Distal and proximal controls on the silicon stable isotope signature of North Atlantic Deep Water
Distal and proximal controls on the silicon stable isotope signature of North Atlantic Deep Water
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DOI：
10.1016/j.epsl.2015.10.025
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发表时间：
2015-12
影响因子：
5.3
通讯作者：
G. F. D. Souza;R. Slater;M. Hain;M. Brzezinski;J. Sarmiento
中科院分区：
文献类型：
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作者：
G. F. D. Souza;R. Slater;M. Hain;M. Brzezinski;J. Sarmiento
北大西洋深水（NADW）独特的高δ 30 Si特征是由模式水和中间沃茨（形成于南大洋并在纬向翻转环流（MOC）的上翼内输送到北大西洋）的同位素分馏的碳酸盐贡献的结果。在这里，我们测试这一假设在一套海洋环流模式（OGCMs）与广泛变化的MOCs和相关途径的营养物质供应到上层海洋。尽管MOC路径不同，但所有模式都再现了NADW中高δ 30 Si特征的观测结果，并显示南大洋模态/中间沃茨对其Si存量的主要或主导（46-62%）贡献。因此，这些模型证实，NADW的δ 30 Si特征确实主要归功于南大洋表面产生的远距离分馏信号的大规模传输。然而，我们也发现，更近端的分馏的Si上升到表面内的大西洋也必须发挥一定的作用，贡献了20-46%的大西洋深部δ 30 Si梯度。最后，该模型套件揭示了NADW的高δ 30 Si特征的机制中的补偿效应，从而通过在输送到NADW形成区域期间产生高δ 30 Si信号来补偿高δ 30 Si模式/中间沃茨向北大西洋的较少输出。这一权衡使来自与MOC相关的深水上升流路径的NADW的δ 30 Si特征变得模糊。因此，虽然我们的研究肯定了南大洋来源的Si的跨赤道运输在产生NADW独特的δ 30 Si特征方面的重要性，但它也表明，大西洋深部δ 30 Si梯度的存在并不唯一地限制深层沃茨返回上层海洋的途径。
It has been suggested that the uniquely highδ30Si signature of North Atlantic Deep Water (NADW) results from the contribution of isotopically fractionated silicic acid by mode and intermediate waters that are formed in the Southern Ocean and transported to the North Atlantic within the upper limb of the meridional overturning circulation (MOC). Here, we test this hypothesis in a suite of ocean general circulation models (OGCMs) with widely varying MOCs and related pathways of nutrient supply to the upper ocean. Despite their differing MOC pathways, all models reproduce the observation of a highδ30Si signature in NADW, as well showing a major or dominant (46–62%) contribution from Southern Ocean mode/intermediate waters to its Si inventory. These models thus confirm that theδ30Si signature of NADW does indeed owe its existence primarily to the large-scale transport of a distal fractionation signal created in the surface Southern Ocean. However, we also find that more proximal fractionation of Si upwelled to the surface within the Atlantic Ocean must also play some role, contributing 20–46% of the deep Atlanticδ30Si gradient. Finally, the model suite reveals compensatory effects in the mechanisms contributing to the highδ30Si signature of NADW, whereby less export of high-δ30Si mode/intermediate waters to the North Atlantic is compensated by production of a high-δ30Si signal during transport to the NADW formation region. This trade-off decouples theδ30Si signature of NADW from the pathways of deep water upwelling associated with the MOC. Thus, whilst our study affirms the importance of cross-equatorial transport of Southern Ocean-sourced Si in producing the uniqueδ30Si signature of NADW, it also shows that the presence of a deep Atlanticδ30Si gradient does not uniquely constrain the pathways by which deep waters are returned to the upper ocean.