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CIRCULATION IN THE GLACIAL NORTH ATLANTIC INFERRED FROM GRAIN-SIZE MEASUREMENTS

机译：粒度测量推论的冰川北大西洋环流

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RECORDS of nutrient proxies in marine sediments indicate that the nutrient distribution-and hence circulation-of the glacial North Atlantic Ocean was markedly different from that of today(1,2). But these tracers are influenced by several biogeochemical factors unrelated to ocean circulation(3-6), and thus do not provide a direct measure of the vigour of circulation. Distributions of grain size in marine sediments can provide such information, owing to the sorting effects of currents(7,8), if the characteristics of the input sediment flux are known. Here we present a record, inferred from grain-size measurements, of variations in the relative strength of deep and intermediate currents in the eastern North Atlantic over the past 25,000 years, We find that glacial intermediate water flowed rapidly at depths of between 1,100 and 2,000 m, In contrast, deepwater circulation was sluggish during the last glaciation, but increased in strength shortly after the glacial maximum, This would have resulted in increased heat flux to high latitudes, and may have triggered sudden deglaciation. Deep current strengths declined again at the start of termination stage IA and during the Younger Dryas, perhaps as a result of iceberg discharges (the so-called Heinrich events(9,10)). A remarkably similar record of grain-size variations has been found in the western North Atlantic(11), indicating that these changes in circulation are ocean-wide. [References: 31]
机译：海洋沉积物中营养物代理的记录表明，北大西洋冰原的营养物分布和因此的环流与今天有显着差异（1,2）。但是这些示踪剂受到与海洋环流无关的几种生物地球化学因素的影响（3-6），因此不能直接衡量环流的活力。如果已知输入泥沙通量的特征，由于洋流的分选效应，海洋沉积物中的粒度分布可以提供此类信息（7,8）。在这里，我们从粒度测量得出的记录是过去25,000年北大西洋东部深海和中流相对强度的变化，我们发现冰川中层水在1,100至2,000的深度迅速流动与此相反，在最后一次冰期期间，深水循环缓慢，但在冰川最大期后不久，强度增加。这将导致高纬度地区的热通量增加，并可能引发突然的冰消。在IA终止阶段开始和Younger Dryas期间，深电流强度再次下降，这可能是由于冰山泄洪（所谓的Heinrich事件（9,10））。在北大西洋西部也发现了非常相似的粒度变化记录（11），表明这些环流变化是在整个海洋范围内。 [参考：31]

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