Deep Atlantic Ocean carbon storage and the rise of 100,000-year glacial cycles
Deep Atlantic Ocean carbon storage and the rise of 100,000-year glacial cycles
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DOI：
10.1038/s41561-019-0334-6
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发表时间：
2019-05-01
影响因子：
18.3
通讯作者：
Kim, J.
中科院分区：
文献类型：
--
作者：
Farmer, J. R.;Honisch, B.;Kim, J.
在过去的300万年里，地球的气候在温暖的间冰期与减少的陆地冰量和较冷的冰川与扩大的极地冰盖之间摇摆。这些气候周期，反映在底栖有孔虫氧同位素，过渡到主导的41-kyr到100-kyr的周期在中更新世1,250至700 kyr前（ka）。由于轨道强迫在这个时候没有改变，中更新世过渡的最终原因仍然是个谜。在这里，我们提出了有孔虫微量元素（B/Ca，Cd/Ca）和Nd同位素数据，表明大西洋纬向翻转环流和深海碳储量之间的密切联系，整个中更新世过渡。具体而言，在950和900 ka之间，碳酸根离子饱和度下降了30 μ mol kg（-1），磷酸盐浓度增加了0.5 μ mol kg（-1），与北大西洋深水对深海南大西洋的贡献减少了20%相一致。这些结果表明，冰川深大西洋碳库存增加了约50千兆吨过渡到100-kyr冰川周期。我们认为，我们的观测结果与陆地冰量增加的证据相吻合，反映了较弱的翻转环流和南大洋生物地球化学反馈如何促进深海碳储存，从而降低了大气中CO2的分压，从而使陆地冰量在中更新世过渡期扩大。
Over the past three million years, Earth's climate oscillated between warmer interglacials with reduced terrestrial ice volume and cooler glacials with expanded polar ice sheets. These climate cycles, as reflected in benthic foraminiferal oxygen isotopes, transitioned from dominantly 41-kyr to 100-kyr periodicities during the mid-Pleistocene 1,250 to 700 kyr ago (ka). Because orbital forcing did not shift at this time, the ultimate cause of this mid-Pleistocene transition remains enigmatic. Here we present foraminiferal trace element (B/Ca, Cd/Ca) and Nd isotope data that demonstrate a close linkage between Atlantic Ocean meridional overturning circulation and deep ocean carbon storage across the mid-Pleistocene transition. Specifically, between 950 and 900 ka, carbonate ion saturation decreased by 30 mu mol kg(-1) and phosphate concentration increased by 0.5 mu mol kg(-1) coincident with a 20% reduction of North Atlantic Deep Water contribution to the abyssal South Atlantic. These results demonstrate that the glacial deep Atlantic carbon inventory increased by approximately 50 Gt during the transition to 100-kyr glacial cycles. We suggest that the coincidence of our observations with evidence for increased terrestrial ice volume reflects how weaker overturning circulation and Southern Ocean biogeochemical feedbacks facilitated deep ocean carbon storage, which lowered the atmospheric partial pressure of CO2 and thereby enabled expanded terrestrial ice volume at the mid-Pleistocene transition.