Wednesday, February 25, 2009

Days 31-33

The next day after our visit to Halley, the ship left the ice shelf to head back to the SASSI moorings line. We left the "winterers" behind, the Halley staff who are going to spend the winter there, who were waving goodbye... their friends on the ship, the Halley staff who are coming back with us to civilization.

Even the Emperor penguins came to say goodbye ! I wish them to survive the harsh winter conditions, and hope to see them again next year...

During the transit to the SASSI line, we prepared the equipment for the last mooring, and rigged the PIES (Pressure Inverted Echo Sounder, in white in the picture below) for deployment.

The next day we had reached the SASSI line, and started some CTD/ADCP stations to see where to deploy the last SASSI mooring. As the ship was sailing offshore, we lost sight of the ice shelf for good. I will miss the beauty of it, but hopefully next year I can see it again... The results were quite different from those obtained 3 weeks earlier, with the core of the westward surface current farther offshore. We decided to deploy the last mooring as deep as we could with the available cables, which was in 2600 m depth. The mooring was 2100 m long, its top end reaching 500 m depth, shallow enough for the top ADCP to measure currents up to the sea surface, but deep enough to avoid the instruments being smashed by passing icebergs. We started deploying the mooring around 9 pm, surrounded by complete darkness. It was the first time since we left the Falkland Islands that I saw a dark sky at night !

We finished deploying the mooring around midnight. We then resumed the CTD/ADCP stations to decide where to deploy the PIES. In the meantime I was running a set of tests on the PIES, to check it was working properly, but when checking the vacuum level inside the glass sphere containing the electronics of the instrument, I was horrified to see that there was almost no vacuum at all, contrary to what I had seen 3 weeks earlier ! We could not deploy the instrument in this condition. We had to reseal it first, but we needed a vacuum pump strong enough to make the required vacuum. We asked the ship's engineer whether we could use the ship's pumps, but he said it would not be feasible. We therefore decided to cancel the deployment. I went to bed at 5 am really disappointed. I slept until 3 pm, and checked the altimeter inside the glass sphere again, to find with amazement that the level was back to where it had been 3 weeks earlier ! The only explanation I could see was that because the PIES had been staying outside for some hours before deployment, the temperature inside had dropped, therefore since the volume was constant, the pressure must have dropped too (recall PV=nRT). Therefore the altimeter level had increased, but since at room temperature it was already close to the maximum value it could display, at below freezing temperatures the needle had rotated counterclockwise past the 0 mark, indicating a low altitude and therefore a weak vacuum !! But during the time I slept, the PIES was in the wet lab at 20 degrees Celcius, and the altimeter reading was back to its "normal" position. Very bad design !!! The PIES manufacturers confirmed by email that this is indeed what must have happened. So the PIES was working fine, and we would have deployed it if only I had not checked this damn gauge ! What a frustration... We decided we would deploy it anyway elsewhere, but we were now too far from the SASSI line to turn back, and in too deep water to deploy it now, so we will have to wait until we reach the South Orkney Islands to deploy it.

Saturday, February 21, 2009

Day 30

Today we visited the English antarctic base Halley. Our shuttle consisted of a platform mounted on skis and pulled by a snowcat. The base was only 15 km away, but it took our shuttle about 50 minutes to complete the journey. With -16 degrees Celcius and a bit of wind, I was pretty cold when reaching the base !

The first sight we got of the base was a row of multi-colored containers. As the wind blows around the containers, the snow is removed along their sides, so they must be sufficiently spaced from each other to prevent them from falling in their neighbors holes. The trail we followed was marked with barrels every 50 m or so, reminding us that visibility can get very poor in bad weather conditions.

Finally there ! Paris was not indicated on the sign post. Ah, these British people...

Below is the main building where the living quarters are located. We ate lunch with the base crew there. Not as good as on the ship... But not too bad for such an isolated place !
The buildings are built on stilts to reduce snow accumulation due to wind transport, but the stilts must be extended every year to prevent the buildings from being buried under the falling snow anyway. Earlier versions of the base, the first one of which was built in 1956, were simple buildings built directly on the ice, but had to be abandoned and replaced every decade or so because they were buried and crushed by the snow.
Below is one of the science buildings. It is located about 200 m from the main building, but imagine having to walk there back and forth every day in the dark during winter with temperatures reaching down to -50 degrees ! Brrr...

Inside is the ozone lab, where they measure the ozone content of the air column above the base. It was there in 1985 that scientists first measured the ozone depletion of the Antarctic stratosphere, the famous ozone hole.

The present base, Halley V, is drifting westward with the ice shelf, and has already entered an unstable area which could suddenly detach and drift away as icebergs. Therefore, a new base will be installed further east around 2012. Some building modules (see below) have already been built and await their turn. They are designed with hydraulic stilts, which can be extended much more easily than the present stilts, and the stilts are mounted on skis so that the buildings will be relocatable, to maintain the base location despite the continuous ice flow motion (about 1-2 m per day).

We then returned to our ship, squeezing ourselves inside the snowcat to avoid freezing in the platform behind. We left some of the crew that will spend the whole winter there, isolated from the rest of the world for months... The rest of the crew joined us on the ship, and partied joyfully to celebrate the end of their work in this extreme environment.

Tomorrow the ship will sail away, and we are going to deploy our last SASSI mooring and our PIES.

Friday, February 20, 2009

Days 27-29

Finally, our work had to be stopped momentarily to dock the ship along the ice shelf (see picture below) near the Halley base for three days, in order to bring them supplies, take their wastes and the people that will not stay there for the austral winter. There are not enough cabins to have our own now, so I had to move into a new cabin which I am sharing with John. We took the opportunity to leave the ship and take a walk on the ice shelf, while the ship and Halley crew were loading and unloading equipment.

We walked from the sea ice in the creek where the ship was docked onto the ice shelf, where a little caboose was set for Halley people operations. The ice shelf is a flat expense of ice for miles and miles around...

It feels good to be able to stretch our legs !

During the walk, we saw a cute Adelie penguin. They are shorter than the Emperor penguins, with blue eyes.

Then he tried to take off to escape from an oncoming snow vehicle, but his wings don't work in the air !...

We also saw an Emperor penguin, who was watching scientists work on the poop deck of the ship. They were setting up the VMP to make repeated casts while the ship was docked, to obtain a time series of dissipation measurements.

Soon lots of friends joined in, to see what these strange human creatures were doing.

Their beautiful feathers were shining in the sun.

Two days have already past since the ship docked along the ice shelf. Tomorrow we are going to visit the Halley base ! And the ship will depart early the next day, for the second part of our work program.

Wednesday, February 18, 2009

Days 24-26

The past few days, we have broken a bit the monotony of the CTD casts by alternating them with VMP casts.
VMP stands for Vertical Microstructure Profiler : it is an instrument designed to measure the dissipation of energy in the ocean, which occurs on centimeter scale. Therefore, it must sample very fast water properties such as temperature, salinity and velocity shear. It must also not be contaminated by any spurious vibrations, and has therefore to be free-falling in the water, so that it is not subjected to any tension in the line linking it to the ship. But since it must be able to sample water properties with a resolution on the order of 1 cm, it must not be falling too rapidly in the water. Therefore, a big plastic fan is attached at the top of the instrument (see picture below, where I am in red, holding the VMP) to slow it down to about half a meter per second. The instrument sensors are mounted at the bottom, so that no structure protrude before them as the instrument is falling through the water.

The game then consists in unspooling enough cable out for the instrument to free fall, and stop it at some level above the bottom, and then respool it to prevent the instrument from hitting the bottom, which could break the fragile sensors ! Given that we do not know the depth precisely (the ship is always drifting a bit over a variable bathymetry), nor the speed at which the cable is unspooled, but only know the pressure at which the instrument is, it is quite of a gamble to approach the bottom as close as possible (turbulent dissipation is often increased near the bottom, so we like to measure it) without running into it. Below, Kjersti is anxiously watching the instrument pressure to give us the signal of spooling back ! She did a very good job : we never hit the bottom, while the people on the other watch hit it twice (without breaking the sensors, fortunately). But they were trying to get much closer to the bottom as we did, since the owner of the instrument was in their watch.

For deep casts, with a lot of cable out, the winch was sometimes not strong enough to respool the cable alone, so we had to help him a bit by pulling the cable in. A good warming exercise when it is cold.

Some winches have an automatic cable driver to help the cable respool properly, but the one we had was lacking such luxury. Therefore we had to do it ourselves with a wooden stick. I literaly became a living cable driver...
NB : the pictures where I appear were taken by Kjersti, who kindly gave them to me.

Saturday, February 14, 2009

Day 23

Whales !
After breakfast, I went outside on the ship deck to take pictures of the rising sun, and suddenly I saw two whales swimming ahead of the ship. Unfortunately, I had my normal lense on, so the whales where barely visible on the shots I took. I was thinking : "do I change my lense and risk missing them, or do I watch and get only disappointing pictures ?" I decided to switch to my zoom lense. Luckily, the whales reappeared and came closer to the ship. They followed us for about 10 minutes before turning away. I took loads of shots ! Below are some of the best sequences. But before, I would like to show this cartoon I had seen earlier in the book Antarctica - A guide to the wildlife, by Tony Soper :

The characteristic features of Minke whales are the insubstantial blow (contrary to that of the fin whale, which can reach up to 6 meters), and the fact that the tail does not come out of the water when they dive (contrary to other whales). Look out for these features in the sequence below :

Now, viewed from behind, as the whales were turning away from the ship :

I can't believe how lucky I was, to be at the right place at the right time !
If I could be as lucky with a killer whale before the end of this trip, I would be blessed...

Days 21-22

On Thursday, the 21st day of the cruise, the Second Chief Officer got injured or fell ill, I don't know, and Hannah, the ship's doctor, could not figure out how to cure him, so he had to get transferred to Halley to be flown from there to the nearest hospital on the Southern American continent I guess. We therefore stopped our work and headed to the ice shelf "dock" where people and equipment are usually transferred to Halley.
The trip took us 16 hours, a welcome break from the otherwise uninterrupted work ! We played cards, then I sorted out the mooring pictures and wrote the previous post. Somehow I did not feel like working on my papers, after 3 weeks of uninterrupted 12-hour work days...

Below are some pictures of the ice shelf again.

Then the snow shuttle arrived from Halley...

and some people from Halley traded the Second Chief Officer room for a one-week trip, before we come back to Halley on February 19.

We then headed back to our work area.
The next day, we deployed another of the Norwegian moorings successfully, along with more CTD casts.

Thursday, February 12, 2009

Day 20

Yesterday, the Norwegian team started deploying their moorings. These moorings are more difficult to deploy than the SASSI moorings, because they are "anchor-first", which means the 500-600 kg anchor is deployed first so the line is always under high tension. The first mooring went well. But during the second mooring deployment, the line suddenly broke, sending the instruments already attached to it to the bottom, lost forever ! Big disappointment and frustration... The mooring was redesigned for an anchor-last deployment, and shortened with the remaining instruments. Since they had enough people helping for the deployment, I took pictures to document how a mooring deployment proceeds.

In an anchor-last deployment, the first equipment to go overboard are the buoyancy devices : glass spheres protected within plastic shells (in red in the picture). Then follows the first instrument : an ADCP (Acoustic Doppler Current Profiler, in yellow in the picture). Helge is pulling the glass spheres out, and Charlie is giving hand signs to the upper winch operator who controls the position of the block through which the line goes.

The glass spheres drift away from the ship, pulling the line out. This is the major inconvenient for anchor-last deployments in these conditions : you need a vast area of ice-free water !

Then various instruments are attached to the line at specific lengths, corresponding to specific depths once the anchor is sunk to the bottom.
Here the instrument is a CTD (Conductivity-Temperature-Depth) sensor.

Ilker in a remake of "The Matrix" !

Keith, the Principal Investigator for the cruise, driving the lower winch, which controls the speed of the line. His casual stance is in fact a way to put his weight on the lever, which is very hard to move and maintain in a fixed position. Given the fact that you have to hold the position for long periods of time when deploying thousands of meters of line at a speed of 1-2 meters per minute, it is a quite tiring job. I was driving this winch for the SASSI deployment.

Watching the line running out between two instruments...

A current meter that works like an anemometer is being attached to the line...

... before going out.
Ilker, the Principal Investigator for these moorings, is watching that everything is going according to plans.

Finally, the anchor, an old train wheel, is lifted up from the deck and held over the water, with a special device to release it when the ship is exactly over the desired location.

Ready to go !

With the big splash, the deployment ends successfully, and everyone cheers and can relax, before the next deployment...