By Kate Green

Faculty Mentor: Pamela Grothe

Abstract

Tridacna spp. clams, also known as giant clams, are the largest living marine bivalves and have been theorized to be reliable indicators of paleoclimate (Yan et. al., 2020). The Tridacna gigas is commonly found throughout the tropical Pacific, and has potential to supplement high-resolution paleoclimate archives from corals. Porites corals, the most commonly used corals for paleoclimate reconstruction in the tropical Pacific, are prone to diagenesis, or alteration of their skeletal material, due to their porous skeletons, affecting the reliability of their geochemistry to accurately record the sea surface temperature (SST) at the time the coral was living. Due to Tridacna gigas’ nonporous shell, they are less susceptible to diagenesis and may provide more unaltered views of the past (Welsh et. al., 2009). Several modern Tridacna gigas shells have been collected from Kiritimati Island in the central tropical Pacific, where well-established Porites records exist. I propose to test the reliability of Tridacna gigas shells from Kiritimati Island through analysis of the δ18O profiles of the clam shells, and measuring the annual and daily growth bands of the clams. I will compare the geochemical results with instrumental records of SST as well as with the modern Porites coral records from the same time and location to assess the reliability of Tridacna gigas as a paleoclimate proxy. I expect that modern Kiritimati Island Tridacna gigas clams will strongly correlate mean SST and the modern d18O record of Porites corals. Moreover, I expect that they will reproduce the El Niño Southern Oscillation (ENSO) variability as told by the monthly SST estimates. Lastly, the Tridacna gigas may precipitate their shell d18O closer to isotopic equilibrium from seawater than Porites corals, providing an additional benefit that removes biological effects on the geochemistry from the coral organism itself. If proven as reliable paleoclimate recorders, this new archive could provide an untapped opportunity to reconstruct the central tropical Pacific climate, considering the large number of available samples on extensive rubble coral fields around Kiritimati Island.