Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1994
Description:
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 paleo-data.
An end-member analysis of the δ13C data indicates a larger volume of AABW and a
smaller volume of Lower NADW during the LGM. It is not yet possible, however, to quantify the
extent of the volume differences between the modern and the glacial distributions, because the
LGM δ13C 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 δ13C and δ18O data
A flux of Lower NADW reduced by 50%, though not needed to explain the LGM tracer
distribution, is also consistent with the data Thus, the paleo-tracers δ13C and δ18O do not suffice
to quantify the flux of NADW in the glacial ocean. The modem ocean circulation is one of many
possible circulations consistent with the available δ13C and δ18O data.
Description:
This research was funded by the National Science Foundation under grant OCE-9205942.
Keywords:
Ocean circulation
;
Radioactive tracers in oceanography
;
Endeavor (Ship: 1976-) Cruise EN129
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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