Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q04009, doi:10.1029/2007GC001620.
An evaluation of C. pachyderma Mg/Ca using a new suite of warm water multicores from the Florida Straits shows that the slope of Mg/Ca with temperature is shallower than previously thought. Using secondary ionization mass spectrometry, we have documented that the distribution of magnesium within the polished walls of foraminiferal tests is Gaussian, suggesting that the Mg/Ca in these samples is not affected by the addition of a secondary high-magnesium calcite in the walls. The Mg/Ca within a typical C. pachyderma test varies by about ±20% (1σ/μ · 100), and the variability increases slightly in tests with higher Mg/Ca. The regression of C. pachyderma Mg/Ca with temperature has a slope of 0.13 ± 0.05 mmol mol−1 per °C, indistinguishable from the slope observed in inductively coupled plasma–mass spectrometry measurements from a different subset of the same multicores, but about one half the slope of previously published calibrations. The largest differences between the calibrations comes at the warm water end of the regression, where previously published C. pachyderma Mg/Ca values from Little Bahama Bank are at least 3 mmol mol−1 higher than observed in these new cores. The reasons for this difference are not fully known but are most likely related to diagenesis at Little Bahama Bank.
research was supported by several grants from the National
Science Foundation: OCE0096469 to W.B.C. for cruise support
to collect the Florida Straits cores; ATM0502428 and
OCE0550271 to W. B. C. for support to obtain the Mg/Ca data
on the ion probe; and OCE0425522 and OCE0550150 to T. M.
for the core top calibration study using ICP-MS.
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