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

Ni, Y., Foster, G. L. , Elliot, T., Schmidt, D. N., Pearson, P., Haley, Brian and Coath, C. (2007) A core top assessment of proxies for the ocean carbonate system in surface-dwelling foraminifers Paleoceanography, 22 (PA3212). DOI 10.1029/2006PA001337.

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Abstract

We have assessed the reliability of several foraminifer-hosted proxies of the ocean carbonate system (d11B,
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 d11B 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 d11B of our Atlantic core top G. sacculifer, but we find that d11B increases with
increasing test size for G. sacculifer in the Pacific. These systematic differences in d11B 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 wellpreserved
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 d11B this influences G. sacculifer but not G. ruber, which has
negligible gametogenic calcite.

Document Type: Article
Keywords: oron isotope, trace element, foraminifer
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
DOI etc.: 10.1029/2006PA001337
ISSN: 0883-8305
Date Deposited: 28 Apr 2009 13:52
Last Modified: 10 May 2017 08:23
URI: http://eprints.uni-kiel.de/id/eprint/2378

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