Jonathan Amos

Complex mesoscale landscapes beneath Antarctica mapped from space The landscape shrouded by the Antarctic Ice Sheet provides important insights into its history and influences the ice response to climate forcing. However, knowledge of this critical boundary has depe...

These subtle ripples have revealed the presence of thousands of previously unknown hills, valleys, ridges and ancient river systems. New paper in Science Magazine from Helen Ockenden et al. www.science.org/doi/10.1126/...

New map reveals landscape beneath Antarctica in unprecedented detail Scientists believe the map could shed light on how Antarctica's vast ice sheet will respond to climate change.

The landscape hidden beneath Antarctica's ice sheet has been mapped from space for the first time. Scientists used hi‑res satellite observations to track how the continent’s frozen surface bunches and dips as it moves over the rugged rock bed below. www.bbc.co.uk/news/article...

A small silver lining: Yes, NASA and NOAA did not do briefings for their global temp data sets released today. And they certainly do not emphasize the human causes. But they *did* release them. The work is still happening.

data.giss.nasa.gov/gistemp/grap...

www.ncei.noaa.gov/access/monit...

🌊❄️ When Antarctic glaciers collapse into the sea, they can trigger huge underwater tsunamis that mix the ocean, affecting ice loss, climate and ecosystems.

The project I lead on this is now in the field and featured on Sky News:
news.sky.com/story/underw...

#Antarctic #OceanMixing #ClimateScience

NASA Modis

One big paddling pool becomes three. Today's view of iceberg A23a (left) and a view from the end of December (right). Notice how the raised rim effect, holding in surface meltwater, has re-established on all three main segments of the broken berg. A23a is turning to slush puppie.

NASA Aqua Modis 11 January

💥 Boom! And it's just happened. The huge volumes of meltwater that had collected on the surface of iceberg A23a have triggered a massive and catastrophic hydrofracture event. Much of the berg has turned to mush. Three major segments remain, the largest about 500 sq km.

NOAA 20 / VIIRS - Iceberg A23a viewed on 24 December 2025

Want to see an iceberg turn to mush? What remains of iceberg A23a (<1,000 sq km) is about to experience death by hydrofracture. Look at all the meltwater sitting atop the berg. The whole thing could just fall apart any day now.

I haven't heard about the disagreements. The ice was sitting on an ice plain - a very flat bed with low basal drag. These are present beneath the downstream parts of many Antarctic glaciers where the sediment they transport has built a depositional body known as a grounding zone wedge.

Rapid Antarctic glacier retreat sparks scientific 'whodunnit' A new study suggests that changes to Hektoria Glacier are unprecedented - but not all scientists agree.

And if you want a longer read, my old mate Mark Poynting has a great write-up on Auntie Beeb. www.bbc.co.uk/news/article...

"Such records are vital for distinguishing between rapid grounding-line retreat, as is reported to have occurred at Hektoria Glacier, versus the retreat of a floating ice margin through “conventional” iceberg calving processes," says polar SAR specialist Frazer Christie at Airbus Defence and Space.

NASA/AQUA/MODIS

But the paper has caused a stir because there is wide disagreement in the glaciology community about precisely where Hektoria had been fully grounded on bedrock due to a lack of high-accuracy satellite records.

Swansea Uni co-author @adrianluckman.bsky.social put this Sentinel-1 movie together. "Although the paleo record indicates some very rapid retreats in the past, the pace of retreat of Hektoria Glacier and its neighbours is unprecedented in the observational record," Adrian says.

Record grounded glacier retreat caused by an ice plain calving process - Nature Geoscience An Antarctic glacier retreated after the loss of landfast ice at a peak rate almost an order of magnitude faster than previously recorded because of buoyancy-driven ice calving, according to an analys...

Ochwat and Colorado/Boulder co-author Ted Scambos described the lightning-fast fracturing as “shocking” and warned that the retreat “changes what’s possible” for important glaciers elsewhere on the continent. www.nature.com/articles/s41...

Satellite images of the terminus of Hektoria glacier taken on 26 October 2022 (left) and 23 February 2023 (Copernicus/ESA/A.Luckman/Swansea University)

Hektoria lost ~25km in 15 months, with 8.2km fragmenting in just the Nov/Dec of 2022. Naomi Ochwat et al point to a particular vulnerability: an "ice plain" - a big section of glacier ice sitting on flat seabed rock that suddenly goes afloat, spitting off icebergs like crazy.

Antarctic glacier's alarming retreat is the fastest ever seen Hektoria glacier on the Antarctic Peninsula retreated 25 kilometres in just 15 months. Its rapid melt could have implications for other glaciers and the rate of sea level rise

A fascinating paper in @NatureGeosci that has already sparked considerable debate in the ice community. It's the super-fast withdrawal of Hektoria Glacier on the eastern side of the Antarctic Peninsula in 2022/23. Words by me in @newscientist.com www.newscientist.com/article/2502...

Speed reading "Science under Siege" - ahead of next week's recording of BBC Science in Action, where co-author @michaelemann.bsky.social joins a panel on the front line of the current assault on science, to answer what can be done.
An appropriate topic for the last edition of the 60yr old series.

Ooops! It's happened again. The remnants of iceberg A23a have been caught on another Taylor Column, this time above the NorthWest Georgia Rise to the north of South Georgia BOT. The fragments have spun around and around for more than a month now.

Fab first data from the UK-supplied Microwave Sounder on the new Metop weather satellite. MWS combines obs from the old MHS & AMSU instruments. MWS measures the temperature and water content sitting at different altitudes. Fundamental data needed by computer models' for medium range forecasts.

NASA Terra/Modis 30/8/25

Really clear view today of Iceberg A23a's big fragmentation event. Going back through the data, I think it happened on the 25th/26th. Image from NASA/Terra/Modis. Each new fragment is probably big enough to get a US National Ice Center designation. Likely A23g, A23h and A23i.

OK, the US National Ice Center was being a bit more generous than me. It logged A23a at 2,371 sq km. For comparison, the current title holder of the "world's biggest iceberg" is A15a at 3,070 sq km, grounded in the Amery Sea off East Antarctica.

Iceberg A23a Nasa Terra/Modis 28/8/25

🚨🚨🚨Boom! Iceberg A23a looks to have undergone a major fragmentation event in the past 24 hours. I count at least three "daughter" bergs (g, h and i ?). Further satellite imagery will confirm. The last intact measurement I made was ~2,250 sq km. @bas.ac.uk

Polar View Sentinel-1

Iceberg A23a update. It's lost another couple of large chunks in the past few days. Are we getting close to a major fragmentation event? Likely so.

Iceberg A23a on 7/7/25 Eumetsat/Meteosat 12

In case you were wondering... Iceberg A23a seen cruising around South Georgia today by Meteosat 12. The old berg still has an area of 2,846 sq km.

Iceberg D15a, grounded in the Amery Sea, is now officially "the world's biggest iceberg".

PolarView 13/5/25

Sentinel-1 has finally got a clear view of iceberg A23a (13/6/25). The berg is much diminished as it skirts around South Georgia. And the US National Ice Center has updated its stats: A23a is now only the world's second biggest berg at 829.79 sqNM, or 2846,11 sqKM.

Grounded position of iceberg A23a in early March off the coast of South Georgia

You can see the original grounded position in this BBC map. The berg is following the expected track, riding the prevailing current and hugging the continental shelf. It could always ground again. But if not, it should sweep around SG and go north.

The movement of iceberg A23a over the past seven days. It's moved about 80km to the southeast of the position where it grounded off the coast of South Georgia in early March. Zoomed in animation from Meteosat-12.

Nasa Worldview measurement of iceberg A23a

And I'm pretty sure now that A23a is no longer the "World's Biggest Iceberg". D15a is larger in my view. But only the US National Ice Center can make that determination and its listing doesn't yet reflect this.

Nasa Worldview image of iceberg A23a

Somebody's got itchy feet! Iceberg A23a has moved in the past couple of days. It grounded close to South Georgia back at the beginning of March. But the erosion and melting since then has clearly allowed it to break free. Does it now reground or sweep off around the island?

Latest #CopernicusAtmosphere AOD forecast (from 30/05 00 UTC) shows smoke plume from devastating (&growing) Canadian #wildfires continuing across the Atlantic with hazy skies for Europe over next few days atmosphere.copernicus.eu/charts/packa... @copernicusecmwf.bsky.social @ecmwf.int