Wednesday, 27 March 2013

Day 13 Land Ahoy!

The final CTD of the South America to Antarctica section is achieved at 7am. It is met with jubilation, elation and relief. Measurements have been taken along this same line every year bar 2 from 1994 - an unprecedentedly comprehensive time-series especially considering it is some of the most inhostpitipal territory known.

Photo Xing Feng (left) manages the Doppler Current Meter thingy while JB and Stevie take blob samples from one of the last casts of the America to Antarctica Section.
Along the way, the no no-nonsense, down to earth Xing Feng from the Massachusetts Institute of Technology has been managing a lesser known 4-letter acronym: the lowered ADCP. The ADCP stands for Acoustic Doppler Current Profiler. If you have switched off already because of all this fancy physics talk...bare with me just a moment...please...please. The ADCP send out an acoustic signal into the water. If the signal comes back faster than it was sent, we know the current is coming towards us if it comes back slower we know the current is moving away from us (this is known as Doppler shift). It is a bit like throwing a ball at your little brother. If he is running away scared the ball will hit him and not bounce back very quickly. If he is angry and running towards you in a fit of rage... the ball will hit you very hard (and probably so will he). If you have never played brandings or have never had a little’ll never get physics...sorry.

So the ADCP can tell us the current speed all the huh! We attach it to the CTD (yes I admit CTD is not a very good name as it does a lot more than conductivity-temperature and depth ...but anyway). As the CTD sinks and is hauled up, Xing Feng’s little Doppler thinging measures the speed of the water.  This helps us measure the Antarctic Circumpolar Current and tell us where the Blob of tracer might be heading and why it might be mixing.


 Photo: The North-East tip of Elephant Island with Cape Petrels in the foreground.

Once the last CTD is on board and the last samples have been taken we see an incredible sight: Elephant Island. As you’d expect, this morning the ocean is grey, windy, misty, frothy (etc...etc...insert adjectives) and...incredibly...a mountain juts out of the water and pierces the low lying clouds. It isn’t the kind of place one would like to be stranded on. Shackleton and his entire where crew where apparently stranded there before managing to row to South Georgia and then climb across it...quite a feat it feels like from our temperature controlled instrument room.

Photo: Navigation charts on the bridge show our path past Elephant Island. (Taken by Gwyn)

Day off today! Hooray! Time to explore this Bar thing they have on the boat...

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