Relationship of magnesium and other minor elements in tests of Cassidulina subglobosa and C. oriangulata to physical oceanic properties

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Abstract
Microanalyses of the chemical compositions of tests of the benthic foraminifera Cassidulina subglobosa Brady and C. oriangulata Belford show that magnesium varies between specimens collected from different physical environments; variations in iron, manganese, and strontium were too small to be analyzed by microprobe. The distribution of magnesium with depth parallels temperature distribution, which suggests that temperature is the primary property controlling variation in magnesium concentration in the tests of these species. The concentration of magnesium is lower in the calcite of these foraminifera than in physiochemically precipitated calcite from comparable depths; the foraminifera precipitate calcite that is in disequilibrium with the surrounding water. Magnesium appears to vary in C. oriangulata in the same way it varies in C. subglobosa, which implies that the chemistries of some members of the same genus behave similarly under similar conditions. The parallel between magnesium variability in benthic foraminifera and in ocean thermal structure suggests that magnesium content in foraminifera is of potential value not only for single paleotemperature determinations, but also for paleoceanographic thermal reconstruction over a broad range of water depths.
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