RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES5004, doi:10.2205/2005ES000180, 2005
[5] With such low present-day snowlines, all the climate-based computer simulations indicate that climate perturbations of the Ice Ages had inevitably led to inception and growth of continental-sized ice sheets on the Northwest Pacific Rim, and that the past ice sheets had covered not only mountains and coastal plains of the region, but also its continental shelves.
[6] The modeling experiments by Verbitsky and Oglesby [1992] were first to demonstrate that the last glaciation of Northeast Siberia had been about as extensive as the Scandinavian and North American ice sheets and, in addition, that it incepted easier and earlier than those ice sheets. Later, the computer models of Budd et al. [1998] more specifically implied that, first, a continuous ice sheet had developed over the highlands of Northeast Siberia and, second, the ice sheet expanded to the southeast and invaded the Sea of Okhotsk. The same extent was obtained in the paleo-ice sheet simulations by Greve et al. [1999] and Bintanja et al. [2002]. Also, according to a modeling of the former glaciation of the Northwest Pacific Rim, produced by Fastook [1997, unpublished], a broad Okhotsk-Sea ice stream not only existed, but it moved at the rate of 2 km yr -1, despite its lower (floating) part being buttressed by the Kurile Island Arc.
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Figure 1 |
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Figure 2 |
[9] Members of the on-board party had little doubt that all these changes clearly indicated that a large-scale glaciation had incepted in the North Pacific Ocean at 2.6 million yr ago - at the same time as in the North Atlantic Ocean.
[10] This was further developed by detailed studies of Kotilainen and Shackleton [1995], which demonstrated that the rate of the ice rafting, reflected in densities of deep-sea cores, had experienced periodic variations. A curve depicting these variations for the last 95,000 years exhibited some 20 cycles of ups and downs in ice rafting, thus implying about 20 cycles of climate coolings and warmings. These researchers stated that the cycles were similar to and likely synchronous with the Dansgaard-Oeschger climate events revealed by the Greenland ice cores.
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Figure 3 |
[12] The consistent LGM oceanographic changes in NW Pacific Ocean were, in fact, an outright "thermal revolution". In particular, extending of a cold, iceberg-infested Oyshio Current to the shores of southern Japan [Oba et al., 1991], and tremendous cooling of the Sea of Japan due to isolation, infilling by the Amur-River water and freezing [Grosswald, 1998b], inevitably resulted in cooling, much deeper than it is generally thought, and glaciation of the Islands of Japan much greater than presently reconstructed [Grosswald, 2002].
[13] Still, a big problem remains: from where did all these erratics come, and what were the path tracks of North Pacific icebergs that transported the erratics?
[15] From our perspective, only the second option is realistic. The ODP Leg 145 drilling site and Honshu Island, on the one hand, and the coastal zones of Alaska and Siberia, on the other, are thousands of miles apart, and such a long-distance rafting of erratics appears hardly possible. By contrast, a marine ice sheet, or ice sheets, on the Northwest Pacific Rim would explain not only the distribution of erratics, but also the entire complex of paleoceanographic changes established by the deep-sea drilling. In particular, it would account for the abrupt acceleration of abyssal circulation in the North Pacific, and for the sudden growth in influx of all kinds of continental materials (including the erratics). Being located in marginal seas of the ocean, the ice sheet or ice sheets would be much closer to the depositional sites than the coasts of Alaska and Siberia and also would be a much more productive source of icebergs and meltwater than any mountain glaciers. They would even account for the enormous increase in volcanic activity, as, according to computations by Nakada and Yokose [1992], there are direct links between glacial and volcanic phenomena. Specifically, these geophysicists have found that ice sheets placed upon the Northwest Pacific Rim would have been a sufficiently heavy load to push the hydrostatic pressure in deep magma centers over critical thresholds and trigger massive volcanic eruptions.
[16] Where were those hypothetical ice sheets located? Members of the Roberts [1993] speculated that the Sea of Okhotsk had been the most probable source of the icebergs. Our analyses of the Okhotsk Sea and its environ's geomorphology, of the pattern and causes for Amur River reorganizations, coupled with new climate-based modeling experiments, strongly suggest that this assumption was correct.
Citation: 2005), "Back-arc" marine ice sheet in the Sea of Okhotsk, Russ. J. Earth Sci., 7, ES5004, doi:10.2205/2005ES000180.
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