Reconstructing Paleoclimate from Oxygen Isotopes and Trace Element Ratios in Olivella biplicata shells
Abstract
High resolution records of past sea surface temperature (SST) are not as common in mid to high latitudes as they are in tropical areas. In higher latitude regions, proxy data preserved in marine mollusk shells, often found in archaeological shell middens, could potentially provide these critical records. One promising candidate is the Purple Olive Snail Olivella biplicata, a marine mollusk with an aragonite shell that occurs in subtidal to shallow intertidal zones along the eastern Pacific coast in large quantities. The ubiquity of the snail spatially (from Baja California to British Colombia) and temporally makes it an ideal candidate for study. Previous studies have shown seasonal changes in isotopic signatures from O. biplicata (Eerkens et al 2005, 2007, 2010), however high resolution trace elemental analysis has not been conducted. We measured stable isotope (δ18O and δ13C) and trace element (Sr/Ca, Mg/Ca) composition in two modern shells collected in La Jolla, California and two archaeological shells from ~AD1410 to AD1500 excavated on San Miguel Island (Channel Islands, California). The shells were micromilled along growth lines at 100-150 μm intervals. The resulting powder was analyzed for stable isotopes and trace elements by IRMS and HR-ICPMS respectively. The modern shell data was compared to instrumental SST records from the Scripps Pier. δ18O data from modern O. biplicata follows monthly trends in SST, though fractionation due to biological effects leads to an offset from isotopic equilibrium values. Mg/Ca and Sr/Ca measurements on modern shells allow us to test the viability of these as additional proxies that could help us deconvolve SST from salinity effects. Archaeological sample measurements are utilized to assess the possible effects of early diagenesis on shell geochemistry. Given that a single shell can record nearly a decade of SSTs at monthly resolution and that the species can be found in archaeological sites dating back 10,000 years B.P., O. biplicata has great potential to increase our understanding of high latitude climate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP41A1734N
- Keywords:
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- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry;
- 1041 GEOCHEMISTRY / Stable isotope geochemistry