Ross Claire L, Falter James L, McCulloch Malcolm T
Oceans Institute and School of Earth Sciences, The University of Western Australia, Perth, Australia.
Australian Research Council Centre of Excellence for Coral Reef Studies, The University of Western Australia, Perth, Australia.
Sci Rep. 2017 Oct 23;7(1):13830. doi: 10.1038/s41598-017-14066-9.
Coral calcification is dependent on both the supply of dissolved inorganic carbon (DIC) and the up-regulation of pH in the calcifying fluid (cf). Using geochemical proxies (δB, B/Ca, Sr/Ca, Li/Mg), we show seasonal changes in the pH and DIC for Acropora yongei and Pocillopora damicornis growing in-situ at Rottnest Island (32°S) in Western Australia. Changes in pH range from 8.38 in summer to 8.60 in winter, while DIC is 25 to 30% higher during summer compared to winter (×1.5 to ×2 seawater). Thus, both variables are up-regulated well above seawater values and are seasonally out of phase with one another. The net effect of this counter-cyclical behaviour between DIC and pH is that the aragonite saturation state of the calcifying fluid (Ω) is elevated ~4 times above seawater values and is ~25 to 40% higher during winter compared to summer. Thus, these corals control the chemical composition of the calcifying fluid to help sustain near-constant year-round calcification rates, despite a seasonal seawater temperature range from just ~19° to 24 °C. The ability of corals to up-regulate Ω is a key mechanism to optimise biomineralization, and is thus critical for the future of coral calcification under high CO conditions.
珊瑚钙化既依赖于溶解无机碳（DIC）的供应，也依赖于钙化液（cf）中pH值的上调。利用地球化学指标（δB、B/Ca、Sr/Ca、Li/Mg），我们展示了在西澳大利亚罗特尼斯岛（南纬32°）原位生长的鹿角珊瑚和多孔鹿角珊瑚钙化液中pH值和DIC的季节性变化。pH值的变化范围从夏季的8.38到冬季的8.60，而夏季的DIC比冬季高25%至30%（是海水的1.5至2倍）。因此，这两个变量均上调至远高于海水的值，且在季节上彼此不同步。DIC和pH值这种反周期行为的净效应是，钙化液的文石饱和状态（Ω）比海水值升高了约4倍，且冬季比夏季高约25%至40%。因此，尽管季节性海水温度范围仅为约19°C至24°C，这些珊瑚仍能控制钙化液的化学成分，以帮助维持全年近乎恒定的钙化速率。珊瑚上调Ω的能力是优化生物矿化的关键机制，因此对于高CO₂条件下珊瑚钙化的未来至关重要。
