Experimental determination of barium uptake in shells of the planktonic foraminifera Orbulina universa at 22°C

Details Experimental determination of barium uptake in shells of the planktonic foraminifera Orbulina universa at 22°C Experimental determination of barium uptake in shells of the planktonic foraminifera Orbulina universa at 22°C

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56.2673l&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 56, Issue 7, pp.2673-2680

Computer Science

18

Scientific paper

We have sought to directly test the assumption that the Ba / Ca ratio of foraminifera shells is proportional to the Ba / Ca ratio of the seawater in which the shells precipitated via experiments with living planktonic foraminifera. Specimens of the symbiont-bearing species, Orbulina universa , were grown in seawater with five different Ba concentrations at a temperature of 22°C. Individual foraminifera shells (spherical chambers) were then cleaned and analyzed for Ba / Ca . We found that the response for Ba incorporation is linear within and somewhat above the range of Ba concentrations found in the ocean. The calculated distribution coefficient for Ba incorporation lies between 0.14 and 0.17. The value determined previously by comparison of core-top fossil planktonic foraminifera and surface water compositions was 0.19 ± 0.05. Foraminifera grown under low-light conditions to simulate reduced symbiont photosynthetic activity did not have significantly different Ba / Ca . This suggests that for this species, biogenic precipitation rates of calcite varying in response to changing light levels do not affect the degree of Ba discrimination. Earlier observations of Ba incompatibility and lack of substitution in inorganically precipitated calcite at higher Ba activities do not apply to coprecipitation of Ba in the planktonic foraminifera Orbulina over the range of Ba concentrations found in seawater.

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