涠洲岛海水文石饱和度的变化及其对造礁石珊瑚钙化作用的影响

The change of aragonite saturation state in seawater and its effect on calcification of scleractinian corals at Weizhou Island

关键词:  涠洲岛  文石饱和度  造礁石珊瑚  钙化作用  海洋酸化

Key words:  Weizhou island  aragonite saturation state  scleractinian corals  calcification  ocean acidification

摘要:

结合海表二氧化碳分压（PCO2）、表层水温、表层盐度和表层pH的数据资料，采用Excel macro CO2SYS计算涠洲岛的海水文石饱和度（ΩArag）。分析ΩArag变化对造礁石珊瑚钙化作用的影响及对水温、盐度和pH等环境因子变化的响应，为涠洲岛珊瑚礁的保护和监测预警提供科学依据。结果表明：2006-2020年涠洲岛海域的平均水温为22.1-28.4℃，呈逐年上升的趋势；盐度平均29.5-32.0，基本稳定在31.0左右；PCO2波动上升，平均350.96-380.37 μatm，但基本低于全球海洋的同期值；pH波动上升，平均7.99-8.24，而同期的全球海洋则以-0.022pH/10a的速度持续酸化；ΩArag平均2.61-7.42，夏季较高，秋季次之，春季最低；ΩArag为临界值4时，平均水温不能低于22.1℃，盐度不能低于25.6，pH不能低于8.12，pH是ΩArag变化的关键因子。春季涠洲岛的水温和ΩArag较低，不利于造礁石珊瑚的钙化增生；夏季的ΩArag高，但水温常大于30℃，亦不利于造礁石珊瑚的钙化增生；秋季的ΩArag较高，水温适宜，适于造礁石珊瑚的钙化增生。全球气候变化引起的水温升高不会降低涠洲岛海域的ΩArag，但极端低温引起的ΩArag降低可能会影响珊瑚骨骼结构的稳定性。涠洲岛海域的盐度稳定，不会引起ΩArag的较大变化。受全球PCO2增加的影响，涠洲岛海域将以-0.011pH/10a的速率酸化，预计2038年ΩArag将小于临界值4。

Abstract:

ΩArag in seawater at Weizhou Island was calculated from the partial pressure of sea surface carbon dioxide（PCO2）, surface-seawater temperature, surface-seawater salinity and surface-seawater pH using the Excel macro CO2SYS. In order to lay a scientific foundation for the conservation of the coral reefs and development of an early warning monitoring protocol, the effect of aragonite saturation state (ΩArag) on the calcification of scleractinian corals at Weizhou Island and the response of ΩArag to the changes of temperature, salinity and pH were analyzed. The results showed that the average seawater temperature of Weizhou Island from 2006 to 2020 varied between 22.1℃ and 28.4℃ and increased gradually year by year. The average salinity ranged from 29.5 to 32.0, stable at about 31.0. PCO2 rose in fluctuation, and its average values varied between 350.96 μatm and 380.37 μatm, lower than the global ocean annual mean values of the same period. The average values of pH rose in fluctuation and ranged between 7.99-8.24, while the ocean was constantly acidified globally at a speed of -0.022pH/10a. The average values of ΩArag ranged between 2.61-7.42, and were higher in this order summer>autumn>spring. ΩArag could not maintained more than the threshold value of 4 if the average seawater temperature, salinity and pH are lower than 22.1℃, 25.6 and 8.12 respectively. pH is a critical environmental factor that will affect the variation of ΩArag. In spring, the seawater temperature and ΩArag of Weizhou Island are lower, which will slow down the calcification of scleractinian corals. Although the ΩArag in summer is high, the temperature in seawater is usually higher than 30℃, which is not conducive to the calcification of scleractinian corals. The high ΩArag and favorable seawater temperature in autumn is beneficial to the calcification of scleractinian corals. The rise of seawater temperature caused by global climate change will not reduce the ΩArag at Weizhou Island, but the decrease of ΩArag caused by extreme low temperature may affect the stability of coral skeleton. The stable salinity of Weizhou Island will not cause the significant change of ΩArag. Due to the increase of global PCO2, the seawater of Weizhou Island will acidify at a rate of -0.011pH/10a, and the ΩArag is expected to be less than the threshold of 4 in 2038.