21 November 2008

Stacy writing

Today we had an Expedition with a capital E.  All seven of us, plus volunteer Joe, headed out for a science assault on one of the icebergs at Cape Evans.  We were such a large group that we took 3 snowmobiles as well as our Pisten Bully and trailer.  We also needed the snowmobiles so that in case DJ’s extension of his time here was not granted, he could get back and pack to leave tomorrow.

When we arrived at the icebergs we cautiously drove to the area we thought it most likely that the iceberg had come from – from the Ross Sea.  Our goal is to look at the area of the seafloor that was disturbed by the passage of the iceberg.  As the ‘bergs are driven by wind and currents into shallow water, they plough across the bottom of the sea, tearing up sponges, ripping out anemones, sending sea stars flying, and gouging into the gravel and rocks beneath.  Okay, so it doesn’t happen really quickly, it can take weeks to months or even years for icebergs to move across the seafloor, but to a sponge that may be living for thousands of years, that’s still pretty fast.

Our teamwork was amazing as people saw what needed to be done and pitched in.  We are all familiar enough with the deployment operation now that the whole operation moves very smoothly and with almost no supervision.  Cameo and I drilled the holes.  DJ set up the computers and control room.  Bob set up the tether system and vehicle.  Joe did a little (or a lot) of everything, wherever an extra pair of hands were needed, which was everywhere.  Marco, Francois and Scott dealt with the new navigation challenges of this location.  Theirs was the tough part – the GPS cannot “see” the base station at McMurdo from this location, so in order to know where we are, we need to establish our frame of reference.  This is done by setting the GPS receiver in one place and letting it collect data for half an hour or so.  The longer term average of the location is more accurate than a quick measurement.  In the mean time, to get us started quickly, they measured the distances between our holes with a tape measure.  Then there was some simple trigonometry, well, it should have been simple, but because everyone was cold, and writing in small notebooks, it took a while.  Eventually though, by two separate methodologies, they came up with two sets of numbers that agreed to within 1 mm.  As the dive went on using the local frame of reference, Scott went out and accurately surveyed the locations of each hole, which we can later combine with the longer term data to shift to the real world frame of reference.  He had one small delay when he went to wipe a snotcicle off his nose and allowed the antennae to dip and lose contact with the satellites.  He had to start the 8 minute process over.

Meanwhile, in the control room, a wonderful perspective of the seafloor was developing.  We know that this ‘berg came in last year, as it was not here last season.  And the drag marks across the seafloor were churned up gravel with not a bit of life remaining on it.  There has not been enough time for animals to move into the newly opened areas.  Away from the trail of the iceberg there were sponges galore, seastars, tunicates, bryozoans, a full rich community like the one we saw at Cape Armitage at the same depth.  The contrast was quite amazing.  The berm pushed up at the edge of the iceberg trough was a high jumble of rocks, overturned sponges, and gravel piles.  I had thought that there would be one stright path where the iceberg had come in and gotten stuck but it looks instead like it bounced around for quite a while here before getting stuck in the forming annual ice.  The areas of destruction are mixed and churned, an interaction between the bathymetry of the seafloor and the underwater shape of the ‘berg.

We did not quite get to the direct contact area between the iceberg and seafloor.  It was very overhung and that caused us to lose navigation as the signals bounced around between ice and tranducer.  We remembered the overhangs and holes on the iceberg above water we were leery of driving where we did not know where we were going -  the worst thing would be to get stuck and not know how to retrace your path out.  But the textures in the surface of the ice were beautiful.

After the welter of tumbled and confused seafloor and frantic collection of as much data as possible for several very intense hours it was a deep relief to finally crawl out of the dark Pisten Bully into the bright Antarctic sunshine and stretch a bit while recovering the vehicle.  A long and successful day working towards our second science goal left us tired but very happy with our progress.

I hope that your steps today were forward!
Smiles, Stacy