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Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing

机译：最后一次冰河极盛期期间的深海大西洋环流：限制了运输与垂直混合之间的比率

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摘要

The ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales remains an unresolved issue in paleoclimatology. Reduced mixing between deep water masses may have aided oceanic storage of atmospheric CO2 during the Last Glacial Maximum (LGM), but data supporting this idea have remained elusive. The δ13C of benthic foraminifera indicate the Atlantic Ocean was more chemically stratified during the LGM, but the nonconservative nature of δ13C complicates interpretation of the LGM signal. Here we use benthic foraminiferal δ18O as a conservative tracer to constrain the ratio of meridional transport to vertical diffusivity in the deep Atlantic. Our calculations suggest that the ratio was at least twice as large at the LGM. We speculate that the primary cause was reduced mixing between northern and southern component waters, associated with movement of this water mass boundary away from the zone of intense mixing near the seafloor. The shallower water mass boundary yields an order of magnitude increase in the volume of southern component water, suggesting its residence time may have increased substantially. Our analysis supports the idea that an expanded volume of Antarctic Bottom Water and limited vertical mixing enhanced the abyssal ocean's ability to trap carbon during glacial times.
机译：在冰川-冰川间的时间尺度上，海洋在调节大气中二氧化碳中的作用在古气候学中仍未解决。在最后一次冰期最大值（LGM）期间，深水物质之间减少的混合可能有助于海洋中大气CO2的存储，但是支持该想法的数据仍然难以捉摸。底栖有孔虫的δ13C表示在LGM期间大西洋被化学分层了，但是δ13C的非保守性质使LGM信号的解释变得复杂。在这里，我们使用底栖有孔虫δ18O作为保守示踪剂，以限制深大西洋中子午输运与垂直扩散率的比率。我们的计算表明，LGM的比率至少是其两倍。我们推测，主要原因是北部和南部成分水之间的混合减少，这与该水团边界从海底附近强烈混合区的运动有关。较浅的水质量边界使南部成分水的体积增加了一个数量级，这表明其停留时间可能已大大增加。我们的分析支持这样一种观点，即增加的南极海底水量和有限的垂直混合将增强深海海洋在冰川时期捕集碳的能力。

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