In the lee of an iceberg
The Gentoo cruise is now a week old and there has been lots of activity since we left the Falkland Islands. The iRobot glider was today deployed for the second time. This time the glider should remain in the Weddell Sea until the end of February, when the RSS James Clark Ross will collect it after visiting the Halley base. The iRobot glider, lovingly nicknamed "The Flying Pig", is a special variety and is a little bigger than usual. That's because it is carrying two instruments that are not normally found on gliders. One is used for measuring current speeds and the other is used to bounce sound off the little bits and pieces in the water to estimate what is there. It is this second instrument that is of most interest to me as my colleagues and I at the British Antarctic Survey will use it to detect krill so that we can understand more about how these important animals live and the paths that they follow.
Krill are important in this ecosystem because of how much of the wildlife that they support. They are a major source of food for penguins and whales and they form swarms of millions and millions of individuals. Using acoustic instrument (devices that use sound) on the ship we can see that the swarms often stretch for hundreds of metres. Depending on the time of day, the krill may be eating phytoplankton near the surface when it's dark, or hiding hundred of metres deep down when the sun is high in the sky. We have been using nets to capture a few hundred grams at a time, storing some for scientists in Cambridge and measuring others to analyse their populations. Some swarms are made up almost entirely of juveniles and some might have mostly female adults, for example.
Euphausia superba (Antarctic krill) ... whale food!
I have been to sea many times in Europe and North America but working in Weddell Sea with GENTOO has presented sights like I have never seen before. Yesterday we came close to the coast and very surrounded by icebergs that seemed as though they had been carved by sculptors and they had the most beautiful blue shades. Today, we spent the morning working in the shelter of a giant iceberg. The iceberg was estimated to be about 40 km long and 37m from the sea level to the table-like top. Because we only see about 10% of the ice, the scale of the berg is hard to imagine, yet it is likely very small compared to the glaciers from which it broke free. After we had finished with the physical measurements and the net sampling we set sail for the next site.
Not all icebergs are created equal. This one is huge.
During the next CTD (Conductivity, Temperature, Depth) sampling, while Sophie and I were tidying cables on the back deck, we heard a slapping noise and at first thought that it was the sound of gentle waves breaking against the side of the ship, like we often hear. It struck us as odd though because the sea was calm and the ship was not moving much. When we heard the rush of air, we knew what up so ran (don't tell the captain that we ran!) to the side only to find three humpback whales swimming under the ship. Humpbacks are one of the animals that eat krill. The clear water allowed us to see their white fins as they swam to the surface to take a breath. They were only a few metres from them and could see their entire bodies from fluke (tail fin) to the tip of their nose. Before long, nearly all the scientists and crew were crowded around to see this rare sight. The whales, it seems, were just as interested in us as we were in them and wanted to get a good look at us too. They swam slowly to the surface, straight up and poked their long jaws out of the water in a behaviour called "spy hopping". From this close range we could see the barnacles growing on them and the blow towered over us. The highlight came when one of the whales came to the surface and gave us a slow roll, sticking his enormous white fins in the air almost as though waving at us then diving quickly. The three humpbacks must have decided that they had learned enough about us because shortly after this amazing display they swam to port (left if you're facing forward) and after showing us their flukes high in the air, swam into the distance. We were truly privileged to witness such a display.
A humpback dives near the ship. Each fluke is like a fingerprint and unique to the whale.
We all went back to work with big smiles on our faces and the whales were the main topic of conversation for the rest of the day. The wonderful part of a job like this is waking up in the morning and not knowing what may come. The day might be misty with no visibility or we may cruise through some ice, or perhaps have a spectacular sunset. On the really, really special days, like today, we might be lucky enough to see one of the most amazing animals on the planet.
Back to the journals.