Tag Archives: antarctica

Iceberg A68 calved from the Larsen C ice shelf earlier this year. I wrote about before.

As the berg calved it is starting to reveal a patch of seafloor that has been covered by thick glacial ice, and as the BAS press release says this has revealed:

a mysterious marine ecosystem that’s been hidden beneath an Antarctic ice shelf for up to 120,000 years.

To have the chance of making  observations in an untouched environment like that is so exciting, that the British Antarctic Survey are running an expedition to investigate. You can read about it in a great piece by Victoria Gill on the BBC news site, and the brilliant Katrin Linse has done some great work with Radio 4 and the BBC Breakfast program (2hrs 20 mins in source BAS twitter account) explaining both the purpose and the work.

I was looking this morning at the recent Sentinel-1 imagery on Polarview, this is an image of A68 captured on 11 February 2018. It's big - about 5,200 km2.

Iceberg A68 and the Larsen C Ice shelf captured from with the Sentinel-1 SAR sensor 11 February 2018.
Iceberg A68 and the Larsen C Ice shelf captured from with the Sentinel-1 SAR sensor 11 February 2018.

I labelled some features in the image: the iceberg and the ice shelf are the relatively solid grey colour. The blue overlay is where land and the ice shelf roughly were (it's called a land mask).

One thing you can see is the speckled grey colour which covers the top right hand side.

This speckled grey is sea ice.

It's a relatively thin cover of a typically 1-3 m thick.

Antarctic Sea ice.
Antarctic Sea ice.

If you map the current sea ice distribution, and the location of iceberg A68 you can see how much sea ice they are going to have to sail through to reach the region.

Larsen C, the iceberg A68 and the sea ice extent on 11 February 2018.
Larsen C, the iceberg A68 and the sea ice extent on 11 February 2018.

There is a lot of high concentration sea ice between the ice edge and the iceberg that the ship will have to traverse. RRS James Clark Ross is a very capable ship, and she will be able to make way through the ice.

The issue is this can take a lot of time.

And time whilst ice breaking is fuel.

In open water a research ship can cover ~22 km per hour, in sea ice if you are breaking ice then maybe 5 km per hour would be good, and you probably wouldn't break ice 24 hours per day.

They have 3 weeks.

Plus if you sail 400 km in the ice, unfavourable winds can easily compress the sea ice and trap a ship. It's happened before, and in the modern era even capable ships get can get held up.

The satellite I used to make the image doesn't do so well in coastal regions, so given some favourable winds there could be a nice channel for them. I am going to be watching the visible satellite imagery for that.

It's easy to make pronouncements from 14,000 km away, but really the people on the ground will  work it out.

Whatever happens I know that the researchers on board will do some great research. Plus I would be surprised if A68 moves too far from the region in the next year.

Breaking ice in Antarctica.

Breaking Antarctic sea ice on the RRS James Clark Ross.
Breaking Antarctic sea ice on the RRS James Clark Ross.

(Apologies to the Rolling Stones  for the title,

But if you try sometimes, you might find you get what you need.

*** Update 16 Feb 2028

This on twitter from Dr Stef Lhermitte

At the moment they will have to get through ~300 km of sea ice.

Being interested in the Weddell Polynya I plotted some time series data from 1 September 2017 to 23 November 2017. On the left-hand panel, you can see the see the sea ice concentration, on the right-hand panel, the anomaly of the concentration each day compared with a mean from 1989-93.

The Weddell Polynya is the low concentration region at approximately 12:00 in the movies below.

 

You can see the Weddell Polynya isn’t stationary.

You can also see the sea ice is still relatively low compared to the historic record. We should expect this after the extreme low sea ice from ~October 2016 onward.

Antarctic sea ice extent (with greater >15% sea ice cover) 23 November 2017. From NSIDC.
Antarctic sea ice extent (with greater >15% sea ice cover) 23 November 2017. From NSIDC.

I will write some more about this next week but for interest here is the Antarctic sea ice extent anomaly for 2017.

I made these movies using the excellent Antarctic Mapping Toolbox by Chad Greene. Antarctica is the Landsat Image Mosaic Of Antarctica (LIMA), and the coastline and shelf outlines come from the BEDMAP2 data set. Sea ice data is from NSDIC.

Antarctic sea ice extent remains low compared with the 1981-2010 median extent. This image shows the mean from 1989-93, the extent on 20 November 2017 and the difference between the two. Red colours imply that there is a decreased sea ice extent compared with the mean.

The mean Antarctic sea ice for the years 1989-93 on 20 Nov, the sea ice concentration on 20 Nov 2017 and the difference between the two data sets. Reds imply decreased sea ice compared with the mean, blue shades imply more. The original data come from the DMSP SMMI data set at the NSIDC.
The mean Antarctic sea ice for the years 1989-93 on 20 Nov, the sea ice concentration on 20 Nov 2017 and the difference between the two data sets. Reds imply decreased sea ice compared with the mean, blue shades imply more. The original data come from the DMSP SMMI data set at the NSIDC.

And obvious low region is the vicinity of the Weddell Sea Polynya. I have written about the polynya this season on 17 September and 25 September, as well showing how it developed through the winter on 11 September 2017.

Something exciting is happening in the ocean under the polynya, and based on new data sources such as the SOCCOM buoy that surfaced in the polynya:

Last month, SOCCOM scientists were astonished to discover that a float in the Weddell Sea had surfaced inside the polynya, making contact with satellites in the dead of winter. Its new ocean measurements, transmitted when it surfaced, are being analyzed as part of a study in preparation on Weddell Sea polynyas. With these new observations comes the possibility that the polynya’s secrets may finally be revealed.

We should expect some exciting research articles soon.

Sea ice extent currently ~1.2 million km2 low

The overall sea ice extent is currently ~1.2 million km2 below 1981-2010 median extent. This sounds a lot.

Antarctic sea ice extent (with greater >15% sea ice cover) 18 November 2017. From NSIDC.
Antarctic sea ice extent (with greater >15% sea ice cover) 18 November 2017. From NSIDC.

But at this time of the year the Antarctic sea ice is about to dramatically fall as spring develops. If spring "arrives" early then the extent will - as we see, be relatively low.

Seasonal cycle of Antarctic sea ice extent
Seasonal cycle of Antarctic sea ice extent

Whilst the full on development and opening of the Weddell / Maud Rise Polynya is unusual, if you compare the sea ice on 18 November 2017 with the extent from the same day on 1989-1995 it is clear that the extent is often lower over Maud Rise, at this time.

This is the sea ice on 18 November for 1989, 91, 92, 93, 94, 95 and 18 November 2017. The original data come from the DMSP SMMI data set at the NSIDC.
This is the sea ice on 18 November for 1989, 91, 92, 93, 94, 95 and 18 November 2017. The original data come from the DMSP SMMI data set at the NSIDC.

I will keep watching the sea ice as the summer season develops

MODIS mosaic from the AQUA satellite on 18 November 2017.
MODIS mosaic from the AQUA satellite on 18 November 2017.

** UPDATED 20th November 2017 replacing the first figure from 17  November to 20 November.

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As daylight has returned to Antarctica it is straightforward to pick out polynya forming on the edge of the Antarctic continent.

This one by the Stange Ice Shelf and Rydberg Peninsula caught my eye. It is a latent heat polynya formed as the winds push the sea ice away from the land to reveal the ocean that appears black beneath.

The wispy trails of grey which appear in the black are new sea ice forming as frazil ice.

A wind formed latent heat polynya forming in front of the Rydberg Peninsula and Stange ice Shelf, 22-26 October 2017.
A latent heat polynya forming in front of the Rydberg Peninsula and Stange ice Shelf, 22-26 October 2017.

This is the location of the peninsula.

The location of the Rydberg Peninsula.
The location of the Rydberg Peninsula.

I visited that area in 2007 and took this picture. You can a thin skim of young nilas ice in front of the ice shelf, and sea smoke too.

The Stange Ice Shelf with a thin skim of sea ice in front.
The Stange Ice Shelf with a thin skim of sea ice in front.

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The polynya over Maud Rise was visible in a beautiful clear MODIS image on 25 September. It is currently ~40,000 km2 of open water in the middle of the Antarctic winter sea ice. This will be some impressive heat loss.

MODIS image of the polyna over Maud rise on 25 Sept 2017. The black is ~40,000km2 of open water.
MODIS image of the polyna over Maud rise on 25 Sept 2017. The black is ~40,000km2 of open water.

This is the polynya in the SMMI Data for the same day.

Location of Maud Rise polynya 25 Sept 2017.
Location of Maud Rise polynya 25 Sept 2017.

A while back I calculated the heat loss through 2,000 km2 of open water in the Arctic as being ~600 GW. This is about 20 times as much open water…

As I said then, the heat loss is making the surface waters denser, so they sink away from the surface

More to come on this I expect.

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Quick post on the Maud Polynya in the Weddell Sea that I wrote about last week. This is the sea ice data 17 September 2017, and the polynya is both clear and large.

The location of the polynya over Maud Rise. Sea ice data from DMSP SMMI.
The location of the polynya over Maud Rise. Sea ice data from DMSP SMMI.

An enlargement of the polynya shows that it is practically open water.

...continue reading

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The Weddell Sea polynya is an area of open water that sometimes appears in the Weddell Sea over a relatively shallow region called Maud Rise.

The Antarctic sea ice concentration 9 September 2017. The location of the polynya is marked and the original data come from the DMSP SMMI data set at the NSIDC.
The Antarctic sea ice concentration 9 September 2017. The location of the polynya is marked and the original data come from the DMSP SMMI data set at the NSIDC.

In the latest satellite imagery from the DMSP satellite you can see the lower concentration sea ice as the darker blue colour. If you look at the MODIS imagery for the same date you can clear see black which indicates open water in the pack ice.

The MODIS imagery mosaic of Antarctica from 7 September 2017 from the MODIS sensor on the Terra satellite. The pattern in the centre of the image is because high latitudes of Antarctica are still dark at this time in winter.
The MODIS imagery mosaic of Antarctica from 7 September 2017 from the MODIS sensor on the Terra satellite. The pattern in the centre of the image is because high latitudes of Antarctica are still dark at this time in winter.

...continue reading

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Project MIDAS shows us that the iceberg A68 is about one trillion tonnes.

This is the Antarctic Peninsula and the outline of A68 from the satellite image on 14 July 2017 shown in black. The ice front is from the Bedmap2 data set (so a little out of date), and the bathymetry from the IBCSO data set.

Larsen C Ice shelf on the Antarctic Peninsula and the location and area of iceberg A68. The outline of A68 is derived from a satellite image of the ice shelf 12 July 2017.
Larsen C Ice shelf on the Antarctic Peninsula and the location and area of iceberg A68. The outline of A68 is derived from a satellite image of the ice shelf 14 July 2017.

There are some astonishingly beautiful processed satellite images of A68 out there such as this one via ESA from Adrian Luckman and the excellent Project MIDAS.

One image I haven't seen is how good is knowledge of the bathymetry around A68?

The iceberg is going to drift and likely ground quite quickly. (I wrote about this on the conversation a while ago: When an Antarctic iceberg the size of a country breaks away, what happens next?)

In the map below, the shaded colour is the distance of any point on the sea bed to the closest actual depth measurement.

The distance to the nearest good depth measurement around the Antarctic Peninsula.
The distance to the nearest good depth measurement around the Antarctic Peninsula.

So the dark blue stripes labelled in the Weddell Sea are actually ship tracks - and the dark colours are good depth data. These measurements will have been made by icebreaker.

Just in front of A68 there is a very large area where no ship has been within ~80 km.

One small note on the size. I digitized the iceberg from a satellite image (a KML File can be downloaded). On twitter today there were satellite images showing fractures already.

But Martin O'Leary of the MIDAS team posted today on twitter that to the untrained eye looks like iceberg, is very likely fast ice (so thick sea ice that is "fast" to A68 - but only a few metres thick.)

At this time of the year we should expect the Antarctic sea ice to be growing rapidly, but after the historic lows of last Antarctic summer, we can see that whilst it is rapidly advancing, the sea ice extent (the area of ocean covered by >15% of sea ice) it is still ~1 ¼ million km2 below the median from 1981-2010.

Antarctic sea ice extent (with greater >15% sea ice cover) 15 May 2017. From NSIDC.
Antarctic sea ice extent (with greater >15% sea ice cover) 13 May 2017. From NSIDC.

There is not a consistent trend in Antarctic sea ice extent, and much regional interannual variability. The plot below shows the sea ice extent on 13 May for each of the years 1989-95, and 13 May 2017.

Antarctic sea ice extent on 13 May for the years 1989, 1990, 1991, 1992, 1993, 1994, 1995 and 2017. Data from DMSP SMMI.
Antarctic sea ice extent on 13 May for the years 1989, 1990, 1991, 1992, 1993, 1994, 1995 and 2017. Data from DMSP SMMI.

The image above shows the sort of variability we expect in the Antarctic sea ice extent. It is helpful too to see where the sea is currently is and isn't compared with the mean from 1989-93.

The mean Antarctic sea ice for the years 1989-93 on 13 May, the sea ice concentration on 13 May 2017 and the difference between the two data sets. 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.
The mean Antarctic sea ice for the years 1989-93 on 13 May, the sea ice concentration on 13 May 2017 and the difference between the two data sets. 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.

The regions in May 2017 with the greatest deficit of sea ice remain the Amundsen and Ross Sea, and the Eastern Weddell Sea and off the coast of Dronning Maud land. As I said in my last Antarctic sea ice post it is likely the freeze up is delayed because of the heat gained by the ocean in the Antarctic summer of 2016/17.

You can also see in the South West Weddell Sea the Ronne Polynya I wrote about in March 2017 is still seen in the sea ice concentration data. In the visible satellite data you can also see this open water.

The Ronne Polynya can see seen in the South West Weddell Sea satellite data on 15 May 2017. The box marks the approximate image of the SAR image below.
The Ronne Polynya can see seen in the South West Weddell Sea satellite data on 15 May 2017. The box marks the approximate image of the SAR image below.

In the Sentinel 1 SAR data from the 15 May (From PolarView), the growth of the sea ice in the polynya is clear.

Sentinel 1 Synthetic Aperture Radar (SAR) Image 15 May 2017 in the South West Weddell Sea. From PolarView.
Sentinel 1 Synthetic Aperture Radar (SAR) Image 15 May 2017 in the South West Weddell Sea. From PolarView.

This ice growth is important for the ocean as it means the salinity of the waters just beneath the sea ice will be increasing.

I'll keep watching the polynya to see if and when it closes up. And I will also keep looking at the sea ice.

 

The polynya I saw forming in early February is still clear, and very large in the Southern Weddell Sea. At the moment it is more than than 80,000 km2, although there is clearly a lot of young sea ice covering a large part of the polynya.

The Weddell Sea 5 March 2017 in the Terra MODIS true colour image.
The Weddell Sea 5 March 2017 in the Terra MODIS true colour image.

In my original post I said this was likely formed by winds from the Ronne Ice Shelf.

Well Dr Stef Lhermitte (Delft) has put together the most amazing movie showing the development of the polynya over January and February. It shows satellite sea ice data with winds from the ECMWF overlain.

You can clearly see the winds pushing the sea ice away from the ice shelf as time progresses.

It is just as @StefLhermitte said in his tweet yesterday:

...continue reading