestus; c, Bostryx conspersus;
d, Scutalus proteus; e, Scutalus versicolor; f, Bostryx scalariformis. (Photograph by B. Collantes.)
16
R. Ramirez et al.
Weyrauch 1967). Individuals of B. conspersus
aestivate during the dry season buried in the
ground, mainly next to perennial plants. They
are also found buried adjacent to rocks, or in
small interstices between them. During the wet
season the snails become active again (Pulido
and Ramirez 1982; Ramirez 1988).
B. conspersus shares the lomas with other
land snail species. For example, in Lachay the
following native species are also present: Bos-
tryx aguilari Weyrauch, 1967; B. modestus
(Broderip, 1832) (Fig. 6b); B. scalariformis
(Broderip, 1832) (Fig. 6f); Scutalus proteus
(Broderip, 1832) (Fig. 6d); Scutalus versicolor
(Broderip, 1832) (Fig. 6e); Succinea peruviana
Philippi, 1867 (Fig. 6a); and the two minutes
Pupoides paredesi (d'Orbigny, 1835) and Gas-
trocopta pazi (Hidalgo, 1869), as well as the
introduced Helix aspersa (Miiller, 1774).
Monitoring
Lomas of Iguanil. The study area in the lo-
mas of Iguanil was the Quebrada El Granado.
The quantitative survey was carried out 1 day
a month in a transect of 20 X 470 m (= 9,400
m 2 ) between 420 and 600 m above sea level.
The transect is located in a hilly area along the
center of the ravine, with perennial vegetation
(mainly shrubs, e.g., Trixis cacalioides,
Ophryosporus pubescens, Cestrum auriculatus,
Dicliptera tomentosa, Heliotropium spp.).
There is also annual herbaceous vegetation
(e.g., Nicotiana paniculata, Chenopodium pe-
tiolare, Oxalis sp., Sicyos baderoa). The survey
was carried out from May 1982 to July 1983
(except June 1983). The search for unburied
snails was conducted by direct observation. R.
Ramirez carried out this part of the work as a
member of a team of the CIZA/UNA-La Mo-
lina (Lima, Peru), which conducted botanical,
faunal, and anthropological research in several
lomas of the central coast of Peru during the
1970s and 1980s.
Lomas of Lachay. The Museum of Natural
History of the University of San Marcos, Lima,
Peru, has been engaged in monitoring vegeta-
tion and mollusks to track El Nino events in the
lomas ecosystems as part of the RIB EN study
(Red de Impacto Biologico de los Eventos El
Nino, CONCYTEC) from May 1995 to the
present.
For a quantitative survey, we selected an area
dominated by shrubs (e.g., Ophryosporus pe-
ruvianus, Senecio spp., Trixis cacalioides, Cro-
ton spp.), including annual herbaceous vegeta-
tion (e.g., Loasa urens, Nicotiana paniculata,
Urocarpidium peruvianum, Nolana humifusa).
Monitoring of the land snails at the two lomas
was carried out as independent projects. Al-
though we tried to maintain the same area in
Lachay for quantitative sampling as in Iguanil,
it did not work as well because of the greater
abundance of B. conspersus. We delimited four
plots of 10 X 10 m (= 400 m 2 ), 50 m apart,
along a transect between 470 and 550 m in al-
titude. We counted the unburied snails observed
in 1 day per month, except during 1998, when
we needed an extra day because of the high
number of individuals and the exuberant her-
baceous vegetation. The data we present here
are from July 1995 to September 1998. No sur-
vey was conducted in July 1996 or in January,
February, April, or June of 1997.
Principal Component Analysis
We used principal component analysis (PCA) to
ascertain whether changes in monthly density
of B. conspersus along with changes in air tem-
perature, relative humidity, or ground cover
could help discriminate El Nino months from
non-El Nino months. We did not use the pre-
cipitation data, which were incomplete. Micro-
soft Excel was used for data management and
the analyses were performed using SPSS (Sta-
tistical Package for the Social Sciences, V05)
software.
Results
Iguanil (1982-1983)
The monthly variation in number of unburied
individuals of Bostryx conspersus in the lomas
of Iguanil did not show the same trend from
one year to the next. In 1982 the snails were
active during part of the winter and spring,
whereas in 1983 the activity period started ear-
lier, at the end of the summer. The highest num-
ber of snails recorded in 1983 was recorded ear-
lier, in July, and was almost threefold (118 in-
dividuals in 9,400 m 2 ) the number recorded in
Response of a Land Snail Species (Bostryx conspersus)
17
1982 (October, 43 individuals) (Table 1, Fig.
7a).
In relation to the differences among survey
months, PCA of data on snails, ground cover,
air temperature, and relative humidity generated
four components to explain the total variance.
The PCI analysis explained 62.157% of the
variance, with variation in number of snails
having the greatest influence, followed by var-
iation in the relative humidity. In the PC2 anal-
ysis (28.492%) ground cover was the principal
factor, followed rather distantly by air temper-
ature (Table 3). In the scatter diagram of PCI
X PC2, three groups of months are formed,
with the months of the 1982-1983 El Nino ep-
isode in two of them (December 1982-March
1983, and May-July 1983) (Fig. 8).
Lachay (1995-1998)
During the almost 4 years of survey of B. con-
spersus in the lomas of Lachay, the higher num-
ber of active snails (unburied) per observation
period decreased from 1995 through 1997, but
in 1998 exceeded the highest counts of previous
years. The lowest numbers of snails occurred
during the summer of 1996 and the summer of
1997, corresponding to the aestivation period
(Table 2, Fig. 7b).
In relation to the differences among the sur-
vey months, PCA generated four components
to explain the total variance, of which the first
two accounted for 71.412% of the variance. In
PCI (52.046%), variation in relative humidity
had the greatest influence, followed by variation
in air temperature, while in PC2 (19.366%), the
number of snails and the ground cover were the
variables with greatest influence (Table 4). In
the scatter diagram of the first two components,
five groups of months were formed. Those of
the 1997-1998 El Nino segregated into two
groups (March-July-August 1997, and Septem-
ber-December 1997-January-April 1998); the
following months (post-El Nino) also formed a
separate group (June-September 1998). The
two other groups were formed by (1) August-
November 1995 and (2) December 1995-Jan-
uary-May 1996 and November-December
1996 (Fig. 9).
Discussion
Bostryx conspersus has seasonal behavior,
showing a clear response to the seasonal cli-
mate of the lomas ecosystem (Pulido and Ra-
mirez 1982; Ramirez 1988). The intensity of
change in the climatic regimen can be detected
from the variation in monthly number of un-
buried snails, as described here. El Nino events
change the seasonality of the lomas, mainly be-
cause of summer rains (Oka and Ogawa 1984;
Pinche 1994).
Climatologically, no one year was similar to
any other during the study (Figs. 4 and 5), nor
were the monthly density variations in active
land snails similar (Fig. 7). Analysis of the sea-
surface temperature anomalies at Puerto Chi-
cama during the periods of our studies (1982-
1983, 1995-1998) (Fig. 2; Quispe 1993) shows
that in this respect too, there were not two equal
years (Rasmusson and Arkin 1985). This dem-
onstrates the direct influence of the ocean on
the climate of the lomas as well as other con-
tinental areas (Obregon et al. 1985). Likewise,
we cannot say that during the period of survey
in the lomas of Lachay there was a "normal"
year for the lomas. On the contrary, we had the
El Nino years (1997-1998), an unusually cold
year (La Nina, 1996), and a mixed warm and
mildly cold year (1995).
Using the data of B. conspersus along with
those of air temperature, relative humidity, and
ground cover, then performing a principal com-
ponent analysis, we arrived at assemblages of El
Nino months that were arranged in a different
way from those of non-El Nino ones. At the
same time, months during El Nino events were
segregated into two groups; we call them the first
phase and the second phase of El Nino (Figs. 8
and 9). Checking the anomalies of sea-surface
temperature, it is also possible to see that the two
El Nino events were indeed different.
The 1982-1983 and 1997-1998 El Nino ep-
isodes are considered to be extraordinary be-
cause the sea-surface temperature anomalies
differed by more than 2.7 SD (Fig. 2) (Aguilar
1990; Quinn 1993). At the same time, the El
Nino events differed in starting point and in du-
ration. For example, in the 1982-1983 El Nino
event, warm water reached the central coast of
Peru late in 1982 November in Callao (Go-
mez 1985) and did not affect the wet season
of the year very much. B. conspersus showed a
typical seasonal behavior during that year. The
18
R. Ramirez et al.
140
120 -I
100
80
60
40
20
10000
1000
o
I
1 100
i
b)[
O Lachay 95-96
Lachay 97-98
Figure 7. Monthly density of unburied individuals of Bostryx conspersus in two lomas on the central coast of
Peru: a, Iguanil; b, Lachay.
second instance of warming of the sea-surface
water occurred during the fall of 1983 April-
July (Zuta et al. 1985) which brought more
precipitation to the lomas, marking an early be-
ginning of the wet season in 1983 (Fig. 10). The
usual brown landscape of the summer was re-
placed by a nice carpet of herbaceous vegeta-
tion (Torres 1985). The population of B. con-
spersus from the lomas of Iguanil also respond-
ed to the quasi-lomas season, the difference be-
ing that the air temperatures were higher than
during the winter wet season (Fig. 4). The bi-
ological impact on the snails was positive; the
snails awoke earlier from the aestivation period,
and the recruitment was successful (Ramirez
1984). The population reached the levels of the
previous wet season very early (Fig. 7). A pos-
sible reason for this could be the survival of
TABLE 3. Results of PCA for the lomas of Iguanil (1982-1983).
Initial Eigenvalues
Compo-
% of
Cumula-
Component
nent
Total
Variance
tive %
Variables
1
2
3
4
1
2.486
62.157
62.157
Air temperature
-0.801
0.561
0.165
0.127
2
1.140
28.492
90.649
Relative humidity
0.872
-0.197
0.444
0.052
3
0.332
8.302
98.951
Ground cover
0.495
0.860
0.074
-0.099
4
0.042
1.049
100.000
Bostryx conspersus
0.916
0.214
-0.319
0.115
Response of a Land Snail Species (Bostryx conspersus)
19
-2
-1
PCI (62.157%)
Figure 8. Plots of the first two principal components for the months May 1982 to July 1983 for the lomas of
Iguanil.
more eggs and snails (especially just hatched
and juveniles) than usual (Ramirez 1984) be-
cause of the high humidity (the main cause of
death is desiccation [Pollard 1975]) and more
available shelter (Lomincki in Pollard 1975) be-
cause of the high amount of annual vegetation.
The two instances of sea-surface warming
during the 1997-1998 El Nino event occurred
earlier than those of the 1982-1983 El Nino
event. The first arrival of the warm water was
early during the fall of 1997 (Fig. 2). The whole
year was abnormally warm in the lomas, and
during the winter the high relative humidity val-
ues characteristic of the "lomas season" were
never reached; the contrary happened during
the late spring, which had high relative humid-
ity values, as shown in the climatogram for La-
chay (Fig. 5). The characteristic herbaceous
vegetation of the wet season was negatively af-
fected. For example, Isemene amancaes had
both a late beginning and a short development
period during 1997 (Agiiero and Suni 1999).
The population of B. conspersus was also neg-
atively impacted. Most of the snails stayed bur-
ied, and those that "woke up" were more ex-
posed to desiccation. As a consequence, the re-
cruitment was very poor (Fig. 1 1 ). The second
occurrence of warming of the 1997-1998 El
Nino event was at the beginning of the summer
of 1998 (Fig. 2) and brought an unusual amount
of water to the lomas (Fig. 12), extending the
late wet season of 1997 into the summer of
1998. Here the impact of the El Nino event was
positive for B. conspersus, which showed a
TABLE 4. Results of PCA for the lomas of Lachay (1995-1998).
Initial Eigenvalues
Compo-
% of
Cumula-
Component
nent
Total
Variance
tive %
Variables
1
2
3
4
1
2.082
52.046
52.046
Air temperature
-0.707
0.218
0.622
0.255
2
0.775
19.366
71.412
Relative humidity
0.833
0.160
-0.076
0.524
3
0.704
17.602
89.014
Ground cover
0.698
0.578
0.288
-0.308
4
0.439
10.986
100.000
Bostryx conspersus
0.633
-0.606
0.478
-0.064
20
R. Ramirez et al.
-2
-1
1
PCI (52.046%)
Figure 9. Plots of the first two principal components for the months July 1995 to September 1998 for the lomas
of Lachay.
population explosion. The recruitment was very
successful; and that, along with the high hu-
midity and exuberant herbaceous vegetation
(Arana et al. 1998, 1999), led to a high survival
rate among the snails.
The cold year of 1996 (La Nina) had a rel-
atively negative impact on B. conspersus com-
pared with the maximum number of snails
counted in the 1995 "wet season." The weather
was colder and drier than during the other years
(Figs. 5 and 12). The mortality rate of individ-
uals of all size classes was high, and the re-
cruitment was poor (Fig. 1 1 ; Ramirez et al.
1999). Affected in this way, the population ex-
perienced an El Nino the following year (1997),
with a hot winter and without the characteristic
high humidities (Fig. 5), depleting the popula-
tion even more. Finally, the arrival of the sec-
ond phase of the 1997-1998 El Nino event in-
jected some life into B. conspersus. The range
10 -,
9
! ?:
10
9
8 ^
7
9
c 6
o
j= 5
a 4
1
1
r
5 E
4 I
,,
o 3^
Q- 2
/
f
^>'
, ^
\
3 o
2 W
1 -
I
V
1
*^ v\ J ^"1 ^r* fiiL-J *^ w\ J ^5
XT V*^ ^ oP ^J
\
^^
\=n PRECIPITATION (mm)
-o SOIL HUMIDrTY (%)
Figure 10. Precipitation and soil humidity in the lomas of Iguanil, 1982-1983 (measured 1 day per month).
Response of a Land Snail Species (Bostryx conspersus)
21
10000
1000
100
>15mm
10.1 -15mm -A-5-10mm
-<5mm
Figure 11. Structure of the population of Bostryx conspersus by size classes from August 1995 to September
1998 in the lomas of Lachay. The El Nino event occurred from May 1997 to April 1998. (After Ramirez et al. 1999.)
of the population expanded as far as the her-
baceous vegetation did. The post-El Nino
months following the 1997-1998 event coincid-
ed with the 1998 wet season, which resulted in
an even higher density of active B. conspersus.
This was probably also the case for 1995 (end
of a weaker but much longer-lasting El Nino
than the two episodes analyzed here). Precipi-
tation and ground cover were greater than in
1996 (Table 2, Fig. 12), and B. conspersus
reached higher densities than in 1996 and 1997
(Figs. 7b and 9).
100
c
"5.
. 40
|
20
*
. . .1,
1
J
i
nJ
i
D
* * >
b <<
> * ^ ^ > * *
Lachay (1995-96)
D Lachay (1997-98)
Figure 12. Precipitation in the lomas of Lachay, 1995-1998 (cumulative monthly values).
22
R. Ramirez et al.
Thus, although the two El Nino episodes dif-
fered from each other, they were similar in that
their second phase had a positive impact on the
biota. The increase in humidity led to an in-
crease in herbaceous vegetation, and both of
these factors contributed to an increase in the
population of B. conspersus. At the same time,
predation on this population, mainly by rodents
and birds, also increased (Ramirez et al. 1999).
Acknowledgments. The work carried out on
the lomas of Iguanil was possible thanks to the
Arid Zones Research Center of the Agrarian
University (CIZA-UNA, La Molina, Peru). Di-
ana Silva y Juan Torres facilitated the work at
Iguanil. The monitoring of land mollusks on the
lomas of Lachay was made possible with the
aid of the American States Organization
(through RIBEN-CONCYTEC), the University
of San Marcos (FEDU-UNMSM), and the Na-
tional Council of Science and Technology
(CONCYTEC). We are grateful to the Institute
Nacional de Recursos Naturales for permits to
perform research in the National Reserve of La-
chay. Jose Arenas, Sergio Cano, Doris Florin-
dez, Marisa Ocrospoma, and Maria Samame
participated enthusiastically in the fieldwork,
and Asuncion Cano and Cesar Arana provided
the data on ground cover. Finally, we thank Ser-
gio Solari and Sonia Valle, who helped prepare
the illustrations.
Literature Cited
AGUERO, S., AND M. SUNI. 1999. Influencia del evento
"El Nino 1997-98" en la fenologfa de Iseme aman-
caes (Amaryllidaceae, Liliopsidae). Revista Peru-
ana de Biologia, Volume Extraordinario, pp. 118-
124.
AGUILAR, R 1954. Estudio sobre las adaptaciones de
los artropodos a la vida de las lomas de los alrede-
dores de Lima. Ph.D. diss., Universidad Nacional
Mayor de San Marcos, Lima, Peru.
. 1985. Fauna de las lomas costeras del Peru.
Boletfn de Lima (Peru), 41: 17-28.
1990. Sinopsis sobre los eventos del feno-
meno "El Nino" en el Peru. Boletfn de Lima, 70:
69-84.
AGUILAR, P., AND J. ARRARTE. 1974. Moluscos de las
lomas costeras del Peru. Anales Cientificos, Univ-
ersidad Nacional Agraria (Peru), 12(3-4): 93-98.
ARANA, C., A. CANO, J. ROQUE, AND M. ARAKAKI.
1999. Patrones de respuesta poblacional de las her-
baceas de "lomas" al evento "El Nino." VIII Re-
union Cientffica, Institute de Investigacion de Cien-
cias Biologicas "Antonio Raimondi," 14-16 April,
1999; abstracts, p. 101.
ARANA, C., A. CANO, J. ROQUE, M. ARAKAKI, AND M.
LA TORRE. 1998. Respuesta de la comunidad de
herbaceas de las lomas de Lachay al evento "El
Nino" 1997-98, p. 48. In Seminario Taller "El
Nino" en America Latina, sus Impactos Biologicos
y Sociales: Bases para un Monitoreo Regional.
CONCYTEC-RIBEN. Lima, Peru, 9-13 November
1998.
ARNTZ, W., AND E. FAHRBACH. 1996. El Nino: Exper-
imento climatico de la naturaleza. Causas fisicas y
efectos biologicos. Fondo de Cultura Economica,
Mexico, D.F., 312 pp.
ARNTZ, W., A. LANDA, AND J. TARAZONA, EDS. 1985.
"El Nino": Su impacto en la fauna marina. Boletfn
del Institute del Mar del Peru, Boletfn Extraordi-
nario, 222 pp.
DILLON, M., AND P. RUNDEL. 1989. The botanical re-
sponse of the Atacama and Peruvian desert floras
to the 1982-83 El Nino event. In Glynn, ed., Global
Ecological Consequences of the 1982-83 El Nino-
Southern Oscillation. Elsevier, New York.
FERREYRA, R. 1993. Registros de la vegetacion en la
costa peruana en relacion con el fenomeno El Nino.
Bulletin Institute Francais Etudes Andines, 22(1):
259-266.
GOMEZ, D. 1985. Analisis de las anomalfas de la pre-
sion y temperatura en la costa peruana como indi-
cadores de la presencia del fenomeno "El Nino,"
pp. 241-261. In Vegas, M., ed., Ciencia, tecnologfa
y agresion ambiental: El fenomeno "El Nino."
CONCYTEC, Lima, Peru.
OBREGON, G., E. CISNEROS, AND A. DIA. 1985. El fen-
omeno "El Nino" 82-83 y la alteracion termica en
Lima, pp. 263-278. In M. Vegas, ed., Ciencia, tec-
nologfa y agresion ambiental: El fenomeno El Nino.
CONCYTEC, Lima, Peru.
OKA, S., AND H. OGAWA. 1984. The distribution of
lomas vegetation and its climatic environments
along the Pacific coast of Peru. Geographical Re-
ports of Tokyo Metropolitan University, 19: 113-
125.
ONO, M. 1986. Definition, classification and taxonom-
ic significance of the lomas vegetation, pp. 5-14.
In Ono, M., ed., Taxonomic and Ecological Studies
on the Lomas Vegetation in the Pacific Coast of
Peru: Reports for Overseas Scientific Survey. Ma-
kino Herbarium, Tokyo Metropolitan University,
Japan.
ORDONEZ, J., AND J. FAUSTINO. 1983. Evaluacion del
potencial hfdrico en lomas costeras del Peru (lomas
de Lachay-Iguanil). Zonas Aridas, 3: 29-42.
PINCHE, C. 1994. Estudio de las condiciones climati-
cas y de la niebla en la costa norte de Lima. Boletfn
de Lima, 16(91-96): 39-43.
POLLARD, E. 1975. Aspects of the ecology of Helix
pomatia L. Journal of Animal Ecology, 44(1): 305-
329.
PULIDO, V, AND R. RAMIREZ. 1982. Distribucion y ac-
tividad estacional de los caracoles terrestres de las
Lomas de Lachay. VII Congreso Nacional de Biol-
ogia y II Simposium de Educacion en Ciencias
Response of a Land Snail Species (Bostryx conspersus)
23
Biologicas, Lima, Peru, 22-27 Noviembre. Bitacora
Biologica (Libro de Resumenes), 1(1): 52.
QUINN, W. 1993. The large-scale ENSO event, the El
Nino and other important regional features. Bulletin
Institute Fran?ais Etudes Andines, 22(1): 13-34.
QUISPE, J. 1993. Variaciones de la temperatura super-
ficial del mar en Puerto Chicama y del Indice de
Oscilacion del Sun 1925-1992. Bulletin Institute
Fran9ais Etudes Andines, 22(1): 1 1 1-124.
RAMIREZ, R. 1984. Aspectos de la ecologfa de Bostryx
conspersus (Sowerby, 1833) (Mollusca, Bulimuli-
dae) en las lomas de Iguanil, Huaral-Lima. Informe
de Practicas Pre-Profesionales para optar el Tftulo
Profesional de Biologo. Universidad Nacional May-
or de San Marcos, Lima, Peru.
. 1988. Morfologia y biologfa de Bostryx con-
spersus (Sowerby) (Mollusca, Bulimulidae) en las
lomas costeras del Peru central. Revista Bras. Zool.,
5(4): 609-617.
RAMIREZ, R., K. CARO, S. CORDOVA, J. DUAREZ, A.
CANO, C. ARANA, AND J. ROQUE. 1999. Respuesta
de Bostryx conspersus y Succinea peruviana (Mol-
lusca, Gastropoda) al evento "El Nino" 1997-98
en las lomas de Lachay (Lima, Peru). Revista Per-
uana de Biologia, Volume Extraordinario, pp. 143-
151.
RASMUSSON, E., AND P. ARKIN. 1985. Interannual cli-
mate variability over South America and the Pacific
associated with El Nino episodes, pp. 179-206. In
Vegas, M., ed., Ciencia. tecnologia y agresion am-
biental: El fenomeno "El Nino." CONCYTEC,
Lima, Peru.
SAITO, C. 1976. Bases para el establecimiento y ma-
nejo de una unidad de conservacion en las Lomas
de Lachay, Peru. Ministerio de Agricultura, Direc-
cion General Forestal y de Fauna, Direccion de
Conservacion, 205 pp.
SANDWEISS, D. H., K. A. MAASCH, AND D. G. ANDER-
SON. 1999. Transitions in the Mid-Holocene. Sci-
ence, 283: 499-500.
TORRES, J. 1985. Anomalias observadas en la vege-
tacion y sus factores fisicos determinantes en las
lomas de la Costa Central, durante el verano (Ene-
ro-Abril) de 1983, pp. 625-642. In Vegas, M., ed.,
Ciencia, tecnologia y agresion ambiental: El feno-
meno "El Nino." CONCYTEC, Lima, Peru, 692
pp.
VEGAS, M., ED. 1985. Ciencia, tecnologia y agresion
ambiental: El fenomeno El Nino. CONCYTEC,
Lima, Peru, 692 pp.
WEYRAUCH, W. 1967. Descripciones y notas sobre
gasteropodos terrestres de Venezuela, Colombia,
Ecuador, Brasil y Peru. Acta Zool. Lilloana, 21:
457-499.
ZUTA, S., M. FARFAN, AND O. MORON. 1985. Fluctua-
ciones de la TSM y SSM durante el evento El Nino
1982-83, pp. 57-94. In Vegas, M., ed., Ciencia,
tecnologia y agresion ambiental: El fenomeno El
Nino. CONCYTEC, Lima, Peru.
Debris-Flow Deposits and El Nino Impacts
Along the Hyperarid Southern Peru Coast
Luc Ortlieb and Gabriel Vargas
The coastal regions of Ecuador, Peru, and Chile,
which today experience the strongest meteoro-
logic and oceanographic impacts of El Nino,
are also the areas where paleoclimatologic re-
search is likely to yield relevant information
about former El Nino processes. The extreme
aridity that characterizes the coast of southern
Peru and northern Chile is favorable for the rec-
ord of episodic rainfall events that induce floods
and debris flows and the subsequent preserva-
tion of these deposits. This chapter compiles
available instrumental, documentary, and geo-
logic data on such deposits formed along the
coast at 17-18S latitude and discusses the re-
lationships that can be inferred between dated
debris-flow deposits and the occurrence of El
Nino events. The approach thus involves an
analysis of temporal correlations between El
Nino events, debris-flow episodes, and instru-
mental measurements of rainfall data during the
last several decades. This analysis shows a
weak statistical correlation between monthly or
yearly rainfall amount and the warm phase of
El Nino-Southern Oscillation (ENSO), but also
that strong rainfall, sufficient to provoke debris
flows, generally occurs during El Nino years.
Documentary data from the last few centuries
also tend to indicate that heavy rainfall episodes
along the coast of southern Peru have common-
ly occurred during El Nino years, even though
many El Nino years did not experience rains.
We conclude that, for at least the last few cen-
turies, El Nino conditions have been favorable
for the formation of exceptionally short-lived
but intense rainfalls, but that these conditions
are not sufficient per se. Several regional and
local meteorologic mechanisms and situations
are apparently involved in the episodic occur-
rence of strong rainfalls and debris-flow activity
along the coast of southern Peru.
Debris-flow activity during the early Holo-
cene and at the end of the Pleistocene, when
regional hydrologic conditions were different
than at present, is more difficult to interpret in
relation to ENSO. Unlike previous authors, we
consider that debris-flow deposits formed prior
to the mid-Holocene do not constitute strong
enough evidence for past El Nino conditions.
Similarly, we presume that lack of debris-flow
evidence during a given time period cannot be
taken as an indication that no El Nino events
occurred during that period. Until we have a
better understanding of the meteorologic pro-
cesses driving exceptional intense rainfalls in
the area and of the paleohydrologic regime, it
would be misleading to infer the existence of
El Nino, or La Nina, conditions from the exis-
tence of debris-flow deposits in this particular
region.
The Relevance of Paleo-ENSO
Studies
El Nino Southern Oscillation, or ENSO, is the
main source of global ocean climate variability
on an interannual time scale. Understanding the
variability of ENSO through geologic time is
necessary to determine the boundary conditions
that drive the phenomenon, to examine the in-
terrelationships between this mode of ocean cli-
mate variability and other, longer-term sources
of climate change, and to constrain coupled
oceanic-atmospheric models. There is also
24
Debris-Flow Deposits and El Nino Impacts
25
strong societal interest in improved forecasting
of El Nino events and in estimating the intensity
and frequency of future ENSO events under
conditions of global warming. Moreover, stud-
ies of the evolution of the dynamics of the
ENSO trough time are necessary to better un-
derstand the influence of the ocean climate sys-
tem on the development of different cultures
around the world.
Because instrumental records have been
maintained for only a short time, whereas cli-
mate modelers require longer-term records,
there is a growing need for paleo-ENSO proxy
records such as coral reef sequences, ice cores,
dendroclimatic analyses, lacustrine and alluvial
sedimentary sequences, beach ridge series, and,
for the last few centuries, documentary data.
These different proxy records generally aim to
reconstruct the frequency and intensity of for-
mer El Nino events the warm phase of ENSO.
Up to now, however, none of these records by
itself has yielded a complete series of El Nino
occurrences. For instance, Quinn and collabo-
rators (Quinn et al. 1987; Quinn and Neal 1992;
Quinn 1993) provided historical El Nino se-
quences based on documentary data that have
been widely used by ENSO researchers. But
other researchers (Hocquenghem and Ortlieb
1992; Whetton and Rutherfurd 1994; Whetton
et al. 1996; Ortlieb 1998, 1999, 2000; Ortlieb
et al. 2002) have questioned the accuracy of
many so-called reconstructed El Nino events
between the sixteenth and the eighteenth cen-
turies. This is not surprising, because some of
the documentary data come from areas as far
away as the Nile delta, China, and South Amer-
ica, where ENSO teleconnections are moderat-
ed by other atmospheric and oceanic processes.
As a result, no consensus has been reached on
a historical El Nino (or ENSO) chronological
sequence prior to the instrumental record. At
longer time scales the problem is still more
acute, if for different reasons: the scarcity of
high-resolution sequences, geochronological
uncertainties, alteration or partial erosion of the
records, and so on. In all cases, for very recent
(documentary) or older (geologic) records, one
particular problem must be addressed: Which
regions record the former occurrences of the
phenomenon with highest reliability? How can
we be sure that a geographic area that today
satisfactorily registers ENSO anomalies also
did so in the past, under different regional and
global circulation patterns?
El Nino Manifestations in Peru and Chile
The El Nino phenomenon was first identified in
northern Peru, near the border with Ecuador
(Carranza 1891), as the combination of an
anomalous seasonal (summer) warming of the
coastal waters and heavy rainfall in the desert
of Sechura (4-6S). Later, it was observed
along the coast of southern Ecuador to central
Chile that the phenomenon is also characterized
by a lowering of the thermocline and the nu-
tricline and by a rise in sea level that may reach
several decimeters within several weeks. The
coast of northern Peru is where the El Nino
phenomenon provokes the highest sea level rise
(more than half a meter in 1982-1983), greatest
seawater warming (up to 10C at Paita, in
1982-1983), and greatest rainfall anomalies (lo-
cally up to 4,000 mm, compared to 100 mm
mean). It is thus natural that this region is fa-
vored in the search for paleo-El Nino evidence
(Quinn et al. 1987; DeVries 1987; Ortlieb and
Machare 1993; Machare and Ortlieb 1993).
Another favorable area that faithfully regis-
ters the occurrence and intensity of ENSO man-
ifestations is central Chile (Quinn and Neal
1983). Rutllant and Fuenzalida (1991) showed
that at least since the end of the nineteenth cen-
tury, the warm phase of ENSO is characterized
by an excess of winter precipitation and the
cold phase is generally marked by a deficit of
rainfall. Over the last 120 years, for which there
are reliable instrumental rainfall data, there is a
good correlation between El Nino in northern
Peru (during the austral summer) and central
Chile (during the preceding austral winter) (Ort-
lieb 1998, 1999, 2000; Ortlieb et al. 2002). This
coincidence reflects a teleconnection mecha-
nism involving large-scale atmospheric pro-
cesses in the eastern Pacific region (Caviedes
1981; Hastenrath 1985; Hamilton and Garcia
1986; Deser and Wallace 1987; Aceituno 1988,
1990; Philander 1991; Allan et al. 1996). It is
because of this teleconnection that Quinn et al.
(1987) and Quinn and Neal (1992) relied on
documentary data on historical climatic anom-
alies from either central Chile or northern Peru
to reconstruct past occurrences of El Nino
events. However, Ortlieb and co-authors (Ort-
lieb 2000; Ortlieb et al. 2002) noted that before
1817, very few heavy rainfall events recon-
structed from documentary evidence from
northern Peru and central Chile did coincide in
time. Ortlieb (1997, 1998, 2000) thus suggested
26
L. Ortlieb and G. Vargas
that the teleconnection mechanisms had possi-
bly been affected by other modes of climatic
variability, such as those related to the Little Ice
Age. This hypothesis remains to be further test-
ed, for example, by comparing with data from
tropical ice core and coral reef sequences.
Meanwhile, it is plausible that the regional te-
leconnections observed today may not have
been operating in past centuries and millennia.
When Did the El Nino Phenomenon Appear
in Peru?
In the last few decades, there has been some
discussion regarding the onset of the El Nino
system of climate variability in Peru. Sandweiss
and co-authors (Sandweiss 1986; Rollins et al.
1986; Sandweiss et al. 1983, 1996, 1999) pro-
posed that no ENSO manifestation was recorded
in Peru before the mid-Holocene and supported
the hypothesis that the onset of the El Nino oc-
curred at about 5000 B.P. This interpretation re-
lied heavily on observations that some warm-
water mollusks occurred in different localities
prior to 5000 B.P. (noncalibrated age) along the
coast of north-central Peru. The mentioned au-
thors suggested that a large reorganization of the
ocean-atmosphere circulation system in the east-
ern Pacific took place during the mid-Holocene.
They claimed that prior to 5000 B.P., the coastal
waters of that area were significantly warmer
than today, and that after the mid-Holocene, the
boundary between the cold Humboldt (Peru)
Current and the warm equatorial waters would
have moved northward by about 500 km, to
reach its present position (at about 5S).
Other researchers (DeVries and Wells 1990;
Diaz and Ortlieb 1993; Perrier et al. 1994; Bearez
et al. 2003) have not shared the interpretation that
coastal waters were warmer in the past in north-
central Peru and instead have argued that the
warm-water molluscan species were all lagoonal
forms that lived in protected, marginal lagoons
that provided a higher temperature than the open
ocean. Other biological proxy data also failed to
support the theory of a major shift of the bound-
ary between the cool Humboldt domain and the
warm equatorial waters. Perrier et al. (1994)
showed through stable isotope serial analyses that
Trachycardium shells from north-central Peru dat-
ed to 5500 B.P., 5800 B.P., and 6100 B.P. contained
growth irregularities similar to those observed to-
day in response to El Nino events, registering
short-term thermal anomalies of the water that
amounted to several degrees C (like those record-
ed after the very strong 1982-1983 El Nino
event). Furthermore, DeVries et al. (1997) argued
that it was precisely because the El Nino system
already existed before 5000 B.P. that the lagoons
which formed during mid-Holocene maximum
sea level, near 7000 B.P. (Wells 1988), could be
fed episodically with larvae of warm-water spe-
cies that normally live in the Panamic molluscan
Province (i.e., north of 6S). Similar conditions of
lagoonal environments that previously enabled the
survival of extralimital warm-water species have
also been found in deposits of prior interglacial
stages in southern Peru and northern Chile (Ort-
lieb et al. 1990, 1996; Diaz and Ortlieb 1993;
Guzman et al. 2001).
Recently, additional terrestrial proxy data have
tended to indicate that El Nino extended back to
the end of the Pleistocene, although with differ-
ent characteristics. Rodbell et al. (1999) reported
data from a high-elevation Andean lake in south-
ern Ecuador, whereas Keefer et al. (1998) pre-
sented data from alluvial and debris-flow depos-
its in southern Peru (Fig. 1). Both studies suggest
that ENSO mechanisms were not restricted to the
second half of the Holocene. However, both
studies relied on an interpretation of alluvial pro-
cesses in two quite different depositional envi-
ronments, and both assumed that present-day hy-
drologic phenomena linked to ENSO were also
operative at the end of the Pleistocene and in the
early Holocene.
Here we evaluate interpretations of climatic
significance of alluvial deposits formed in the
southernmost part of the Peruvian coastal des-
ert. To what extent can we assume, as Keefer
et al. (1998) did, that remnants of debris flows
and floods in the coastal region of southern
Peru were related to El Nino conditions in the
latest Pleistocene and early Holocene times?
The relationships between paleo-ENSO impacts
and alluvial and debris-flow deposits in the area
will be analyzed at different time scales with
different kinds of data: ( 1 ) for the last half-cen-
tury, using instrumental measurements; (2) for
the last few centuries, based on documentary
sources; and (3) for the last 12,000 years, using
radiocarbon-dated geologic deposits. Recently
acquired data from southern Peru are presented
and discussed with respect to other published
El Nino proxy data (Keefer et al 1998; Fontug-
ne et al. 1999).
Debris-Flow Deposits and El Nino Impacts
27
Piu
Lima
< 13mm
Iquique
t
Rainfall (mm)
V ^
JH : n tu
Antofagasta
V
H 1020-2030
\1
^| 760-1020
1 510-760
( '
J
[250-510
1 0-250
< 13 mm /
\ \
_] iJ
Pacific Ocean
Ilo
Quebrada Tacahuay
j- 1 8S Punta El Ahogado
72W Quebrada Los Burros
Quebrada El Cation
100km
Hi"'
Rio San Jose
B
Figure 1. A. Location of sites studied in southern Peru and northern Chile, with indication of mean interannual
rainfall (modified from Kendrew 1961). B. Details of the coast of southernmost Peru, with localities studied.
El Nino Impact on Rainfall and
Debris-Flow Events in Southern
Peru During the Second Half of the
Twentieth Century
El Nino and Rainfall Anomalies in Peru
After the very strong 1982-1983 El Nino event,
which was characterized by a severe drought in
the southern half of Peru and on the Bolivian
Altiplano, many authors (e.g., Huaman Solis
and Garcia Pena 1985; Francou and Pizarro
1985; Garcia Pena and Fernandez 1985; Rope-
lewski and Halpert 1987; Thompson et al.
1984) considered that the precipitation deficits
in this area were typical of El Nino conditions.
At present it is considered that the relative
drought that was observed during El Nino years
may be more specific to the Andean part of
southern Peru, and not precisely specific to the
coastal region of southern Peru (Rome-Gaspal-
dy and Ronchail 1998). Recent analyses of in-
strumental rainfall data from the second half of
the twentieth century confirm that the positive
rainfall anomalies over the coastal regions of
Ecuador and northern Peru exhibit the only sta-
28
L. Ortlieb and G. Vargas
tistically significant correlation with El Nino
events within the region encompassing Ecuador,
Peru, and Bolivia (Aceituno 1988; Rossel 1997;
Rome-Gaspaldy and Ronchail 1998; Rossel et
al. 1998). Analysis of monthly rainfall data be-
tween 1960 and 1990 indicates that only the
coastal area of northern Peru (Piura region)
shows a positive correlation between rainfall
and the warm phase of ENSO, and intensified
drought during the cold phase of ENSO (La
Nina) (Rome-Gaspaldy and Ronchail 1998).
More specifically, no clear correlation between
rainfall anomalies and ENSO (either the El
Nino or the La Nina phase) has been observed
for the southern Peru region (Minaya 1994;
Rome-Gaspaldy and Ronchail 1998). The very
strong 1982-1983 El Nino event was charac-
terized by intensified drought in Arequipa and
a strong deficit of the Majes River flow (17,058
km 2 watershed, 450 km long, spring at 4886 m
on the western flank of the Andean Cordillera),
but other strong El Nino events, such as the
1972-1973 event, were marked by exceptional
rainfall at Arequipa and maximum flows of the
Majes River (Minaya 1993, 1994) (Fig. 2).
These inconsistencies are linked to complex cli-
matic mechanisms operating in this particular
region involving a variable position of the In-
tertropical Convergence Zone, substantial dif-
ferences in the atmospheric circulation patterns
during different ENSO events, and interactions
between the coastal area and the cordilleran
zone.
Debris-Flow Episodes and Strong Rainfalls
in Southern Peru
In arid countries, debris-flow activity is tightly
linked to the occurrence of relatively intense
rainfalls. In the Chile-Peru coastal desert, de-
bris-flow activity may be observed with precip-
itation amounts above 20 or 30 mm, and after
rainfall episodes that last more than 3 hours
(Vargas et al. 2000).
The occurrence of heavy rainfall episodes,
debris flows, and inundations of the coastal re-
gion of Tacna (southern Peru) was compared
with available monthly rainfall data, informa-
tion obtained from local newspapers, and
ENSO indexes for the period 1960-2000. The
mean annual rainfall at Tacna for this period
was 19 mm. The total annual rainfall data and
the annual mean Southern Oscillation Index
(SOI) do not show any significant correlation.
However, a coincidence between years with an
excess of rainfall and low values of SOI (Fig.
3) was observed. On the other hand, not all the
years characterized by low SOI values exhibit
an annual excess of rainfall. Between 1960 and
2000, there were 1 1 "rainy" months (rainfall >
19 mm per month). Three of them (September
1960, September 1961, and September 1962,
with 20.2, 34.6, and 33.0 mm of total accu-
mulation, respectively) do not correlate with El
Nino events (as defined by Trenberth 1997). For
the rest of the cases (January 1983 and January
1998, with respectively 24.0 mm and 21.2 mm
total rainfall; July 1963 and July 1972, with re-
spectively 32.0 mm and 59.0 mm total rainfall;
September 1963, September 1965, and Septem-
ber 1997, with respectively 33.1, 22.6, and 31.7
mm total rainfall; and December 1997, with
28.2 mm of total rainfall), a correlation is ob-
served with El Nino events as defined by Tren-
berth (1997). During La Nina episodes, -an ex-
cess of precipitation events has not occurred.
Information published in local newspapers in
Tacna allows a historical reconstruction of the
heavy rainfall episodes and debris flows in this
region for the last 40 years (Table 1). In the 1 1
months with heavy rainfall previously men-
tioned, debris flows occurred in January 1983
and September 1997, and to a lesser extent in
July 1972 and January 1998. In these cases, the
heavy rainfall episodes occurred during El Nino
events of strong intensity, characterized by low
SOI values and important anomalies of the sea-
surface temperature at Puerto Chicama (Table
1, Fig. 4). The chronicles indicate a great spatial
variability in the total amount of precipitation
related to the strong convective character of the
storms. During these heavy rainfall events, as
was shown for the coast of northern Chile by
Vargas et al. (2000), the rain frequently oc-
curred at night.
A similar relationship between heavy rainfall,
debris flows, and El Nino events was deter-
mined for the coastal area of the Atacama des-
ert, and particularly at Antofagasta (23S), in
northern Chile (Vargas et al. 2000). In northern
Chile, not all El Nino events provoke "heavy"
rainfall episodes, but all the events able to pro-
duce debris flows (rain intensity > 20 mm/3
hours; Hauser 1997; Vargas et al. 2000) oc-
curred during the development phase of El Nino
events, in the austral winter (Rutllant and Fuen-
zalida 1991; Garreaud and Rutllant 1996). In
Debris-Flow Deposits and El Nino Impacts
29
Figure 2. Comparison of annual streamflow anomalies of Majes River (southern Peru) and variation in the
Southern Oscillation Index (SOI) during the 1950-1991 period (streamflow data from Corporation de la Aviaci6n
Civil, CORPAC, in Minaya 1994). No clear-cut correlation is observed between El Nino (negative SOI values) or
La Nina (positive SOI values) and the Majes River streamflow.
1925, 1930, 1940, 1982, 1987, and 1991, heavy
rainfall episodes in northern Chile were linked
to storms coming from mid-latitude regions.
In the coastal area of southern Peru, the cli-
matic mechanisms involved in the generation of
"heavy" rainfall events are not yet totally un-
derstood. While debris-flow events related to
heavy rainfall episodes were contemporary with
strong El Nino events (Fig. 4), some of them
occurred during the austral summer (January
1983 and January 1998), while others occurred
during the austral winter or spring (July 1972
and September 1997). The strong rainfall events
occurring in the coastal area during the austral
summer should be linked to the activity of the
rainy season on the Altiplano and the cordillera.
Those occurring in winter during El Nino years
are not clearly understood and cannot be readily
related to the same processes described in
northern Chile (frontal systems coming from
mid-latitude regions).
Because the reliable instrumental data cover
a relatively short time period, we investigated
the relationship between regional strong rain-
falls and ENSO during the last few centuries.
Historical Rainfall Data and
El Nino Manifestations During the
Last Four Centuries
Documentary data on climate in Peru and Chile
were largely used by Quinn et al. (1987), Quinn
and Neal (1992), Hocquenghem and Ortlieb
(1992), and Ortlieb (1999, 2000) to try to es-
tablish a sequence of El Nino events during the
last few centuries. Documentary sources consist
of reports on droughts, river flooding, the de-
struction of bridges and buildings, good and
poor crops, heavy storms, and other impacts of
meteorologic conditions. Information was ob-
tained from a variety of official, ecclesiastical,
and particular documents left by the Conquis-
tadores and the later inhabitants of these regions
during colonial times and after independence
from Spain. These data led to different inter-
pretations by the above-mentioned authors.
Whereas Quinn tended to interpret reports of
storms and heavier rainfall than usual along the
coastal desert of Peru or in central Chile as ev-
idence of past El Nino conditions, Ortlieb
(2000) considered that only information on pre-
cipitation excess in coastal northern Peru and in
central Chile could be reliably used as an El
Nino indicator. Hocquenghem and Ortlieb
(1992) and Ortlieb (2000) argued that, based on
instrumental records of the last decades, Rimac
River floods (in Lima) and unusual vegetation
cover along the coast of southern Peru should
not be taken by themselves as evidence of El
Nino conditions. Unusual vegetation growth in
the lomas (hilltops) in the area of Ilo could be
due to intensified winter garuas (coastal fogs),
not necessarily to strong rainfall. In some cases
it was shown that droughts in coastal northern
Peru were coeval with vegetated lomas in
southern Peru, probably during La Nina con-
ditions.
Previous work on documentary sources on
climate anomalies in the Norte Grande of Chile
showed that reliable data for the scarcely in-
30
L. Ortlieb and G. Vargas
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Debris-Flow Deposits and El Nino Impacts
31
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Debris-Flow Deposits and El Nino Impacts
33
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ft
habited Atacama desert were for practical pur-
poses limited to the last two centuries (Ortlieb
1995). However, some additional and fragmen-
tary data from northernmost Chile and southern
Peru have recently turned up (Ortlieb 2000). Ta-
ble 2 presents data gathered on unusual rainfall
and debris-flow activity in the coastal areas of
southern Peru and (present-day) northernmost
Chile (north of 23S) since the earliest docu-
mentary record, dated 1619. Information on
heavy rainfalls in the central depression of
northern Chile, and floods in the quebradas
coming from the cordillera, which are linked to
La Nina conditions in the Altiplano and the An-
dean Cordillera, were not considered (unless
they co-occurred with precipitation anomalies
along the coast). The precipitation excesses are
compared with past occurrences of El Nino (or
La Nina) events as proposed by Quinn and Neal
(1992), Ortlieb (2000), and Ortlieb et al. (2002).
The last three columns of Table 2 do not con-
tain all the reconstructed El Nino (and La Nina)
events (according to the cited authors) but only
those that are contemporaneous with the hydro-
logic anomalies indicated in the first two col-
umns at left.
Table 2 shows that most heavy rainfall epi-
sodes and debris-flow activity registered in the
coastal study area occurred during El Nino
years, as determined by either one or all of the
cited authors. Several cases of flooding of the
San Jose or Azapa Rivers at Arica are not re-
lated to rainfall in the coastal area but reflect
precipitation excess in the Andean Cordillera,
during La Nina (or normal) conditions.
The historical data presented here cannot be
regarded as definitive, for several reasons. First,
documentary data are inherently fragmentary
and subject to error, exaggeration, and misin-
terpretation. Second, we still lack a reliable
chronological sequence of El Nino occurrences,
as evidenced by conflicting accounts in the last
three columns of Table 2. Third, the informa-
tion on river floods does not always show the
effects of cordilleran versus coastal rains. Rain-
fall in the upper part of the watersheds, in both
southern Peru and northern Chile, follows dif-
ferent regimes and has quite different mecha-
nisms from precipitation in the coastal areas.
Nevertheless, the historical data presented in
Table 2 tend to confirm that in a longer term
than the last few decades, precipitation excess
in the studied coastal area was generally ob-
served during El Nino years, and that El Nino
34
L. Ortlieb and G. Vargas
-1.5
to to to ^^v
!I
II
^ /10.560BP
\ 4 \10.895BP
( 12,490 BP
< 1 2.670 BP
* 12,730 BP
Debris flow
Sheetflood or channel flood
Aeolian
Midden
Occupation layer (aeolian
with water-laid silt)
Desiccation crack filled with
aeolian sand
Figure 5. Composite stratigraphic sequence of
the Quebrada Tacahuay. south of Ilo (from Keefer et
al. 1998). Ages are expressed in calibrated years (cal.
B.P.). Units Kl, K2, K3, K4cl, K4c2. K6, and K7 are
described as debris flows. Unit K8 is the main occu-
pation layer. Radiocarbon data from this sequence are
shown in Table 3.
cal. B.P., a sequence of eight debris-flow de-
posits, three aeolian sand layers, and two ma-
jor flood units. From an infrared-stimulated
thermoluminescent (TL) dating at 38.2 ka at
the base of this sequence, Keefer et al. (2001)
later inferred that these 10 debris-flow and
alluvial events occurred between 38,200 ka
and 12,700 cal. B.P.
Between 12,500 cal. B.P. and about 8800 cal.
B.P., four extensive debris-flow deposits were
formed (their units 2, 3, 6, and 7 [see Fig. 6],
which we will refer to here as K2, K3, K6,
and K7).
Between 8800 and 5300 cal. B.P., they rec-
ognized one debris-flow unit, which can be
subdivided into two thin layers (subunits
K4cl and K4c2, observed in a single profile)
overlying an aeolian sand unit (K4c3).
At ca. 5300 cal. B.P. (= 4550 60 B.P.) one
last major debris-flow deposit (unit Kl)
formed just before the main channel of Que-
brada Tacahuay began to be incised.
Presently, the floor of Quebrada Tacahuay
lies about 30 m below the top of the sedimen-
tary sequence. This sequence, cut by the paved
coastal road, is located about 1 km inland from
the shoreline.
In their study, Keefer et al. (1998) empha-
sized the archaeological aspects of their find-
ings. The major and oldest human occupation
was dated to 12,700-12,500 cal. B.P. and was
apparently interrupted because of the occur-
rence of a large debris flow (unit K7; see Fig.
5). The archaeological remains, including a
well-preserved hearth, which are found in a 10-
to 50-cm-thick layer of water-laid silt, with in-
terstratified lenses of aeolian fine sand (unit K8
in Fig. 5), are atypical because they include
very few marine shells, abundant seabird bones,
some remnants of pelagic fishes, and a few lith-
ic artifacts.
Our Data. During a brief visit to this locality
(in 1998), observation and sampling were con-
ducted in the southwestern part of the area stud-
ied by Keefer et al., to the west of the road.
Figures 6 and 7 show the studied sequence,
36
L. Ortlieb and G. Vargas
Debris-Flow Deposits and El Nino Impacts
37
ll
38
L. Ortlieb and G. Vargas
with units numbered Tl to T6 from bottom to
top. The upper layer, designated T6 (equivalent
to unit Kl of Keefer et al. 1998) is a thick de-
bris-flow deposit that is colored dark by abun-
dant organic matter. Below it occur (from top
to bottom) a composite debris-flow deposit
(T5), an alluvial (sheet flood) unit (T4), another
debris-flow unit (T3), a composite alluvial layer
(T2), and a coarse fluvial conglomerate (Tl).
Radiocarbon data (Table 3) were obtained on
the two alluvial layers T2 and T4, both water-
laid deposits that incorporate a high amount of
reworked aeolian sand. Unit T4 contains char-
coal fragments, seemingly related to washed-
out hearths; marine shells brought by man; and
abundant terrestrial gastropods (not necessarily
linked to a human occupation). This unit T4
includes remnants of a relatively young phase
of human occupation dated to about 9000 cal.
B.P. and referred to as "the shell midden" by
Keefer et al. (1998). Unit T2, which is practi-
cally devoid of marine shells and contains many
bird bones, is the major "occupational" layer
of Keefer et al. (1998) that is, their unit K8.
Our chronological data and those of Keefer
et al. are presented in Table 3.
Paleohydrologic and Paleoclimatologic In-
terpretations. The Quebrada Tacahuay se-
quence thus consists in a succession of alluvial
and sheet flood units, debris-flow deposits, and
aeolian sand units. The water-laid sediments
can be separated in two categories: the alluvial
units, which were deposited in the bed (or the
banks) of the Tacahuay river, and the debris-
flow and sheet flood units, which are linked to
superficial runoff, not necessarily within the
valley. The dark brown (T6) or reddish (T5 and
T3) colors of the debris-flow units (Fig. 6) re-
sult from the proportions of clay, silt, and re-
worked soil in the matrix; the larger size com-
ponents may be subrounded to angular. The al-
luvial units are generally gray or yellowish;
their matrix is coarse-grained, and they include
pebbles and blocks of varying size, which may
be rounded to subangular. The sheet flood de-
posits generally consist of thin layers or lenses
of sands that show current figures, laminations,
cross-bedding structures, and the like. They
may include layers bearing reworked material
(shells, bones, charcoal fragments).
The petrographic composition and the shape
of the coarse elements found in the thickest al-
luvial units of the sequence clearly indicate that
the material comes from upstream in the rela-
tively large watershed of the Quebrada Taca-
huay. Because the watershed is of limited size,
there is no doubt that the hydrologic regime
was controlled by rainfalls in the coastal region.
The >25-m-thick sequence of (mainly) alluvial
deposits that predate the T1/K9 unit (Fig. 7)
corresponds to a late Pleistocene episode of ac-
tive, aggrading, sedimentation processes. It is
inferred that the hydrologic regime was con-
trolled by regular and abundant rainfalls. The
scarcity of chronological data from the Pleis-
tocene sequence (besides the 38.2 ky TL date
obtained by Keefer et al. 2001) hampers any
precise paleoclimatic and paleohydrologic in-
terpretation.
The debris-flow units are mainly formed
from superficial material eroded from the to-
pographic surface, including interfluves and
nearby hill slopes. The formation of these de-
posits implies that relatively strong and intense
rainfalls occurred in the immediate vicinity of
the outcrops. The debris-flow units have a lim-
ited lateral extension. As shown in Figure 7, the
debris-flow unit T6/K1 formerly extended on
both northern and southern sides of the present-
day thalweg of Quebrada Tacahuay. This ob-
servation provides a maximum age (5290 cal.
B.P.) for the beginning of the incision of the
quebrada at this locality. We surmise that the
downcutting of the thalweg responded more di-
rectly to retrogradation processes of the incision
related to the mid-Holocene high sea level than
to paleoclimatologic factors. Sometime around
5000 cal. B.P. linear erosion took over the up-
ward aggradation processes, at this locality rel-
atively close to the coastline. We interpret that
it was not precisely because of a variation in
the hydrologic regime that the thalweg was
formed and progressively entrenched. This is
not easy to demonstrate because the erosive
processes dominated during the second half of
the Holocene, and thus no subsequent sedimen-
tary deposit was preserved in this locality. In
other words, the morphologic evolution of the
locality during the late Holocene prevents us
from making any comparisons between present
(or recent) hydrologic conditions and those that
existed prior to the mid-Holocene.
Keefer et al. (1998) interpreted as evidence
for El Nino manifestations the half-dozen epi-
sodes of debris-flow events (units K7 to Kl,
Fig. 5) identified between 12,500 and 5300 cal.
B.P. They further suggested that, because of the
Debris-Flow Deposits and El Nino Impacts
39
Quebrada El Canon
Holocene eolian sand
Late Pleistocene aljuvial sequence
~S" JtSK 1 ,
Figure 8. Late Pleistocene coarse alluvial units overlain by an early Holocene sandy layer and by a late Holocene
occupational horizon (sand and silts with abundant charcoal and ceramic fragments) in Quebrada El Canon, about 1
km south of Quebrada Los Burros, southern Peru. The Pleistocene alluvial units are most probably coeval with those
of Quebrada Tacahuay and with the oldest debris-flow deposits of Punta El Ahogado.
sedimentologic similarity between these debris-
flow deposits and those that predate unit K8
(i.e., older than 12,700 cal. B.P.) in the sequence
of Quebrada Tacahuay, El Nino conditions were
also present during the late Pleistocene. These
interpretations are essentially based on the as-
sumption that, as at present, violent rainfalls in
this coastal area would characteristically have
occurred during El Nino years.
We disagree with the interpretations of Kee-
fer et al. regarding the character of ENSO prox-
ies of the debris-flow units. Too little is known
about the morphoclimatic and paleohydrologic
local conditions at the end of the Pleistocene in
the Tacahuay region, and more generally in
coastal southern Peru. The superposition of
sheet flood, debris-flow, and alluvial sediments
has no modern equivalent and does not repre-
sent climatic conditions comparable to present
conditions. Instead, the abundance of alluvial
layers for the late Pleistocene part of the Ta-
cahuay sequence suggests a more humid cli-
mate, with stronger and more regular flow ep-
isodes, than in the late Holocene. If this was the
case, there is no reason to infer that debris-flow
activity was linked to El Nino conditions.
Quebrada Los Burros Area
Fontugne et al. (1999) also addressed the prob-
lem of the local impact of El Nino during the
Holocene. Their study was performed in the
framework of another archaeological project
centered on Quebrada Los Burros, an early Ho-
locene site located some 40 km south of Taca-
huay (see Fig. IB) (Lavallee et al. 1999). Ac-
cording to Fontugne et al. (1999), two major
debris-flow deposits (huaycos) were formed in
Quebrada Los Burros: the oldest one occurred
around 8980 cal. B.P. (between QLB2: 8160
70 B.P. and QLB3: 8040 105 B.P., conven-
tional ages), and the youngest one was dated to
slightly after 3380 cal. B.P. (see Table 3). Be-
tween these two units, ten layers of organic
matter and pseudo-peat accumulations were in-
terstratified (Fig. 8). These layers were inter-
preted by Fontugne et al. (1999) as representing
40
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