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