Paleoceanography

Upper ocean circulation in the glacial North Atlantic from benthic foraminiferal isotope and trace element fingerprinting

Authors

  • Claudia Willamowski,

  • Rainer Zahn


Abstract

Benthic Cd/Ca and δ13C records from the midlatitude and northern North Atlantic are used to derive nutrient inventories and water mass distribution patterns for the past 50,000 years. Inferred Holocene water column Cd concentrations (CdW′) and δ13C values are 0.17–0.24 nmol kg−1 and 1.0–1.3‰ Peedee belemnite (PDB), which document the dominance of nutrient-depleted Mediterranean Outflow Water (MOW) and Upper North Atlantic Deep Water (UNADW). Glacial benthic Cd/Ca and δ13C indicate a continued contribution of UNADW to the northern North Atlantic and upper Portuguese margin (CdW′=0.08 nmol kg−1; δ13C=+1.86‰ PDB). At the upper Moroccan margin, glacial CdW′ (0.23 nmol kg−1) is higher, and δ13C (+1.44‰ PDB) is lower. During “Heinrich” events, benthic δ13C decreases by up to 1.3‰, and peak Cd/Ca increases by 0.1–0.14 µmol mol−1; water column phosphorus equivalents are 1.8–2.8 µmol kg−1. The combined Cd/Ca and δ13C pattern indicates that during mean glacial conditions Antarctic Intermediate Water, (AAIW) reached the midlatitude northeast Atlantic (30°N). During Heinrich events, AAIW contribution maximized so that Southern Hemisphere waters filled the North Atlantic basin from bottom water to middepth levels.

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