I haven’t done a lot of science over the last two days. We’ve been sat bow into force 8 winds in the Drake Passage, between Cape Horn and the Antarctic Peninsula, waiting for the weather to ease. I’m on the RRS James Clark Ross, a British Antarctic Survey (BAS) ship on a research cruise in the Southern Ocean. The main rationale behind the cruise is to investigate mixing in the Southern Ocean as part of the DIMES project (www.dimes.ucsd.edu). Jim Ledwell (WHOI) and colleagues are measuring the concentration of the catchily named tracer trifluoro methyl sulphur pentafluoride, 76 kg of which was released on a cruise in the Southeast Pacific 5 years ago and has been making its way eastwards in the Antarctic circumpolar current (ACC) ever since. Seeing how the tracer’s distribution changes in time and space provides information on how the water masses of the region mix, both horizontally, along density surfaces (isopycnally) and vertically, across density gradients (diapycnally). Jim’s machine is able to detect the tracer at concentrations as low as 10-17 moles/L (prizes available for the best popular science rehash of this ridiculous number in units of your choice – teaspoons per million swimming pools etc). Siobhan Moran and Mike Boniface from Exeter Uni. are sampling for CFCs which, because of their short and well documented atmospheric history, also provide a useful tool for tracing the pathways of water movement in the ocean.
As well as measuring something that’s hardly there at all and gas from old fridges there are several other things going on onboard. The usual suite of physical parameters are being measured from the CTD and Katy Sheen and Alex Forryan from the National Oceanography Centre, Southampton have been using a vertical microstructure profiler. This torpedo shaped instrument freefalls to the bottom of the ocean and apparently works a bit like a record player to resolve small-scale velocity fluctuations before rising back to the surface…if you’re lucky.
But as everyone knows, biogeochemistry is where it’s at. Who would want to perfectly resolve a parameter in the water column in minute detail in real time when you can painstakingly sample a handful of chilly bottles for something which will take months to analyse? Kim Pyle (Cardiff Uni) and I haven’t once doubted which side of the fence we stand on while processing carbon, nutrient and barium samples in our homely, windowless lab. I’m ‘monster’ing (monster is the word for sample in dutch) for inorganic carbon because I’m interested in how the Southern Ocean takes up, stores and transports carbon. Once I get back to the UEA I’ll analyse the samples for dissolved inorganic carbon and total alkalinity and look at the distribution of these parameters in the water masses of the Southern Ocean and compare them with results from previous cruises. I’ll also try to calculate how much of the carbon I measure comes from man’s activities.
The Southern Ocean sequesters huge amounts of carbon from the atmosphere to the deep ocean through two mechanisms. Firstly, the subduction of recently ventilated water- in other words, water that has recently been at the surface and has taken up CO2 from the atmosphere sinks underneath other water masses because it’s denser. This happens near the poles because the intense cooling makes the water really dense and forms deep water masses which spread out across the bottom of the world’s oceans. The second mechanism is biological export (things growing near the sea surface and then dying and sinking). Despite the importance of the Southern Ocean carbon sink we still find it hard to accurately quantify and are unsure how it will change in the future, largely due to the paucity of data in this remote region…. hence the coming to sea and getting cold fingers.
It hasn’t all been fun with pipettes, spreadsheets and bottles though- we’ve had to endure the odd whale, seal, penguin and albatross and we got to set foot on Antarctica when we visited Rothera (a BAS base) and Palmer (a US base) on the West Antarctic Peninsula. For more information on the science behind the cruise, some Antarctic exploration history and lots of pretty photos of icebergs and wildlife check out Katy and Siobhan’s excellent blog adropinthesouthernocean.blogspot.co.uk