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:

为给涠洲岛珊瑚礁的保护修复和监测预警提供科学依据 ，本研究结合海表二氧化碳分压（p_("C" "O" _2 ) ）、表层水温、表层盐度和表层pH值的数据资料，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，以及对水温、盐度和pH值等环境因子变化的响应。结果表明：2006-2020年春季、夏季和秋季涠洲岛海域的平均水温为22.1-28.4 ℃，呈逐年上升的趋势；盐度平均为29.5-32.0，基本稳定在31.0左右；p_("C" "O" _2 )波动上升，平均为350.96-380.37 μatm（1μatm=101.325×10-3 Pa ），但基本低于全球海洋的同期值；pH值波动上升，平均为7.99-8.24，基本高于同期的全球海洋pH值；涠洲岛海域的p_("C" "O" _2 )以﹢3.20 μatm/10 a的速率波动上升，预计将引起的表层海水酸化速率为﹣0.002 pH/10 a，而全球海洋的酸化速率为﹣0.011 pH/10 a；ΩArag平均为2.61-7.42，夏季较高，秋季次之，春季最低；ΩArag为临界值4.00时，平均水温不能低于22.1 ℃，平均盐度不能低于25.6，平均pH值不能低于8.12，pH值是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。受全球海洋p_("C" "O" _2 )增加的影响，预计2038年涠洲岛海水的ΩArag将小于临界值4.00。 涠洲岛海水的ΩArag主要受水温和pH值的影响，其波动变化直接影响着造礁石珊瑚的钙化增生。

Abstract:

In order to lay a scientific foundation for the conservation and restoration of the coral reefs and development of an early warning monitoring protocol, aragonite saturation state (ΩArag) in seawater at Weizhou Island was calculated from the partial pressure of sea surface carbon dioxide（p_("C" "O" _2 )）, surface-seawater temperature, surface-seawater salinity and surface-seawater pH value using the Excel Macro CO2SYS. The effect of 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. p_("C" "O" _2 ) 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, higher than the global ocean values of the same period. The p_("C" "O" _2 ) in coastal area around the Weizhou Island rose in fluctuation with a rate of ﹢3.20 μatm/10 a, which will cause acidification in surface seawater at a rate of -0.002 pH/10 a, while the rate of acidification in global ocean will be -0.011 pH/10 a.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 4.00 if the average of seawater temperature, salinity and pH value are lower than 22.1 ℃, 25.6 and 8.12 respectively. pH value 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 p_("C" "O" _2 )in the global ocean, the ΩArag in the surface seawater of Weizhou Island is expected to be less than the threshold of 4.00 in 2038. The ΩArag of the seawater around the Weizhou Island which affecting the calcification of coral reef, is mainly related to the seawater temperature and pH.