Abstract Future acidification of coastal seas will depend not only on the development of atmospheric CO2 partial pressure (pCO2), but also on changes in the catchment areas, exchange with the adjacent ocean, and internal cycling of carbon and nutrients. Here we use a coupled physical-biogeochemical Baltic Sea model to quantify the sensitivity of pH to changes both in external forcing and internal processes. The experiments include changes in runoff, supply of dissolved inorganic carbon (DIC) and total alkalinity (AT), nutrient loads, exchange between the Baltic and North Seas, and atmospheric pCO2. We furthermore address the potential different future developments of runoff and river loads in boreal and continental catchments, respectively. Changes in atmospheric pCO2 exert the strongest control on future pH according to our calculations. This CO2-induced acidification could be further enhanced in the case of desalination of the Baltic Sea, although increased concentrations of AT in the river runoff due to increased weathering to some extent could counteract acidification. Reduced nutrient loads and productivity would reduce the average annual surface water pH but at the same time slightly increase wintertime surface water pH (the annual pH minimum). The response time of surface water pH to sudden changes in atmospheric pCO2 is approximately one month, whereas response times to changes in e.g. runoff and AT/DIC loads are more related to residence times of water and salt (>30 years). It seems unlikely that the projected future increase in atmospheric pCO2 and associated pH reduction could be fully counteracted by any of the other processes addressed in our experiments.

中文翻译：

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波罗的海未来的酸化——敏感性研究

摘要 未来近海酸化不仅取决于大气CO2分压（pCO2）的变化，还取决于集水区的变化、与邻近海洋的交换以及碳和养分的内部循环。在这里，我们使用耦合的物理-生物地球化学波罗的海模型来量化 pH 值对外部强迫和内部过程变化的敏感性。实验包括径流变化、溶解无机碳供应 (DIC) 和总碱度 (AT)、养分负荷、波罗的海和北海之间的交换以及大气 pCO2。此外，我们还分别解决了北方和大陆集水区径流和河流荷载未来潜在的不同发展。根据我们的计算，大气 pCO2 的变化对未来的 pH 值有最强的控制。在波罗的海海水淡化的情况下，这种 CO2 引起的酸化可能会进一步增强，尽管由于风化增加而导致河流径流中 AT 浓度增加在一定程度上可以抵消酸化。减少养分负荷和生产力会降低年平均地表水 pH 值，但同时会略微增加冬季地表水 pH 值（年度最低 pH 值）。地表水 pH 值对大气 pCO2 突然变化的响应时间约为 1 个月，而对径流和 AT/DIC 负荷等变化的响应时间更多地与水和盐的停留时间有关（>30 年）。我们的实验中涉及的任何其他过程似乎不太可能完全抵消大气 pCO2 预计的未来增加和相关的 pH 值降低。