The last glacial maximum global overturning circulation: A perspective from foraminiferal oxygen and carbon isotope composition.

摘要

In an effort to better characterize the global overturning circulation during the last glacial maximum (LGM), four segments of the global circulation are investigated using measurements of stable carbon and oxygen isotope composition (δ13C and δ18O) in foraminiferal calcite tests isolated from deep sea sediment cores.; The deep water nutrient content of the LGM Pacific Ocean is reconstructed with benthic foraminiferal δ13C. New δ13 C measurements from the southeast and northwest Pacific, when combined with published δ13C data, indicate that during the LGM the nutrient content below 2500 m increased from the North Atlantic to the North Pacific, with the deep Southern Ocean having intermediate values. This nutrient distribution is similar to the Holocene nutrient distribution, as inferred from core top δ13C data, and is entirely consistent with the modern deep water circulation.; The glacial Southern Ocean thermal structures near the surface and at depth are reconstructed using planktonic and benthic foraminiferal δ 18O. In the Atlantic sector between latitudes 30°S and 70°S, new δ18O data together with published δ 18O data indicate that the thermal structures at approximately 200 m and 3000 m during the LGM were nearly the same as during the Holocene and consistent with the modern Southern Ocean hydrography. This suggests that the mean position of Antarctic Circumpolar Current and the contribution of Antarctic Bottom Water to the deep ocean during the two times remained largely unchanged.; Finally, the Gulf Stream separation from the western margin of the North Atlantic is reconstructed using planktonic foraminiferal δ18 O measurements. Latitudinal distribution of foraminiferal δ 18O along the North American continental slope show that the Gulf Stream, clearly distinct from the colder subpolar waters to the north, separated from the continent at approximately the same latitude in the vicinity of Cape Hatteras as during the Holocene and today.; While these reconstructions only give partial views of the global ocean circulation during the LGM and Holocene, their consistent similarity suggests that large scale ocean circulation is robust under very different global climates.