USCGC Healy Cruise HLY-1502

US Arctic Geotraces

Weekly CTD/Hydrographic Team Report 07

from Jim Swift, UCSD/SIO, CTD/hydro team scientific leader at sea

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)

Note: This is a hydrography-oriented report from Jim Swift, who is working with the SIO Oceanographic Data Facility (ODF) CTD/hydrographic team on the US Geotraces Arctic Ocean expedition led by Dr. David Kadko, FIU, chief scientist. This is not a report from Dr. Kadko or the other science teams.

Dear 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.

During the past several days the weather warmed to only a few degrees under freezing, which is easier to contend with. We have 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. 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.

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. We even saw temperature-salinity intrusion features and a small decrease in light transmission at the appropriate level at a propitiously-located Repeat Hydrography station, signs of boundary water intruding into our basin-interior location.

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. I sent a selection of ice photos in my weekly outreach report. For this science report I will include a few favorites. (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 generated by 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 spatial scales. On this trip I saw some unusually large scale rafting - football field size (note the right angled ‘fingers’ in this photo I took):

All is well.

Jim Swift

Research Oceanographer

UCSD Scripps Institution of Oceanography