Ocean acidification from fossil fuel burning is lowering the mean global ocean saturation state (Ω = $\frac{\left[C{a}^{2+}\right]\left[C{O}_3^{2-}\right]}{K_{\mathit{sp}}^{\prime }}$), thus increasing the thermodynamic driving force for calcium carbonate minerals to dissolve. This dissolution process will eventually neutralize the input of anthropogenic CO₂, but the relationship between Ω and calcite dissolution rates in seawater is still debated. Recent advances have also revealed that spectrophotometric measurements of seawater pHs, and therefore in-situ Ωs, are systematically lower than pHs/Ωs calculated from measurements of alkalinity (Alk) and total dissolved inorganic carbon (DIC). The location of the calcite saturation horizon, defined as the depth in the water column where Ω = 1, therefore shifts by ~5–10% depending on the parameters used to calculate Ω. The “true” saturation horizon remains unknown. To resolve these issues, we developed a new in-situ reactor and measured dissolution rates of ¹³C-labeled inorganic calcite at four stations across a transect of the North Pacific Ocean. In-situ saturation was calculated using both Alk-DIC (Ω_{(Alk, DIC)}) and Alk-pH (Ω_{(Alk, pH)}) pairs. We compare in-situ dissolution rates with rates measured in filtered, poisoned, UV-treated seawater at 5 and 21 °C under laboratory conditions. We observe in-situ dissolution above Ω_{(Alk, DIC)} = 1, but not above Ω_{(Alk, pH)} = 1. We emphasize that marine carbonate system equilibria should be reevaluated and that care should be taken when using proxies calibrated to historical Ω_{(Alk, DIC)}. Our results further demonstrate that calcite dissolution rates are slower in-situ than in the lab by a factor of ~4, but that they each possess similar reaction orders (n) when fit to the empirical Rate = k(1-Ω)ⁿ equation. The reaction orders are n < 1 for 0.8 < Ω < 1 and n = 4.7 for 0 < Ω < 0.8, with the kink in rates at Ω_crit = 0.8 being consistent with a mechanistic transition from step edge retreat to homogenous etch pit formation. We reconcile the offset between lab and in-situ rates by dissolving calcite in the presence of elevated orthophosphate (20 μm) and dissolved organic carbon (DOC) concentrations, where DOC is in the form of oxalic acid (20 μm), gallic acid (20 μm), and d-glucose (100 μm). We find that soluble reactive phosphate has no effect on calcite dissolution rates from pH 5.5–7.5, but the addition of DOC in the form of d-glucose and oxalic acid slows laboratory dissolution rates to match in-situ observations, potentially by inhibiting the retreat rate of steps on the calcite surface. Our lab and in-situ rate data form an envelope around previous in-situ dissolution measurements and may be considered outer bounds for dissolution rates in low/high DOC waters. The lower bound (high DOC) is most realistic for particles formed in, and sinking out of, surface waters, and is described by R_{(mol cm^-2 s^-1)} = 10^–14.3±0.2(1-Ω)^0.11±0.1 for 0.8 < Ω < 1, and R_{(mol cm^-2 s^-1)} = 10^–10.8±0.4(1-Ω)^4.7±0.7 for 0 < Ω < 0.8. These rate equations are derived from in-situ measurements and may be readily implemented into marine geochemical models to describe water column calcite dissolution.

化石燃料燃烧引起的海洋酸化正在降低全球平均海洋饱和度（Ω= $\frac{\left[C{\mathrm{一种}}^{2+}\right]\left[C{Ø}_3^{2-}\right]}{{ķ}_{\mathit{SP}}^{\prime }}$），从而增加了碳酸钙矿物溶解的热力学驱动力。这种溶解过程最终将中和人为CO ₂的输入，但是Ω和方解石在海水中的溶解速率之间的关系仍存在争议。最近的进展还表明，分光光度法测量海水的pH值，因此原位Ωs总体上低于根据碱度（Alk）和总溶解无机碳（DIC）的测量结果计算得出的pHs /Ωs。方解石饱和层的位置，定义为水柱中Ω= 1的深度，因此根据用于计算Ω的参数而偏移〜5–10％。“真实的”饱和水平仍然未知。为了解决这些问题，我们开发了一种新的原位反应堆和在北太平洋横断面上四个站点测得的¹³ C标记的无机方解石的溶解速率。使用Alk-DIC（Ω _{（Alk，DIC）}）和Alk-pH（Ω _{（Alk，pH）}）对计算原位饱和度。我们将原位溶解速率与在实验室条件下于5和21°C的经过滤，中毒，经紫外线处理的海水中测得的速率进行比较。我们观察到在Ω _{（Alk，DIC）}  = 1以上时原位溶解，但在Ω _{（Alk，pH）}  = 1以上时原位溶解。我们强调应重新评估海洋碳酸盐系统的平衡，并且在使用校准为历史值的代理时应格外小心Ω_{（Alk，DIC）}。我们的结果进一步证明，方解石的原位溶解速率比实验室中的溶解速率慢约4倍，但当拟合为经验速率= k（1-Ω）ⁿ方程时，它们各自具有相似的反应阶数（n）。  。 对于0.8 <Ω<1，反应阶数为n <1， 对于0 <Ω<0.8，反应阶数为n = 4.7，在_Ωcrit  = 0.8时的扭折率与从台阶边缘后退到均质蚀刻坑形成的机械过渡一致。我们调和实验室与原位之间的偏差通过在高正磷酸盐（20μm）和溶解的有机碳（DOC）浓度存在的情况下溶解方解石而获得的速率，其中DOC为草酸（20μm），没食子酸（20μm）和d-葡萄糖（100微米）。我们发现可溶性活性磷酸盐在pH 5.5-7.5范围内对方解石的溶出速率没有影响，但是以d-葡萄糖和草酸的形式添加DOC会减慢实验室的溶出速率以与原位观测值相匹配，这可能是通过抑制撤离来实现的。方解石表面的台阶率。我们的实验室和原位速率数据构成了先前原位的信封溶出度测量值，可以认为是低/高DOC水溶出率的界线。下限（高DOC）对于在地表水中形成和下沉的颗粒最为现实，用R _{（mol cm ^-2 s ^-1）}  = 10 ^–14.3±0.2（1-Ω）^{0.11±来描述。} 0.8 <Ω<1时为^0.1，R _{（mol cm ^-2 s ^-1）}  = 10 ^–10.8±0.4（1-Ω）0 <Ω<0.8时为^4.7±0.7。这些速率方程式是从现场测量得出的，可以很容易地实现到海洋地球化学模型中以描述水柱方解石的溶解。