Oxygen isotope composition of living Neogloboquadrina pachyderma (sin) in the Arctic Ocean

Data from the Nansen Basin of the Arctic Ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer Neogloboquadrina pachyderma (sin.) calcifies. The vertical distribution of delta(18)O values of net-sampled specimens, together with their abundances and proportion of calcification, are compared with delta(18)O values from both water samples and foraminiferal tests from core-top sediments. Within the Nansen Basin the average depth of habitat of N. pachyderma (sin.) changes from about 150 m in the southern part to about 80 m in the northern, The average depth of calcification, however, in both regimes varies between 100 and 200 m water depth. delta(18)O data from net sampled N. pachyderma (sin.) are directly reflected in the core-top sediment data, but compared to equilibrium calcite delta(18)O values derived from measurements of the ambient water, a consistent offset of about 1 parts per thousand over all depth intervals is observed. While in the southern part of the Nansen Basin advection through Fram Strait of planktic foraminifers from further south may play a role, the data from the northern part of the Nansen Basin give clear evidence that the observed offset in delta(18)O values is caused by a vital effect of N. pachyderma (sin.).