B22B-02
Ba/Ca Ratios in North Pacific Bamboo Corals Record Changes in Intermediate Water Biogeochemistry
Tuesday, 15 December 2015: 10:35
2002 (Moscone West)
Gabriela Serrato Marks, Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA, United States, Michèle LaVigne, Bowdoin College, Department of Earth and Oceanographic Science, Brunswick, ME, United States, Tessa M Hill, University of California Davis, Davis, CA, United States, Wilson Sauthoff, University of California Santa Cruz, Santa Cruz, CA, United States, Thomas P Guilderson, Lawrence Livermore National Laboratory, Livermore, CA, United States, E Brendan Roark, Texas A & M University College Station, College Station, TX, United States and Robert B Dunbar, Stanford University, School of Earth Sciences, Los Altos Hills, CA, United States
Abstract:
Trace elemental ratios preserved in the skeleton of bamboo corals, which live for hundreds of years at >500m depth, have been utilized as archives of deep-ocean conditions. However, it was previously unclear whether trace element data from these corals were internally reproducible and could therefore be used as reliable climate proxies. This study tests the internal reproducibility of Ba/Ca in the calcite of nine bamboo corals to further develop a new proxy for dissolved Ba in seawater (BaSW). Trace element LA-ICP-MS data were collected along three replicate radii of varying lengths of the calcitic internodes of well-dated corals collected live from the Gulf of Alaska (720m and 643m) and the California Margin (870m, 1012m, 1295m, 1500m, 1521m, 1954m, and 2054m; samples from 1295-1521m are not yet dated). Data were aligned using visible bands measured with a petrographic microscope to account for irregular growth. Ba/Ca data filtered with a 50µm (1.5-2 year) moving average were reproducible within each coral to 2.9 ± 2.1% (n=3 radii/coral, 9 corals), suggesting that regional geochemical signals are recorded as reproducible Ba/Ca signals on >annual timescales. Coral Ba/Ca presents an excellent proxy for BaSW, which has been found to be correlated with refractory nutrients (e.g. silicate) and oxygen minima. Increasing BaSW with depth and increased variability near 1000m suggests that BaSW is not constant with depth or with time. Several factors, including barite saturation state, particulate organic carbon (POC) remineralization rate, and particle sinking time, may be involved in the observed changes in BaSW. Further examination of such mechanisms could provide new insights into modern changes in deep-sea biogeochemistry.
