HLY1502 letter 08 from Jim Swift
Sunday, 27 September 2015, 1:30 pm, local date and time (2130 27 September UTC)
77°27’N, 147°54’°W (over the Canada Basin)
air -2 degC / 28 degF
water -1.2 degC / 30 degF
wind 4 knots from WNW
on station 052 (a Geotraces ‘full’ station)
Dear Family, Friends, and Colleagues,
We experienced a Big Change on Friday: We left the Arctic ice pack. There are some ice bits around, and we are not far south of a few belts of broken up new ice, but we have left the pack behind. Another big change is that our internet access returned yesterday evening when we arrived at this station. Most of us have taken a start at examining our shore email - that part of the outside world making its return to our lives byte by byte, plus we can now send and receive somewhat larger emails (such as this one).
During the past several days the weather warmed to the upper 20s (in Fahrenheit degrees), which is easier to contend with. We had a fair bit of snow, but the ship puts out enough heat that the decks are less icy now. It’s a noticeable change. The ship can now transit day or night, and the work goes on (and on). We also have full darkness every night, and we are keeping our hopes up for a clear night with an auroral display. (At Sunday brunch today a couple of the grad students said they could see shifting illumination - presumably an aurora - behind the clouds last night.)
We are greatly pleased that the engineers repaired the second evaporator, so everyone has now caught up on laundry, are we’re back to regular dishes and silverware in the mess.
The work carried out by the CTD/hydrographic team is going quite well. Although steady vigilance on equipment, procedures, and data is always beneficial, few problems have been popping up. The lack of problems is partly attributable to the warmer weather we have experienced much of the past week. Those few degrees make quite a difference to sensors that are at risk in past weeks’ deeper cold but are fine at -2°C (28°F; i.e. temperatures near the seawater freezing point).
Healy’s track is now (and next week) over the deep, flat abyssal plain of the Canada Basin. During pre-cruise planning I had asked that this part of our transect from the Pole to Alaska be moved east a bit to help assure a ‘miss’ of boundary currents associated with a major feature in the bathymetry west of us called the Chukchi Borderlands and Northwind Ridge. The point was that there are indications from past data that boundary waters spread from there into the Canada Basin, and so I wanted to be sure that any ‘boundary water’ we saw was truly in the basin and not just an artifact of our coming close to the boundary itself. Preliminary data indicate this is all working out as planned, i.e. that we are seeing the boundary-separated waters well away from the boundary itself.
Observing and enjoying sea ice is one of the highlights of working in the polar regions. Thus when I realized that we would be leaving the ice - perhaps for good for me - I spent a bit more time up on the bridge. We do not see icebergs (glacial ice) here; the ice here is formed over the open ocean, shelf seas, and near river mouths. In fact, new sea ice has been forming the past few weeks as winter nears. To provide an idea of what I’ve seen this trip, I have included some ice photos. (The small file size versions that fit into email may not do the scenes justice, but it’s the best I can do for now.)
On a cold, windy day, new ice crystals form off the edge of solid ice and as they are blown away from the ice edge they form into windrows caused by a phenomenon called Langmuir circulation (photo by Bill Schmoker, Polar Trec):
If the wind is still, a thin sheet of ice forms, and then when that sheet is disturbed from the edge (say by the pressure wave ahead of the ship), it will fracture in right-angle patterns - a wonderful macroscopic effect of a microscopic aspect of ice crystals - called finger rafting (my photo):
Finger-rafting occurs on a wide variety of special scales. On this trip I saw some unusually large scale rafting - football field size (note the right angled ‘fingers’ in this photo I took):
“Frost flowers’ can form on undisturbed thin/new sea ice on a clear, cold still night (photo by Bill Schmoker, Polar Trec):
If brine is wicked from underneath into frost flowers, these can be clumpy looking (my photo):
Pressure ridges form when floes and sheets are pushed by the wind. These can pile up dramatically (just think how deep they reach!). Sea ice from near river mouths can be dirty. Here is a photo of one of the crew obtaining a dirty ice sample from a small pressure ridge (photo by Cory Mendenhall, US Coast Guard):
One of the most unusual ice formations I have seen was miles and miles of circular features in the ice - almost like giant pancake ice - in the young ice near the southern edge of the pack (my photo):
Then there are endless varieties of icescapes, some of which become dramatic when illuminated near sunrise or sunset. I will end this letter with a photo of mine which seemed to be of an almost alien scene:
All is well.
UCSD Scripps Institution of Oceanography