Fish Guts May Shed Light on Mystery of Upper Ocean’s Chemistry

Fish guts may hold the answer to a mystery that’s puzzled ocean chemists for decades: Why seawater becomes more alkaline the deeper you go.

Ocean waters become more alkaline, or less acidic, as carbonates produced by plankton dissolve. The chemical compounds typically don’t break down until a depth of several kilometers where the pressure is enough, said Rod Wilson, lead author of a study today in the journal Science. The ocean’s alkalinity increases by about 4 percent in the first kilometer, his team said.

“That left a mystery of what’s causing this increasing alkalinity in the surface layers,” Wilson, a fish biologist at the University of Exeter, southwest England, said in a telephone interview. His team found fish produce a more soluble form of carbonate in their gut that can dissolve in shallower waters.

United Nations scientists warned in 2007 that man-made carbon- dioxide emissions threaten to acidify the oceans as they absorb increasing amounts of the gas. Wilson’s findings suggest fish may have a role to play in offsetting some of this effect by adding a source of alkalinity in their excretions. Alkalis neutralize acids.

“Given that fish are probably involved in replenishing that alkalinity in the surface layers of the ocean, then fish carbonate might help the oceans absorb more CO2,” Wilson said. “It may be in the right direction but we don’t know if it’s quantitatively large enough to buffer the increased acidity brought on by higher CO2 absorption from the atmosphere.”

Alex Morales, Bloomberg, 15 January 2009. Full article.

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