Seawater carbonate chemistry and calcification during experiments with coral communities, 2000

Previous studies have demonstrated that coral and algal calcification is tightly regulated by the calcium carbonate saturation state of seawater. This parameter is likely to decrease in response to the increase of dissolved CO2 resulting from the global increase of the partial pressure of atmospheric CO2. We have investigated the response of a coral reef community dominated by scleractinian corals, but also including other calcifying organisms such as calcareous algae, crustaceans, gastropods and echinoderms, and kept in an open-top mesocosm. Seawater pCO2 was modified by manipulating the pCO2 of air used to bubble the mesocosm. The aragonite saturation state (omega arag) of the seawater in the mesocosm varied between 1.3 and 5.4. Community calcification decreased as a function of increasing pCO2 and decreasing omega arag. This result is in agreement with previous data collected on scleractinian corals, coralline algae and in a reef mesocosm, even though some of these studies did not manipulate CO2 directly. Our data suggest that the rate of calcification during the last glacial maximum might have been 114% of the preindustrial rate. Moreover, using the average emission scenario (IS92a) of the Intergovernmental Panel on Climate Change, we predict that the calcification rate of scleractinian-dominated communities may decrease by 21% between the pre-industrial period (year 1880) and the time at which pCO2 will double (year 2065).

既往研究已证实，珊瑚与藻类的钙化过程严格受海水碳酸钙饱和状态调控。该参数会随着大气二氧化碳分压（pCO2）全球升高所引发的溶解态二氧化碳增加而降低。本研究针对以石珊瑚（scleractinian corals）为优势类群，同时涵盖钙化藻类（calcareous algae）、甲壳类（crustaceans）、腹足类（gastropods）与棘皮动物（echinoderms）等其他钙化生物的珊瑚礁群落，在开顶式中宇宙（open-top mesocosm）系统中开展了响应实验。通过向中宇宙系统鼓入经二氧化碳分压调控的空气，以此改变系统内海水的二氧化碳分压。实验期间，中宇宙系统内海水的文石饱和状态（aragonite saturation state, Ω_arag）介于1.3至5.4之间。群落钙化速率随二氧化碳分压升高与文石饱和状态降低呈下降趋势。该结果与此前针对石珊瑚、珊瑚藻及珊瑚礁中宇宙系统的观测数据一致，尽管其中部分研究并未直接对二氧化碳分压进行人工调控。本研究数据显示，末次冰盛期的钙化速率可能为工业化前速率的114%。此外，参照政府间气候变化专门委员会（Intergovernmental Panel on Climate Change, IPCC）的平均排放情景IS92a，我们预测：从工业化前时期（1880年）至二氧化碳分压翻倍时段（2065年），以石珊瑚为主导的群落钙化速率或将下降21%。