Hydrological impact of Middle Miocene Antarctic ice-free areas coupled to deep ocean temperatures
Hydrological impact of Middle Miocene Antarctic ice-free areas coupled to deep ocean temperatures
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DOI：
10.1038/s41561-021-00745-w
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发表时间：
2021-05-13
影响因子：
18.3
通讯作者：
de Boer, Agatha M.
中科院分区：
文献类型：
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作者：
Bradshaw, Catherine D.;Langebroek, Petra M.;de Boer, Agatha M.
海洋沉积物中的氧同位素（δ O-18）用于重建过去的大陆冰量，还记录了深水温度（DWT）。传统上，这些被假定为耦合的（冰量变化引起DWT变化）。然而，δ O-18记录在中新世温暖高峰期（类似于1600 - 1500万年前）记录了巨大的快速波动（类似于千分之1-1.5），难以解释为巨大的南极冰盖（AIS）体积变化。在这里，使用气候建模和数据比较，我们显示DWT耦合到AIS的空间范围，而不是体积，因为南极洲的气候变化修改水文循环，影响南极深水生产区。我们认为中中新世AIS已经从之前的渐新世极大期大幅度撤退。剩余的冰盖在轨道时间尺度上的空间变化比以前认为的更快，使DWT摆动（高达4摄氏度）。当中新世中期温暖终止（类似于1300万年前），大陆尺度的AIS已经稳定下来，进一步的冰量变化主要是在高度而不是范围，对DWT的影响很小。我们的研究结果意味着，当AIS撤退暴露出以前被冰覆盖的土地时，海洋对冰盖变化的敏感性发生了变化;相关的反馈可能会降低地球系统维持大型AIS的能力。这表明冰盖的变化不仅应该以冰量为特征，而且还应该以空间范围为特征。
Oxygen isotopes from ocean sediments (delta O-18) used to reconstruct past continental ice volumes additionally record deep water temperatures (DWTs). Traditionally, these are assumed to be coupled (ice-volume changes cause DWT changes). However, delta O-18 records during peak Middle Miocene warmth (similar to 16-15 million years ago) document large rapid fluctuations (similar to 1-1.5 parts per thousand) difficult to explain as huge Antarctic ice sheet (AIS) volume changes. Here, using climate modelling and data comparisons, we show DWTs are coupled to AIS spatial extent, not volume, because Antarctic albedo changes modify the hydrological cycle, affecting Antarctic deep water production regions. We suggest the Middle Miocene AIS had retreated substantially from previous Oligocene maxima. The residual ice sheet varied spatially more rapidly on orbital timescales than previously thought, enabling large DWT swings (up to 4 degrees C). When Middle Miocene warmth terminated (similar to 13 million years ago) and a continent-scale AIS had stabilized, further ice-volume changes were predominantly in height rather than extent, with little impact on DWT. Our findings imply a shift in ocean sensitivity to ice-sheet changes occurs when AIS retreat exposes previously ice-covered land; associated feedbacks could reduce the Earth system's ability to maintain a large AIS. This demonstrates ice-sheet changes should be characterized not only by ice volume but also by spatial extent.