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Science 10 January 2003:
Vol. 299. no. 5604, p. 203
DOI: 10.1126/science.1076173
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Technical Comments

Comment on "Otolith &dgr;18O Record of Mid-Holocene Sea Surface Temperatures in Peru"

Andrus et al. (1) asserted that oxygen isotope profiles from modern and mid-Holocene otoliths of the Peruvian sea catfish Galeichthys peruvianus, and diversity indices derived from midden collections of fish bones, provide evidence for warmer sea surface temperatures (SSTs). They further inferred weaker coastal upwelling off the north-central and northern coast of Peru before 5000 years before present (yr B.P.). We contend that their evidence is flawed and does not support these conclusions.

Our first concern deals with the use of otoliths from G. peruvianus. The common range for this fish is 6°S to 18°30'S; it is not a "tropical" eastern Pacific species and was not prior to the mid-Holocene (2-10). Hence, its presence at the archaeological Siches site (4°30'S) should imply cooler SSTs during the mid-Holocene than today, not SSTs 3° to 4°C warmer, as proposed by Andrus et al. (1). We further contend that G. peruvianus is a poor choice as a proxy for SSTs. Contrary to (1), populations of G. peruvianus do migrate latitudinally, especially in response to El Niño events (2, 11, 12). They range from the coastline to nearly 150 km offshore and are found from the surface to mesopelagic depths (13-16). Spawning individuals might also enter estuaries like other ariids (17). Thus, sea catfish otoliths could record a complex life history that does not provide reliable paleo-SST reconstructions of nearshore surface waters at a given latitude.

We also question the correct identification of otoliths by Andrus et al. G. peruvianus was not originally identified at Siches or Ostra (17, 18) and no modern specimens of G. peruvianus were collected near Siches (1). A mid-Holocene lapillus shown in a photomicrograph submitted by Andrus et al. to the World Data Center for Paleoclimatology (19) clearly differs from the modern lapillus shown in figure 2 in (1). The former is from an undetermined ariid species that likely belongs to one of several taxa now inhabiting the Gulf of Guayaquil (20). It has a regularly convex, almost semicircular ventral margin, whereas the latter otolith from G. peruvianus has a flattened ventral margin with a medial swelling.

Our second concern is with the data from Siches. This site is located at 4°30'S (19, 21, 22), not 4°40'S (1) or 4°20'S (17). Small differences in latitude are important at this site because the SST gradient between 4°30'S and 4°S is very steep--typically 2° to 4°C (23). Therefore, it should be no surprise that isotopically derived SSTs at Siches appear warmer than modern SSTs at Paita (5°04'S). The Siches data should be more appropriately compared with modern Talara (4°35'S) SSTs (24). The high proportion (90%) of warm-tropical taxa at the early mid-Holocene Siches site (1) is entirely consistent with the long-standing high diversity of warm-tropical mollusks on modern beaches, late Holocene beach ridges, and late Pleistocene marine terraces near Talara (25-28).

Our third concern is with species lists from the six sites listed in figure 4 of (1) and on the World Data Center site (19). Andrus et al. attributed a decrease in diversity and trophic level indices after 5000 yr B.P. to an increase in anchovy numbers. However, figure 4 of (1) confounds time with geography. Three of the four oldest sites (high diversity, low anchovy numbers) are from northern Peru, where few anchovies are ever found (29). The two youngest sites, both with low diversity indices, are from north-central Peru. One site (Alto Salaverry) has no anchovy bones. Its low indices result from a great abundance (70%) of sciaenids. Anchovies are only present at a single younger site (Pampa de Las Llamas-Moxeke) for reasons that cannot be inferred from the data.

The anomalous site in figure 4 of (1) is Ostra. This site is older than 5000 yr B.P. and situated in north-central Peru, but has high diversity indices comparable to tropical northern sites. Among the distinctive and common taxa from Ostra (19) are sea catfish (Ariidae), bonefish (Albula), and pufferfish (Sphoeroides)--all of which inhabit or favor shallow estuarine or lagoonal environments (5, 17, 30-32), such as the nearby coeval Santa lagoon (33-36). Incidentally, if mid-Holocene G. peruvianus spawned in the Santa lagoon and Santa River estuary, as presumed by Reitz and Sandweiss (17), any conclusion that seasonally elevated delta 18O anomalies in Ostra otoliths are largely due to warmer open-ocean summer SSTs (1) must be considered suspect.

In the absence of persuasive evidence (1, 21, 37, 38), we believe it is still premature to draw any conclusions regarding the Holocene oceanographic history of the Peruvian margin (39). Convincing reconstructions for seasonal and interannual SST variations and for upwelling conditions during the Holocene should more appropriately be obtained through detailed measurements of biogenic carbonates from less mobile organisms, or offshore laminated sediments.

Philippe Béarez
Muséum National d'Histoire Naturelle
Laboratoire d'Ichtyologie Générale et Appliquée
43 rue Cuvier
75231 Paris Cedex 05, France
E-mail: bearez{at}mnhn.fr
Thomas J. DeVries
Box 13061
Burton, WA 98013, USA
Luc Ortlieb
Ur "Paleotropique"
Institut de Recherche pour le Développement
32 avenue Henri-Varagnat
F-93143 Bondy Cedex, France

REFERENCES AND NOTES

1. C. F. T. Andrus, D. E. Crowe, D. H. Sandweiss, E. J. Reitz, C. S. Romanek, Science 295, 1508 (2002) [Abstract/Free Full Text].
2. F. De Buen, Zonarida. Bol. Depto. Invest. Cien. Aplicadas (Univ. Chile Zona Norte, Antofagasta, Chile) 4, 2 (1961).
3. G. R. Allen, D. R. Robertson, Fishes of the Tropical Eastern Pacific (Crawford House Press, Bathhurst, Australia, 1994).
4. P. J. Kailola, W. A. Bussing, in Guía FAO para la Identificación de Especies para los Fines de la Pesca: Pacífico Centro-Oriental, W. Fischer, F. Krupp, W. Schneider, C. Sommer, K. E. Carpenter, V. Niem, Eds. (U.N. Food and Agriculture Organization, Rome, 1995), 2, 860. 
5. R. Froese, D. Pauly, Eds., FishBase 2000: Concepts, Design and Data Sources [Int. Center for Living Aquatic Resources (ICLARM), Los Baños, Laguna, Philippines, 2000].
6. The entry for G. peruvianus in FishBase (www.fishbase.org/Summary/SpeciesSummary.cfm?ID=13493&genusname=Galeichthys&speciesname=peruvianus) cites 'tropical,' which is defined in the FishBase glossary as a band of latitudes close to the equator with characteristic temperatures, humidity, and water temperatures. This definition is an inaccurate generalization for most species that inhabit the northern range of the Peruvian Current ecosystem.
7. R. Cooke, personal communication.
8. A. Acero, personal communication.
9. P. Béarez, Archaeofauna 9, 29 (2000) .
10. Remains of G. peruvianus are found in middens dating to the early Holocene near 18°S at Quebrada de los Burros (9).
11. I. Kong, M. Oliva, L. R. Marinovic, "Seminario-Taller: Estado del Conocimiento sobre ENSO en el norte de Chile" (Vol. Resumenes 34, Org. Estados Am., Univ. Antofagasta, Coquimbo, Chile, 1999).
12. G. peruvianus appeared off the coast of Antofagasta, Chile (23°24'S) and other parts of northern Chile during the 1957-1958 and 1982-1983 ENSO events (2, 11).
13. J. Zevallos, V. Blaskovic, in La Merluza Peruana (Merluccius gayi peruanus): Biología y Pesquería, M. Espino, M. Samamé, R. Castillo, Eds. [Inst. Mar Perú (IMARPE), Callao, Peru, 2001], p. 42. 
14. G. peruvianus is a common by-catch in the merluza (hake) fishery (13).
15. P. R. Castillo, et al., Inf. Inst. Mar Perú 159, 7 (2001) .
16. M. Samamé, personal communication.
17. E. J. Reitz and D. H. Sandweiss, J. Archaeol. Sci. 28, 1085 (2001) [CrossRef].
18. E. J. Reitz, Int. J. Osteoarch. 11, 163 (2001) [CrossRef].
19. C. F. T. Andrus, D. E. Crowe, D. H. Sandweiss, E. J. Reitz, C. S. Romanek, www.ngdc.noaa.gov/paleo/pubs/andrus2002/andrus2002.html.
20. P. Béarez, Rev. Biol. Trop. 44, 731 (1996) .
21. D. H. Sandweiss, J. B. Richardson III, E. J. Reitz, H. B. Rollins, K. A. Maasch, Science 273, 1531 (1996) [Abstract].
22. Inst. Geográfico Nac., Lima, Peru, Talara and Lobitos 1:100,000 quadrangle maps (1985).
23. A database of present and weekly archived SST maps of coastal Peru from Centro de Predicción Numérica del Tiempo y Clima, Inst. Geofísico del Perú, are available at www.met.igp.gob.pe/cpntc/sst/.
24. SST data from the Int. Res. Inst. Climate Prediction/Lamont Doherty Earth Observatory (IRI/LDEO) Climate Data Library for Chicama, Paita, and Talara for Jan. 1963 to Sept. 1983, are available at http://ingrid.ldeo.columbia.edu/.
25. T. J. DeVries, thesis, Ohio State University (1986).
26. V. Alamo, V. Valdivieso, Lista sistemática de moluscos marinos del Perú [Inst. Mar Perú (IMARPE), Callao, Peru,1987].
27. A. Diaz, L. Ortlieb, VII Congr. Peruano de Geol. (Lima, Peru, 1991), p. 407. 
28. A. Diaz, thesis, Univ. Ricardo Palma, Lima, Peru (1992).
29. J. L. Borgo, I. Vasquez, A. Paz, Informe Inst. Mar Perú (Lima, Peru, 1966), vol. 19. 
30. L. M. Sierra, R. Claro, O. A. Popova, in Ecología de los Peces Marinos de Cuba, R. Claro, Ed. (Inst. Oceanología Acad. Cien. Cuba and Centro de Invest. Quintana Roo, Mexico, 1994), pp. 263-284.
31. P. J. P. Whitehead, R. Rodríguez-Sánchez, in Guía FAO para la Identificación de Especies para los Fines de la Pesca: Pacífico Centro-Oriental, W. Fischer, F. Krupp, W. Schneider, C. Sommer, K. E. Carpenter, V. Niem, Eds., (U.N. Food and Agriculture Organization, Rome, 1995), vol. 2, p. 851. 
32. W. A. Bussing, in Guía FAO para la Identificación de Especies para los Fines de la Pesca: Pacífico Centro-Oriental, W. Fischer, F. Krupp, W. Schneider, C. Sommer, K. E. Carpenter, V. Niem, Eds. (U.N. Food and Agriculture Organization, Rome, 1995), vol. 3, p. 1629. 
33. T. J. DeVries and L. E. Wells, Palaeogeogr. Palaeoclim. Palaeoecol. 81, 11 (1990) [CrossRef].
34. L. E. Wells, J. Coast. Res. 12, 1 (1996) .
35. C. Perrier, C. Hillaire-Marcel, L. Ortlieb, Geogr. Phys. Quat. 48, 23 (1994) .
36. Implications of thermally anomalous molluscan assemblages (TAMAs) in the mid-Holocene Santa lagoon have been intensely debated (1, 21, 33-35, 37-39). The lagoon was connected to the ocean throughout most of its history and supported distinctive molluscan assemblages whose distribution closely reflects substrate and paleohydrography (33). The association of transported and in situ warm-tropical and transitional-tropical lagoonal mollusks on a tidal delta at the mouth of the lagoon, and comparably preserved warm-temperate mollusks on nearby sand banks, argues strongly for a warm-water lagoon fronted by a cooler ocean. This specific juxtaposition has never been acknowledged by detractors of the paleogeographic explanation for the Santa TAMA (1, 21, 37, 38). The 14C analyses of numerous lagoonal bivalves (Ostrea palmula, Argopecten circularis, Chione broggi, Trachycardium procerum), which are all represented by in situ or paired valves, establish the lagoon's age as about 6500 to 4000 yr B.P. (35). Erroneous citations of data and statements regarding the ecology, ages, and distribution of molluscan taxa in the Santa lagoon (21, 37, 38) obscure the straightforward history of eustatic sea level rise and transgression, Santa lagoon formation, occupation by warmwater mollusks, progradation, and lagoon abandonment (33-35).
37. D. H. Sandweiss, J. B. Richardson III, E. J. Reitz, H. B. Rollins, K. A. Maasch, Science 276, 967 (1997) .
38. D. H. Sandweiss, K. A. Maasch, D. F. Belknap, J. B. Richardson III, H. B. Rollins, J. Coast. Res. 14, 367 (1998) .
39. T. J. DeVries, L. Ortlieb, A. Diaz, L. Wells, C. Hillaire-Marcel, Science 276, 965 (1997) [Free Full Text].
15 July 2002; accepted 4 November 2002
10.1126/science.1076173
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Science. ISSN 0036-8075 (print), 1095-9203 (online)