Ocean acidification may shift coral reefs from a state of net ecosystem calcification (+NEC) to net ecosystem dissolution (–NEC). Changes in NEC are typically inferred from either measured or calculated total alkalinity (TA) or the dissolved calcium (Ca) to salinity ratio relative to a reference value. The alkalinity anomaly technique has historically been the primary method to estimate NEC due to the greater analytical challenges and uncertainty associated with dissolved Ca measurements in seawater. However, this method assumes that changes in salinity-normalized TA are exclusively the result of calcification and dissolution processes. In many cases, this assumption is valid, but in some environments additional processes can significantly influence seawater TA (e.g., nutrient fluxes and redox processes). Seawater Ca is unaffected or less sensitive to these processes, and therefore, Ca and TA anomalies can be used to estimate absolute or relative changes in NEC with greater confidence. Here, we present a two-year time series of monthly seawater Ca and TA measurements across the Bermuda carbonate platform and the nearby Bermuda Atlantic Time-series Study (BATS) location offshore. High precision Ca measurements (±6 μmol kg⁻¹) were conducted using an improved spectrophotometric titration system and showed mostly good agreement with changes in TA over the same spatial and temporal scales. Ca and TA measurements across the Bermuda platform showed seasonal fluctuations relative to offshore waters, with +NEC during summer months and near-zero or possible –NEC (net dissolution) during winter months. These seasonal patterns were most pronounced at the inshore locations with the longest residence times (10+ days), which allow stronger biogeochemical signals to develop relative to the offshore source water. Although obtaining high accuracy and precision Ca measurements remains challenging, parallel measurements of Ca and TA from both inshore and offshore waters over a multi-annual timescale could strengthen the validity of predictions for when and where a reef system, such as the Bermuda platform, may shift from +NEC to –NEC.

海洋酸化可能会使珊瑚礁从净生态系统钙化 (+NEC) 状态转变为净生态系统溶解 (-NEC)。NEC 的变化通常通过测量或计算的总碱度 (TA) 或溶解钙 (Ca) 与参考值的盐度比来推断。由于与海水中溶解钙测量相关的更大的分析挑战和不确定性，碱度异常技术历来是估计 NEC 的主要方法. 然而，这种方法假设盐度归一化 TA 的变化完全是钙化和溶解过程的结果。在许多情况下，这个假设是有效的，但在某些环境中，额外的过程会显着影响海水 TA（例如，养分通量和氧化还原过程）。海水 Ca 对这些过程不受影响或不太敏感，因此，Ca 和 TA 异常可用于更有信心地估计 NEC 的绝对或相对变化。在这里，我们展示了跨百慕大碳酸盐平台和附近的百慕大大西洋时间序列研究 (BATS) 近海位置的每月海水 Ca 和 TA 测量值的两年时间序列。高精度 Ca 测量（±6 μmol kg ^-1) 是使用改进的分光光度滴定系统进行的，并且在相同的空间和时间尺度上与 TA 的变化大多显示出良好的一致性。百慕大平台上的 Ca 和 TA 测量值显示出相对于近海水域的季节性波动，夏季月份为 +NEC，冬季月份接近零或可能为 -NEC（净溶解）。这些季节性模式在具有最长停留时间（10 天以上）的近海位置最为明显，这使得相对于近海源水产生更强的生物地球化学信号。尽管获得高精度和高精度的 Ca 测量仍然具有挑战性，但在多年时间尺度内对近海和近海水域的 Ca 和 TA 进行平行测量可以加强对珊瑚礁系统何时何地的预测的有效性，