Stable isotope and ecological habitat of planktonic foraminifera adjacent to the ice edge in the western Weddell Sea

Abstract

Planktonic foraminifera collected from the entire 200 m water column in the western Weddell Sea using vertically-towed nets consisted largely of Neogloboquadrina pachyderma (s) and Globigerina quinqueloba. Peak abundance of planktonic foraminifera occurred in low-nutrient waters adjacent to the sea ice margin. Nearly all specimens of N. pachyderma (s) in the > 250 μm size class possessed a kummerform final chamber, but less than 20% added gametogenic calcite to the exterior of their shells. The frequent occurrence of δ18O values of N. pachyderma (s) lighter than the δ18Ocalcite in equilibrium with ambient surface waters presumably indicates that significant growth occurred either out of isotopic equilibrium or in water beneath the ice shelf containing 18O-depleted snow melt. We suggest herein that the variation between δ18Owater and δ18O foraminifera is most likely due to secretion of shell carbonate in water influenced by snow melt or glacier melt.