My previous posts on Amundsen Sea Polynya and their development showed ~37,600 km2 of open water in front of the ice shelves. It is very early spring in Antarctica at this time of the year and it’s still cold.
That means sea ice can still grow.
This is the Dotson Getz polynya on 9 October 2016. It has a perimeter of ~800 km and an area of ~25,500 km2.
I put together the satellite data from 9-12 October 2016 and it shows extremely rapid sea ice growth.
You can see that the polynya in the centre of the picture can be seen from the very beginning. This is forming in front of the Dotson Ice Shelf - and from the scale bar you can see it is big. This polynya really starts to develop as open water around 5 October 2016.
The coastal polynya on the northern land boundary appear in mid September - and develop throughout the record.
The image below was in my previous post and it shows the three polynya from a MODIS image on 9 October 2016.
Next diversion will be a area of open water / time plot.
The Amundsen Sea currently has some very large polynya. In front of the Dotson, Getz and Pine Island ice shelves they are clear in the satellite data.
A polynya is an area of open water in the winter pack ice.
These are likely latent heat polynya, and strong winds are pushing the sea ice away from the coasts to make the open water. In the open water there will be a lot of sea ice generation. I wouldn't be surprised if the weather that is keeping the sea ice compressed against the Antarctic Peninsula is also responsible for opening them.
Taking the MODIS data from the TERRA satellite and importing that into google earth, the open water shows up as black. At the top of the image in front of Pine Island Glacier the polynya are partially obscured by cloud.
In Google Earth you can measure the area quite easily.
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 iceberg A66 is about 15 km at it's widest point in this image.
We can do a bit simple maths. Estimate the iceberg has a 200 m thickness and it is triangular in shape with a base of ~4 km.
the volume = 0.5 x 15 km x 4 km x 0.2 km = 6 km3.
So the relatively small A66 contains of 6000 gigtons of water. It's a lot. But it's not a lot.
Icebergs get their reference number depending on where they originate from. This one has an identifier "A" which means it came from the sector 0° to 90°W - that's the Bellingshausen and Weddell Sea region. You can track icebergs like this both visually - like in in the image above - or using something called a Scatterometer. A scatterometer can measure the winds over the ocean, and because the winds change over the ice one can track the icebergs. Prof David Long at Brigham Young University provides an excellent database of Antarctic iceberg data based on that idea (this is their research paper on how they do that).
If we look at the location data from the ASCAT sensor you can see that A66 is at the tip of the Antarctic Peninsula - but this data is only from this year. I will have to dig a little deeper. A job for later.
And some of these icebergs (although not A66) ground at South Georgia and ultimately can affect the ecosystem. Jon Amos wrote about some work I did at a San Francisco conference in 2010 about that - it's still available on the BBC website: Giant icebergs head to watery end at island graveyard.
Overall A66 is nothing special, this is not an unusual observation.
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...
By visiting this region Protector achieved a latitude of 77 Degrees 56 Minutes South – the very edge of the vast Ross Ice Shelf, named for James Clark Ross who led the exploration of the area.
No official British ship has been this far south since 1936 and it is believed not since James Clark Ross’s own expedition in 1842.
I don't think this is true. The British Antarctic Survey Ship RRS Bransfield reached likely a little further south. According to this note from the Second Officer Chris Elliot which is published on the website The LOFTSMAN which is about the shipyards of Leith.
RRS Bransfield reached 77°56' 44"S.
So 44 seconds further south than HMS Protector.
Which is what? 1.3 km?
I know it's not much further south and Protector likely matched it (they don't give their decimal). I just wanted to make the point that it is close. Very close.
The second officer in the note - Chris Elliot went on to become the Captain of the RRS John Biscoe, and then he was a member of the team that built the RRS James Clark Ross for many years, before becoming one of the Captains of that great ship.
UPDATE See comment below by Radio Officer of the RRS James Clark Ross Mike Gloistein.