Complicated oceans

North Atlantic cold-water sink returns to life : Nature News

Here's the opening paragraph from the above report:

Scientists have found evidence that convective mixing in the North Atlantic, a mechanism that fuels ocean circulation and affects Earth's climate, has returned after a decade of near stagnation – thanks, perhaps, to a dramatic loss of sea-ice in the Arctic during the summer of 2007.

From a global warming/greenhouse gas point of view, this appears to be good news. Certainly, the oceans are proving remarkably complicated to understand, probably because they are huge and hence hard to study:

Reduced convection should in theory weaken the entire Atlantic meridional overturning circulation (MOC) — responsible for carrying warm tropical water northwards — with far-reaching consequences for Earth's climate. But so far at least, scientists have not observed any significant changes to that large-scale circulation. Findings published in 2005 that seemed to indicate a big slowing of the MOC were later found to be in the range of natural fluctuations (see 'Ocean circulation noisy, not stalling').

One reason, says Fischer, is that the observational basis is still thin. The Argo programme, a global array of 3,000 robots that measure temperature, salinity and water pressure, has only last year become fully operational, for example.

But already it's clear that the response of the Atlantic Ocean circulation to high-latitude changes is much more complex than has been assumed.

(And by the way, I don't know that this has much influence on the issue of ocean acidification as a concern.)