Tag Archives: Larsen C

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 The ice front is from the Bedmap2 data set (so a little out of date), and the bathymetry from the IBCSO data set.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.)

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:

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Project MIDAS publicised on Friday that a huge iceberg is going to calve from the Larsen C Ice Shelf. This was written up a a great story on the BBC news website Huge Antarctic iceberg poised to break away.  I understand a little about this stuff so got drawn into the media around it. Here is a BBC News interview on 6 January 2017.

It was great to see Antarctica in the news and it was brilliant to see so many high quality interviews from so many colleagues to different outlets. I may try and collate some of these in the next few days.