The direct observation and interpretation of gas hydrate decomposition with ocean depth

An exposed gas hydrate (EGH) evolutional model as a function of water depth was established by in situ EGHs ascent experiments in cold seep areas of Haima (1509 m, 2.88 degrees C and 15.22 MPa), Lingshui (1760 m, 2.56 degrees C, 17.76 MPa and pH = 7.97) and Site F (1100 m, 3.57 degrees C, 11.09 MPa...

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Bibliographic Details
Published in:Geochemical Perspectives Letters
Main Authors: Ma, L., Luan, Z., Du, Z., Zhang, X., Zhang, Y.
Format: Report
Language:English
Published: EUROPEAN ASSOC GEOCHEMISTRY 2023
Subjects:
Geochemistry & Geophysics
IN-SITU
METHANE HYDRATE
DEEP-SEA
STABILITY
BUBBLE
CARBON
SEEPS
SLOPE
VENT
Methane hydrate
Online Access:http://ir.qdio.ac.cn/handle/337002/184392
http://ir.qdio.ac.cn/handle/337002/184393
https://doi.org/10.7185/geochemlet.2327
Description
Summary:An exposed gas hydrate (EGH) evolutional model as a function of water depth was established by in situ EGHs ascent experiments in cold seep areas of Haima (1509 m, 2.88 degrees C and 15.22 MPa), Lingshui (1760 m, 2.56 degrees C, 17.76 MPa and pH = 7.97) and Site F (1100 m, 3.57 degrees C, 11.09 MPa and pH = 7.69) in the South China Sea. A remotely operated vehicle was used to reproduce the in situ EGH ascent. Changes and temperature variations during EGH ascent were monitored in real time using a Raman insertion probe and dissolved oxygen sensor. The EGH ascent involved three stages of change: i) the metastable stage where no morphology changes, but where gas escapes and there is a decrease in internal temperature; ii) a second stage of coexistence of peripheral hydrate decomposition and internal hydrate growth; iii) a third stage of internal hydrate decomposition at shallower depths. Experimental results indicated that EGHs can carry gas bubbles to shallow depths and even to the sea surface. This could be an important transport mode for cold seep gases affecting shallow waters or the atmosphere.

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