By Samuel Jaccard,
geologist and member of the Oeschger Centre for Climate Change Research at the University of Bern, taking part in the ACE project Understanding the plankton’s strategy to survive.
We’re now stationed at Mertz Glacier (67°S, 145°E). The ship is literally docked against the glacier, since it has to keep its position for more than 8 hours for the submersible to be deployed. It’s somewhat surprising to see this huge ship with its bow stuck in the ice to make sure it doesn’t move. The footage recorded by the submersible diving under the ice tongue is broadcasted live on the mess’ TV. One can watch the submersible slowly making its way under the ice, sampling various organisms on the seafloor using its robotic arms. The image quality is absolutely stunning.
The weather has been quite good all day yesterday and in the afternoon today, allowing the helicopters to fly out a series of scientists onto the ice field. One of the teams drilled more than 12 m of snow and ice to reconstruct the climate of the past few decades in conjunction with the cyclic oscillations of the glacier. The movement of the ice plays an important role in modulating the regional atmospheric and oceanographic circulation.
The marine environment at the mouth of Mertz Glacier is also of great interest to oceanographers. Yesterday I told you how the ship had to fight its way through the ice pack. Surprisingly, there is no sea ice in the immediate vicinity of Mertz Glacier. The strong and unpredictable katabatic winds, blowing from the continent interior transport the sea ice away from the continent. The ice-free ocean loses heat, which induces convection, allowing warmer (relatively speaking) water from the subsurface to be transported upwards, melting more ice. These waters also carry high concentrations of nutrients such as nitrate and phosphate allowing the phytoplankton to grow.
The last essential ingredient to life here in the Southern Ocean, iron, is supplied in large quantities by the glacier itself. These polynya are characterized by the most productive environments around Antarctica and large amounts of carbon are being taken up from the atmosphere and eventually transported into the ocean interior. The production is so intense that the phytoplankton can only develop in the very surface of the ocean. The cell density is indeed high enough that the algae are preventing sunlight to penetrate to deeper depths. We have collected a full vertical profile in this environment yesterday and hope we can unravel some of the yet unknown mechanisms driving these particular, rather unique environments.