Abstract Due to decreases in seawater pH resulting from ocean acidification, permeable calcium carbonate reef sands are predicted to be net dissolving by 2050. However, the rate of dissolution and factors that control this rate remain poorly understood. Experiments performed in benthic chambers predict that reefs will become net dissolving when the aragonite saturation state (Ωa) in sea water falls below ∼3, as underlying reef sediments start net dissolution due to lower saturation states in the pore water. We used flow-through reactors to investigate the rate of dissolution at various Ωa at the pore scale. The sediment became net dissolving at Ωa = 1.68–2.25, which is significantly greater than 1. This indicates that the bulk pore water does not represent conditions at the site of dissolution, and dissolution probably occurs in microniches inside porous sand grains. Measured dissolution rates were much higher under oxic conditions than anoxic conditions, but were not affected by the addition of carbonic anhydrase. Analysis of δ13C-CO2 produced in the flow-through reactors revealed a bias in the conventional alkalinity anomaly method under anoxic conditions, showing that some of the CO2 attributed to metabolism by may actually be derived from carbonate dissolution. This deviation likely originates from alkalinity consumption by fermentation, which masks the alkalinity generated by dissolution. Therefore, dissolution rates determined by alkalinity changes in reef sands with anaerobic metabolisms may underestimate actual values.

中文翻译：

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驱动礁砂中碳酸钙溶解的孔隙水条件

摘要 由于海洋酸化导致海水 pH 值降低，预计到 2050 年可渗透碳酸钙礁砂将净溶解。然而，溶解速度和控制该速度的因素仍知之甚少。在底栖舱室中进行的实验预测，当海水中的文石饱和状态 (Ωa) 低于 3 时，珊瑚礁将变为净溶解，因为底层珊瑚礁沉积物由于孔隙水中的饱和状态较低而开始净溶解。我们使用流通式反应器来研究不同Ωa 在孔隙尺度下的溶解速率。沉积物在 Ωa = 1.68-2.25 时变为净溶解，明显大于 1。这表明大量孔隙水不代表溶解位置的条件，并且溶解可能发生在多孔砂粒内部的微孔中。在有氧条件下测得的溶解速率远高于缺氧条件，但不受添加碳酸酐酶的影响。对流通式反应器中产生的 δ13C-CO2 的分析揭示了在缺氧条件下常规碱度异常方法的偏差，表明某些归因于代谢的 CO2 实际上可能来自碳酸盐溶解。这种偏差可能源于发酵消耗的碱度，它掩盖了溶解产生的碱度。因此，由厌氧代谢的礁砂中碱度变化确定的溶解速率可能会低估实际值。但不受添加碳酸酐酶的影响。对流通式反应器中产生的 δ13C-CO2 的分析揭示了在缺氧条件下常规碱度异常方法的偏差，表明某些归因于代谢的 CO2 实际上可能来自碳酸盐溶解。这种偏差可能源于发酵消耗的碱度，它掩盖了溶解产生的碱度。因此，由厌氧代谢的礁砂中碱度变化确定的溶解速率可能会低估实际值。但不受添加碳酸酐酶的影响。对流通式反应器中产生的 δ13C-CO2 的分析揭示了在缺氧条件下常规碱度异常方法的偏差，表明某些归因于代谢的 CO2 实际上可能来自碳酸盐溶解。这种偏差可能源于发酵消耗的碱度，它掩盖了溶解产生的碱度。因此，由厌氧代谢的礁砂中碱度变化确定的溶解速率可能会低估实际值。表明一些归因于代谢的 CO2 实际上可能来自碳酸盐溶解。这种偏差可能源于发酵消耗的碱度，它掩盖了溶解产生的碱度。因此，由厌氧代谢的礁砂中碱度变化确定的溶解速率可能会低估实际值。表明一些归因于代谢的 CO2 实际上可能来自碳酸盐溶解。这种偏差可能源于发酵消耗的碱度，它掩盖了溶解产生的碱度。因此，由厌氧代谢的礁砂中碱度变化确定的溶解速率可能会低估实际值。