Hi Simon We have had a dive research program in Antarctica since 2001. Our latest experimental work involves securing incubation chambers to the underside of the sea ice to measure the metabolic rates in the algal mat. We have a problem getting the chambers in place without disturbing / dislodging the mat with our Scuba bubbles and I was thinking about O2 rebreathers for this work. The working depths would not exceed 6m as new sea ice is only 2m thick and even old multi-year sea ice is normally only 4m thick. Our dive camps have heated polar haven tents over the holes so divers and equipment stay warm prior to dives. Sea temp is -1.95C. I was wondering if you were able to point me in the direction of a suitable, simple, robust O2 rebreather (I assume someone like draeger still make them??), and where I might start looking for training. Thanks for your time. Best ..Rod