A high resolution record of ocean circulation during the last glacial cycle from neodymium isotopes.

摘要

One of the most important debates in paleoclimate research concerns the link between ocean circulation and climate change. It is currently unknown whether rapid climate changes were triggered by shifts between "glacial" and "interglacial" ocean circulation regimes, or were externally forced and amplified within the atmosphere before affecting the loci and intensity of deepwater formation. This is the first study of its type to present a millennial-scale Nd isotope record of ocean circulation through the last glacial cycle. It shows that the relative balance of northern- and southern-sourced waters in the Cape Basin was closely coupled to rapid change in northern hemisphere climate. During the deglaciation, the relative proportion of North Atlantic Deep Water (NADW) in the Cape Basin began to strengthen prior to the Bolling warming, tracking increasing Northern Hemisphere insolation. Millennial-scale variability was superimposed on this gradual baseline increase, and corresponded to rapid changes in North Atlantic sea ice cover rather than meltwater input. This suggests that sea ice coverage in the North Atlantic amplifies, and perhaps causally links the ocean and atmosphere on short-timescales. A sensitive climate-ocean connection is also apparent during the last ice age, as major interstadial warm periods were associated with stronger Atlantic meridianal overturning, while Heinrich Events appear to be related to a substantial reduction in deepwater circulation. Glacial-interglacial Nd isotope pairs measured at South Atlantic sites deeper than 2000 mbsl indicate a consistent reduction in the relative proportion of NADW during the last glacial.; Observing a lead-lag relationship between ocean circulation and climate change is key to differentiating causality, and the record presented in this thesis shows that global climate change consistently lead ocean circulation change at glacial-interglacial boundaries. During glacial-interglacial transitions, ice volume, deep water temperature, and the global carbon budget changed before the balance of NADW and AABW in the Cape Basin. This is further indication that climate change forced glacial-interglacial changes in ocean circulation.