By Sandy Zicus, Antarctic Climate & Ecosystems Cooperative Research CentreWe’re now a bit more than three weeks into our six-week Sea Ice Physics and Ecosystems eXperiment (SIPEX) adventure.
On 18 September, we entered a section of land-fast ice surrounded by huge grounded icebergs, some of which have walls up to 50 metres high. It was impossible to capture the true scale with a camera (although most of us kept trying), especially when there was nothing of a known size in view to serve as a reference.
Land-fast ice, often called just ‘fast ice’, is sea ice that is attached to land or to grounded icebergs. Fast ice is a bit different in character from regular sea ice. It is more or less permanent in one area and is generally not moved around, broken or piled up as much by wind and currents. It grows slowly by freezing from the bottom, so the ice crystals are more uniform and tend to grow in a columnar fashion. The fast ice here was much easier to walk across and pull sleds on because the surface was smoother and more even than at our previous stations. A view of the underside of the ice would also show the same, relatively level plane.
When we headed out onto the ice after lunch, it was beautifully sunny but extremely cold with an air temperature of -21°C. Combined with 25 to 30 knot winds, we had a wind chill factor of nearly -50°C. That seemed absolutely tropical, however, compared with the following day when the weather started to deteriorate. The Remotely Operated Vehicle (ROV) team had drilled their hole in the ice the previous day in preparation for launching the vehicle. It’s a fair amount of work to chop a hole large enough for the ROV, so they weren’t about to let the chance go by – weather or no weather.
Before deploying the ROV, they had to clear out all the new snow and ice that had partially filled the hole overnight. The ROV was then brought out wrapped in a blanket to keep it from freezing and quickly dropped into the water. After getting it into the relatively warm ocean water (the air temperature was - 22°C, the water only about -1.8°C), the team poured warm water from a water bottle over the optical sensor to remove any ice crystals that had formed and sent the ROV on its way.
The ROV pilot had the easiest job in some ways because he was controlling the unit from a computer inside the ship. The ROV was sent out along a predetermined survey line on a 350-metre tether. As it moved along under the ice, it used a number of instruments to record data about the environment under the ice.
Footage from the video camera can be used to study the structure of the underside of the ice, and look at the abundance and behaviour of krill. A combination of a depth gauge on the ROV and an upward-looking sonar (which gives information about the depth of the underside of the ice) can be used to estimate ice thickness. Finally, an instrument called a hyperspectral radiometer measures the wavelengths of light that manage to penetrate the ice. Ice, snow and algae growing in the ice will each absorb different wavelengths, so this data can give us an estimation of the amount of algae (an important food for krill) living in the sea ice. The next day was spent waiting as the winds remained a persistent 30-40 knots from the east all day long. The ship was cocooned in an envelope of white and there was no horizon to be seen.
Sunshine, mild temperatures (-15°C) and almost no wind the following day made our next ice station a pure joy. We arrived at the southernmost point of our journey early on the morning of 21 September after navigating west along the fast ice edge all night. The ice at this station was different from anything we’d seen so far – it was fast ice, but formed of a jumbled mess of huge ice blocks that had been crunched together and stacked up, creating long twisting ridges. There was very little snow cover, in most places less than 1 centimetre, and the ice blocks glowed varying shades of blue and turquoise under the sun.
While incredibly scenic, the heavily ridged ice made work difficult for many of the teams. The ROV team had to drill 3 different holes before they found an area where the large drill they were using could get through all of the blocks of ice. The oceanographers ran into similar problems with their equipment.
The team on the transect survey also had a challenging time. The jumbled blocks of ice made many of their measurements very difficult. There were often gaps filled with water between the blocks, making it difficult to know when a drill had gone through the bottom layer of the ice and messing up the signals received by the electromagnetic (EM) equipment. Some sections of piled up ice blocks were more than 3 metres thick and, therefore, too deep to drill through.
Things were to get still more complicated in the next few days. During the stormy weather, a large ocean swell had passed through the area we were in, fragmenting the ice pack. We could see from ice reconnaissance flights along our intended route that the pack was even more broken up to the north of us. This meant that we had to adjust our plans and headed farther west instead of north. Early morning found us just north of the tip of the Dalton Iceberg Tongue, a graveyard of grounded icebergs connected by fast ice that extends out from the Antarctic continent.
We took another helicopter flight to check out the nearby surroundings and try to find an appropriate site for the day’s ice station. We flew about 23 kilometres to the west of the ship without finding any ice that was suitable for an ice station. Finally, we decided to have a short ice station right near the ship to give the biology teams a chance to gather a few ice cores for analysis back on the ship.
We started moving again by lunchtime, but progress was halted in late afternoon when we became wedged in the ice. Loud grinding noises and shuddering movements informed us that we had driven into an ice floe that was under a great deal of compression. The pressure jammed the ice against the sides of the ship and we could move neither forward nor back. Fortunately, the crew managed to free us from the grip of the ice after a couple of hours of manoeuvring the stern of the ship from side to side.
On Monday, 24 September, the afternoon’s reconnaissance flight showed a large, fairly level ice floe with good snow cover to our south that appeared suitable for our next ice station. In view of the blizzard that was forecast, we stopped about 10 nautical miles to the north of the floe to wait out the weather. The following morning brought 50 to 60 knot winds and blowing snow.
It began to clear in early afternoon; however, the improvement was short-lived. Around 3 pm, the easterly winds shifted and began blowing from the north. This started pushing ice that was to the north of us southward. Soon we were hearing the ominous, but familiar, crunching and scraping noises against the hull of the ship. We weren’t moving, but the ice was. The movement of the ice from the north was causing the pack around us to squeeze against the hull. It’s not a good idea to just sit and wait when the ice starts compressing around you (think Shackleton), so we turned and started working slowly northward.
The north winds and snow continued into the night, so we hove to in an area of thin ice and waited for the weather to clear. In the morning, radar images showed that the ice to the south of us was blocked off by a large pressure ridge that would be impossible for the ship to penetrate. We therefore spent most of the day picking our way slowly westward through a jumble of heavily ridged ice, broken up floes and sections of flat, thin ice. We finally located a suitable floe in the early afternoon. By 4:00 pm, most teams were out on the ice setting up their stations.
Every ice station has been different and had a different feel to it. Here, the ice was rather thin and brittle. Heavy snow cover in some areas had depressed the ice so that sections had been flooded with sea water under the snow. We had to be careful walking to avoid sinking through the snow and into knee-deep water. While not particularly dangerous, this could be quite unpleasant (as at least one member of our party found out). The average ice thickness was only about 45 cm, so we couldn’t use the heavier machinery on it. The station was planned to last two days, but the floe began to break up during the night and all of the equipment had to be hauled back to the ship at 4 am. A few people managed to get out and finish their surface measurements later in the morning and the good weather allowed the helicopters to complete several radar and laser altimetry flights. We then set off in search of better ice.
As of now, we’re still searching. We’ve been heading west-northwest but have encountered a section of heavily ridged ice that is making progress very difficult. We are currently stationary, waiting for the floes to split up a bit from the southerly winds before continuing towards the northwest.
The Sea Ice Physics and Ecosystems eXperiment (SIPEX) research is an international project that is jointly organised by the Antarctic Climate & Ecosystems Cooperative Research Centre and the Australian Antarctic Division. It involves 45 researchers from ten different countries and is part of a larger International Polar Year (IPY) project looking at sea ice in the Antarctic.
SIPEX is an interdisciplinary program that is examining interactions between sea ice structure, sea ice biology and the ocean food web. It departed Hobart, Tasmania on 4 September and will return on 17 October.