Core-top evaluation of benthic foraminiferal isotopic ratios for paleo-oceanographic interpretations
Abstract The benthic foraminifera Cibicides wuellerstrofi, Oridforsalis tener and Pyrgo rotalaria from twelve core-tops in the Norwegian-Greenland Sea and C. wuellerstorfi, O. tener, and O. umbonatus from four core-tops on the Rio Grande Rise were analysed for oxygen and carbon isotopes. The Norwegian-Greenland Sea data yield statistically discrete means for both δ 18O and δ 13C for each species. The interregional comparison of our data to published data from the East Pacific Rise shows that C. wuellerstorfi δ 18O and δ 13C variations reflect oceanographic differences between sites, whereas the data on Oridorsalis and Pyrgo do not. We conclude that C. wuellerstorfi is a reliable sensor of bottom water conditions whereas other taxa are of unproven utility. Supportive biological studies and the lack of positive covariance of δ 18O to δ 13C among deep-sea benthic taxa lead us to reject models calling for incorporation of metabolic CO2 to explain the isotopic variation among deep-sea benthic foraminifera. We propose a within-sediment microhabitat hypothesis to explain the δ 13C variations among taxa.