sea ice | Mallemaroking – Part 3

by maximios • North Pole

The extent and thickness of the Arctic sea ice is decreasing for every month of the year. But looking at straight lines on graphs with a relentless downward trend it’s easy to lose the geographic sense of what is happening.

The red areas in the plot below show where ice was absent on 3 March 2016 compared with the mean 1989-93 at the height of the winter. I chose 1989-93 the comparison period as it is just before the start of the relatively rapid decline in we observe in Arctic sea ice.

The difference between the daily ice extent, in each grid cell and the mean based on historical data for the years 1989-93. Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean. The original data come from the DMSP SMMI data set at the NSIDC.

As you would expect there is not a lot of blue in the plot, and the ice edge has retreated virtually everywhere. The stand out region is the Northern Barents Sea. On the NSDIC website you can see that the decline of sea ice in the Kara and Barents Seas is part of the long-term trend.

The seasonal cycle of sea ice extent in Antarctica has been fairly stable over the length of the satellite record. There is a slow growth of sea ice from a minimum of ~3×10⁶ km² in February to a maximum of ~19 x10⁶km² in September, before there is a relatively rapid fall in the Antarctic spring.

But this year something different is happening.

Below is Tamino’s image for the Southern Hemisphere sea ice extent, the red line is 2016 up to 16 November 2016.

The annotated seasonal extent of sea ice in the Southern hemisphere. From Tamino’s post Sea Ice, North and South.

From January up to September the sea ice extent in 2016 follows all previous data.

But what happened in September?

For completeness here is a gif of the growing season in the Arctic this year from 1 September 2016 to 16 November 2016.

The 2016 Arctic Growing Season 1 September to 16 November.

The summer of 2016 saw the joint second lowest Arctic sea ice extent. But in the middle of October unusual Arctic weather has led to it becoming the lowest extent. At the same time, Antarctic sea ice extent has also reached record lows. Tamino has a simple and clear post about what a surprising thing this is.

The Northern Hemisphere Sea Ice extent from Tamino’s blog “Open Mind”. The current year 2016 is in Red

Why is it so low?

The plot below shows the mean November Arctic sea ice extent, the sea ice extent on 16 November 2016, and the difference between the extents from 1993 to 2016. Regions shaded at the top end of the scale (the red colours) mean there is less ice now compared with in 1993.

The mean Arctic sea ice extent in November 1993, the daily sea ice extent on 16 November 2016, and the difference between them.

The stand out region (to me!) is North Russia where the Kara Sea is almost entirely clear, followed by Hudson Bay, Baffin Bay, East Greenland and the edge of the Chukchi Sea. I was interested in what was going on in the Kara Sea so I made a movie of the sea ice extent from 1 November 2016 to 16 November 2016.

Arctic sea ice 1 to 16 November 2016.

The striking thing in the clip for November 2016 is that the sea ice extent has actually reduced in the Kara Sea!

The sea ice extent in Chukchi Sea is increasing, but very slowly – and you can see from my previous image that it is very low compared with 1993.

Clearly the Arctic is experiencing strange conditions at the moment. On the climatereanalyzer.org website you can see the 5-day forecast from 17 November 2016 (tomorrow).

The temperature departure from average is off the scale over the Arctic Ocean. It’s much colder over Russia.

The 5 day forecast from 17 November 2016 from ClimateReanalyzer.org.

These are astonishing observations. When the winds change and the cold air currently over Russia ends up over the ocean I would expect it to freeze up rapidly (once the surface layers have cooled). But starting so late in the year the sea ice could end up thin enough for something impressive in the near future.

I made a gif of the full current Arctic growing season up to 16 November 2016.

I have already written a little about the this years Antarctic sea ice extent in the Antarctic Peninsula sea ice late winter 2016, in The Western Weddell Sea ice factory, in The development of the Amundsen Sea Polynya, in Dotson Getz Polynya ice growth, and in The Prince Gustav Channel is opening.

For interest, I chose November 1993 for comparison for two reasons, first it’s just before the big Arctic sea decline, and secondly I was in the Arctic for 4 months that year doing my PhD research.

Tamino is noting that the global sea ice is “About 6.9 standard deviations below the 1981-2010 mean.” . Amazing times.

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.

The Prince Gustav Channel early spring Antarctic summer 2016/7 from MODIS satellite imagery on the TERRA satellite.

This map shows the location of the channel.

The Antarctic Peninsula showing the location of the Prince Gustav 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?

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.

The Dotson Getz polynya on 9 October 2016. Open water is black and streaks of sea ice growth are clear. The location of the Bear Peninsula Automatic Weather Station is marked.

I put together the satellite data from 9-12 October 2016 and it shows extremely rapid sea ice growth.

I was interested in how long the polynya I blogged about yesterday had existed.

I made a gif of the previous months sea ice data.

The sea ice extent in Pine Island Bay 11 September to 10 October 2016. Data from DMSP SSMI. The development of the polynya can be seen in the growth of the dark regions.

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.

The MODIS imagery 9 October 2016 from the TERRA satellite overlain in Google Earth

Next diversion will be a area of open water / time plot.

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.