As winter has settled in Antarctica, we can see the changes to the landscape. Rock that was exposed during the summer is now covered with thick layers of snow and many of the buildings on station have snow drifts build up to the roof but one of the most striking changes is the formation of sea ice.
During summer the water temperatures in the Ryder Bay are about 2°C. Unlike fresh water, sea water freezes at -1.8°C owing to its salt content. So after a few weeks of low temperatures and little wind, the surface layer of the sea was cold enough to freeze and the area surrounding Rothera point was completely covered with ice.
This brings several changes to the station; the most noticeable of all is the absence of animals on land, as seals, penguins and most birds follow the edge of the sea ice where they can still hunt and most importantly, especially for seals find holes in the ice through which they can breathe. However the area has also become almost eerily still, as the normal background noise of waves breaking on shore has ceased. For the marine team, sea ice brings a significant change in the way we operate. Where usually we would travel by and dive of a boat, we are now using skidoos and sledges to get to our site and instead of dropping of a boat we are now sliding in a hole in the ice. Once we established that the ice is thick enough for safe travel (ca. 35 cm) we bring a chainsaw to our desired dive site where we cut a hole in the ice (this is very easily said – however took in fact almost a day to complete, as chainsaws apparently aren’t keen on very cold conditions and seawater – who knew?).
Sometimes these holes get discovered by seals who then become very possessive of them and will not let the divers safely enter the water or even worse re-surface. Because of this we need to cut a secondary hole as a back-up in case the primary ice hole becomes occupied. As normal, preparations to go for a dive entails a lot of faff and diving through the ice means even more faff. We put hot water bottles in with all the vital equipment such as our masks and our hoods and gloves, our dive kit is being covered with a thick blanket during transport and we are squeezing ourselves in even thicker undersuits – which makes moving on land feel like being drowned in jelly.
Generally by the time you are ready to go in the water you resemble a bug on its back on hot tarmac. Your kit pins you down and is too heavy to move when sitting down, you feel hot and sweaty despite the cold temperatures and extremely uncharitable with anybody attempting to prolong your agony (who needs pre-dive checks anyway – you know you’ve opened your air cylinder!… or – have you?).
Dropping through the ice hole brings a feeling of immediate relief, not only are you cooling to an acceptable temperature but movement becomes so much easier as the weight of the dive kit and suit are removed.
After this first feeling of liberation, we become aware of our surroundings and discover that all the effort we have just gone through was completely worth it. The water underneath the ice is incredibly clear with up to 30 m of visibility, we are surrounded by grounded icebergs frozen into the sea ice rising up imposingly from the sea bed. Some are perfectly smooth and rounded, some are more perforated and degraded showing the impact of the elements and time. Looking up, icy stalactite are hanging on the ceiling formed by the sea ice above us and the water itself is sparking with ice crystals.
It feels like the world under water has come to a standstill – yet is still supremely full of life and colour in an otherwise black and white and very still world. There is no current or waves to waft up the sediment or disturb any of the animals. The sea floor is covered in sea urchins (red spikey things), Anemones, Sponges, Nematodes (fairly disgusting, almost eel like worms), brittle stars, lots and lots of limpets and the occasional fish. All of these animals are incredible adapt to this environment and are fantastic in surviving these extremely harsh conditions.
The filter feeders are able to starve over almost 6 months, as the plankton bloom (all the teeny tiny algae in the water column) is intense over the summer months, but also very short lived and one reason why the water is so clear underneath the ice, is because there is virtually nothing in it at the moment that mussels or sponges could feed on. Everything in this environment has to cope with temperatures below freezing point. Marine mammals obviously are well insulated with blubber, invertebrates or fish however, manage differently. Some fish have anti-freeze proteins in their blood, and many invertebrates have proteins that prevent their cells from freezing while the space outside their cells freezes.
This underwater world is incredible and full of wonders, many of which we haven’t even discovered yet. Diving next to gigantic icebergs and sharing the world of these small survival artists even for the shortest amount of time, must surely be one of the greatest privileges about my time here.