Gp. Wu et C. Hillairemarcel, OXYGEN-ISOTOPE COMPOSITIONS OF SINISTRAL NEOGLOBOQUADRINA-PACHYDERMA TESTS IN SURFACE SEDIMENTS - NORTH-ATLANTIC OCEAN, Geochimica et cosmochimica acta, 58(4), 1994, pp. 1303-1312
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 Pleistoce
ne-Holocene planktonic deltaO-18 records. In this study the deltaO-18
compositions of N. pachyderma (L) tests from deep-sea surface sediment
s are compared with surface water deltaO-18 values and summer sea surf
ace temperatures (SST) in the North Atlantic Ocean, the Norwegian-Gree
nland Sea, and the labrador Sea. We document that for a temperature ra
nge of 2-8-degrees-C, the planktonic deltaO-18 values follow paleotemp
erature equations with an offset of less than 0.4 parts per thousand,
and that above 8-degrees-C the planktonic deltaO-18 compositions becom
e almost independent of SST and remain nearly constant. This pattern s
uggests that N. pachyderma (L) precipitates its shell nearly at isotop
ic equilibrium with surface waters colder than 8-degrees-C. and that i
n warmer surface waters N. pachyderma (L) changes its habitat depth or
its growth season to secrete its shell at an ambient temperature arou
nd 7-9-degrees-C.