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

doi:10.13745/j.esf.sf.2022.1.4

Abstract

Abstract:

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 (1.54-6.28)×10¹⁰m³, with (9.36-38.3)×10⁷ m³ methane released. (3) The annual hydrate dissociation affected by the CWP climate warming reached (5.5-22.5)×10⁵m³and produced (9.02-36.9)×10⁷m³ methane. The amount of methane that reached the atmosphere was (3.61-14.8)×10⁵m³, which accounted for 0.01%-0.06% of the annual methane contribution from human activities in China. Meanwhile, (1.77-7.23)×10⁷ m³ methane might be oxidized to form weak acids in seawater, which worsened acidification of the northern slope of the South China Sea.

Key words: current warm period, hydrates dissociation, bottom water temperature, sea level, northern slope of the South China Sea

CLC Number:

P467

JIA Yonggang, RUAN Wenfeng, HU Naili, QIAO Yue, LI Zhenghui, HU Cong. Hydrate dissociation on the northern slope of the South China Sea: Potential effects from climate warming in the current warm period[J]. Earth Science Frontiers, 2022, 29(4): 191-201.

Figures/Tables 7

References 76

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地区	水合物资源量/ m³	文献
全球	(1.8~2.1)×10¹⁶	[2]
南海	8.27×10¹³	[3]
南海北部	4.3×10¹³	[3]
东海	2.41×10¹³	[4]

地区	水合物资源量/ m³	文献
全球	(1.8~2.1)×10¹⁶	[2]
南海	8.27×10¹³	[3]
南海北部	4.3×10¹³	[3]
东海	2.41×10¹³	[4]

区域	水合物储层分布水深/m	水合物饱和度	孔隙度	渗透率/ mD	热导率/ (W·m^-1·K^-1)	地温梯度/ (℃·100 m^-1)	水合物储量/ 10⁸ m³	文献
东沙海域	600~1 100	0.15~0.53	0.3~0.6	—	1.12~1.28	3.27~3.97	9.14	[3,33⇓⇓⇓⇓⇓⇓⇓-41]
神狐海域	900~1 500	0.2~0.7	0.33~0.55	0.2~20	0.65~1.31	5.18~8.42	1 500	[30,42⇓⇓⇓-46]
西沙海域	600~2 500	—	0.35~0.47	2~20	0.8~1.04	9.25~10.72	69	[5,37,47-48]
琼东南海域	650~2 000	—	0.26~0.59	—	1.55~1.81	4~6.08	2 500	[5,49⇓-51]

区域	水合物储层分布水深/m	水合物饱和度	孔隙度	渗透率/ mD	热导率/ (W·m^-1·K^-1)	地温梯度/ (℃·100 m^-1)	水合物储量/ 10⁸ m³	文献
东沙海域	600~1 100	0.15~0.53	0.3~0.6	—	1.12~1.28	3.27~3.97	9.14	[3,33⇓⇓⇓⇓⇓⇓⇓-41]
神狐海域	900~1 500	0.2~0.7	0.33~0.55	0.2~20	0.65~1.31	5.18~8.42	1 500	[30,42⇓⇓⇓-46]
西沙海域	600~2 500	—	0.35~0.47	2~20	0.8~1.04	9.25~10.72	69	[5,37,47-48]
琼东南海域	650~2 000	—	0.26~0.59	—	1.55~1.81	4~6.08	2 500	[5,49⇓-51]

区域	水深/m	现代暖期初期底层水温度/℃	目前底层水温度/℃	孔隙度	渗透率/ mD	热导率/ (W·m^-1·K^-1)	地温梯度/ (℃·100 m^-1)
东沙海域	600	5.27	6.77	0.45	10.1	1.2	3.62
神狐海域	900	3.75	5.25	0.44	10.1	0.98	6.8
西沙海域	600	5.27	6.77	0.41	11	0.92	10
琼东南海域	650	4.94	6.44	0.43	11	1.68	5.04