Tracking Ocean-Atmosphere Conditions in the Eastern Equatorial Pacific: Shell Preservation and the Record

Large scale patterns of oceanic and atmospheric circulation dictate climate in the eastern equatorial Pacific and along coastal Peru. Coastal ocean conditions reflect the larger climate system, and impacted the local environment throughout the Holocene and the cultures developing within the region at that time. Shell middens located at archaeological sites provide a record of the coastal ocean conditions and a means of examining larger scale climate change. In particular, isotopic data from the surf clam Mesodesma donacium provides a record of the annual cycle of sea surface temperatures through time. This annual cycle is linked to oceanographic processes controlling climate variability in the eastern equatorial Pacific. The quality of the isotopic record depends on preservation of the shell material. We examined the potential influence of natural and anthropogenic action on shells from within middens in various archaeological sites along central coastal Peru. Microscopic viewing of shell structure, staining, and shell treatment experiments indicate good preservation of the climate signal from the shells within these middens. The arid coastal environment has resulted in little diagenesis, and likely human use of the clams had no significant impact on isotopic values.