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.

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.

This example from 26 August 2018 shows even more clearly a view through the clouds.

Now you understand what you are looking at, here are the all the brightness temperature images from 1 May 2018 to 26 August 2018 in which I could clearly identify iceberg A68a. The date is in the top right hand corner.

You can see at between 7-12 July 2018 the weather conditions and ocean currents conspire to swing the trillion tonnes of the giant iceberg A68 in an anticlockwise direction.

Sentinel-1 SAR satellite imagery from 29 August 2018 shows that to the north of the iceberg the wind is pushing the sea ice northwards faster than the iceberg is rotating.

This has created an area of open water where there is intense sea ice generation happening right now. In the high resolution imagery you can clearly see large frazil ice slicks developing in this open water region.

My guess is that A68a will continue rotating as it is now around that western point, until what is currently the northern edge collides with the Larsen C ice front.

It has a spectacular amount of momentum and it's not going to stopped easily. I should think we will see some interesting collisions with the ice shelf in the next few months.

What happened in July 2018 to start the drift?

This should be another blog post! Larsen C has an Automatic Weather Station (AWS14, Larsen C North) operated by the Utrecht University Institute for Marine and Atmospheric Research.

This is the data for 2018, and the horizontal axis shows day of year.

Just before A68a starts to rotate the wind speed drops to what appears to be the calmest period of 2018 up until then.

Air Temperatures fell below -40°C - their lowest values of the year, before a few days later rising above 0°C.

The air pressure sensor clearly reads bad data as that was happening. I know this doesn't tell us anything about the data, but it indicates the period was unusual compared with the rest of the year. Basically something odd was happening...

I have looked at the weather maps - but I am no meteorologist. I will come back to that data in the future.

What I do know is it takes a lot of energy to get a trillion tonnes of ice moving.

Once it was in motion a reanalysis data product from the University of Maine shows on 20 July 2018:

It was almost 20 °C warmer than the mean over the Weddell Sea and Larsen Ice shelf – and this is what we see in the weather data from AWS14 above. At the same time London, UK was coping a very significant heatwave, this area had some extreme temperatures. There is actually an emperor penguin colony in that region - I wonder how this affected them?

I am going to continue to track A68a.