CaCO3 dissolution in carbonate-poor shelf sands increases with ocean acidification and porewater residence time
CaCO3 dissolution in carbonate-poor shelf sands increases with ocean acidification and porewater residence time
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DOI：
10.1016/j.gca.2022.04.031
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发表时间：
2022-06-13
影响因子：
5
通讯作者：
Berelson, William
中科院分区：
文献类型：
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作者：
Lunstrum, Abby;Berelson, William
缺乏碳酸盐的砂质沉积物构成了大陆架的大部分区域，尽管它们的CaCO3含量很低，但它们含有大量的CaCO3碱，可以中和海洋酸。在这里，我们对从加利福尼亚州卡塔利娜岛获得的渗透性、碳酸盐贫乏的沙子进行了流过柱实验，以量化CaCO3在当前和未来海水条件下的溶解。利用13C同位素质量平衡，我们发现溶解既取决于流入海水的CaCO3饱和状态(X)，也取决于孔隙水的停留时间。在目前的海洋条件下（Xaragonite = 2.4， x方解石= 3.7），当孔隙水停留时间< 1.8小时时，溶解可以忽略不计，但在有氧呼吸产生足够的二氧化碳后，溶解会增加。随着入口水X的降低，模拟未来海洋条件，溶解开始得更早，速率增加。对酸化的反应与之前报道的在富含碳酸盐的陆架环境中观察到的类似，这表明，如果有足够的CaCO3基质，缺乏碳酸盐的沉积物有可能在酸化的海洋中支持增强溶解。随着本世纪酸化的持续发生，当上覆海水Xaragonite达到0.96 ~ 0.69 （x方解石= 1.50和1.07）时（取决于孔隙水停留时间），这些沉积物可能从酸的净来源转变为上覆海水（碱性产生溶解无机碳，DAlk/DDIC < 1）和缓冲能力的净来源（DAlk/DDIC bbb1）。在一些有天然酸性水的地区，这个阈值已经达到了。(c) 2022 Elsevier Ltd.版权所有。
Carbonate-poor sandy sediments comprise much of the shelf area, and-despite their low CaCO3 content-contain a significant pool of CaCO3 base available to neutralize ocean acid. Here, we conducted flow-through column experiments on permeable, carbonate-poor sand obtained from Catalina Island, CA, to quantify CaCO3 dissolution across a range of current and future seawater conditions. Using 13C isotope mass balance, we show that dissolution depends both on the CaCO3 saturation state (X) of the inflowing seawater, as well as porewater residence time. At current ocean conditions (Xaragonite = 2.4 and Xcalcite = 3.7 at our field site), dissolution was negligible for porewater residence times < 1.8 h, but increased thereafter, following sufficient production of CO2 from aerobic respiration. As X of inlet water was lowered, simulating future ocean conditions, dissolution began earlier and rates increased. The response to acidification was similar to previously reported observations in carbonate-rich shelf environments, suggesting that carbonate-poor sediments have the potential to support enhanced dissolution in an acidifying ocean, given sufficient CaCO3 substrate. With continued acidification projected to occur this century, these sediments could transition from a net source of acid to the overlying seawater (production of alkalinity to dissolved inorganic carbon, DAlk/DDIC < 1) to net source of buffering capacity (DAlk/DDIC > 1) when overlying seawater Xaragonite reaches 0.96 to 0.69 (Xcalcite = 1.50 and 1.07), depending on porewater residence time. In some areas with naturally acidic water, this threshold has already been reached. (c) 2022 Elsevier Ltd. All rights reserved.