Scientific Results of Drilling the North Pacific Transect

Abstract

Ocean Drilling Program Leg 145 crossed the North Pacific Ocean from Japan to Canada in the summer of 1992, the first deep ocean drilling in the Subarctic Pacific since the 1971 cruises of Deep Sea Drilling Project Legs 18 and 19. All of the Cenozoic paleoceanographic objectives of the cruise were accomplished. We determined the history of silica deposition in the North Pacific and resolved the timing of the late Miocene "silica switch" when the locus of silica deposition changed from the North Atlantic to the North Pacific. A depth transect drilled on the flanks of Detroit Seamount in the far northwestern Pacific allowed the reconstruction of the calcite compensation depth for the North Pacific over the past 70 Ma. The Meiji sediment tongue was shown to be a drift deposit, identical in nature to those better known from the North Atlantic. The Meiji Drift contains northern-source diatoms and minerals from the Bering Sea region and has been accumulating since the early Oligocene. This means that southward-flowing bottom water has been exiting the Bering Sea to the North Pacific basin for the past 35 million years. Presently, water exits the Bering Sea at the same rate, 10 to 20 Sv (1 Sv = I0 6 m 3 /s), as North Atlantic Deep Water leaves the northwesternmost Atlantic. Late Cenozoic cooling was determined to have been underway by the end of Miocene time when ice-rafted debris first occurs at the Leg 145 drill sites. A middle Pliocene warm interval interrupted the high-latitude cooling for about a million years. Large-scale Northern Hemisphere glaciation is shown to have begun rather abruptly at 2.6 Ma by a rapid increase in the delivery of terrigenous hemipelagic and ice-rafted debris sediment to the North Pacific. At this same time abyssal circulation begins to modify sediment depositional patterns in the northwestern Pacific deep basin. The sequence of ash layers recovered downwind from both the Kamchatka Peninsula (the world's most active Pliocene-Pleistocene volcanic field) and the Aleutian arc allows the geochemical evolution of these volcanic centers to be determined. An order of magnitude increase in the number and thickness of ash layers occurred at 2.6 Ma. High-resolution studies of the past 4.0 Ma show that biogenic sediment fluxes are generally higher during interglacial periods. This observation indicates that more rapidly circulating deep ocean waters during interglacial episodes is the dominant source of nutrients to the Subarctic Pacific rather than those supplied by regional runoff or dust input.

Opal sedimentation shifts in the World Ocean over the last 15 Myr

“…Other hypotheses for the biogenic bloom event invoke a global scale nutrients increase, linked to the Andean-Himalayan uplift and its impact on stronger continental weathering, leading to higher discharge of nutrients in the ocean [53,54]. Moreover, the rising mountain chains would have also affected atmospheric circulation and precipitation patterns, with the resulting rainfalls providing positive feedback to the higher nutrient levels in rivers and oceans.…”

New perspectives on Beringian Quaternary paleogeography, stratigraphy, and glacial history

“…Oceanographic modeling (cf. Reason and Power, 1994;Sha!er and Bendtsen, 1994) and paleoceanographic work from ODP Leg 145 in the North Paci"c and other projects (e.g., Keigwin and Gorbarenko, 1992;Rea et al, 1995) provided the science community with increasing recognition of the role of the North Paci"c/Bering Strait region in the global ocean/atmosphere system. The rich contributions of the National Science Foundation's PALE Program (Paleoclimate of Arctic Lakes and Estuaries), in concert with the development of the Beringian Atlas (PALE Beringian Working Group, 1999), demonstrates the important insights to be gained from intense study of a region where the controls on regional climate, and e!ects on global climate are so much di!erent than in the North Atlantic region.…”

グローバル気候変動と新第三紀の終わり／第四紀の始まり：石灰質ナンノ化石層序から

“…and Site 1308 Jansen et al, 1988;Whitman and Berger, 1992;Rea et al, 1995;Thiede and Myher, 1996;Maslin et al, 1996;Sato and Kameo, 1996Keigwin 19821970Saito, 1976Keigwin, 1978 Sato and Kameo, 1996, 201211 Sato et al, 2002Morimoto et al, 2010, 2012, 1988b, 1988a, 2003, 1987 , …”