It was great to see Antarctica in the news and it was brilliant to see so many high quality interviews from so many colleagues to different outlets. I may try and collate some of these in the next few days.
The Prince Gustav Channel was covered by an ice shelf which collapsed in the 1990's, and for many years it was possible to sail a ship around James Ross Island.
Recently it has been covered with sea ice frozen to the land - we call this fast ice, and it's usually only a few metres thick of frozen sea water - rather than hundreds of metres thick snow derived ice shelf.
Recent images from the TERRA satellite show that this fast sea ice is finally breaking out.
It'll soon be possible to circumnavigate James Ross Island once more.
This map shows the location of the channel.
Now it has started I wonder how long it will take to finally clear. Or more fun, I wonder if tour ships will be able to get around the island?
If you look at the sea ice concentration on the western Antarctic Peninsula you can see the effect of these westerly winds.
Towards the end of September 2016 the ice edge is compacted as the sea ice is pushed against the Peninsula.
The westerly winds (from bottom left to top right) compress the sea ice against the land (left hand side of the Antarctic Peninsula). This also creates open water on the eastern (right hand side ) of the Peninsula as the sea ice is pushed away from the land.
You can see the very sharp ice edge on the west, and the open open water in the MODIS satellite imagery.
The sea ice concentration anomaly for September 2016 shows that on both sides of the Antarctic Peninsula the westerly winds have reduced the amount of ice we would expect to observe by up to ~40%. On the west side because the sea ice is compressed, on the east side because the sea ice is being pushed away from the land.
This is just late winter weather.
There are a lot of Antarctic research stations on the west of the Antarctic Peninsula, including Rothera, the largest British Base. If the winds maintain the westerly direction then I can imagine it could be slow to resupply the base this season. There is time for it to change. According to the published schedule the ship is not due to arrive until 27 November 2016.
A slow resupply is not uncommon and I have been on at least one unsuccessful resupply voyage in my career. I took the picture below on 11 December 2004 under similar conditions.
I noticed in a blog post last week that there was a finger of open water extending down the Western Weddell Sea. I've carried on watching this open water in the MODIS satellite data. Whilst it's been opening and closing, there is a lot of open water. It's clearly a major sea ice generating factory at the moment.
The open water is clear in the lower resolution passive microwave sea ice data too.
If you look at some model output there are air temperatures above this open water of between -10° to about -25°C.
What is really good is if you look at the temperature anomaly (i.e. the departure from the average with a 1979-2000 baseline), it is very warm over the Weddell Sea.
I think the reason it is warmer is because the Weddell Sea pack ice is looser this year. So (as you can see in the picture above) there is lots of open water. The atmosphere is being warmed by the ocean as the sea ice is being generated.
I think the Weddell Sea pack ice is more mobile this winter. This is also telling us something about the difference between sea ice extent and sea ice thickness. The sea ice extent is large and easy to measure in the Antarctic - but we don't know how thick it is.
The open water that shows up as black in the image above extends to at least as far south as the Antarctic Circle (66° 33′S). Open water along this part of the Antarctic Peninsula is unusual at any time of the year let alone the height of winter. The image below is from the National Snow and Ice Data Centre. It shows sea ice extent >15% with an outline of the typical extent for that day based on a 30-year (1981-2010) median (orange line).
The open water is also very clear in the MODIS imagery as the black wedge between the Antarctic Peninsula, and the sea ice of the Weddell Sea.
In my previous post I pointed at weather systems as likely being responsible. Now to me it looks like a large system is pushing the whole Weddell Sea sea ice to the east and away from Antarctic Peninsula.
There is always some open water in the pack ice at any time of the year, but it's clear that their is a pathway south right now. I imagine it will close soon and wouldn't be keen to be on a ship in that open water heading south.
What is interesting is the heat transfer from the ocean to the atmosphere that far south at this time of the year will be huge. This is what I wrote about that heat loss for the Arctic.
Just noticed this on the MODIS sensor on the TERRA satellite image from 10 September 2016. (Tile Antarctica_rc05c01 if you are interested in that sort of thing)
The Antarctic sea ice ice extent map for 10 September 2016 shows an interesting and large low concentration right at the tip of the Antarctic Peninsula
So why the missing sea ice at the top of the Peninsula? It could be a storm, or could be heat from the ocean keeping the area ice free. I'll have a look at the data when I've time, but for now I would bet on the ocean.
Interestingly historically it has been a bit of a tough place. Otto Nordenskjöld navigated the sound in December 1902 on the Swedish Antarctic Expedition before their ship, the Antarctic was crushed and lost. They were stranded for two years...
In the old days Antarctica wasn’t mapped and measured by satellites like it is now. In the past it was all about exploration. Scientists were dropped at bases by ship, and then left for at least a year - sometimes two. Very occasionally more.
When winter comes the sea ice freezes up and the area of sea ice is vast. But after the winter, spring brings long days of light, and that meant travel by dog sled was possible over the ice!
To make the sled journeys more efficient food caches were left along the coast the previous summer perhaps by the same ship that left them. Then the scientists could journey easily over the frozen sea ice to the food cache, and then work inland in their area of operations.
Which brings me to these pictures. This is a food cache left by a ship (I think) in 1962 for a science team setting out from Hope Bay.
Hope Bay Food Dump
Antarctic Chocolate and meat
In Antarctica Marmite can come in tubes
Butter and meat
A tin of biscuits in an Antarctic Food Cache
Oxtail soup and a meat bar
A pile of wooden sledge boxes that contain all human needs: chocolate, biscuits, marmite, meat and soup. What more could you want?
In a previous post I showed the temperature cycle on the Antarctic Peninsula, and pointed out that the monthly mean atmospheric temperatures show that it is actually surprisingly moderate. Whether you consider the temperature cycle moderate or not, the cold temperatures and strong winds drive an amazing amount of seasonal sea ice production.
This plot shows the average seasonal cycle of Antarctic sea ice extent against date.
The daily average extent is calculated from the satellite record from 1981-2010, and the grey shading either side of the line is the standard deviation.
Here are three obvious things to pick out of this plot.
Antarctic Sea Ice extent varies a lot: From 2.9x106 km2 in February to 18.6 x106 km2 in September. This is a range of 15.7 x106 km2.
The seasonal cycle is not symmetrical: There is a slow growth followed by a relatively rapid decay.
To really get an idea of what this asymmetric growth / decay pattern looks like watch the following you tube clip a few times. (The data for the movie is from the AMSR-E Satellite and it is from Climate Central.
So slow growth, and then rapid retreat. Ice tends to advance away from the continent, but as it retreats it can melt first within south of what you would consider the ice edge.
How the Antarctic sea ice extent is changing is for a future post, but it is currently increasing. There are significant regional changes over the duration of our satellite record. For a couple of good accesible comments on the trends in Antarctic sea extent you could read Professor John Turner in the Guardian, or Tamino on the Antarctic Sea Ice increase.
Fetterer, F., K. Knowles, W. Meier, and M. Savoie. 2002, updated daily. Sea Ice Index. Daily Sea Ice Extent Climatology. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5QJ7F7W.