Modern and late Pleistocene B/Ca ratios of the benthic foraminifer Planulina wuellerstorfi determined with laser ablation ICP-MS.

Raitzsch, Markus, Hathorne, Ed C. , Kuhnert, Henning, Groeneveld, Jeroen and Bickert, Torsten (2011) Modern and late Pleistocene B/Ca ratios of the benthic foraminifer Planulina wuellerstorfi determined with laser ablation ICP-MS. Geology, 39 (11). pp. 1039-1042. DOI 10.1130/G32009.1.

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Abstract

Incorporation of boron into foraminiferal shells is thought to be primarily governed by the carbonate chemistry of the ambient seawater, suggesting that it can be reconstructed from B/Ca ratios. To this end, B/Ca ratios of the benthic foraminifer Planulina wuellerstorfi from South Atlantic core top samples have been analyzed using laser ablation−inductively coupled plasma−mass spectroscopy (LA-ICP-MS) to provide additional information on intratest trace element heterogeneity. Results show that boron is heterogeneously distributed within and between shells, with content variations of approximately ±43% displayed within a single shell. B/Ca is higher in the youngest chambers, opposite to the observed between-chamber variability of Mg/Ca. This may be explained by ontogenetic changes of physiological processes that increase the pH of the calcifying fluid and thus the borate concentration while decreasing Mg/Ca to promote calcification. Despite this heterogeneity, mean B/Ca ratios are positively correlated with the deepwater calcite saturation state (Δ[CO32–]), in line with previous studies. We apply this empirical relationship to reconstruct Δ[CO32–] for the late Pleistocene to Holocene using samples from a depth transect in the equatorial Atlantic. Reconstructed Δ[CO32–] values confirm previous studies suggesting that CaCO3-oversaturated North Atlantic Deep Water was reduced during glacial periods, whereas CaCO3-undersaturated Antarctic Bottom Water expanded vertically and propagated northwards. In summary, our data demonstrate that bulk B/Ca in P. wuellerstorfi reliably reflects variations in Δ[CO32–], despite the strong physiological control of boron incorporation.

Document Type: Article
Keywords: Paleoceanography; Geology; Benthic foraminifera
Research affiliation: AWI
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1130/G32009.1
ISSN: 0091-7613
Projects: EUROPROX
Date Deposited: 08 Dec 2011 13:47
Last Modified: 28 Jun 2019 11:49
URI: http://oceanrep.geomar.de/id/eprint/12836

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