Iron in the Antarctic: Bad Luck

Bad luck

After about 17 successful deployments of our trace metal clean rosette, we were faced with a little tragedy. The trace metal rosette broke and we can no longer use it to collect our samples. This does not only affect us for the iron measurements, but other scientists on board were also relying on trace metal clean water for the work they are doing. So we had to explore alternative methods to collect water without contaminating it for iron and other metals.

We tried collecting water with the zodiac. We would lie flat on our stomach on the tip of the rubber boat while it was slowly going against the wind and current and dipping a clean bottle just below the surface. This way you can collect water that has not been contaminated by the boat. This worked relatively well, but it is quite time consuming and you can only get a surface sample and nothing from deeper in the ocean. Also when there is wind and a lot of waves it becomes quite tricky to not lose the sampling bottle or yourself for that matter. During the last zodiac sampling exercise when the sea was quite choppy, Rob was held by two guys while sampling from the tip of the zodiac and got very refreshed by waves splashing seawater of about -1.7°C (salt seawater freezes below about -1.8°C) in his face.

Sampling from the little zodiac in the open ocean. On this day the water was quite calm but the zodiac looks awfully small on the big ocean

Rob going to get some trace metal clean samples from the zodiac

In the mean time we had been pondering about a way to get more samples, also from deeper in the ocean. We still had two spare GO-FLO’s left and with the help of Tom, a marine technician on board the ship, Rob managed to rig the GO-FLO’s so that they could be attached to the cable by themselves and be closed by dropping a ‘messenger’. A messenger is a weight that wraps around the cable that you can then drop into the water. It sinks quite fast along the cable until it meets the first GO-FLO that is attached to the wire. The messenger then hits a bar that is subsequently pushed down and the GO-FLO closes and releases a second messenger to close the second GO-FLO that is attached to the wire below.

Left: Getting the GO-FLO’s on and off the wire takes a couple more hands, luckily everyone is helping out. Marine Technician Alec and scientist Anna are very happy they managed to get the GO-FLO attached. Right: Taking the GO-FLO back of after deployment, you can see the messenger weight on top of the white push bar that Tom made from scratch.

This was how trace metal clean sampling with GO-FLO’s was originally done before trace metal clean rosettes existed, but the GO-FLO’s we had were modified to fit on the trace metal clean rosette and did not have the necessary parts to be deployed on the wire. Luckily Rob knew how this was supposed to work and Tom is a very skilled craftsman who was able to make the missing parts. It took a bit of tinkering and improvements as we were going, but we now have two working GO-FLO’s that we can deploy on the cable. Based on the length of cable used, we know how deep we sample and we have successfully sampled to 750 m depth. It takes the messenger about three minutes to reach this depth, but overall the whole process is very time consuming. To get samples at six depths, we have to deploy three times and in between have to wait for the samples to be drawn from the GO-FLO’s , taking about three hours. With the trace metal clean rosette it would take only an hour and we would have twice the amount of samples! But at least we are still able to continue our work in this spectacular place on earth where Rob finally managed to photograph a lonely penguin.