High-Resolution Elemental Analysis In Mollusks as Proxy for Upwelling

Deep water upwelling is an important component of global oceanic circulation. Measuring upwelling rates during the past may contribute to a better understanding of past climate conditions. Unfortunately there are comparatively few upwelling proxies. Radiocarbon concentrations in coral and mollusk shells have been used successfully to assess paleo-upwelling but the comparatively large minimum sample size and high cost of analysis limits its application. Thus a new molluscan upwelling proxy would be valuable. To help achieve this goal a Trachycardium procerum shell that survived El Niño upwelling variation in Peru generated during the 1982-1983 event was analyzed via LA-ICP-MS. The warming during the El Niño caused a distinct growth scar on the shell, permitting independent knowledge of the period of upwelling variation. The shell was previously analyzed for δ¹⁸O, δ¹³C, and radiocarbon and contains a detailed record of upwelling and sea surface temperature. Analysis focused on elements with similar ionic potential (z/r=2) to calcium and that could replace it in a calcium carbonate lattice (e.g. Cd, Ba, Pb, Ni, and Mn); other non Ca-replacing elements abundant as nutrients in upwelled seawater were also analyzed. These data were measured at the same spatial resolution as the previous geochemical analyses. Comparison of these elemental profiles to the radiocarbon profile may indicate if any of these elements may serve as an upwelling proxy.