Ocean's carbon dioxide uptake reduced by climate change

July 10, 2011 by Jill Sakai, University of Wisconsin-Madison

(PhysOrg.com) -- How deep is the ocean's capacity to buffer against climate change? As one of the planet's largest single carbon absorbers, the ocean takes up roughly one-third of all human carbon emissions, reducing atmospheric carbon dioxide and its associated global changes.

But whether the ocean can continue mopping up human-produced carbon at the same rate is still up in the air. Previous studies on the topic have yielded conflicting results, says University of Wisconsin-Madison assistant professor Galen McKinley.

In a new analysis published online July 10 in Nature Geoscience, McKinley and her colleagues identify a likely source of many of those inconsistencies and provide some of the first observational evidence that is negatively impacting the ocean carbon sink.

"The ocean is taking up less carbon because of the warming caused by the carbon in the atmosphere," says McKinley, an assistant professor of atmospheric and and a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies.

The analysis differs from previous studies in its scope across both time and space. One of the biggest challenges in asking how climate is affecting the ocean is simply a lack of data, McKinley says, with available information clustered along shipping lanes and other areas where scientists can take advantage of existing boat traffic. With a dearth of other sampling sites, many studies have simply extrapolated trends from limited areas to broader swaths of the ocean.

McKinley and colleagues at UW-Madison, the Lamont-Doherty Earth Observatory at Columbia University, and the Universite Pierre et Marie Curie in Paris expanded their analysis by combining existing data from a range of years (1981-2009), methodologies, and locations spanning most of the North Atlantic into a single time series for each of three large regions called gyres, defined by distinct physical and biological characteristics.

They found a high degree of natural variability that often masked longer-term patterns of change and could explain why previous conclusions have disagreed. They discovered that apparent trends in ocean carbon uptake are highly dependent on exactly when and where you look – on the 10- to 15-year time scale, even overlapping time intervals sometimes suggested opposite effects.

"Because the ocean is so variable, we need at least 25 years' worth of data to really see the effect of carbon accumulation in the atmosphere," she says. "This is a big issue in many branches of climate science – what is natural variability, and what is climate change?"

Working with nearly three decades of data, the researchers were able to cut through the variability and identify underlying trends in the surface CO2 throughout the North Atlantic.

During the past three decades, increases in have largely been matched by corresponding increases in dissolved in the seawater. The gases equilibrate across the air-water interface, influenced by how much carbon is in the atmosphere and the ocean and how much carbon dioxide the water is able to hold as determined by its water chemistry.

But the researchers found that rising temperatures are slowing the carbon absorption across a large portion of the subtropical North Atlantic. Warmer water cannot hold as much carbon dioxide, so the ocean's carbon capacity is decreasing as it warms.

In watching for effects of increasing on the ocean's uptake, many people have looked for indications that the carbon content of the ocean is rising faster than that of the atmosphere, McKinley says. However, their new results show that the ocean sink could be weakening even without that visible sign.

"More likely what we're going to see is that the ocean will keep its equilibration but it doesn't have to take up as much carbon to do it because it's getting warmer at the same time," she says. "We are already seeing this in the North Atlantic subtropical gyre, and this is some of the first evidence for climate damping the ocean's ability to take up carbon from the atmosphere."

She stresses the need to improve available datasets and expand this type of analysis to other oceans, which are relatively less-studied than the North Atlantic, to continue to refine carbon uptake trends in different ocean regions. This information will be critical for decision-making, since any decrease in uptake may require greater human efforts to control carbon dioxide levels in the atmosphere.

Explore further: Climate change will affect carbon sequestration in oceans, model shows

More information: www.nature.com/ngeo/index.html

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1.8 / 5 (11) Jul 10, 2011
Well it is a good thing that as temps rise, so do plants ability to use more and more Co2.

1.4 / 5 (16) Jul 10, 2011
What's causing the oceans to warm? Given the density differences, oceans can warm the air, but air cannot warm the ocean. So where is the heat coming from?

Does the author even spend a minute's times thinking about any of this? Is this really science?
4.3 / 5 (11) Jul 10, 2011
The real question is did you think about it?
The ocean warms for the same reason everything else warms, in that particles of the substrate absorb electromagnetic radiation.

Better get your facts straight before placing your ignorance on display by making such a petulant comment.
1.4 / 5 (14) Jul 10, 2011
So, Al Gore's movie was merely a scare tactic like the Patriot Act?
4.4 / 5 (7) Jul 10, 2011
I don't understand what the ad "End of the Delusion - Climategate exposed the fraud But climate hucksters carry on - climateconference.heartland.org" is doing tucked in this article, but if physorg is going to take advertising revenue from anti-science organizations, I don't see any reason to keep reading here.
5 / 5 (5) Jul 10, 2011
Lino235 - That part is pretty simple - sun heats the ocean the same regardless of CO2, but the warmer air slows the transfer of heat from the ocean to the air. The ocean has to be warmer to transfer the heat it absorbs to the warmer air. Thus the ocean warms.

Twango - it may not be physorg that accepted the ad. Physorg probably just deals with an ad service, and that service sold a keyword to the highest bidder.
1.7 / 5 (11) Jul 11, 2011
I just wish the next ice age would get here soon. Need some serious alarmist junk science buried in a block of ice.
1.4 / 5 (10) Jul 11, 2011
Of course warm water holds less CO2. What's new? Mauna Loa observations show that the ocean warms suring the summer and CO2 increases about 3 months later. Then the oceans cool and CO2 eventually levels off or dros temporarily. The 30 years referred to is the normal 30 year warm phase following the end of the 30 year cooling phase in th 70s. THis has been going on for several cycles. The author will use every trick in the book to promote the AGW hoax.
1.6 / 5 (7) Jul 11, 2011
CO2 buildup FOLLOWS rising temps, not the other way around. Rising temperatures, in other words, result in rising levels of the trace gas. That's the first flaw here. The second is, the authors were not able to quantify the amount of methane entering the ocean from underwater vents; increasing volcanism accounts for rising CO2 levels in seawater. No matter, the mighty Wurlitzer of the AGW hoaxers plays on....
1 / 5 (2) Jul 11, 2011
How does she know that the subtropic N Atlantic is a sign the rest of the ocean is headed that way, esp if there isn't much data from other regions? What previous data even suggests that's a new trend, and not just the nature of this region?

Seems like she is guilty of the same extrapolation that she accuses other scientists of.

Repeatedly this article says the equilibrium hasn't shifted anywhere else.

Simply because the rate of absorption may decrease, doesn't mean the max volume that is able to be contained has decreased either.

5 / 5 (7) Jul 11, 2011
Looks like the usual anti-science trolls are here in different guises. Notice their bleating becoming more desperate as global temperatures rapidly warm and Arctic and Antarctic ice levels reach historic lows. Their arses are getting burnt and they don't realise this because their heads are still stuck in the sand.

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