Rising atmospheric CO2 is acidifying the world’s oceans, affecting both calcification and dissolution processes in coral reefs. Among processes, carbonate dissolution by bioeroding microflora has been overlooked, and especially its impact on seawater alkalinity. To date, this biogeological process has only been studied using microscopy or buoyant weight techniques. To better understand its possible effect on seawater alkalinity, and thus on reef carbonate budget, an experiment was conducted under various seawater chemistry conditions (2 ≤ Ωarag ≤ 3.5 corresponding to 440 ≤ pCO2 (µatm) ≤ 940) at 25 °C under night and daylight (200 µmol photons m−2 s−1) with natural microboring communities colonizing dead coral blocks (New Caledonia). Both the alkalinity anomaly technique and microscopy methods were used to study the activity of those communities dominated by the chlorophyte Ostreobium sp. Results show that (1) the amount of alkalinity released in seawater by such communities is significant and varies between 12.8 ± 0.7 at ΩArag ~ 2 and 5.6 ± 0.4 mmol CaCO3 m−2 day−1 at ΩArag ~ 3–3.5 considering a 12:12 photoperiod; (2) although dissolution is higher at night (~ 80 vs. 20% during daylight), the process can occur under significant photosynthetic activity; and (3) the process is greatly stimulated when an acidity threshold is reached (pCO2 ≥ 920 µatm vs. current conditions at constant light intensity). We show that carbonate dissolution by microborers is a major biogeochemical process that could dissolve a large part of the carbonates deposited by calcifying organisms under ocean acidification.

中文翻译：

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珊瑚礁微生物蛀虫的碳酸盐溶解：在不同 pCO2 条件下产生碱度的生物地质过程

不断上升的大气二氧化碳正在使世界海洋酸化，影响珊瑚礁的钙化和溶解过程。在过程中，生物侵蚀微生物群落导致的碳酸盐溶解被忽视，尤其是它对海水碱度的影响。迄今为止，仅使用显微镜或浮重技术研究了这种生物地质过程。为了更好地了解其对海水碱度的可能影响，从而对珊瑚礁碳酸盐收支可能产生的影响，在各种海水化学条件（2 ≤ Ωarag ≤ 3.5 对应于 440 ≤ pCO2 (µatm) ≤ 940）、25 °C 和日光（200 µmol 光子 m−2 s−1）与自然微孔群落定殖死珊瑚块（新喀里多尼亚）。碱度异常技术和显微镜方法都用于研究以叶绿体 Ostreobium sp 为主的群落的活动。结果表明 (1) 此类群落在海水中释放的碱度量是显着的，在 ΩArag ~ 2 处的 12.8 ± 0.7 和 ΩArag ~ 3-3.5 处的 5.6 ± 0.4 mmol CaCO3 m−2 day−1 之间变化，考虑到 12： 12光周期；(2) 尽管夜间溶解度较高（约 80% vs. 白天 20%），但该过程可以在显着的光合活动下发生；(3) 当达到酸度阈值时（pCO2 ≥ 920 µatm 与恒定光强度下的当前条件），该过程受到极大刺激。