Amazon powers tropical ocean's carbon sink

Jul 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: NASA's HS3 mission spotlight: The HIRAD instrument

add to favorites email to friend print save as pdf

Related Stories

The rise and fall of oxygen

Dec 11, 2013

How long has Earth's atmosphere included oxygen? A recent paper suggests low levels of oxygen appeared in the atmosphere approximately 2.95 billion years ago. That's about 550 million years earlier than p ...

El Nino cycle has a big effect on a major greenhouse gas

Sep 27, 2013

Nitrous oxide is commonly associated with laughing gas—the pleasantly benign vapor that puts patients at ease in the dentist's chair. But outside the dentist's office, the gas plays a serious role in the ...

Pollutant-eating bacteria not so rare

Aug 26, 2013

(Phys.org) —Dioxane, a chemical in wide industrial use, has an enemy in naturally occurring bacteria that remove it from the environment. Researchers at Rice University have found that these bacteria are ...

Recommended for you

NASA's HS3 mission spotlight: The HIRAD instrument

1 hour ago

The Hurricane Imaging Radiometer, known as HIRAD, will fly aboard one of two unmanned Global Hawk aircraft during NASA's Hurricane Severe Storm Sentinel or HS3 mission from Wallops beginning August 26 through ...

Fires in the Northern Territories July 2014

15 hours ago

Environment Canada has issued a high health risk warning for Yellowknife and surrounding area because of heavy smoke in the region due to forest fires. In the image taken by the Aqua satellite, the smoke ...

How much magma is hiding beneath our feet?

16 hours ago

Molten rock (or magma) has a strong influence on our planet and its inhabitants, causing destructive volcanic eruptions and generating some of the giant mineral deposits. Our understanding of these phenomena ...

User comments : 1

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?