Amazon powers tropical ocean's carbon sink

July 21, 2008

Nutrients from the Amazon River spread well beyond the continental shelf and drive carbon capture in the deep ocean, according to the authors of a multi-year study.

The finding does not change estimates of the oceans' total carbon uptake, but it reveals the surprisingly large role of tropical oceans and major rivers.

The tropical North Atlantic had been considered a net emitter of carbon from the respiration of ocean life. A 2007 study estimated that ocean's contribution to the atmosphere at 30 million tons of carbon annually.

The new study, appearing in PNAS Early Edition the week of July 21, finds that almost all the respiration is offset by organisms called diazotrophs, which pull nitrogen and carbon from the air and use them to make organic solids that sink to the ocean floor.

Diazotrophs "fix" nitrogen from the air, enabling them to thrive in nutrient-poor waters. They also require small amounts of phosphorus and iron, which the Amazon River delivers far offshore.

That is all the diazotrophs need to pull carbon from the air and sink it in the ocean.

The other great tropical rivers of the world also may contribute to carbon capture, said senior author Doug Capone, professor in the USC Wrigley Institute for Environmental Studies at the University of Southern California, adding that studies on such rivers are in progress.

The study's results present new options for the controversial practice of iron fertilization. Some biologists believe that seeding the oceans with iron could increase production of carbon-fixing organisms and help mitigate climate change.

Upwelling circulation in cooler waters makes them unlikely candidates for long-term carbon capture, said Capone, who explained that a permanent carbon sink instead may be more feasible in the warm oceans.

Capone said that iron fertilization would increase diazotroph activity and that the stratified tropical waters should be able to keep captured carbon solids from returning to the surface in the short term.

"The most appropriate places are probably not the high latitudes but rather the low-latitude areas where nitrogen fixation is a predominant process," Capone said.

But Capone also noted the risks of iron fertilization, including increased production of other greenhouse gases and unpredictable effects on the food web.

Nevertheless, he said, "if we choose as a human society to fertilize areas of the oceans, these are the places that probably would get a lot more bang for the buck in terms of iron fertilization than we would at high latitudes."

Source: University of Southern California

Explore further: Behind the iron curtain: How methane-making microbes kept the early Earth warm

Related Stories

Conundrum of missing iron in oxygen minimum zones solved

October 28, 2016

Iron is an essential nutrient for biological productivity in the oceans. However, dissolved iron quickly combines with oxygen and is then no longer usable by or-ganisms. For a long time it has been a conundrum why even in ...

Recommended for you

Collapse of the European ice sheet caused chaos

June 27, 2017

Scientists have reconstructed in detail the collapse of the Eurasian ice sheet at the end of the last ice age. The big melt wreaked havoc across the European continent, driving home the original Brexit 10,000 years ago.

Lightning sparking more boreal forest fires

June 27, 2017

A new NASA-funded study finds that lightning storms were the main driver of recent massive fire years in Alaska and northern Canada, and that these storms are likely to move farther north with climate warming, potentially ...

Greenland now a major driver of rising seas: study

June 26, 2017

Ocean levels rose 50 percent faster in 2014 than in 1993, with meltwater from the Greenland ice sheet now supplying 25 percent of total sea level increase compared with just five percent 20 years earlier, researchers reported ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

jeffsaunders
4 / 5 (3) Jul 21, 2008
whole scale iron fertilization to offset wholesale nitrogen, carbon and phosphorus pollution I think we are going to end up with a cure that could be worse than the disease.

How about the novel idea or cutting back on the pollution in the first place?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.