Oxygen isotope compositions of sinistral Neogloboquadrina pachyderma tests in surface sediments: North Atlantic Ocean

Abstract

Neogloboquadrina pachyderma (Left-coiled) is a planktonic foraminifer indicator species for polar waters. It is present in both the glacial and interglacial sediments of the high-latitude oceans, and therefore is frequently used as a signal-carrier for constructing late Pleistocene-Holocene planktonic δ 18 O records. In this study the δ 18 O compositions of N. pachyderma (L) tests from deep-sea surface sediments are compared with surface water δ 18 O values and summer sea surface temperatures (SST) in the North Atlantic Ocean, the Norwegian-Greenland Sea, and the Labrador Sea. We document that for a temperature range of 2–8°C, the planktonic δ 18 O values follow paleotemperature equations with an offset of less than 0.4%., and that above 8°C the planktonic δ 18 O compositions become almost independent of SST and remain nearly constant. This pattern suggests that N. pachyderma (L) precipitates its shell nearly at isotopic equilibrium with surface waters colder than 8°C, and that in warmer surface waters N. pachyderma (L) changes its habitat depth or its growth season to secrete its shell at an ambient temperature around 7–9°C.