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Response to Comment on "Otolith 18O Record of Mid-Holocene Sea Surface Temperatures in Peru"
We find the arguments of Béarez et al.
unconvincing. We did not contend that Galeichthys
peruvianus is a tropical species.Rather, G. peruvianus
was selected for its wide temperature toleranceand was captured during
both El Niño and La Niña events at Huanchaco,Peru
(1, 2). The northern range boundary Béarezet
al. cite (6°S) is incorrect. In a prior publication
(3)Béarez stated that this species is native to
Ecuador, an observationcorroborated by other authors
(4), which undermines thecool climate suggestion.
Our sea surface temperature (SST) conclusionsrely on
18O data, not the presence or absence of species
[although presence-absencedata show predominantly tropical fauna at
Ostra and Siches (5,6)].
Béarez et al. confuse individual migration with
species range and provide no data supporting migration. Between 91 and
94%of Peruvian G. peruvianus are caught in coastal water
less than15 m deep (and all in water <35 m deep)--thus, their
habitat isideally suited to reflect regional SST
(7). All age/sizeclasses were captured throughout
the El Niño/Southern Oscillation(ENSO) SST cycle in
north-central Peru (2), suggestingno ontogenetic or
seasonal migration. Strong correlation betweenmodern
18Ootolith profiles and SST at Puerto
Chicama demonstrates thatthese fish remained in nearby waters
throughout their lives (1,2).
Béarez et al. fail to explain how their hypothetical
migration scenarios could cause the
18Ootolith profiles. The seasonal
18O range of the Ostra otoliths is similar to that
caused by the1997-1998 El Niño in modern otoliths, with
negative summer 18O values similar to modern otoliths
during El Niño (1,2). Therefore, neither southerly
nor vertical migration,both of which would result in more positive
18O values, can account for the data. For migration to
cause seasonallynegative 18O values, the fish would
have had to transit between tropicalEcuador and central Peru twice
annually. This scenario is highlyunlikely for many reasons, including
the tendency for fish tonarrow, not expand, their ambient temperature
range. 18O values at the Ostra otoliths' margin,
indicating the seasonof death, show both winter and summer capture,
further underminingthe migration hypothesis.
The suggestion that local estuaries caused the
18Ootolith profiles is misleading to those
unfamiliar with the Peruvian coast.Compared to other regions, the
Peruvian shore face is steep, thetidal range is narrow, and the volume
of water in the braidedrivers is low. The Peruvian "estuaries" are
only small river mouths.The 18Owater in the
mouth of the Santa ranges from -12.8 to -14.1(8).
No otoliths record any value similar to this.
Regarding the proper identification of otoliths, archaeological
remains were originally identified to family level for seacatfish
(Ariidae) at Ostra and Siches (5, 9).The otoliths were
later identified as G. peruvianus because theyare
morphologically most similar to otoliths from that species,which is
the only common ariid in the area today. All archaeologicalG. peruvianus are identified this way, including those of
Béarez(10). As Béarez et al. note,
the only alternative speciesto G. peruvianus are tropical,
contradicting their assertion oftemperate SST. The otoliths in
(1, 8) were bisectedat perpendicular angles; thus curvature
variation is an artifactof sample preparation and meaningless for
identification.
Although Béarez et al. are correct that Siches is
4°30'S, their argument regarding its significance is unfounded. The
differencein mean SST between the Paita and Talara datasets is less
than0.4°C, not 2° to 4°C (11, 12). This smallvariation is within the ~3° to 4°C range we stated in
(1)and does not change our conclusions. Furthermore, the
Siches samplescontain the smallest 18O range of all the
otoliths. This suggests that these fish didnot pass through a large
temperature gradient, supporting ourarguments for the non-migratory
nature of the fish and the significanceof our paleotemperature
estimates.
The comments by Béarez et al. focusing on
diversity, equitability, and trophic level are based on a
misinterpretation ofour text. We do not attribute causality to
presence/absence ofanchovies alone, but to changes in the overall food
web in responseto upwelling variation (1). Thus, the
comments relatedto anchovy range have no bearing on our conclusions
about multispeciesecosystem changes.
In their discussion of Ostra, Béarez et al. suggest
that the former embayment near this site could have provided habitatfor some fish species. Geochemical records from embayment molluskssuggest this environment was evaporative (13, 14).As stated in (1), fish entering the embayment would recordmore positive, not more negative, 18Ootolith
values. Thus, the embayment cannot account for the
18Ootolith profiles.
Béarez et al. suggest that a sessile proxy may be
better suited for SST reconstructions. To that end, we present
18O data from the cockle Trachycardium
procerum (Figs. 1and 2) that corroborate our
enhanced seasonality interpretationof otolith data from Ostra. Modern
T. procerum were collectednear Casma in 1984 after the
strong 1982-1983 El Niño (15).The
18Oshell range measured during El Niño
is 1.5 (Fig. 1).Including published data from contemporaneous
T. procerum, themean El Niño range is ~1.3 (13,
15). The18O range from an Ostra shell (5830 ± 90 14C yrs B.P.) is 1.6 (Fig. 2).
The mean 18O range in four T. procerum from
fossil deposits near Ostra is~1.5 (13). All but one
ancient shell have 18O ranges greater than that measured
in carbonate precipitatedbefore the 1982-1983 El Niño depicted
in Fig. 1 (13).It is unlikely that each of these five
shells, dating to fourdifferent periods (5500 ± 150 to 6100 ± 150 14C yrs B.P.), grew during an El Niño event of
equal or greatermagnitude than the 1982-1983 event. A more likely
explanationis enhanced seasonality similar to that measured in
the contemporaneousotoliths (1). This conclusion is
supported by the Ostraspecimen (Fig. 2) that contains two consecutive
18O oscillations indicative of seasonal, not
inter-annual, variation.Unfortunately no absolute paleotemperatures
can be calculatedbecause the Santa embayment was evaporative, thus the
molluscan18O values are elevated relative to nearby
marine values (13,14).
Fig. 1.18O profile through ontogeny (left to
right) of T. procerum collected in 1984. The bracket
indicates samples taken from shell aragonite precipitated during the
1982-1983 El Niño.
[View Larger Version of this Image (12K GIF file)]
Fig. 2.18O profile through ontogeny (left to
right) of T. procerum excavated from the Ostra site
(5830 ± 90 14C yrs B.P.). Note that because of lower
sampling resolution than that depicted in Fig. 1, the range in seasonal
18O is potentially underestimated relative to the modern
valve.
[View Larger Version of this Image (9K GIF file)]
Béarez et al. argue that warm-tropical,
transitional (wide temperature-tolerant species), and warm-temperate
mollusks co-existedin the Santa embayment. We addressed this
previously (16),demonstrating DeVries and Wells'
data (17, 18)do not support contemporaneity of these
faunas. We have now analyzedthe data (13) cited by
Béarez et al. and find the radiocarbondates on
mollusks in the Santa and adjacent Salinas de Chao embaymentsunequivocally support our contention of warmer SSTs before 5800cal
B.P. and cooler SSTs thereafter (Fig. 3) (1,6,
19).
Fig. 3.
Dated mollusks from Perrier et
al. (table III in 8). Red symbols are warm-tropical
("warm") species, green symbols are transitional species that live
in warm-tropical and warm-temperate conditions, and blue symbols are
warm-temperate ("cool") species. Circles, samples from the Santa
paleoembayment; squares, samples from the Salinas de Chao
paleoembayment. Dates are calibrated using Calib 4.3 (26)
but, following DeVries and Wells (17) and Perrier et
al. (8), are not adjusted for R. These data,
referenced by Béarez et al. (note 36), demonstrate
that all warm-water mollusks in these locales predate 5,800 cal B.P.
and all cool-water mollusks postdate that time.
[View Larger Version of this Image (23K GIF file)]
Close examination of the comments and citations of Béarez
et al. strengthen our original interpretations. Our data
representthe most direct measurement of mid-Holocene paleotemperature
onthe coast of Peru, and are part of a larger body of research
supportingthe hypothesis of significant changes in mid-Holocene
PacificSST and ENSO history (6, 20-25).
C. Fred T. Andrus
Savannah River Ecology Laboratory University of Georgia Drawer
E Aiken, SC 29802, USA E-mail: andrus{at}srel.edu Douglas E. Crowe
Department of Geology University of Georgia Athens, GA 30602, USA Daniel H. Sandweiss
Department of Anthropology and Institute for Quaternary and Climate Studies S. Stevens Hall University of Maine Orono, ME
04469, USA Elizabeth J. Reitz
Department of Anthropology and Georgia Museum of Natural History Natural History Building University of Georgia Athens, GA 30602, USA Christopher S. Romanek
Department of Geology University of Georgia Athens, GA 30602, USA
and Savannah River Ecology Laboratory Drawer
E, Aiken, SC 29802, USA Kirk A. Maasch
Department of Earth Sciences and Institute for Quaternary and Climate Studies University of Maine Bryand Global Sciences
Center Orono, ME 04469 USA
P. J. Kailola, W.A. Bussing, in Guia FAO para
Identification de Especies para lo Fines de la Pesca, Pacifico
Centro-Oriental, W. Fischer et al., Eds. (FAO, Rome,
1995), pp. 860-886.
U. Brand, personal communication. Sr/Na analyses performed
through ontogeny on T. procerum from the Ostra site were
indicative of significantly elevated salinity, potentially as high as
40, due to evaporation.
Funded in part by Department of Energy grant
DE-FC09-96SR18546 (C.F.T.A., C.S.R.), Geological Society of America
(C.F.T.A.), Explorer's Club International (C.F.T.A.), NSF Grant
ATM-0082213 (D.E.C), the Heinz Charitable Trust (D.H.S.), and the
University of Maine Faculty Research Fund (D.H.S.).
19 August 2002; accepted 4 November
2002
10.1126/science.1077525 Include this information when citing this paper.
The editors suggest the following Related Resources on Science sites:
In Science Magazine
TECHNICAL COMMENTS
Philippe Béarez, Thomas J. DeVries, and Luc Ortlieb (10 January 2003) Science299 (5604), 203a.
[DOI: 10.1126/science.1076173] |Full Text »|PDF »
REPORTS
C. Fred T. Andrus, Douglas E. Crowe, Daniel H. Sandweiss, Elizabeth J. Reitz, and Christopher S. Romanek (22 February 2002) Science295 (5559), 1508.
[DOI: 10.1126/science.1062004] |Abstract »|Full Text »|PDF »
18O Record of Mid-Holocene Sea Surface Temperatures in Peru"
18O data, not the presence or absence of species
[although presence-absence data show predominantly tropical fauna at
Ostra and Siches (
R. These data,
referenced by Béarez et al. (note 36), demonstrate
that all warm-water mollusks in these locales predate 5,800 cal B.P.
and all cool-water mollusks postdate that time.
, due to evaporation.
