Variability of North Atlantic ice rafting during the last two glacial intervals.

摘要

North Atlantic sediment contains a wealth of paleoclimate data, and has provided significant clues to understanding climate variability in the past, both at orbital (Milankovitch) and sub-orbital time scales. In addition, there is considerable evidence of "abrupt" climate change---extreme swings of the mean climate state that occur on timescales as short as a few years or decades. Much of what we understand about North Atlantic abrupt climate change comes from the last glacial-interglacial cycle, due largely to the limited time span of the Greenland ice cores, a key archive in regional and global climate studies. Considerable effort has been made to correlate regional North Atlantic records, including sediment records and ice core records, and it is apparent that the abrupt climate changes observed in Greenland ice are recorded in North Atlantic sediment as well. Some of the most prominent abrupt climate change events recorded in North Atlantic sediment are the Heinrich events, periods of a dramatic flux of icebergs to the North Atlantic.;Presented here are marine sediment records that extend our knowledge of extreme ice rafting events back through Marine Isotope Stage (MIS) 6. Using a multi-proxy approach, this thesis examines ice rafting during the penultimate glaciation, where significant differences exist with respect to the Heinrich events of the last glacial interval. In particular, the large and repeated Hudson Strait-sourced events of MIS 2-4 do not appear to be present in MIS 6 sediment records. This suggests fundamental differences in climate, ice sheet configuration, or both, between the last two glacial intervals.;Additional work expands our knowledge of Heinrich event 3 (H3), which is examined in the context of the ice rafting events observed during MIS 6. H3 and the MIS 6 events share some important characteristics, and it appears the mechanisms operating during H3 and MIS 6 IRD events could be similar in nature. In addition, this thesis demonstrates that an analysis of multiple isotope systems in terrigenous sediment from marine cores provides important and time-continuous constraints on the behavior of large continental ice sheets. Analyses such as these should provide important insights into the behavior of ice sheets from glacial intervals where we have little or no land-based evidence of their behavior.