Eocene emergence of highly calcifying coccolithophores despite declining atmospheric CO2
Eocene emergence of highly calcifying coccolithophores despite declining atmospheric CO2
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DOI：
10.1038/s41561-022-01006-0
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发表时间：
2022-09-01
影响因子：
18.3
通讯作者：
Rickaby, R. E. M.
中科院分区：
文献类型：
--
作者：
Claxton, L. M.;McClelland, H. L. O.;Rickaby, R. E. M.
颗石藻是一组单细胞钙化浮游植物，自从它们产生的方解石板（颗石藻）首次出现在2亿多年前的化石记录中以来，一直是海洋碳酸盐生产的主要贡献者。这一过程对进化时间尺度上环境变化的反应仍然知之甚少，特别是在温暖的气候中。在这里，我们整合了一个数据集组成的碳同位素比的大小分离的颗石方解石从海洋沉积物与细胞尺度模型，通过始新世（类似于55-34马），地球最热的间隔在过去的1亿年来询问细胞的碳通量和p（CO2）。我们发现，大型颗石藻上升到主导海洋通过始新世有较高的钙化固碳比比他们的前辈，而较小的颗石藻是正确的。这些变化发生在海洋碱化增加的背景下，可能在明显的正碳循环反馈中发挥了作用，以减少p（CO）（2）。我们的方法还提供了独立的支持，多代理为基础的证据一般p（CO）（2）下降，通过始新世与温度的步骤。总之，这挑战了新出现的观点，即p（CO）（2）的普遍下降减少了进化时间尺度上的钙化。
Coccolithophores, a group of unicellular calcifying phytoplankton, have been major contributors to marine carbonate production since the calcite plates that they produce (coccoliths) first appeared in the fossil record over 200 million years ago (Ma). The response of this process to changes in environment on evolutionary timescales remains poorly understood, particularly in warm climates. Here we integrate a dataset consisting of carbon isotope ratios of size-separated coccolith calcite from marine sediments with a cell-scale model to interrogate cellular carbon fluxes and p(CO2) through the Eocene (similar to 55-34 Ma), Earth's hottest interval of the past 100 million years. We show that the large coccolithophores that rose to dominate the oceans through the Eocene have higher calcification-to-carbon fixation ratios than their predecessors while the opposite is true for smaller coccolithophores. These changes, which occurred in the context of increasing ocean alkalization, may have played a role in an apparent positive carbon cycle feedback to decreasing p(CO)(2). Our approach also provides independent support of multiproxy-based evidence for general p(CO)(2) decline through the Eocene in step with temperature. Together, this challenges the emerging view that a general decline in p(CO)(2) reduces calcification on evolutionary timescales.