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A core top assessment of proxies for the ocean carbonate system in surface-dwelling foraminifers

Ni, Yunyan, Foster, Gavin L., Bailey, Trevor, Elliott, Tim, Schmidt, Daniela N., Pearson, Paul Nicholas, Haley, Brian and Coath, Chris 2007. A core top assessment of proxies for the ocean carbonate system in surface-dwelling foraminifers. Paleoceanography 22 (3) , PA3212. 10.1029/2006PA001337

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We have assessed the reliability of several foraminifer-hosted proxies of the ocean carbonate system (δ 11B, B/Ca, and U/Ca) using Holocene samples from the Atlantic and Pacific oceans. We examined chemical variability over a range of test sizes for two surface-dwelling foraminifers (Globigerinoides sacculifer and Globigerinoides ruber). Measurements of δ 11B in G. ruber show no significant relationship with test size in either Atlantic or Pacific sites and appear to provide a robust proxy of surface seawater pH. Likewise there is no significant variability in the δ 11B of our Atlantic core top G. sacculifer, but we find that δ 11B increases with increasing test size for G. sacculifer in the Pacific. These systematic differences in δ 11B are inferred to be a consequence of isotopically light gametogenic calcite in G. sacculifer and its preferential preservation during postdepositional dissolution. The trace element ratio proxies of ocean carbonate equilibria, U/Ca and B/Ca, show systematic increases in both G. ruber and G. sacculifer with increasing test size, possibly as a result of changing growth rates. This behavior complicates their use in paleoceanographic reconstructions. In keeping with several previous studies we find that Mg/Ca ratios increase with increasing size fraction in our well-preserved Atlantic G. sacculifer but not in G. ruber. In contrast to previous interpretations we suggest that these observations reflect a proportionally larger influence of compositionally distinct gametogenic calcite in small individuals compared to larger ones. As with δ 11B this influences G. sacculifer but not G. ruber, which has negligible gametogenic calcite.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Additional Information: Pdf uploaded in accordance with publisher's policy at (accessed 20/02/2014).
Publisher: American Geophysical Union
ISSN: 0883-8305
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 03:00

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