Carbon isotope constraints on glacial Atlantic meridional overturning: Strength vs depth
Carbon isotope constraints on glacial Atlantic meridional overturning: Strength vs depth
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DOI：
10.1016/j.quascirev.2021.106844
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发表时间：
2021-04
影响因子：
4
通讯作者：
J. Muglia;A. Schmittner
中科院分区：
文献类型：
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作者：
J. Muglia;A. Schmittner
尽管对气候和碳循环具有重要意义，但对末次盛冰期（LGM）期间的深海环流仍然知之甚少。虽然大多数研究表明大西洋经向翻转环流（AMOC）比现在更浅，但对其传输速率存在分歧，估计值从比现在更强到更弱不等。更古老的深海放射性碳年龄被认为意味着更缓慢的环流。在这里，我们使用全球同位素启用海洋气候模式，系统地探讨AMOC深度和强度对碳同位素（13 C和放射性碳）分布和沉积物数据提供的约束的不同影响。我们发现，现有的数据约束AMOC深度以及，有利于模拟一个比现在更浅的LGM AMOC达到2000 - 2500米的深度。然而，它们对AMOC强度的限制较弱。与两个高垂直分辨率LGM δ 13 C剖面的比较表明，LGM AMOC强度在11和18 Sv之间，但需要更多的数据来完善这一估计。与过去的研究相反，我们发现放射性碳年龄与深水输运率只有微弱的相关性，但强烈依赖于南大洋表面水库年龄，这是高度相关的AMOC深度。此外，在深部输运率和/或水团几何形状的变化，在模拟的δ 13 C和放射性碳年龄的变化是高度相关的，这表明他们不作为独立的痕迹物理海洋过程。
Despite its importance for climate and the carbon cycle, the deep ocean circulation during the Last Glacial Maximum (LGM) remains poorly understood. Whereas most studies suggest a shallower Atlantic Meridional Overturning Circulation (AMOC) than at present day, there is disagreement about its transport rate, with estimates ranging from stronger to weaker than today. Older deep ocean radiocarbon ages have been suggested to imply a more sluggish circulation. Here we use a global isotope-enabled ocean-climate model to systematically explore the different effects of AMOC depth and strength on carbon isotope (13 C and radiocarbon) distributions and constraints provided by sediment data. We find that existing data constrain the AMOC depth well, favoring simulations with a shallower-than-present LGM AMOC reaching 2000− 2500 m of depth. However, they provide weaker constraints on AMOC strength. Comparisons with two high vertical resolution LGM δ 13 C profiles suggest LGM AMOC strength between 11 and 18 Sv, but more data are needed to refine this estimate. Contrary to past conjectures, we find radiocarbon age to be only weakly related with deep water transport rates, but strongly dependent on Southern Ocean surface reservoir ages, which are highly correlated with AMOC depth. In addition, upon changes of deep transport rates and/or water mass geometry, variations in modeled δ 13 C and radiocarbon age are highly correlated, suggesting that they do not act as independent traces for physical ocean processes.