Friday Afternoon: Carbon Dioxide, Crushed Ice and Flip-Flops

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500 posters cram a cavernous meeting hall
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A crush of oceanographers navigated through more than 500 posters Thursday evening. Click enlarged image for a full panoramic view. (David Fisichella, WHOI)


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We're carbonating the ocean, but by how much?

As the meeting wound down, I started thinking about relaxing drinks on the beach. But it wasn’t a daydream; it was two final talks: one on dissolved carbon dioxide and the other on crushed ice.

As Scott Doney writes in this month’s Scientific American, carbon dioxide from fossil fuel emissions is dissolving into the ocean and making it more acidic. Eventually, the change may be so great that corals and other sea life may not be able to make their calcium shells.

So lots of people, including Doney’s student Naomi Levine, are trying to get a better grasp on how much anthropogenic carbon dioxide finds its way into the ocean. A first step is to measure ocean carbon dioxide levels to see if they’re climbing (Levine spent 56 days at sea last year doing just that).

But emissions are only one of three main ways carbon dioxide levels change. The other two are natural processes unrelated to human activities. In productive years, sea life thrives and releases vast amounts of the gas into the water.

And some years currents change, sweeping water with different carbon dioxide concentrations past the measuring points. Levine is working on modeling these two natural processes, so she can subtract them out of her measurements and calculate anthropogenic carbon dioxide more precisely.


The world's biggest crushed-ice factory

After getting properly carbonated at Levine’s talk, I heard Jason Hyatt discuss storms, splintering sea ice and ocean mixing.

Oceanographers study the way water mixes because that’s how heat moves back and forth from air to sea, and how nutrients get from the bottom sediments up to the realm where plankton can use them.

Ocean water mixes in weird ways, very different from what happens when you top up the bathtub with hot water. That’s because saltier parcels of sea water don’t mix well with fresher currents, and the Earth’s spin has an effect on where drifting water goes.

Add a layer of ice floes jostling around on top of the water, Hyatt said, and things get really convoluted.

Using data from underwater moorings left in place through the winter, Hyatt and adviser Robert Beardsley were able to watch the way water mixed as ice grew, melted, and got blown around Marguerite Bay on the Antarctic Peninsula.

In spring and fall, storm winds set ice drifting in the bay. A characteristic effect of the Earth’s rotation, called inertial oscillation, makes the ice drift in circles, stirring up the water beneath it. Hyatt’s instruments saw evidence of water mixing as far as 233 meters (764 feet) below the surface.

During half of each rotation the ice drifts out to sea, opening spaces between the floes and freezing sea water in the frigid Antarctic air. As the ice moves back toward shore during its circular drift, the floes slam together, shattering the new ice.

Estimates indicate this constant sloshing can create as much as a fifth of the region’s sea ice. Which makes Hyatt’s study area one of the biggest crushed-ice factories in the world.

And with that Ocean Sciences 2006 drew to a close. Shaved ice, anyone?



 

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Last updated March 28, 2006
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