Seawater Cadmium in the Florida Straits Over the Holocene and Implications for Upper AMOC Variability
Seawater Cadmium in the Florida Straits Over the Holocene and Implications for Upper AMOC Variability
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DOI：
10.1029/2021pa004379
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发表时间：
2022-04
影响因子：
3.5
通讯作者：
Shannon G. Valley;J. Lynch‐Stieglitz;T. Marchitto;D. Oppo
中科院分区：
文献类型：
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作者：
Shannon G. Valley;J. Lynch‐Stieglitz;T. Marchitto;D. Oppo
大西洋经向翻转环流（AMOC）在突然和长期气候变化期间的全球热量和降水重新分配中发挥着核心作用。在下个世纪，AMOC 预计将因温室气体变暖而减弱，尽管预测其未来行为取决于对 AMOC 变化如何被迫的更好理解。为了解决 AMOC 趋势与最近古记录之间的明显矛盾，我们重建了佛罗里达海峡过去约 8,000 年（重点是上千年）的海水镉（一种营养物类示踪剂）。过去 8000 年海水中 Cd 的逐渐减少可能是由于 AMOC 的减少，这与北半球气温下降和热带辐合带向南移动一致。然而，很难将这一发现与同一时期佛罗里达海峡地转流增加的证据相一致。我们结合中水深度沉积物岩心的数据，以足够的分辨率将该记录扩展到公元纪元，以应对这一时期的广泛尺度变化。相对于中世纪气候异常，小冰期晚期的镉浓度略有下降，但这种变化比全新世和冰消期观测到的变化要小得多。这表明，过去一千年中 AMOC 实力的任何趋势都必定非常微妙。
Atlantic Meridional Overturning Circulation (AMOC) plays a central role in the global redistribution of heat and precipitation during both abrupt and longer‐term climate shifts. Over the next century, AMOC is projected to weaken due to greenhouse gas warming, though projecting its future behavior is dependent on a better understanding of how AMOC changes are forced. Seeking to resolve an apparent contradiction of AMOC trends from paleorecords of the more recent past, we reconstruct seawater cadmium, a nutrient‐like tracer, in the Florida Straits over the last ∼8,000 years, with emphasis on the last millennium. The gradual reduction in seawater Cd over the last 8,000 years could be due to a reduction in AMOC, consistent with cooling Northern Hemisphere temperatures and a southward shift of the Intertropical Convergence Zone. However, it is difficult to reconcile this finding with evidence for an increase in geostrophic flow through the Florida Straits over the same time period. We combine data from intermediate water depth sediment cores to extend this record into the Common Era at sufficient resolution to address the broad scale changes of this time period. There is a small decline in the Cd concentration in the Late Little Ice Age relative to the Medieval Climate Anomaly, but this change was much smaller than the changes observed over the Holocene and on the deglaciation. This suggests that any trend in the strength of AMOC over the last millennium must have been very subtle.