Geology

Uptake Uptick

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Science  22 Nov 2013:
Vol. 342, Issue 6161, pp. 910
DOI: 10.1126/science.342.6161.910-b
CREDIT: G. NEHRKE ET AL., BIOGEOSCIENCES 10 (29 OCTOBER 2013) © COPERNICUS PUBLICATIONS ON BEHALF OF THE EUROPEAN GEOSCIENCES UNION

Foraminifera are tiny aquatic organisms that have mineralized shells composed of calcium carbonate. In marine environments, these structures precipitate from seawater; thus foraminifera shells preserved in the sedimentary record reflect the chemistry and temperature of ancient oceans. However, models of the uptake of Ca and other trace elements do not entirely explain the concentration and ratio of ions preserved in carbonate shells. Using a combination of isotopic and fluorescent imaging of incubated cultures, Nehrke et al. show that passive ion transport is important for trace elements such as Mg and Sr in an extant foraminifera species, but not Ca. Transmembrane transport as the predominant uptake mechanism of Ca helps explain not only the observed Mg/Ca and Sr/Ca ratios in recently grown shells but also their relation to changes in seawater chemistry, and thus past ocean temperatures.

Biogeosciences 10.5194/bg-10-6759-2013 (2013).

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