Ocean Oxygen, Preformed Nutrients, and the Cause of the Lower Carbon Dioxide Concentration in the Atmosphere of the Last Glacial Maximum
Ocean Oxygen, Preformed Nutrients, and the Cause of the Lower Carbon Dioxide Concentration in the Atmosphere of the Last Glacial Maximum
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DOI：
10.1029/2023pa004775
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发表时间：
2024-01
影响因子：
3.5
通讯作者：
D. Sigman;M. Hain
中科院分区：
文献类型：
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作者：
D. Sigman;M. Hain
在其他条件不变的情况下，如果海洋的“生物[碳]泵”加强，海洋内部的溶解氧(O2)含量就会下降。现在人们很有信心认为，在冰河时代，海洋内部作为一个整体含有的氧气较少。这有力地证明，在冰河时代，海洋的生物泵在海洋内部储存了更多的碳，这为冰河时代大气中二氧化碳(CO2)浓度较低提供了解释的核心。Vollmer等人。(2022年，https://doi.org/10.1029/2021PA004339)结合了底层水域氧气和营养物质含量的替代指标，表明在最后一次冰川盛期，海洋营养物储存库更完全地被生物泵利用，海洋内部溶解的营养物质的比例增加，这些营养物质是“再生”的(作为下沉的有机物从海洋表面输送到内陆)，而不是“预先形成的”(通过海洋循环溶解的营养物质输送到内陆)。这表明南大洋发生了变化，这是现代海洋中预制营养物质的主要来源，北大西洋形成的内陆水中预制营养物质含量的下降显然也起到了额外的作用。Vollmer等人。此外，还发现在溶解无机碳的预制13C/12C比值中缺乏LGM与全新世的差异。这一发现可能使今后的研究能够确定所提出的哪种南大洋机制对冰期期间海洋二氧化碳储存的增加负有最大责任：(A)海洋环流和生物生产力的双重变化，或(B)对海-气交换的物理限制。
All else equal, if the ocean's “biological [carbon] pump” strengthens, the dissolved oxygen (O2) content of the ocean interior declines. Confidence is now high that the ocean interior as a whole contained less oxygen during the ice ages. This is strong evidence that the ocean's biological pump stored more carbon in the ocean interior during the ice ages, providing the core of an explanation for the lower atmospheric carbon dioxide (CO2) concentrations of the ice ages. Vollmer et al. (2022, https://doi.org/10.1029/2021PA004339) combine proxies for the oxygen and nutrient content of bottom waters to show that the ocean nutrient reservoir was more completely harnessed by the biological pump during the Last Glacial Maximum, with an increase in the proportion of dissolved nutrients in the ocean interior that were “regenerated” (transported as sinking organic matter from the ocean surface to the interior) rather than “preformed” (transported to the interior as dissolved nutrients by ocean circulation). This points to changes in the Southern Ocean, the dominant source of preformed nutrients in the modern ocean, with an apparent additional contribution from a decline in the preformed nutrient content of North Atlantic‐formed interior water. Vollmer et al. also find a lack of LGM‐to‐Holocene difference in the preformed 13C/12C ratio of dissolved inorganic carbon. This finding may allow future studies to resolve which of the proposed Southern Ocean mechanisms was most responsible for enhanced ocean CO2 storage during the ice ages: (a) coupled changes in ocean circulation and biological productivity, or (b) physical limitations on air‐sea gas exchange.