On coastlines around the Earth, at water depths between 450 and 700 meters the high water pressure and low water temperature allow methane hydrates (methane clathrates) to be stable on the ocean floor.
It is estimated that there is about 1,800 GtC stored in these methane hydrates around the planet, with about 3.5% of the total in and around the above methane hydrate stability depth.
As the oceans continue to warm throughout the water column, there is increased risk of thawing many of these hydrates, but much of the methane released at those depths is absorbed within the water column and doesn’t make it into the atmosphere.
Unfortunately, a new peer reviewed study just published online shows that methane released from hydrates at much deeper depths and embedded within the ocean sediments can migrate up to a least 40 km and be released in much shallower depths varying from 300 meter water depth to 100 meters water depth. This methane is derived from the 96.5% methane pool not located near the 450-700 meter depths; and also much of what is released at the shallower depths can make it through the water column into the atmosphere to spike the atmosphere and global temperatures.
Paper: “Long-distance migration and venting of methane from the base of the hydrate stability zone”
https://www.nature.com/articles/s41561-023-01333-w
The paper uses three-dimensional seismic surveys to map the sediments and methane clathrates within off the Mauritanian coast in far-western Africa, however there is nothing unique about methane hydrates in this region. In fact, methane hydrates can be found along coastlines around the planet.
We can easily identify the regions on the ocean floor where there have been sizeable methane eruptions due to the large pockmark features left in the sediments. When a pockmark is on the surface of the ocean floor, we know it is a very recent methane burst. Older methane bursts create pockmarks that become covered by sediments settling down to the ocean floor and building up. This, the further down in the sediments the pockmark is, the longer ago the methane burst. This, knowing the sedimentation rates in the region, we can estimate how long ago the large methane releases occurred.
The paper uses three-dimensional seismic surveys to map the sediments and methane clathrates within off the Mauritanian coast in far-western Africa, however there is nothing unique about methane hydrates in this region. In fact, methane hydrates can be found along coastlines around the planet.
We can easily identify the regions on the ocean floor where there have been sizeable methane eruptions due to the large pockmark features left in the sediments. When a pockmark is on the surface of the ocean floor, we know it is a very recent methane burst. Older methane bursts create pockmarks that become covered by sediments settling down to the ocean floor and building up. This, the further down in the sediments the pockmark is, the longer ago the methane burst. This, knowing the sedimentation rates in the region, we can estimate how long ago the large methane releases occurred.
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by paulhenrybeckwith