MILLENNIAL-SCALE CHANGES IN SEA SURFACE TEMPERATURES AND INTERMEDIATE WATER CIRCULATION IN THE NORTHWEST PACIFIC DURING THE PAST 20,000 YEARS


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Lars.Max [ at ] awi.de

Abstract

During the late Pleistocene to Holocene transition global climate changed dramatically. In particular, during the end of the late Pleistocene, the large-scale shift from the last glacial state to the recent interglacial state took place (between 18,000–11,000 years ago) and was accompanied by millennial- scale climate fluctuations that are well known from the North Atlantic realm. On the other hand, detailed paleoceanographic reconstructions of the subarctic North Pacific climate history are scarce and patchy, thus an incomplete picture of short-term climate fluctuations of the late Pleistocene to Holocene remains so far. The principal aim of this thesis was the reconstruction of the poorly studied (millennial-scale) climate variability of the subarctic northwest Pacific, which has become more into focus of climate research, as it is believed that past climate dynamics in this region are a key to gain more understanding in the mechanisms that drove late Pleistocene climate dynamics. For this purpose, a variety of different geochemical proxies were used for detailed paleoceanographic investigations in order to give detailed insights into past dynamics of sea surface temperatures, sea-ice variability and intermediate water ventilation characteristics of the northwest Pacific realm during the past 20,000 years. From high-resolution SST records it has been shown that the deglacial SST changes in the far northwest Pacific realm matched the climate variability in other parts of the North Pacific and beyond that, were remarkably similar to the timing and nature of the North Atlantic/Greenland temperature variability. From this, a close linkage to deglacial variations in the Atlantic Meridional Overtuning Circulation was inferred, which invoked rapid atmospheric teleconnections to allow a quasi- synchronous (on centennial time-scales) SST development between the North Atlantic and the North Pacific. Reconstructions of past sea-ice variability points to strong changes in sea-ice extent and a close coupling to SST fluctuations in the subarctic North Pacific, thereby further underpins the sensitivity of the atmosphere/cryosphere in the subarctic northwest Pacific realm to rapid climate fluctuations during the last deglacial period. By combination of different SST-proxies (Mg/Ca ratio from planktonic foraminifers/alkenone-paleothermometry) it has also been shown that the structure of the upper-ocean was subject to tremendous changes during millennial-sale climate variability of the last deglaciation. It also points to a more recent development of the density-driven upper-ocean stratification in the subarctic northwest Pacific during the Preboreal. Furthermore, investigations of past ventilation changes revealed that the North Pacific Ocean was marked by enhanced intermediate water formation during cold stages of Heinrich 1 and the Younger Dryas and are related to tremendous changes in upper-ocean hydrography occurred during the deglaciation. Altogether these results are in accordance with the proposed impact of rapid atmospheric teleconnections between the North Atlantic and North Pacific during meltwater-driven reductions of the Atlantic Meridional Overtuning Cell, which induced fast (on centennial time-scales) dynamics in climate and oceanography in the western North Pacific during the last deglaciation. Hence, the sensitivity of the subarctic North Pacific Ocean to millennial-scale climate fluctuations of the past has to be taken much more in consideration to gain an accurate understanding of past and future climate dynamics.



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Thesis (PhD)
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35099
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Max, L. (2012): MILLENNIAL-SCALE CHANGES IN SEA SURFACE TEMPERATURES AND INTERMEDIATE WATER CIRCULATION IN THE NORTHWEST PACIFIC DURING THE PAST 20,000 YEARS , PhD thesis, University of Bremen.


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