Abrupt changes in deep Atlantic circulation during the transition to full glacial conditions
Abrupt changes in deep Atlantic circulation during the transition to full glacial conditions
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DOI：
10.1002/palo.20025
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发表时间：
2013-06
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影响因子：
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通讯作者：
D. Thornalley;S. Barker;Julia Becker;I. Hall;G. Knorr
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文献类型：
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作者：
D. Thornalley;S. Barker;Julia Becker;I. Hall;G. Knorr
[1]西北大西洋的六个大洋钻探计划（ODP）站点已被用于调查在海洋同位素阶段5a/4边界（约7万年前）的完整冰川条件发展期间“西部边界暗流”（WBUC）的运动学和化学变化。采用可分选的粉砂平均粒度SS <$测量值来检查近底流速的变化，并结合底栖有孔虫中测量的碳同位素和南极有孔虫碎片%作为水团化学变化的替代。一个深度样带的核心，跨越1.8-4.6公里的深度，允许的强度和深度的WBUC的变化，以限制跨千年规模的事件。SS的测量结果表明，WBUC在温暖的间隔（“interstadials”）的流速结构与现代（全新世）条件相当。然而，在寒冷的间隔期间观察到显着差异，在所有寒冷的“Stadial”间隔（包括Heinrich Stadial 6）期间，WBUC的浅分量（~2 km深度）推断出较高的相对流速，在完整的冰川条件下，深层分量（~3-4 km）大幅减弱。因此，我们的研究结果表明，充分的冰川条件的开始与制度转变到一个较浅的模式的循环（涉及冰川北大西洋中层水），定量不同于以前的冷stadial事件。此外，我们的化学代用品数据表明，在末次冰期初期的WBUC的物理响应可能是耦合到流域范围内的变化，在深层西北大西洋的水团组成。
[1] Six Ocean Drilling Program (ODP) sites, in the Northwest Atlantic have been used to investigate kinematic and chemical changes in the “Western Boundary Undercurrent” (WBUC) during the development of full glacial conditions across the Marine Isotope Stage 5a/4 boundary (~70,000 years ago). Sortable silt mean grain size SS¯ measurements are employed to examine changes in near bottom flow speeds, together with carbon isotopes measured in benthic foraminifera and % planktic foraminiferal fragmentation as proxies for changes in water-mass chemistry. A depth transect of cores, spanning 1.8–4.6 km depth, allows changes in both the strength and depth of the WBUC to be constrained across millennial scale events. SS¯ measurements reveal that the flow speed structure of the WBUC during warm intervals (“interstadials”) was comparable to modern (Holocene) conditions. However, significant differences are observed during cold intervals, with higher relative flow speeds inferred for the shallow component of the WBUC (~2 km depth) during all cold “stadial” intervals (including Heinrich Stadial 6), and a substantial weakening of the deep component (~3–4 km) during full glacial conditions. Our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation (involving Glacial North Atlantic Intermediate Water) that was quantitatively distinct from preceding cold stadial events. Furthermore, our chemical proxy data show that the physical response of the WBUC during the last glacial inception was probably coupled to basin-wide changes in the water-mass composition of the deep Northwest Atlantic.