First contact with the grounding zone

January 9, 2015

We got our first peek at the grounding zone using an instrument we call the Doctor, which has a lamp at the bottom and a camera trailing behind.  Members of our team lowered the Doctor down the borehole and brought it back up again, gaining a couple hours' worth of footage of the ice walls and of the cavity between the bottom of the ice shelf and the ocean floor.  From these video images we were able to tell that the hole was wide enough for all 750 meters of its length that it would allow our instruments to pass through.  We were hoping to also find out the depth of the ocean cavity, which decreases the closer you get to the grounding zone itself.  Towards the bottom of the borehole, the camera did not get enough light to see exactly where this transition was.  We would have to wait another 4 hours for the conductivity, temperature, and depth (CTD) instrument to bring us that answer.  Once we were close to the seafloor, the reflected light was sufficient for the camera to bring us images of a muddy bottom with rocks of a range of sizes littered on the surface.

The Doctor

Slawek Tulaczyk and other scientists look at the Doctor footage

Jill Mickuki, a microbial ecologist at U Tennessee, ran the CTD instrument down the hole next, when we learned from a contrast in salinity (we had made the borehole by pumping hot freshwater) and temperature (the seawater is around -1.2 degrees Celsius here) that the ocean cavity was 10m thick.  We were thrilled to get so close to the grounding zone and excited to start collecting samples.