An achievement of Olympian proportion

It’s hard to overstate the achievement of three Hobart scientists (and their British-based collaborator) in describing and locating deep-ocean carbon sinks in the Southern Ocean. [7 August 2012 | Peter Boyer]

Red indicates regions where ocean winds and eddies set up conditions in which carbon dioxide can be taken from surface waters down to depths of around 1000 m. Blue indicates regions in which there is a net release of carbon from ocean to atmosphere. ORIGINAL GRAPHIC BAS-CSIRO

I don’t know about you, but I’m suffering from Olympic fatigue. Early symptoms appeared about ten days ago not long after the opening ceremony, and I’ve been feeling it ever since.

My problem isn’t lack of sleep — not for me the all-night television marathon — but the relentless 24-7 barrage of chatter that fills every last gap between events, as if these games were the only thing in the world that matters.

Of course, they’re exactly that for the athletes who’ve trained for years for their moment in the spotlight. It’s no wonder that hubris, self-pity or petulance sometimes get the better of them. We should forgive the occasional lapse, especially among our younger competitors.

There’s so much at stake. Every Olympic winner can expect to attract commercial interest, if only the odd 30-second ad for your favourite snack food. For a fortunate few, what’s in prospect is tens or hundreds of thousands in sponsorship dollars.

Such is the nature of elite sport today. No wonder the chatterers go on about it.

But all this hoopla has distracted from a gold medal performance by three of our own: three people at the top of their game who have chosen Tasmania as their home. Plus a fourth, a French-born resident of the UK who once worked for CSIRO. National boundaries aren’t important in this arena.

These people didn’t cross a line first or perform tricky manoeuvres or send a ball into a goal. They haven’t made the headlines, yet their achievement is set to reshape the way we view our world’s climate processes, in particular the ways in which atmospheric carbon is taken up by our oceans.

This is a big, big question. Human fossil fuel use has thrown the natural carbon cycle out of kilter, raising atmospheric carbon dioxide levels and leading to warming of the air. But natural “sinks”, notably the oceans and trees, absorb some of this carbon to keep a lid on the rate of warming.

Scientists have been concerned that the rate at which carbon in the air is reabsorbed by the ocean and plants isn’t keeping pace with our carbon emissions, but a meticulous analysis of decades of data by US scientists, published last week by the journal Nature, found no sign that the global carbon sink was weakening.

That doesn’t mean we have nothing to worry about — the sinks aren’t capturing all our emissions so the proportion of carbon dioxide in the air continues to rise, and all indications are that the rate of natural sequestration will weaken — but it’s a reassuring sign that nature can still work in our favour.

But the ocean remains an elusive target. We know it’s a kingpin of the global carbon cycle but we have yet to nail the processes by which this happens. This has limited our ability to discern how much reabsorbed carbon remains near the surface (where it can be re-released to the air) and how much is taken into the deep ocean for long-term storage.

The current issue of the journal Nature Geoscience includes a paper by Jean-Baptiste Sallée, of the British Antarctic Survey, and Richard Matear, Steve Rintoul and Andrew Lenton, all of CSIRO’s Hobart-based Division of Marine and Atmospheric Research.

Matear, born and raised in Canada, specialises in the interaction of the ocean’s physical, chemical and biological processes, while US-born Rintoul is an authority on how Southern Ocean circulation affects global climate systems. Australian-born Lenton specialises in past and present changes to the ocean carbon sink.

Nearly half of all oceanic carbon dioxide absorption occurs in waters south of latitude 35 degrees, a proportion of which is dragged down into deeper ocean layers, where it can remain for thousands or (if it finds its way into sediments) millions of years.

Based on a decade of observational data from ships, floating buoys and satellites covering a vast area of Earth’s surface, the paper seeks to establish for the first time how and where in these waters the heavy work of dragging dissolved carbon into the deep ocean is done.

What’s truly novel among the paper’s findings is that when it comes to transport of captured carbon into deep water, the Southern Ocean is far from an amorphous mass. The team discovered and mapped a handful of “hotspots” that account for a fifth of the global ocean’s entire uptake of carbon.

The places to watch are the two big ones — Drake Passage (the stormy waters between South America and the Antarctic Peninsula) and a region southeast of South Africa — and smaller ones south and southeast of New Zealand and a spot due south of the mid-Pacific.

The paper also described what these “hotspots” actually do. Where elsewhere there’s a barrier between the surface layer of relatively fresh water and colder, saltier layers below, local combinations of winds and currents form eddies that funnel carbon-carrying waters through this barrier to a kilometre or more down, where it can be locked up for a very long time.

These eddies aren’t like anything you might have seen before, in a bath or a river, maybe. They can be hundreds of kilometres wide, transporting in total about 1.5 billion tonnes of carbon to the deep ocean each year. Because they operate vertically as well as horizontally, they are vital to ocean health, which depends on mixing of layers.

The team’s discovery makes it that much easier to monitor global processes. Knowing about the existence and location of these places, we can keep a better eye on how the oceans are performing, including how changing climate might reduce the ocean’s efficiency in sequestering carbon.

CSIRO is on the lookout for sponsorship. Here’s hoping this gold medal achievement by three of their best can help secure it for them.

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