Mallemaroking | Thoughts on polar research and polar science – Part 5

by maximios • North Pole

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.

The sea ice extent along the Antarctic Peninsula 9 October 2016. Data from DMSP SSMI.

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.

It is October and it is the Arctic sea ice growing season. The MODIS imagery yesterday shows this beautiful image of sea ice on the North East Greenland coast.

North East Greenland in a MODIS image 5 October 2016 from the TERRA satellite

The image below shows roughly where we are looking:

I’ve been watching the open water down the eastern side of the Antarctic Peninsula. I said the cause of that was most likely strong westerly winds.

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 Antarctic Peninsula sea ice 24 August to 5 October 2016. Data from DMSP SSMI

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.

MODIS image of the Antarctic Peninsula 5 October 2016 from the Aqua satellite.

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.

Antarctic sea ice concentration anomaly for Sep 2016. Yellow rectangle approx area of images above. Image from NSIDC

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.

RRS James Clark Ross making very slow progress in compressed sea ice in Marguerite Bay, the Western Antarctic Peninsula 11 December 2004.

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.

MODIS image of the Western Weddell Sea 30 September 2016. The Open Water is clear.

The open water is clear in the lower resolution passive microwave sea ice data too.

The sea ice extent along the Antarctic Peninsula 2 October 2016. Data from DMSP SSMI

If you look at some model output there are air temperatures above this open water of between -10° to about -25°C.

Surface temperature at 2m from NCEP output. 3 October 2016. From Climate Reanalyzer.org

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.

The temperature departure from average for NCEP output 3 October 2016. Image from climateReanalyzer.org.

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.

Another pointer to the pack being looser this year is that in August 2016 in the Eastern Weddell Sea there was a rare sighting of the Weddell Polynya.

The Weddell Polynya as observed on 14 August 2016 in passive satellite data. It is a polynya with its own wikipedia page.

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.

On 26th September 2016 the MODIS sensor on The TERRA satellite captured this beautiful image of South Georgia, with Iceberg A66 drifting past.

Iceberg A66 passing South Georgia captured in a MODIS image on the 26 September 2016. The image is available on a KML file on the MODIS Websites.

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.

The track of Iceberg A66 from the BYU database

Once the icebergs reach the edge of the Weddell Sea they get to South Georgia very quickly. I did write about that in a paper in the OU database Physical oceanography in the Scotia Sea during the CCAMLR 2000 survey, austral summer 2000.

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.

Giant icebergs head to watery end at island graveyard. By Jon Amos

Overall A66 is nothing special, this is not an unusual observation.

It is a beautiful image though.

The low sea ice extent I noticed in my previous blog post about Antarctic Sound has extended southwards along the east side of the Antarctic Peninsula.

The sea ice extent along the Antarctic Peninsula 24 September 2016. Data from DMSP SSMIS

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).

NSIDC Antarctic sea ice extent 24 September 2016 with the median extent (1981-2010) for this day.

You can see how unusual this observation is, and I wrote a general post Antarctic Sea Ice Extent a while ago.

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.

The MODIS imagery for the Antarctic Peninsula 25 September 2016.

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)

Antarctic Sound on the tip of the Antarctic Peninsula 10 Sept 2016

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

The sea ice extent around Antarctic 10 September 2016. Yellow box is roughly where the MODIS image is, and Antarctic Sound is labelled. Data from DMSP SMMI

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…

This just on twitter from the UK Ministry of Defence about the recent magnificent voyage of HMS Protector.

The Tweet posted by MOD on 18th Jan 2016

On the web page in the link it says

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.

Furthest South of the RRS Bransield was 77 56′ 44”

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.

Yet more beautiful MODIS imagery showing some wonderful patterns in a plankton bloom in the Barents Sea.

Plankton patterns in the Barents Sea

The screen grab is from the 250m resolution imagery, and the whole arctic panel shows just where the bloom is located.

The Arctic on 29 July 2015 in MODIS imagery

This particular region seems to show plankton blooms regularly in the MODIS imagery and the Wikipedia page has a similar (but not as nice) image dated summer 2009.

There is a lot happening at the edge of the Greenland Ice Sheet as summer progresses, and the MODIS sensor on the TERRA and AQUA satellites is a wonderful way to observe it.

I noticed the other day (8 July 2015) this beautiful image of fast ice breaking out of a Fjord on the east coast at 76N

Fast ice breaking out of an East Greenland fjord

The full image can get down to 250 m per pixel and it is amazing stuff. The image below (from Google Earth) shows the location.

Location of the enlargement

And now in the 9 July MODIS image you can see very many large pools of water on the edge of the Greenland Ice sheet. Again, remember each pixel of this image is 250 m across – they look small but that are large pools.