Investigating the influence of temperature and seawater δ18O on Donax obesulus (Reeve, 1854) shell δ18O

The coastline of Peru lacks long-lived marine organisms useful for paleoclimatic reconstructions generating a need for novel archives. Short-lived (<5 years) bivalves are commonly found in geological and archaeological deposits and thus can provide snapshots of past climatic variability (i.e., seasonal range), similar to data obtained by individual foraminifera analysis, rather than continuous, cross-dated time series (e.g., trees and corals). Previous studies have found success using the short-lived intertidal clam Mesodesma donacium. However, M. donacium are vulnerable to die-offs from the warmer sea surface temperatures (SST) associated with El Nino events and are functionally extinct in northern Peru thus limiting the possibility of modern analog studies for that region. Here we investigate the short-lived (1-3 years) surf clam, Donax obesulus, commonly found in northern Peru, as a paleoclimate archive. Donax obesulus populations are able to survive the warmer SSTs present during El Nino years although they are vulnerable to colder SSTs associated with La Ninas. We assessed the environmental drivers underlying subannual delta O-18 variability in D. obesulus from live collected shells from fish markets and coastal beaches near the Nepena Valley, Peru in 2012 (La Nina), 2014 (ENSO-neutral), and 2016 (El Nino). Forward modeling of pseudo-shell delta O-18 reveals that SST variations are a dominant driver with secondary contributions from seasonally-varying seawater delta O-18( delta O-18(sw)). By accounting for varying delta O-18(sw), we isolated the temperature dependent variable resulting in a paleotemperature equation for D. obesulus delta O-18. We verified our results with the delta O-18 record of a D. obesulus shell collected in 2006. Our results suggest that the paleotemperature equation we developed is useful for reconstructing El Nino-Southern Oscillation (ENSO)-related climatic variations in this region and the pseudo-shell approach may be useful for understanding shell delta O-18 in other locations.

Automated summary

The coastline of Peru lacks long-lived marine organisms useful for paleoclimatic reconstructions, leading to a need for novel archives. Short-lived bivalves such as the surf clam Donax obesulus, commonly found in northern Peru, may serve as a paleoclimate archive despite vulnerabilities to temperature fluctuations. By isolating temperature-dependent variables, a paleotemperature equation for D. obesulus delta O-18 has been developed, showing potential for reconstructing ENSO-related climatic variations in the region and may have broader applications in understanding shell delta O-18 in other locations.