The ongoing uptake of anthropogenic carbon by the ocean leads to ocean acidification, a process that results in a reduction in pH and in the saturation state of biogenic calcium carbonate minerals aragonite ( Ω arag ) and calcite ( Ω calc ) 1 , 2 . Because of its naturally low Ω arag and Ω calc (refs. 2 , 3 ), the Arctic Ocean is considered the region most susceptible to future acidification and associated ecosystem impacts 4 – 7 . However, the magnitude of projected twenty-first century acidification differs strongly across Earth system models 8 . Here we identify an emergent multi-model relationship between the simulated present-day density of Arctic Ocean surface waters, used as a proxy for Arctic deep-water formation, and projections of the anthropogenic carbon inventory and coincident acidification. By applying observations of sea surface density, we constrain the end of twenty-first century Arctic Ocean anthropogenic carbon inventory to 9.0 ± 1.6 petagrams of carbon and the basin-averaged Ω arag and Ω calc to 0.76 ± 0.06 and 1.19 ± 0.09, respectively, under the high-emissions Representative Concentration Pathway 8.5 climate scenario. Our results indicate greater regional anthropogenic carbon storage and ocean acidification than previously projected 3 , 8 and increase the probability that large parts of the mesopelagic Arctic Ocean will be undersaturated with respect to calcite by the end of the century. This increased rate of Arctic Ocean acidification, combined with rapidly changing physical and biogeochemical Arctic conditions 9 – 11 , is likely to exacerbate the impact of climate change on vulnerable Arctic marine ecosystems. Sea surface density observations in the Arctic Ocean reveal a relationship between the present-day surface water density and the anthropogenic carbon inventory and coincident acidification, suggesting that recent acidification projections are underestimates.

中文翻译：

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二十一世纪北冰洋酸化的紧急制约

海洋对人为碳的持续吸收导致海洋酸化，这一过程导致生物源碳酸钙矿物文石 (Ω arag) 和方解石 (Ω calc) 1, 2 的 pH 值降低和饱和状态。由于其天然低 Ω arag 和 Ω calc（参考文献 2、3），北冰洋被认为是最容易受到未来酸化和相关生态系统影响 4-7 的区域。然而，预计的 21 世纪酸化程度在地球系统模型中存在很大差异 8 。在这里，我们确定了模拟的北冰洋表层水的当前密度（用作北极深水形成的代理）与人为碳库存和同时酸化的预测之间的紧急多模型关系。通过应用对海面密度的观测，我们将 21 世纪末北冰洋人为碳存量限制为 9.0 ± 1.6 拍克碳，并将盆地平均 Ω arag 和 Ω calc 分别限制为 0.76 ± 0.06 和 1.19 ± 0.09，在高排放代表性浓度路径 8.5 气候情景下。我们的结果表明，区域人为碳储存和海洋酸化比之前预测的更大 3 、 8 ，并增加了到本世纪末中层北冰洋大部分地区方解石不饱和的可能性。北冰洋酸化速度的加快，加上北极物理和生物地球化学条件的快速变化 9 - 11，可能会加剧气候变化对脆弱的北极海洋生态系统的影响。