What Do Paleo-Geochemical Tracers Tell Us About the Deep Ocean Circulation During the Last Ice Age?

• Main Author: LeGrand, Pascal
• Other Authors: MASSACHUSETTS INST OF TECH CAMBRIDGE
• Format: Text
• Language: English
• Published: 1994
• Subjects: Physical and Dynamic Oceanography; Geology; Geochemistry and Mineralogy; Snow; Ice and Permafrost; *OCEAN CURRENTS; *NORTH ATLANTIC OCEAN; *DEEP OCEANS; *PALEONTOLOGY; MATHEMATICAL MODELS; ALGORITHMS; COMPUTERIZED SIMULATION; THESES; VORTICES; NUTRIENTS; OXYGEN; MARINE ATMOSPHERES; OCEANOGRAPHIC DATA; LEAST SQUARES METHOD; CLIMATE; CADMIUM; SALINITY; AIR WATER INTERACTIONS; OCEAN MODELS; WATER MASSES; GEOCHEMISTRY; OCEAN BOTTOM; WATER DISTRIBUTION; SEA ICE; ANTARCTIC REGIONS; GLACIERS; GLACIAL GEOLOGY; TRACER STUDIES; RADIOCARBON DATING; SOUTH ATLANTIC OCEAN; Antarctic; Antarc*; Ice; NADW; North Atlantic Deep Water; North Atlantic; permafrost; Sea ice; South Atlantic Ocean
• Online Access: http://www.dtic.mil/docs/citations/ADA298636; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA298636

Paleo-tracers such as carbon 13 and cadmium show that the deep Atlantic was enriched in nutrients during the Last Ice Age. The conventionally accepted interpretation of these higher nutrient levels is that a reduction of the rate of formation of nutrient-depleted Lower North Atlantic Deep Water (Lower NADW) allowed nutrient-rich Antarctic Bottom Water (AABW) to push further north during the Last Glacial Maximum (LGM) (Boyle and Keigwin, 1982; 1987; Duplessy et al., 1988). The evidence for this interpretation is re-examined in this work, with an emphasis on the quantitative analysis of the paleodata An end-member analysis of the 813C data indicates a larger volume of AABW and a smaller volume of Lower NADW during the LOM. It is not yet possible, however, to quantify the extent of the volume differences between the modem and the glacial distributions, because the LGM omega(13)C end-members are poorly known. The second issue examined in this thesis deals with the interpretation of the water mass distribution, inferred from paleo-tracers, in terms of the oceanic circulation. Using a dynamical inverse model of the North Atlantic and a kinematic inverse model of the South Atlantic, it is shown that a tracer distribution corresponding to a significantly reduced volume of Lower NADW does not necessarily correspond to a reduced flux of NADW. Indeed, a circulation almost identical to a modem ocean reference circulation is consistent with the available LGM 813C and 818Q data. (AN)