Not long ago it was our distinct pleasure to transmit a piece of rare good news from the climate front, the discovery by British researchers that microorganisms living in Antarctic waters are taking up a small but significant amount of atmospheric carbon. Now comes the bad news, and unfortunately it's a lot worse--evidence that our oceans' ability to absorb carbon may be dropping sharply.
It's been long known from direct measurements that the seven seas are sopping up a large fraction of the carbon dioxide that humans are pumping into the atmosphere. Scientists have worried that the fraction might drop as atmospheric levels rise and the oceans become saturated. Now comes a report, published this week in Nature and reproduced on the Lamont Doherty Earth Observatory's website, saying that even though the oceans are continuing to absorb ever larger quantities of carbon dioxide, the fraction of human emissions they've taken up may have dropped by as much as 10 percent since 2000.
"The study reconstructs the accumulation of industrial carbon in the oceans year by year, from 1765 to 2008," explains the Earth Institute’s Kevin Krajick, in a lucid press release. "[Lamont Doherty's Samar] Khatiwala and his colleagues found that uptake rose sharply in the 1950s, as the oceans tried to keep pace with the growth of carbon dioxide emissions worldwide. Emissions continued to grow, and by 2000, reached such a pitch that the oceans have since absorbed a declining overall percentage, even though they absorb more each year in absolute tonnage. Today, the oceans hold about 150 billion tons of industrial carbon, the researchers estimate--a third more than in the mid-1990s."
Khatiwala and his co-researchers developed techniques to infer quantities of industrial carbon in the oceans, working backwards from contemporary levels, and sought to identify the locations of its uptake and its sub-sea transport. They estimate that about 40 percent of the carbon dioxide absorbed by the oceans is taken up in frigid waters near Antarctica, to be carried northwards by ocean currents.
At the uppermost part of the globe, ironically, waters are under-calcified because of freshwater from melting ice streaming into them. A report in this week's Science (appearing tomorrow, Nov. 20) finds that in 2008, in the words of its abstract, “surface waters were undersaturated with respect to aragonite, a relatively soluble form of calcium carbonate found in plankton and invertebrates.” This effect was expected but is showing up about a decade earlier than predicted. It endangers marine organisms that depend on water saturated with calcium carbonate to build their shells and skeletons.