Research Shows Small Methane Releases in Deep-Sea Sediments More Frequent Than Expected

New research describes evidence that deep sea methane deposits change into gas more frequently than could be monitored previously and that a set of fossilized organisms has a unique ability to detect these releases.

PROVIDENCE, R.I. [Brown University] – A team of scientists led by a Brown University researcher has developed a new method for monitoring when deep sea methane deposits convert to gas and rise toward the seafloor in amounts that were previously too small to detect.

The research, published in Earth and Planetary Science Letters, shows that fossils of a single-cell organism called benthic foraminifera from the order Miliolida have a unique ability to serve as a resource for this monitoring because they can record both the location and timing of when crystalized methane goes through – even in small amounts – a process known as methane hydrate dissociation. This is when ice-like methane found beneath the seafloor transforms into gas and rises upward.

In the study, the researchers show through an analysis of 372 individual Miliolida fossils that these previously unrecorded dissociation events have been occurring in the Bay of Bengal in the northern Indian Ocean for the past 1.5 million years, but they were too small to detect through the usual signs of hydrate dissociation. The analysis shows the dissociation events have been largely driven by increasingly warming waters in the region.

Put together, the findings underscore the effects that climate change can have on ancient methane deposits and show that the hydrates transition from their solid phase ice-like to gas more often than previously understood.

“If you look at other drill sites around the area we studied, the records show only two methane dissociation events in the last million years” said Steven Clemens, a professor of geological sciences at Brown and lead author of the study. “Here, we see it pretty much everywhere when we look at these small scales, particularly during times when Earth’s climate was in a warm phase. It’s clear that methane is cycling a lot more rapidly and more often between its ice and dissolved phase than we could previously detect.”

The research team said the study is the first to document that three particular types of Miliolida foraminifera – Pyrgo spp., Quinqueloculina spp., and Spiroloculina spp. – are sensing small-scale dissociation events. Analysis of the other types of foraminifera the researchers collected during a 2015 expedition to the Indian Ocean showed that unlike the Miliolida, they do not detect these smaller-scale dissociation events.

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