Carbon isotopes and habitat of polar planktic foraminifera in the Okhotsk Sea: the ‘carbonate ion effect’ under natural conditions

摘要: The upper 500 or 1000 m of the water column in Okhotsk Sea was sampled for living planktic foraminifera. polar species Neogloboquadrina pachyderma (sinistral) strongly dominates foraminiferal assemblage; subpolar to temperate Globigerina bulloides accounts 10–25%. Other account up 3% only. shell δ18O and δ13C values N. (sin.) are compared dissolved inorganic carbon (DIC). strong gradient composition temperature is reflected (sin.). Relative expected calcite precipitated under equilibrium conditions displays a vital effect about 1‰ δ18O. constant with depth reflection δ13CDIC seems be masked by other effects. Most foraminifera found above slightly below thermocline can assumed calcify 200 column. extends well this depth, therefore lack correlation partly attributed fact. remaining discrepancy between correlates carbonate ion concentration This leads conclusion that ‘carbonate effect’ (CIE), which has been derived from culturing experiments [Spero et al. (1997) Nature 390, 497–500], here natural conditions. When magnitude CIE G. applied (sin.), CIE-corrected direct offset 1.2‰.