Tag Archives: antarctica

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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

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

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Trying to understand the geographic nature of the very low Antarctic sea ice extent I made the following animation:

Antarctic sea ice extent on 1 March for the years 1989, 1990, 1991, 1992, 1993, 1994, 1995 and 2017. Data from DMSP SMMI.
Antarctic sea ice extent on 1 March for the years 1989, 1990, 1991, 1992, 1993, 1994, 1995 and 2017. Data from DMSP SMMI.

The highlight issues in the graphic are the clear lack of sea ice in the Amundsen/Ross Seas and the Southern Ocean off Dronning Maud land. (If you are not familiar with the names off the seas / locations see the map below).

The Weddell Sea is has a relatively compressed sea ice cover this year - but it's clear there is large inter-annual variability.

Off Wilkes Land the sea ice is heavier this year - and it's easy for this to get lost in the headline story around the very low extent. There are several Antarctic research stations along this coast:

The French Station Dumont d’Urville,

Two Australian Stations of Casey and Davis,

and the Russian Mirny Station.

Here is the NSDIC Antarctic sea ice extent 1 March 2017.

Antarctic sea ice extent (with greater >15% sea ice cover) 1 March 2017. From NSIDC.
Antarctic sea ice extent (with greater >15% sea ice cover) 1 March 2017. From NSIDC.

And finally the promised map from the National Snow and Ice Data Center (NSIDC) with regional seas and other features marked.

The oceans and regional seas around Antarctica, along with other geographical features. From NSIDC.
The oceans and regional seas around Antarctica, along with other geographical features. From NSIDC.

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I noticed yesterday that a polynya had formed in front of the Ronne Ice Shelf over the last 2 weeks.

Screengrab from NASA Worldview 17 February 2017
Screengrab from NASA Worldview 17 February 2017

In that image it is about 27,000 kmin area.

I mapped the opening of the polynya from MODIS imagery over the last two weeks. There is cloud in the images but the opening of the polynya is fairly clear.

Formation of the Ronne Polynya 30 January to 14 February 2017.
Formation of the Ronne Polynya 30 January to 14 February 2017.

On 31 January 2017 there is no open water, but then over the 16 day period it opens to the ~27,000 kmin area. If you're eagle eyed you can see that there is thin frazil ice forming in the open water in front of the ice shelf at the end of the sequence.

So what caused it?

...continue reading

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Watching the sea ice extent this summer in Antarctica has been a bit surprising. The Antarctic sea ice extent has been tracking at record lows virtually the whole austral summer. We are very close now to the expected sea ice minimum, and this is where we are:

Antarctic sea ice extent 12 Feb 2017 & diff from mean 1989-93 on same day. Blues imply more ice and reds imply less compared with the mean.
Antarctic sea ice extent 12 Feb 2017 & diff from mean 1989-93 on same day. Blues imply more ice and reds imply less compared with the mean.

On the left is the sea ice extent from the DMSP satellite 12 February 2017, and on the right the difference between the mean sea ice extent on 12 Feb over the period 1989-93 and 12 Feb 2017. I chose this time period as the cycle has been generally quite stable from year to year.

The current sea ice extent is:

Antarctic sea ice extent. Downloaded from NSIDC 14 February 2017.
Antarctic sea ice extent. Downloaded from NSIDC 14 February 2017.

It's clear the sea ice over the summer 2016-17 is showing historic lows. But it's also clear from the sea ice extent above that there is little sea ice left to melt out before the summer turns. Where the sea ice remains - mainly in the Weddell Sea and along the coast of Wilkes Land it is clearly densely packed. If the winds change and the remaining sea ice is decompressed then the extent may fall some more.

This is an animation of the Antarctic sea ice extent from 1 January 2017 to 12 February 2017:

The Antarctic sea ice extent 1 January to 12 February 2017. Data from DMSP SMMI
The Antarctic sea ice extent 1 January to 12 February 2017. Data from DMSP SMMI

And finally the difference between the mean sea ice extent by day for the 5-year period 1989-1993 minus the concentration from 1 Jan to 12 Feb 2017. Blue shades imply an increased sea ice extent compared with a 5-year mean, and reds imply a decreased sea ice extent.

The difference between the mean sea ice extent by day for the 5-year period 1989-1993 minus the concentration from 1 Jan to 12 Feb 2017. Blue shades imply an increased sea ice extent compared with a 5-year mean, and reds imply a decreased sea ice extent.
The difference between the mean sea ice extent by day for the 5-year period 1989-1993 minus the concentration from 1 Jan to 12 Feb 2017. Blue shades imply an increased sea ice extent compared with a 5-year mean, and reds imply a decreased sea ice extent.

Not long until the Antarctic sea ice minimum.