现代暖期气候变暖对南海北部陆坡天然气水合物分解潜在影响

Hydrate dissociation on the northern slope of the South China Sea:Potential effects from climate warming in the current warm period

现代暖期(Current Warm Period,CWP,1850—至今)以来全球气温升高,南海北部陆坡底层海水温度升高、海平面上升影响海底天然气水合物稳定性。为探究现代暖期气候变暖对南海北部陆坡水合物分解影响,本文模拟计算了东沙海域、神狐海域、西沙海域、琼东南海域水合物赋存水深最浅处水合物的饱和度在1000年内变化情况,评估了受现代暖期气候变暖影响水合物赋存水深范围,讨论了水合物分解量及其对环境影响。结果发现:(1)受现代暖期气候变暖影响,东沙海域、西沙海域、琼东南海域水合物分解,神狐海域水合物不分解;当东沙海域、西沙海域、琼东南海域水深分别超过665、770、725 m,水合物不分解;(2)现代暖期自始以来,南海北部陆坡水合物分解量为9.36×10^(7)~3.83×10^(8)m^(3),产生的甲烷量为1.54×10^(10)~6.28×10^(10)m^(3);(3)受现代暖期气候变暖影响,南海北部陆坡每年水合物分解量为5.5×10^(5)~2.25×10^(6)m^(3),产生的甲烷量为9.02×10^(7)~3.69×10^(8)m^(3),这些甲烷中3.61×10^(5)~1.48×10^(6) m^(3)能够进入大气,对温室效应贡献度为每年我国人类生活的0.01%~0.06%;与此同时,1.77×10^(7)~7.23×10_(7) m^(3)甲烷可能会在海水中被氧化形成弱酸,加重南海北部陆坡海水酸化。

The global temperature has been rising during the current warm period(CWP,1850 present).The rise of the bottom water temperature and sea level is affecting the stability of hydrates on the northern slope of the South China Sea.To explore the effects of the CWP climate warming on hydrate dissociation,we simulated the change of hydrate saturation during the past millennium at the shallowest depth in the hydrate reservoirs in the Dongsha,Shenhu,Xisha and Qiongdongnan sea areas,and revealed the depth range of the hydrate stability zone affected by the CWP climate warming,and discussed the extent of hydrate dissociation and its environmental impact.We showed that(1)hydrate dissociation occurred in the Dongsha,Xisha and Qiongdongnan sea areas due to the CWP climate warming,but only at water depths above 665 m,770 m and 725 m,respectively;no hydrate dissociation observed in the Shenhu sea area.(2)Since the start of CWP,dissociated hydrates on the northern slope of the South China Sea amounted to(1.546.28)×10^(10) m^(3),with(9.3638.3)×10^(7) m^(3) methane released.(3)The annual hydrate dissociation affected by the CWP climate warming reached(5.522.5)×10^(5) m^(3) and produced(9.0236.9)×10^(7) m^(3) methane.The amount of methane that reached the atmosphere was(3.6114.8)×10^(5) m^(3),which accounted for 0.01%-0.06% of the annual methane contribution from human activities in China.Meanwhile,(1.777.23)×10^(7) m^(3) methane might be oxidized to form weak acids in seawater,which worsened acidification of the northern slope of the South China Sea.