11 January 2012
This morning we are sailing where no-one has ever sailed before.
The Aurora Australis is in open water where, until February 2010, the giant tongue of the Mertz Glacier existed. It seemed a constant attribute of this coastline, a dominating geographical feature that was discernible even on small-scale maps of the continent. In the lee of that great tongue of ice, the katabatic winds that funnelled down onto Commonwealth Bay maintained a polynya, a beautiful Russian word for the belts of open water within the ring of ice that surrounds Antarctica. In 2010 the iceberg known as B9B (which is the size of theAustralian Capital Territory) was drifting westwards, having earlier calved from the Ross Ice Shelf, and it collided with the Mertz Glacier tongue and sheered it off. It is this new configuration of ice that has complicated our access toCommonwealthBay. The normal polynya has been partly replaced by fast-ice, which is ‘fast’ because it is sea ice connected to the shore. The icebergs now off Commonwealth Bay have also enabled the pack ice to accumulate there.
The exciting result is that we are currently over a sea floor recently liberated from beneath a glacier and in waters thick with phytoplankton. We are surrounded by ice floes inhabited by small groups of busy Adélie penguins. And on our horizon is the new face of the Mertz Glacier, extending for 60 kilometres. The Mertz Glacier is named after Xavier Mertz, the Swiss ski champion who accompanied Douglas Mawson and Belgrave Ninnis on the far eastern sledging journey and died of exhaustion and malnutrition on the return trip. He lies on the inland slopes of the glacier that now bears his name.
The ship is moving slowly between a series of collecting stations where instruments are lowered to measure changes in temperature, salinity, oxygen, carbon and nutrients, from the sea floor to the surface.
One of our voyage leaders, the physical oceanographer Dr Steve Rintoul, views the collision of B9B with the Mertz Glacier as a fascinating natural experiment in ocean circulation and sea-ice production. Every winter as the southern hemisphere tilts away from the sun, so much sea ice forms that the size of the white continent appears to double, only to shrink again in the summer, like a billowing creature rhythmically expanding and contracting. When the surface of the sea turns to ice, it releases a dense brine that plunges to the ocean depths, and that thrust of salty water to the sea floor is the piston-stroke that drives the engine of ocean circulation, sending cold Antarctic bottom-water northwards, even infiltrating the northern hemisphere. The Mertz polynya has been one of the prime sites of the production of Antarctic bottom-water, and it may have been the presence of the vast glacier tongue that made it so active. Steve and his team have discovered that, since the 1970s, Antarctic bottom-water has become less salty and less dense, perhaps as a result of increased inflow of glacial meltwater. What now might be the impact on salinity, circulation and biodiversity of the calving of the Mertz Glacier?
Earlier this morning, at 6 am, before we arrived in the waters liberated by the glacier tongue, we revisited a collecting station of the original Aurora a century ago. The sea temperature data gathered at various depths by the AAE with the aid of reversing thermometers continue to provide illuminating insights today. Our Voyage Leader Robb Clifton reports this afternoon that It feels like history is all around us as we do this work.
I am intrigued by the ways in which humans get drawn, sometimes unwittingly, into the environmental determinants of the continent of ice. So it was no accident that Mawson landed at Commonwealth Bayand that he should thereby condemn his expedition to heroic daily scientific recording in one of the most forbidding places on earth. It makes sense that the water should be open and the sea ice thinner where the offshore winds are strongest and most relentless. Thus ships are naturally lured into the homes of the blizzard.
We have been enjoying a little break in the weather just as they did this day a century ago. On 11 January 1912, the wind dropped at Cape Denison after a two-day blizzard and unloading was able to proceed in earnest. Captain Davis recorded that We have been getting our deck load off and will soon be more like a ship than a Xmas tree.
Biologist Jack Hunter made his first trip ashore: I went ashore with the first boat load. I was able to observe the site for our hut much better than on Monday evening. The site is a much better one than one would think, observing from the ship. A natural little bay forms a good landing harbour and the ice foot being only about five feet high, by cutting down three feet we were able to make an excellent landing. We had to firstly haul the stores etc from the boats on to the ice and it was quite warm working; in fact we were able to work in a single Guernsey. We then hauled the material on the sledges up towards the rocks where our hut is to be built – some hundred yards. There is a gentle slope running up from the shore & it was great fun tobogganing down the slope on the empty sledges.
Our own landing at Commonwealth Bay must await the passing of the next front and, as ever, the easing of the katabatics.