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 (Ω) of the inflowing seawater, as well as porewater residence time. At current ocean conditions (Ω_aragonite =2.4 and Ω_calcite =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 Ω 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, ΔAlk/ΔDIC<1) to net source of buffering capacity (ΔAlk/ΔDIC>1) when overlying seawater Ω_aragonite reaches 0.96 to 0.69 (Ω_calcite = 1.50 and 1.07), depending on porewater residence time. In some areas with naturally acidic water, this threshold has already been reached.

碳酸盐含量低的沙质沉积物占据了大部分大陆架区域，并且尽管 CaCO ₃含量低，但含有大量可用于中和海洋酸的 CaCO ₃碱池。在这里，我们对从加利福尼亚州卡塔利娜岛获得的可渗透、贫碳酸盐砂进行了流过柱实验，以量化当前和未来海水条件下CaCO _{3的溶解情况。}使用¹³ C 同位素质量平衡，我们表明溶解取决于流入海水的 CaCO ₃饱和状态 (Ω) 以及孔隙水停留时间。在当前的海洋条件下（Ω_文石=2.4 和 Ω_方解石= 3.7 在我们的现场），在孔隙水停留时间<1.8 小时时溶解可以忽略不计，但此后随着有氧呼吸产生足够的 CO _{2溶解增加。}随着 Ω 的进水量降低，模拟未来的海洋条件，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的观察结果相似，这表明在有足够的 CaCO _{3的情况下，碳酸盐贫乏的沉积物有可能支持酸化海洋中的溶解增强}基质。随着预计在本世纪继续酸化，这些沉积物可能从酸的净来源转变为上覆海水（碱度产生到溶解的无机碳，ΔAlk/ΔDIC<1）到缓冲能力的净来源（ΔAlk/ΔDIC>1 ) 当上覆海水 Ω_文石达到 0.96 至 0.69（Ω_方解石= 1.50 和 1.07）时，取决于孔隙水停留时间。在一些有天然酸性水的地区，这个门槛已经达到了。