Tuesday 4 November 2014

Measuring Iron

After a crossing the stormy Drake Passage and feeling a bit seasick, we have are now near Antarctica where the sea has been much quieter and filled with ice. You can see where the ship is on this website: http://www.sailwx.info/shiptrack/shipposition.phtml?call=WBP3210


The shore of the Antarctic Peninsula  with small icebergs floating around                      The view from the snow covered back deck

There have been plenty of seabirds such as albatrosses and penguins, but we have not yet spotted a penguin. Other people on the ship have, so will keep an eye out for them! This is not so easy though when you spend most time inside our bubble where the iron measurements system is now working around the clock.
Here you can see our Flow Injection Analysis set up that we use to measure the concentration of iron. On the left, inside the flow bench, is the autosampler with small bottles full of different seawater samples. It gets pumped around into the network of small white tubes you see in the middle. Here the iron in the seawater catalyses the reaction between luminol and peroxide. This reaction produces blue light that we can measure, more light means more iron. The lowest concentration we have measured so far is 0.03 nanomol per litre of seawater (0.03 x 10-9).
Before we can measure a seawater sample, we have to collect it from the ocean. We use a trace metal clean rosette that can collect water at 12 different depths in the ocean. In the next photo you can see the rosette on deck, just before it gets deployed and in the ocean on its way down to the deep. The grey tubes are called GO-FLO samplers. They are almost completely made out of plastic and do not contaminate the seawater with metals. The GO-FLO samplers are open on the way down and when the deepest point has been reached, one can close the samplers on the way back via a computer on the ship. This way we get 12 samples from 12 different depths.

The trace metal clean rosette on deck (left) and in the water (right). The rosette is suspended on a kevlar cable that is also free of metal. On the inside of this cable is the communication wire that allows closing of the GO-FLO’s as well as the reading of the sensors that are attached to the rosette.
After the rosette comes back on deck, the GO-FLO samplers are taken of the rosette and carried to the trace metal van. This is a modified shipping container, that just like the bubble, has clean air inside that is free of dust and metals. To keep it this way we dress up in very fashionable looking suits as you can see in the next photos.

Rob inside the trace metal van wearing a trace metal clean suit. All 12 GO-FLO’s are hanging on the wall and are ready to have water drawn out of them for iron analysis on board the ship. In addition we take samples to take back to the University of Otago to analyse them for other metals such as manganese and zinc.
Inside the trace metal van it is very easy to forget were you are, but when you come out, you might all of a sudden be greeted by an amazing vista of melting Antarctic sea ice! In the next blog we will write about life on board the ship.

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