麻豆传媒

The fossil record of marine plankton (foraminifera and dinoflagellate cysts) and terrestrial spores and pollen along a transect across the western North Atlantic Ocean at approximately 40oN shows that climatic change through the Quaternary was accompanied by oceanographic changes that affected sedimentation, especially along the U.S. margin. The Gulf Stream was deflected from the margin in response to climatic deterioration ca 1.4 Ma, when polar surface water first penetrated between the western boundary of the subtropical gyre and the margin. The "Paleo-Slope Water" mass developed from a mixture of surface water of polar origin, fluvial influx, and water from the Sargasso Sea. The existence of this water mass allowed large-scale instabilities (meanders and warm core rings) to develop in the north wall of the Gulf Stream, and the topographic Rossby waves generated by eddies began to erode the slope, redepositing Quaternary and Neogene sediments onto the rise. When ice sheets reached the eastern U.S. around 0.3 Ma, ice-marginal conditions were gradually established over the New Jersey margin, and the influence of the Gulf Stream above the margin (and accompanying erosion of intercanyon areas of the mid-slope) was suppressed and the Slope Water mass developed ca. 0.2 Ma. The progressive seaward deflection of the Gulf Stream through the Pleistocene resulted in positive-feedback, allowing North American climates to become progressively more continental, forcing ice centres to migrate south and east within range of moist air masses, therefore further deflecting warm ocean currents from the east coast of North America. Because erosion of the New Jersey slope depends primarily on the oceanography of surface waters and not directly on sea level, the Vail depositional model may not be applicable to the Pleistocene sequence of this margin, where glacioeustatic sea-level highstands are marked by erosion of the mid-to lower slope by abyssal currents generated by instabilities of the Gulf Stream.

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