Under The Shelf
A snow drift greets us inside the fish hut as we arrive. (photo: Peter Kimball)
Yesterday was a great day out at the fish hut, but it did not begin exactly as we’d planned. I headed out with Britney, Chris, and Justin to deploy Sunfish. We arrived at the hut to find it filled with snow. One of our fish hut doors doesn’t close quite right, and the weather reached Condition 1 the night before. It only took a few minutes to shovel the snow out of the hut.
The real pandemonium began just after we deployed Sunfish. As Sunfish descended through the hole, Justin and Britney said “wow, that’s a lot of platelet ice!” Sunfish had destabilized a large volume of platelet ice around the bottom of the hole that then floated up into the drill hole. We put Sunfish in station-keeping mode and worked to remove platelet ice from the hole for about half an hour. Bucket after bucket and net after net, we added to the massive “platelet glacier” outside one of the hut doors until the ice pack was loose enough to run the tether freely. Only then could we actually begin our mission. Even more ice had to be removed before we could recover the vehicle later.
This was the first time we’d run the vehicle since taking out its Doppler sonar for current profiling almost two weeks ago. In that time, Chris made some improvements to the vehicle navigation software and pilot interface, we surveyed the alignment of the fish hut, and we used the Doppler current profiler and tide model to plan operation times with low current velocity. All these things came together yesterday to yield our best Sunfish mission yet.
Our timing with respect to the water current was excellent – we experienced only minimal control disturbances, even with a record 250 m of optical fiber and high-strength line paid out in the water behind the vehicle. We traveled 200 m from the drill hole, and got under the Ross Ice Shelf for the first time. There, we observed a 20 – 30 degree slope in the ice ceiling overhead, down to a water depth of about 13 m. We also found a high concentration of ~25 cm fish under the sea ice just outside the shelf. Finally, at the end of the mission, the improved navigation software put us directly beneath the drill hole for an efficient recovery.
Here’s an excerpt of the live feed (with Chris’s updated pilot information overlay) from Sunfish, taken just short of the shelf edge, where the fish density was highest:
And, for our friends in the field with limited bandwidth, here’s a screenshot:
Pilot’s view screenshot as Sunfish approaches the edge of the McMurdo Ice Shelf, near the SIMPLE field site.
The only bad news from the day was that my GoPro (attached to Sunfish) stopped recording about 7 minutes into the dive, and somewhat more seriously, that the platelet ice accumulation beneath our field camp has stacked up to about 6.8 m water depth, enough to completely “bury” the ARTEMIS culvert we installed with the drillers and carpenters a little over a week ago.
By the end of the day, the weather was beautiful and Mt. Erebus was looking spectacular. We heard on the radio that the C-17 was approaching just as we were packing up to head back into town. With each incoming flight, the station population swells. Over winter, the population is around 150. During Winfly (when we arrived), the population is around ~200 – 300. Population peaks at ~1200 – 1300 at the beginning of the summer season. Many groups then depart to field camps and to Amundsen-Scott South Pole Station, leaving the McMurdo population to stabilize at about 800 for the majority of summer.
The next two flights will bring fresh vegetables, ARTEMIS, and three more of our field team members!
Mt. Erebus looks excellent in the evening light. (photo: Peter Kimball)
The C-17 passes close to our field site on landing approach. (photo: Peter Kimball)
Reporting by Peter Kimball