Southern Ocean GasEx Blog

Dispatches from the Southern Ocean Gas Exchange Experiment

Bye Bye Buoy

Posted by sogasex on April 5, 2008

By Christopher Zappa, LDEO

A previous blog entry discussed the carbon measurements from the MAPCO2 buoy using SAMI-CO2 systems, while another post explained how the buoy tracks the patch with the help of the holey sock drogues. The MAPCO2 buoy allows us to measure physical processes very near the ocean surface that we typically can’t measure from the ship because the ship disturbs the flow of the ocean. My project employed a variety of instruments that use sound to measure the ocean currents based on the Doppler velocity backscattered from particles in the ocean. Dave Hebert talked about how he measures the ocean currents using the ship’s ADCP to track the tracer patch. One instrument we use on the buoy is a high-resolution ADCP to measure the currents much closer to the ocean surface. Instead of profiling 1000 m as the ship’s ADCP, this “Dopbeam,” as we call it, measures the profile of velocity over 1 meter with 1-cm bins. While the wind puts energy into the waves that eventually break, the wind also controls the near-surface ocean currents directly and through wave breaking. These fine-scale near-surface currents eventually become chaotic, or turbulent, and develop very small “eddies,” or energetic circular motions. Wave breaking will also generate these fine-scale turbulent eddies. We measure these fine-scale near-surface eddies that mix up the top few meters of the ocean and that work to regulate the gas transfer.

A few days ago, the MAPCO2 buoy was taken out of the water…for the third and final time. Each time, getting the buoy on deck is only half the job. Scientists scurry quickly to download the data that have been accumulating on the instrument. This is an essential task in order to make sure that all is well while the buoy was in the water. Luckily, we had only one problem during all three deployments combined. On the final retrieval, the underwater camera housing was flooded and the camera was damaged (see picture below). Damage caused by the ocean is always a danger with any instrument that goes over the side of a ship and remains underwater for days and weeks on end.

Now that the buoy is out of the water and all the data have been collected, I have only a few systems running (WaMoS II and the wave breaking video). Slowly, there is a sense that the cruise is over… and it’s a little sad. There are signs throughout our day that the experiment on site is coming to a close. Today, we had our last Fire and Abandon Ship Drills. In fact, as I write this we are performing our last CTD of the experiment. After that, we set sail for Montevideo, Uruguay. Even the king penguins were sad to see us go. Soon enough, we will be back on land, getting rid of our “sea legs.” There will be no more crawling into the small bunks, no more rolling back and forth as we sleep. No more day-to-day monotony of data gathering. Nope, we can finally have a nice, frosty, ice-cold, refreshing BEER. And watch the Red Sox beat the Yankees at Fenway. OK, maybe I’m not so sad.

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Dopbeam mounted in its titanium cage being prepared to be deployed from the MAPCO2 buoy. The Dopbeam is roughly 2 feet long and 3 inches in diameter.

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Retrieval of the MAPCO2 buoy with the Dopbeam mounted in its cage chained below.

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Underwater camera housing mounted on MAPCO2 buoy before deployment.

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Underwater camera housing after third deployment. The housing is flooded with ocean water. Notice the orange rust at the top.

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Camera damaged by the ocean water.

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Even the penguins, which flock around the CTD every day, were sad to see us go.

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