Nutrient conditions in the subpolar North Atlantic during the last glacial period reconstructed from foraminifera-bound nitrogen isotopes

摘要: [1] Surface nitrate concentration is a potentially useful diagnostic in reconstructing the past circulation of high-latitude North Atlantic waters. Moreover, nutrient consumption surface impacts atmospheric carbon dioxide. To reconstruct conditions subpolar region during last ice age, record foraminifera-bound δ15N was measured Neogloboquadrina pachyderma (sin.) from core V28-73 south Iceland (57.2°N, 20.9°W). Foraminifera-bound up to 2‰ lower age than Holocene, suggesting as much ~25% less complete former. This consistent with stronger light limitation associated deeper summer mixed layer, perhaps related formation Glacial Intermediate Water previously suggested have occurred near site. However, three single-point maxima glacial section and sharp deglacial rise coincide Heinrich event layers. suggests that increased water column stratification events, presumably due freshening, reduced supply below led nearly summertime layer. The layers are not accompanied by δ18O minima either N. or Globigerinoides bulloides, which we tentatively attribute extreme mixed-layer shoaling. reconstructed upper changes—both glacial/interglacial millennial—are inverse those inferred for Antarctic.