Tuesday, 16 April 2013

Day 31: Sometimes science does work in the real world

We are done with Icebergs. We are done with penguins, done with whales. There will be no more jollies and no more ice-scapes. It is time to work. Between South Georgia and our return to the Falklands we will be doing non-stop CTDs and VMPs. We are crossing the North Scotia Ridge. Those tired of numerical names and acronyms will be pleased to hear we are currently in 'Shag Rocks Passage'. Brian K tells me the last time he was during the 'ShagEx-The Shagrocks Experiment'. The Shag Rocks are a chain of under-sea mountains which interrupt the flow of the Antarctic Circumpolar Current. We expect the blob to be in the core of the current and mixing as it punches through the passage.

Photo 1: You might have seen these 'billows' in the sky. They occur in the deep ocean too!

Just today some 'wow it really works!' science was done. Have you ever looked up to the clouds and seen them swirling like beautiful overturning waves? The type with a long wisp. If you are lucky there are a whole set of them lined up. These billows are formed when a dense fluid - the cloud - flows under light fluid - the air above. If the cloud is flowing one way and the air above the other then little ripples can grow and eventually form the crashing cusps one might surf in a surreal dream. What is cool is that if you know the difference in the speed of the air and the cloud, and you know how much heavier the cloud is than the air - you can predict if the waves will form or not. The theory doesn't only apply to clouds. It is thought that much of the mixing in the ocean (that which is churning up our blob of tracer) is caused by these billows forming and breaking as deep dense currents flow under light surface waters.

Today, while measuring the flow through Shagg-Rocks, Alex and Gwynn's VMP (the mixing thingy) showed a big jump in mixing rates at about 2km down. When we looked at Xing Feng's LADCP (the water velocity thingy) showed a strong current below 2km pushing through the passage. And...when we looked at the CTD data (the salinity-temperature-density thingy) it turned out the velocity difference and the weight difference where spot on to give us the mixing we saw. Having met Louis Howard, one of the guys who came up with the theory simply with a pen and paper and the laws of physics, now in his nineties.  It is really amazing to come out here in the middle of a turbulent ocean, drop something over the side and tada! Physics works!...at least this time.

Photo2 : The measurements which seem to confirm the theory.

Photo 3: Brian K attempting to grab a piece of 'Shag Rock' on the map

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