Tag Archives: A68

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.

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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.)