HR: 0800h
AN: B21B-0873    [Abstracts]
TI: Tidal Modulation of Sr/Ca Ratios in a Pacific Reef Coral
AU: Reves-Sohn, R A
EM: rsohn@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AU: * Cohen, A L
EM: acohen@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AB: The skeletal composition of scleractinian corals reflects a combination of exogenous and endogenous processes, and represents a unique source of information about environmental as well as physiological processes linked to biomineralization. The challenge to paleoceanographic reconstructions based on coral skeletal chemistry is to identify and quantify the contribution of vital effects, thus enabling a more accurate interpretation of the proxy data in terms of climate. A good example is the strontium-to-calcium ratio (Sr/Ca) of coral skeleton, an important paleotemperature proxy that is also influenced by physiological processes. Here we present evidence for tidal forcing of coral Sr/Ca ratios on timescales of weeks to months that cannot be accounted for by changes in ocean temperature. Our ion microprobe measurements of Sr/Ca ratios in a Porites lutea coral from the north-central Pacific reveal high-frequency variations at dominant periods centered on ~6, ~10, and ~25 days. Comparison between coral Sr/Ca and in situ recorded SSTs reveals that the relationship between Sr/Ca and temperature on these short timescales does not follow trends observed at longer (annual) periods. Thus, an additional forcing is required to explain our observations. Our stochastic analyses demonstrate that Sr/Ca is correlated with both tidal water level variations and sea surface temperature, and the contribution of each forcing to the Sr/Ca content of the skeleton varies as a function of forcing period. We propose that water level influences Sr/Ca indirectly via tidal modulation of photosynthetically-active radiation (PAR) that drives large changes in zooxanthellate photosynthesis. The implication of this model is that coral Sr/Ca ratios are sensitive to the distance of the top of the colony from the sea surface. Thus coral colonies collected at different depths, massive colonies that grow and increase in height, and coral communities surviving sea level changes may reflect these changes in their Sr/Ca ratios. Additional studies will be required to determine if sea level forcing of coral Sr/Ca can provide a valuable new proxy for paleoclimate reconstructions
DE: 3670 Minor and trace element composition
DE: 4267 Paleoceanography
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting