PP53B-1209:
Ba/Ca Reproducibility and Growth Banding in Gulf of Alaska Bamboo Corals
Friday, 19 December 2014
Gabriela Serrato Marks, Bowdoin College, Brunswick, ME, United States, Michèle LaVigne, Bowdoin College, Department of Earth and Oceanographic Science, Brunswick, ME, United States, Tessa M Hill, University California Davis, Davis, CA, United States, Wilson Sauthoff, University of California Santa Cruz, Santa Cruz, CA, United States, Thomas P Guilderson, Organization Not Listed, Washington, DC, United States, E Brendan Roark, Texas A&M University, College Station, CA, United States and Robert B Dunbar, Stanford University, School of Earth Sciences, Los Altos Hills, CA, United States
Abstract:
Deep-sea bamboo corals have been proposed as deep-ocean paleoceanographic archives because of their longevity and radial growth bands. Previous work has shown that bamboo coral Ba/Ca is a promising proxy for seawater barium, however, validation of Ba/Ca reproducibility is required. In addition, the growth band formation mechanism is uncertain, with some proposing that crystal orientation causes banding visible under light microscopy. The objective of this study was to evaluate Ba/Ca reproducibility and characterize growth band crystal orientation. Visible bands measured with a petrographic microscope were used to align LA-ICP-MS data collected along three replicate radii of the calcitic internodes of two well-dated corals from the Gulf of Alaska (collected live at 720m and 643m; 48°3’N, 132°44’W). Ba/Ca signals smoothed to ~annual resolution were reproducible within each coral (r=0.6-0.7; p<0.0001; n=3 radii/coral), suggesting that Ba/Ca varies in response to the external environment on annual timescales. Ba/Ca in the 720m coral increased from 1977 to 1998, a warm Pacific Decadal Oscillation (PDO) regime, possibly due to increased export production. The shallower coral (634m) revealed the inverse trend, suggesting variability in seawater barium dynamics with depth. Electron backscatter diffraction analysis of visible growth bands showed a preferred crystal orientation that does not correspond to location of visible bands or elemental composition, suggesting that crystal orientation does not cause bamboo coral banding. Overall, results show that regional oceanic signals are recorded as reproducible Ba/Ca variability in these corals. Comparison of these data to other well-dated records from the northeast Pacific would determine whether the relationship between Ba/Ca and PDO is regional. Additional archives of trace element variability will strengthen our understanding of how rapid climate change impacts intermediate ocean biogeochemistry.
