Chemical Hydrography of the South Atlantic During the Last Glacial Maximum: Cd vs. δ13C

There has been a major contradiction between benthic foraminiferal Cd/Ca and δ13C data concerning the labile nutrient chemistry of the Southern Ocean during the Last Glacial Maximum (LGM). Cd data indicates that LGM South Atlantic nutrient concentrations were as low as they are today, indicative of a persistent influx of nutrient-depleted North Atlantic Deep Water (NADW). δ13C data indicates that LGM South Atlantic nutrient concentrations were much higher than at present (even higher than anywhere else in the ocean at that time), and these data have been interpreted as signifying the complete shutdown of the export of NADW into the global ocean. This paper examines both true geochemical differences and various confounding foraminiferal artifacts for both tracers. While many different processes and artifacts affect both tracers in the margin, we conclude the discrepancy is mainly due to the „Mackensen Effect“of low foraminiferal δ13C as a result of high carbon flux to the sediments, and that LGM Atlantic Sector Southern Ocean nutrient concentrations remained similar to the levels encountered today.