Reconstructing the El Nino-Southern Oscillation (ENSO) in Northern Peru: Perspectives from Donax Obsulus Geochemistry and Archaeomalacology

Abstract

Reconstructing the El Niño-Southern Oscillation (ENSO) during the Holocene is an important goal across multiple disciplines. As the largest driver of interannual climate variability, finding evidence of shifts in ENSO variability (broadly, its intensity, frequency, duration, and geographic extent) leads to better understanding of its impacts on not only natural systems but human societies as well. Particularly important is discerning the uniqueness of modern (Industrial Era) ENSO variability compared to previous time intervals, and when these uniquely modern patterns of ENSO began. However, paleoclimate archives with suitable temporal resolution and extent are rare, especially in the far eastern Pacific, which is considered the traditional epicenter of ENSO signals and impacts. This dissertation seeks to improve our knowledge of ENSO on the north coast of Peru using a novel approach: the geochemistry and morphology of a short-lived (years) intertidal surf clam, Donax obesulus. While previous studies have provided the basis for this approach, they examined a bivalve species (Mesodesma donacium) that is locally extinct in northern Peru, limiting the ability to build modern analog studies in the region. However, D. obesulus shells are common in both modern and archaeological contexts in northern Peru, situating them as a potentially powerful proxy archive for paleo-ENSO. This dissertation is composed of three studies. The first is an examination of the the height of D. obesulus valves from three archaeological sites as a potential proxy for paleoclimate activity. The second tests the stable isotope signal (specifically the annual range of δ18O) of modern populations of D. obesulus as a potential proxy for ENSO. The final study is the application of the results of the second to D. obesulus and M. donacium shells recovered from the archaeological site of Caylán in the Nepeña Valley Peru dating to ~400-200 BCE. When combined, these three studies illustrate the breadth of information that can be recovered from a specific clam species excavated from archaeological contexts. They also point to a previously underreported period of similar to modern ENSO activity on the north coast of Peru ~2400-2200 years ago.