antarctica | Mallemaroking
Mark Brandon • October 15, 2024
I love looking at satellite images of the Antarctic and picking out the icebergs. In the last few years we have had great stories about the giant icebergs A68 in 2020, A76 in 2022 and most recently A23a currently in the Southern Scotia Sea.
At the moment there are two of very large icebergs at the southern end of Antarctic Sound. Here is a map to orientate yourself and show where they are.
A basemap with a MODIS image from 7 October 2024. The yellow box is the location of Antarctic Sound and is expanded on below.
There is a lot in the image above. As well as the Antarctic Peninsula there are clouds, sea ice, and icebergs. Zooming into Antarctic Sound shows the giant icebergs more clearly.
A MODIS satellite image of Antarctic Sound taken on 7 October 2024. Two large icebergs are at the southern end of the Sound. These are A80A and A76C.
And in the radar sensor on Sentinel-1 the icebergs leap out because that sensor “sees” through the clouds.
A Sentinel-1 SAR image from 8 October 2024. Land is coloured blue, the giant icebergs are solid grey, and sea ice and smaller icebergs make up the grey shades colouring the rest of the image.
A80A is 10×9 nautical miles and it calved from the Larsen D Ice Shelf in November 2022. A76C is currently 16×7 nautical miles and was part of iceberg A76 that calved from the Ronne Ice Shelf in May 2021. These are pretty decent sized icebergs: A80A looks to be pinned against Rosamel Island and Andersson Island at the southern end of Antarctic Sound, and A76C grounded against A80A.
Personally I would be surprised if they broke out before the start of the Antarctic season proper, so they could cause some complexities in navigating into the Weddell Sea through Antarctic Sound.
Finally we can’t forget the current monster of them all: A23A at 40×32 nautical miles, and it has been spinning above Pirie Bank north of the South Orkney’s since April 2024. I described it as “the iceberg that just refuses to die” when I spoke to the BBC, and it has been spinning for seven months in pretty much the same location. When it finally breaks free, it’ll head up towards South Georgia and it’s inevitable demise rapid demise.
A MODIS satellite image from 13 October 2024 showing iceberg A23A just north of the South Orkney Islands.
It’s amazing to think that A23A has been in existence since 1986 when it fractured from the Filchner-Ronne Ice Shelf.
The summary? It looks like if you’re going South this season you could see some very big icebergs, and navigation could be complicated in the North West Weddell Sea.
Posted in Science, Uncategorized. Tags: Antarctic Peninsula, Antarctic Sound, antarctica, iceberg, Icebergs on October 15, 2024 by Mark Brandon. Mark Brandon • August 31, 2018
Just over a year ago in July 2017 iceberg A68 calved from the Larsen C Ice Shelf. I appeared on BBC News before it actually calved explaining what was happening.
At first A68 was slow to move and as I predicted back then, it likely got stuck on the sea bed (we say “grounded”). It has stayed pretty much in the same place through to July 2018.
But now A68 has started to swing northwards.
As the light is coming back to Antarctica, at high latitudes visual imagery is very washed out. But if we look at other data such as the brightness temperature, you can see some striking features.
This image is from 20 August 2018.
Corrected Reflectance (True Color) from the Suomi NPP Visible Infrared Imaging Radiometer Suite (VIIRS), and the Brightness Temperature (Band I5, Day). Image from 20 August 2018.
With the brightness temperature data set, brighter colours indicate higher temperatures. The Larsen Ice shelf and A68a are glacial ice and so cold, they appear dark purple. The sea ice is thinner and warmer and in contact with the ocean so the purple shade is lighter. The leads which are cracks in the sea ice and so open water and / or very thin sea ice appear as relatively bright lines. On the bottom right of that image you can see that under certain circumstances the brightness temperature data set can see through clouds.
…continue reading →
Posted in Science. Tags: A68, antarctica, satellite, sea ice on August 31, 2018 by Mark Brandon. Mark Brandon • February 13, 2018
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.
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.
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.
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.
(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
#MODIS Aqua of yesterday on https://t.co/RPVpONbwcO has a clear view (i.e. few clouds) of the area, nicely showing the high sea ice concentration and potential difficulty to reach iceberg #A68 pic.twitter.com/iti8tXmL6C
— Stef Lhermitte (@StefLhermitte) February 16, 2018
At the moment they will have to get through ~300 km of sea ice.
Posted in Science. Tags: A68, antarctica, Larsen C, RRS James Clark Ross, Science, sea ice on February 13, 2018 by Mark Brandon. Mark Brandon • November 24, 2017
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.
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.
Posted in Science. Tags: anomaly, antarctica, sea ice, Weddell Polynya on November 24, 2017 by Mark Brandon. Mark Brandon • November 20, 2017
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.
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.
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
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.
I will keep watching the sea ice as the summer season develops
MODIS mosaic from the AQUA satellite on 18 November 2017.
** UPDATED 20th November 2017 replacing the first figure from 17 November to 20 November.
Posted in Science. Tags: antarctica, extent, Maud Rise, sea ice, SMMI, Weddell Polynya on November 20, 2017 by Mark Brandon. Mark Brandon • October 26, 2017
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 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.
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. Posted in Science. Tags: antarctica, frazil ice, polynya, Rydberg Peninsula, satellite, sea smoke, Stange Ice shelf on October 26, 2017 by Mark Brandon. Mark Brandon • September 27, 2017
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.
This is the polynya in the SMMI Data for the same day.
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.
Posted in Science. Tags: antarctica, Maud Rise, polynya, Weddell Sea on September 27, 2017 by Mark Brandon. Mark Brandon • September 19, 2017
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.
An enlargement of the polynya shows that it is practically open water.
…continue reading →
Posted in Science. Tags: antarctica, Maud Rise, polynya, sea ice, Weddell Polynya, Weddell Sea on September 19, 2017 by Mark Brandon. Mark Brandon • September 11, 2017
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.
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.
…continue reading →
Posted in Science. Tags: antarctica, Maud Rise, MODIS, polynya, satellite, SMMI, SMOS, Weddell Sea on September 11, 2017 by Mark Brandon. Mark Brandon • July 18, 2017
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 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.
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.
New crack on eastern side of Iceberg A68 carves out large chunk of ice, as berg moves further away from #LarsenC Ice Shelf @deimosimaging pic.twitter.com/NagHUSUuH8
— The Antarctic Report (@AntarcticReport) July 18, 2017
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.)
Pretty sure this is some fast ice (i.e. sea ice, maybe a few meters thick) detaching from the berg. Looks totally different in SAR imagery https://t.co/XHDGle0gVv
— Martin O’Leary (@mewo2) July 18, 2017
Posted in Science. Tags: A68, Antarctic Peninsula, antarctica, bathymetry, Larsen C, Weddell Sea on July 18, 2017 by Mark Brandon.