Wednesday, 3 April 2013

 Day 20  - A bus trip to the bottom of the ocean with Genghis and Cesar.

The wind howled last night. As the second last mooring was dropped back into the water the wind picked up to 50 knots. The snow and ice whizzed past as did the sea ice - large slabs colliding with the ship from time to time. The forecast said we’d be bunkered down for the next 3 days.  If you think forecasts in Southern England or Tasmania are poor....try the tip of Antarctica. It worked out in our favour today as we were able to finish of the last of our work here and are now preparing to head east - out of the ice.

Photo: It will be sad to leave the ice-scape tonight.

During the last week we have been recovering and deploying moorings which are measuring the flow of Bottom Water off the coast of Antarctica. The tracer team have also been measuring the amount of CFCs in the water. Sorry to lay on yet another three letter acronym (TLA) on you. You may have heard about Chlorofluorocarbons and how they have been causing the whole in the ozone layer to get bigger. Liking to put a positive spin on the situation, us oceanographers have found a great use for them: they tell us how ‘old’ the water is.

Photo: Fat seals...because they are cute.

I spoke to Andy Watson from the University of East Anglia, the trace gas expert, about htis today. Any given layer of water is made up of a mixture of water from different places and times. Different kinds of CFCs have been in the air at differnt times, so if we know how much of each is in different layers of the ocean we can tell how old the water is...on average.

Knowing the average age of the water at a given level in the ocean is a bit like knowing the average age of all the people on a bus. If the bus is heading to kindergarten there will be mostly young kids and maybe the bus driver and/or someones mother who will bring up the age a little. An outing from an old-persons home will of course be the other way around. We only know the average age of the water at each level in the ocean and use this along with the other measurements we take to figure out where they’ve come from and where they are going:

Surface Ocean (0-200m deep): Bus from the maternity ward at the local hospital (babies with a few young mothers and nurses)
Upper Ocean (200 -1000m deep): Young professionals on their way to work, sharing the bus stop with retirees on their way back from the shops.
Middle Ocean: (1000m-3000m deep) Genghis Kahn shares the bus with Oliver Cromwell, Julius Cesar and friends.
Deep Ocean: (3000m – 6000m) Early humans and the odd dinosaur take the slow bus to Bognor Regis with the odd bus load of teenagers flying through for a Stag Night in Brighton.

The bus load of teenagers is the newly created Antarctic Bottom Water - sinking rapidly into the deep ocean.

Photo: Colourful plots of the data from the different CFCs indicating the average age of the water. Red means toddler, blue means middle aged and pink means Julius Cesar. The blue bit at the bottom is the relatively young Antarcitc Bottom Water flowing out through Orkney Passage.

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