Modern and Prehistoric El Niño-Southern Oscillation (ENSO) Variability: Perspectives from two Short-Lived Bivalve Species, Donax obesulus and Mesodesma donacium

Authors: Jacob Warner*, Louisiana State University, Department of Geography and Anthropology, Kristine L. DeLong, Louisiana State University, Department of Geography and Anthropology, Alan D. Wanamaker, Jr., Iowa State University, Department of Geological and Atmospheric Sciences, David Chicoine, Louisiana State University, Department of Geography and Anthropology, Kaustubh Thirumalai, Brown University, Department of Earth, Environmental, and Planetary Sciences
Topics: Paleoenvironmental Change, Climatology and Meteorology, Oceanography
Keywords: Paleoclimate, ENSO, El Niño, Peru, Archaeology
Session Type: Paper
Day: 4/10/2018
Start / End Time: 8:00 AM / 9:40 AM
Room: Napoleon B2, Sheraton 3rd Floor
Presentation File: No File Uploaded

There is a need for precise El Niño-Southern Oscillation (ENSO) proxies along the Peruvian coast. Unfortunately few long-lived (>50 years) organisms suitable for sclerochronological research exist along this coast. However, short-lived (<5 years) intertidal bivalves abound. Monte Carlo simulations suggest these species live long enough to record ENSO variability. However, Mesodesma donacium (one such intertidal bivalve clam used for reconstructions) is vulnerable to El Niños, possibly biasing seasonal δ18O cycles towards ENSO-neutral and La Niñas. M. donacium are functionally extinct north of ~14°S, limiting the geographic range of modern studies. We present another short-lived intertidal clam as complementary to M. donacium for reconstructing ENSO variability. Donax obesulus lives in warmer SSTs north of ~14°S, yet may be sensitive to La Niñas. Both species are found in archaeological sites along the north-central coast of Peru, allowing comparison between modern and prehistoric ENSO variability. We collected D. obesulus from the Nepeña Valley, Ancash, Peru, in 2012, 2014, and 2016 (La Niña, ENSO-neutral, and El Niño, respectively) and obtained M. donacium and D. obesulus excavated from a prehistoric (~2300 ±100 BP) site (Caylán) in the same valley. Modern La Niña D. obesulus seasonal δ18O range is 0.8‰, less than modern M. donacium (1.1‰). Archaeological D. obesulus seasonal δ18O range is ~1.8‰, indicating greater ENSO variability than modern. Caylán M. donacium seasonal range is ~1.1‰, within previous studies (~0.3 to 1.3‰, ~2900 BP), suggesting possible bias. Modern D. obesulus also show a mean δ18O shift (+0.77‰) compared to Caylán suggesting shifts in seawater δ18O.

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