Thursday, March 7, 2019

Rising Waters Eat CO2

A negative feedback between sea level rise and atmospheric carbon dioxide. The fast the sea level rises, the more carbon that is stored in wetland sediments. From my friends at the Smithsonian (literally, the head tech on this project is the bass player for the band I still play in) and their colleagues: As sea level rises, wetlands crank up their carbon storage
Coastal wetlands, which include marshes, mangroves and seagrasses, already store carbon more efficiently than any other natural ecosystem, including forests. The latest study, published March 7 in the journal Nature, looked at how coastal wetlands worldwide react to rising seas and discovered they can rise to the occasion, offering additional protection against climate change.

"Scientists know a fair amount about the carbon stored in our local tidal wetlands, but we didn't have enough data to see global patterns," said Pat Megonigal, a co-author and soil scientist at the Smithsonian Environmental Research Center.

To get a global picture, scientists from Australia, China, South Africa and the U.S. pooled data from 345 wetland sites on six continents. They looked at how those wetlands stored carbon for up to 6,000 years and compared whether sea levels rose, fell or stayed mostly the same over the millennia.

For wetlands that had faced rising seas, carbon concentrations doubled or nearly quadrupled in just the top 20 centimeters of soil. When the scientists looked deeper, at 50 to 100 centimeters beneath the surface, the difference hit five to nine times higher.

The extra boost comes because the carbon added to wetland soils by plant growth and sediment is buried faster as wetlands become wetter. Trapped underwater with little to no oxygen, the organic detritus does not decompose and release carbon dioxide as quickly. And the higher the waters rise, the more underwater storage space exists for the carbon to get buried.
This is no great shock. We've known that coastal wetlands can keep up with a pretty good rate of sea level rise for years. That fact has even been used to calculate prehistoric rates of sea level rise. And they do it by laying down thicker layers of organic material, hence the carbon storage.
North America and Europe faced the most sea-level rise over the past 6,000 years. Melting glaciers from the last ice age caused water levels to rise, increasing coastal flooding. Continents in the southern hemisphere, by contrast, were largely glacier-free and experienced stable or even falling sea levels.
Now that's just silly. Indeed, the southern hemisphere had less glacial coverage, it  had less much less land in the latitudes where the glaciers formed for one thing. But sea levels rose and fell more or less in concert in the northern and southern hemispheres; water tends to do that (seek it's own level, that is) and the equator is not a barrier to water flow. I assume that's journolist making that up, and not a scientist.

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