20 July, 2015 Rothera
As a small number of us (19) countdown to Midwinters day (June 21st) which for us is the darkest day of the year, the northern hemisphere will celebrate the longest day of the year. Here at Rothera Research Station we said goodbye to the Sun on May 25th and currently have about three-and-a-half hours of twilight in which any outside activities such as diving can take place.
With air temperatures of between -16 and -22ºC and sea temperatures of -1.8ºC (freezing point for sea water) the sea around us has frozen. Once the sea-ice thickness reaches 20cm then Field Assistants head out onto the sea ice wearing a boat suit (just in case), skis to spread the pressure on the ice and a drill to check the consistency of the sea-ice thickness. Every Antarctic winter is different and therefore every year brings different quality of sea ice around Rothera. Looking back over the last seven years both the air temperature and weather have been very different during the winters and the duration of winter sea ice extremely variable. This winter we have seen many weeks of calm, stable and for this time of year cold temperatures (-24ºC at one point) which means the sea ice has come early.
Once the sea ice is 25cm thick the Rothera Marine Team – Terri Souster (Marine Biologist), Sam Poutney (Marine Assistant), Paul Samways (Boating Officer) and Emily Venables (Diving Officer) – can head out onto the ice to cut holes with our Winter Station Leader (Dave Hunt as Chainsaw King!).
Life is much easier once the ice is 30cm thick as this means we can drive a skidoo and sledge with all the heavy equipment onto the ice to within a metre of where our dive holes will be, so no having to drag heavy equipment through deep snow. We are lucky to have the mechanical aid of the chainsaw – Antarctic seals, such as The Weddell seal, use their teeth to break through sea ice to make a breathing hole. It is no surprise, therefore, when we pull the newly cut ice blocks out from the ice that on occasions up pops a seal happy to get a chance to breathe. For this reason we always cut two dive holes about 20m apart as seals can become a bit aggressive if you try and take back what they now claim as their breathing hole. Once the dive holes have been cut we go out daily to break out newly forming ice and maintain that dive hole or if will refreeze and then its another outing onto the sea ice for the chainsaw.
With ice diving, there is one way in and one way out (well two really). The visibility of the sea water is extremely clear, it can be up to 100m which is some of the best visibility in the world. You can walk upside-down under the ice and hear the creaking of the sea ice as it moves with the tide. The diversity of marine life in Antarctica exceeds that of The Arctic and is comparable with temperate and non-reef tropical regions with a large range of colours scattering the sea floor. We are very fortunate to have this opportunity as Rothera is one of the only Antarctic stations to dive all year round, allowing us to carry out marine research in both summer and winter seasons.