Evaluating surface and deep-water changes over Eirik Drift during the late Pleistocene: Implications from geochemical and sedimentological proxies.

摘要

This dissertation attempts to characterize the sedimentological and isotopic characteristics of the various end-member states of oceanic circulation within the North Atlantic Ocean during the Pleistocene. This ocean is a critical area of deep-water formation, and surface water perturbations alter deep-water production and affect global climate. Understanding the possible mechanisms behind these changes is critical. The Eirik Drift is the ideal location to evaluate these changes because it lies directly in the path of an important bottom water current and sedimentation rates are high, allowing for the reconstruction of high-resolution records on Milankovitch and millennial time scales.;Analysis of a swath of cores from Eirik Drift confirms that the deep-water current fluctuates between a deeply penetrating current during the extreme interglacials and a shallow, less buoyant current during the glacial extremes. A third intermediate mode is inferred that dominates the record. Depositional centers shift up and down the drift in tandem with the shifts in circulation modes.;The last deglaciation was marked by a series of abrupt climate changes and disruptions in the production of deep-water. These events are attributed to variations in freshwater fluxes to the surface ocean in response to rapid melting of ice sheets. Reconstructed ?13C values show reduced production during the cold events and vigorous production during warmer intervals. Resumption of deep-water production is coincident with peak meltwater discharge, questioning the validity of the meltwater hypothesis. Results suggest substantial sea-ice cover and we propose, along with perturbations in atmospheric circulation, are the cause of these climatic changes.;To understand the cause and effect of climatic changes, the leads and lags in the proxy records need to be defined with extreme precision and requires the construction of robust age models. Past studies rely on techniques that have inherent errors within the methodology. By combining these methods with additional techniques such as Paleo-intensity Assisted Chronology, the age control on deep-sea sediment records can be greatly improved.