Late Miocene to recent changes in abyssal current strength: Views from the North Atlantic and the Pacific margin of Antarctica.

• Main Author: Hassold, Noralynn J. C.
• Other Authors: Rea, David K., Pluijm, Ben A. van der
• Format: Thesis
• Language: English
• Published: 2006
• Subjects: Abyssal Current; Antarctica; Atlantic Ocean; Changes; Glaciation; Late; Miocene; North; Pacific Margin; Paleoceanography; Recent; Strength; Views; Antarctic; Antarctic Peninsula; Pacific; The Antarctic; Antarc*; Ice cap; North Atlantic Deep Water; North Atlantic
• Online Access: https://hdl.handle.net/2027.42/126047; http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqm&rft_dat=xri:pqdiss:3224898

Changes in ocean circulation, as reflected in physical property changes of sediments from deep-sea drift deposits, were studied using grain size and magnetic fabric. The goal was to gain an understanding of abyssal circulation since the late Miocene, a time of tectonic and climatic change. Sediment samples from two North Atlantic drifts were analyzed, using a variety of physical and geochemical techniques. Sedimentation at these drifts is directly influenced by North Atlantic Deep Water, a pivotal water mass in the global circulation pattern. The data show a marked slowing of abyssal currents at with drift-related deposition slowing at the deeper site occurring 2 m.y. before that at the shallower site. The change at the shallower site occurred at 2.6 Ma, the time of onset of Northern Hemisphere Glaciation. Stable isotope analysis reveals a warmer, more saline water mass at the deeper site prior to approximately 5 Ma that can be associated with late Miocene Mediterranean water. Samples from sediment drifts located along the Pacific margin of the Antarctic Peninsula were studied using magnetic fabric analysis and grain size, as well as mass accumulation rates. The record from the shallower, more proximal site only extends back to the Pliocene and shows that the Antarctic Circumpolar Current has remained essentially constant over the last 3 m.y., despite the beginning of Northern Hemisphere Glaciation, an event previously thought to have been associated with a reduction in ocean circulation. The record at the deeper, more distal site goes back to the late Miocene and records the stabilization of the Antarctic Peninsula Ice Cap at 8 Ma. The abyssal flow at this site has decreased since late Miocene, with a large reduction occurring between 5 and 5.5 Ma. Magnetic fabric analysis and Chemical Remanent Magnetization were used on samples from these two Antarctic Sites to determine the sense of direction of current flow. Results of this study indicate the direction of current flow has not changed over the last 3 m.y. ...