From the UNIVERSITY OF EXETER
A new study reveals the sub-antarctic island of South Georgia — famous for its wildlife — was covered by a massive ice cap during the last ice age.
The results are published today in the journal Nature Communications. South Georgia, the remote UK territory where Sir Ernest Shackleton landed during his dramatic voyage from Antarctica to rescue the team of his Endurance expedition, is home to various species of penguins and seals, and has featured on documentaries including Frozen Planet and Planet Earth II.
The island’s unusual plant communities and marine biodiversity, which are protected within a large Marine Protected Area, have survived and evolved through multiple glacial cycles for tens or even hundreds of thousands of years.
But a research team led by the University of Exeter has discovered that at the peak of the ice age, about 20,000 years ago, ice thickened and extended tens of kilometres from the island — far further than previously believed.
This would have driven its biological communities to small mountain and seabed refuges to survive.
The researchers also found the ice has been sensitive to short-lived cooling and warming — growing and shrinking dramatically as the climate changed.
“Although the island is small framed against Antarctica’s great ice sheets, the discovery of an extensive past ice cap on South Georgia is an important result,” said lead author Dr Alastair Graham, of the University of Exeter.
“The survival of ocean ecosystems is linked heavily to patterns of glaciation, so it is very interesting to know where and how sea-bed creatures lived through the ice age, and how the cycles of ice-cap change have influenced the biodiversity.
“Life must have really only survived at the edges, at and beyond the ice margins.
“Our work also provides a key data point for ice sheet and climate models, which will now need to simulate a large ice field on South Georgia during the last ice age if they are to have confidence in their outputs.”
The team from the UK, Germany and Australia travelled to the island on British Antarctic Survey’s RRS James Clark Ross in 2012, and the German RV Polarstern in 2013 to carry out sonar mapping using sophisticated sonar technology mounted to the hulls of ice-breaking vessels.
They also used weighted gravity corers to retrieve samples of ancient sediment from the ice-carved troughs that radiate from the island to reveal past patterns of glacier expansion and melting.
The researchers discovered hundreds of distinct ridges bulldozed into the seabed by glaciers, showing that — contrary to previous estimates — the ice extended across South Georgia’s vast continental shelf.
Co-author Duanne White, from the University of Canberra, said: “Glaciers in the sub-Antarctic are retreating dramatically today, in response to an ever-warming atmosphere and ocean.
“It is perhaps unsurprising that South Georgia’s glaciers were sensitive to climate change in the past, but our work has really shown that they were dynamic and underwent big changes over geological time.
“Improving the history of glacier behaviour on South Georgia even further is now essential so that we have a long-term context for the alarming recession we are witnessing right now.”
Co-author Dominic Hodgson, from British Antarctic Survey, said: “The sub-antarctic is a region experiencing massive climate changes with rapidly shrinking glaciers and the loss of several ice caps in recent decades.
“Studying the longer-term history of glacial changes in the region is key to understanding the sensitivity of glaciers to climate change, and their impacts on biodiversity and species survival.”
The paper is entitled: “Major advance of South Georgia glaciers during the Antarctic Cold Reversal following extensive sub-Antarctic glaciation.”
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The real star of this show is the bipolar seesaw. The article is about a specific episode during the process of deglaciation from the last glacial maximum which began with slow warming in the southern ocean around Antarctica 20k years ago. About 15k years ago Antarctic warming went into reverse for a couple of thousand years, an event called the Antarctic Cold Reversal. At the same time the episode of abrupt warming of the NH took place due to a strong excursion of the AMOC and Gulf Stream. This event was the Bolling-Alerod NH warming. The Gulf Stream warms the North Atlantic by stealing ocean heat from the SH in the Atlantic, a process known as heat piracy and which takes place, appropriately, in the vicinity of the Caribbean.
The Bolling-Alerod warming was a D-O event, the last one during the recent glacial period. Immediately after the B-A there followed cooling as the AMOC petered out and this led to the retro-cold period in the NH that is called the Younger Dryas. Due to the operation of the bipolar seesaw however, NH cooling in the NH was accompanied by SH warming, as the Antarctic Cold Reversal was itself reversed and Antarctic and SH deglaciation warming resumed. South to north heat piracy declined as the AMOC died down and with it the Gulf Stream.
What triggered the B-A and simultaneously the Antarctic Cold Reversal was a huge ice sheet collapse in the slowly warming Antarctica 15k years ago. This released a large meltwater pulse into global ocean circulation which had the indirect effect of kick-starting the AMOC in the North Atlantic. And the AMOC was itself terminated – as always – by meltwater from Greenland interfering with formation and downwelling of cold North Atlantic deep water.
The article in question focuses mainly on this Antarctic Cold Reversal, a brief episode of reversal of deglaciation warming; not the previous glaciation ad a whole. It shows the strength of the bipolar seesaw.
see saw = conservation of energy
Of course it bloody well was. The south of New Zealand was glaciated for Christ’s sake!
Glaciers in NW Nelson at the top of the South Island and even in the Tararua Ranges in the North Island during the LGM. Still small glaciers in Mt Ruapehu in the Central North Island even now.
See! The ice is melting.
We’re doomed.
Do you know how much the ice-albedo feedback is contributing to climate change?
About 25% of CO2.
K. Pistone, I. Eisenman, and V. Ramanathan (2014). Observational determination of albedo decrease caused by vanishing Arctic sea ice. Proc Natl Acad Sci USA 111, 3322-3326.
http://eisenman.ucsd.edu/papers/Pistone-Eisenman-Ramanathan-2014.pdf
Shackleton, Worley and Crean had to cross South Georgia’s glaciated mountains to reach the whaling station from the isolated beach where they had made landfall, after their 800 mile crossing from Elephant Island that was the final part of the incredible bid for survival after their stranding in Antarctica in 1914. Shackleton’s survival epic is increasingly recognised and maybe the most remarkable feat of survival in known history. Of all the dangers they faced on the ice and sea and in freezing gales, their trial on the Montains of South Georgia was probably the most dangerous, where the group’s three leaders came closest to death. Equipped only for a one-day quick crossing of the mountains, they were stranded on a glacial ridge as night approached and with it probable death from cold. Shackleton understood the stakes and chose to “slide”. They found a snow covered slope and without seeing what lay further down – rocks, cliffs etc, they just tobbogganed downhill blindly hoping for the best. They rode their luck and got away with it – reaching the other side of the ridge safely and walking to the whaling station and eventual rescue. This is all recorded in the book “Endurance” by Albert Lansing and I understand another film, “Ice” is now being made of this adventure.
http://www.goodreads.com/book/show/139069.Endurance
Shackleton was probably mightily pleased to find that South Georgia was NOT glaciated when he arrived.
Indeed – they had not been away quite that long!
Shackleton died from a heart attack in Grytviken on a subsequent expedition and is buried in the Norwegian cemetery there.
In a way he was lucky. If he had died in England and been buried in Westminster Abbey, who would have known or cared today?
While almost everybody who has visited South Georgia for the last 100 years (including yours truly) have visited Shackleton’s grave to pay homage one of the greatest polar explorers ever.
South Georgia will be added to my bucket list
More interesting reading – Antarctica used to be a tropical paradise https://www.nap.edu/read/12168/chapter/4#22
So you agree that the Antarctic climate can be highly variable….
Never said it wasn’t – but it’s not going to change any time soon. Not as long as the tilt of the planet and the orbit remains the same.
Earth’s Milankovitch factor are right now changing by -0.003 W/m2/yr.
That’s right — negative. Implying cooling.
Instead we’re warming. Fast.
crackers
indeed warming exactly as fast as we have already 19 times during the Holocene.
And the current warming number 20 is special because…?
I’d like to see the data showing that the Holocene has warmed 19 times before at today’s rate (+0.17 C/decade for the last 30 years, according to NOAA and other groups).
WUWT, thank you; occasionally you come up with a valuable tit-bit. This is another tell-tale of something science has not yet come to terms with. That the earth’s tilt changes beyond the 22-24 deg range, and that change is abrupt (how abrupt is ??? but definitely less than decades). There is a need to check the basics.
melitamegalithic, what’s the evidence the tilt angle changes abruptly?
The calendars tell the date by following sunrise point on horizon over the year. The angle equinox to solstice, at latitude 35.8 deg N, tells the earth obliquity at that time. One later calendar started at 18deg (same as most of the earlier ones) sometime post 3000bce, then was modified to today’s obliquity. In fact it corroborates Dodwell’s claim of an obliquity change at 2345bce. There are earlier changes, all abrupt, with tell-tales of events that appear in proxies. You may find all recent findings in the Facebook page set up update my earlier publication. Link to here, there is a lot of material on proxies and how the calendars work::: https://www.facebook.com/melitamegalithic/
All changes seen from archaeology are confirmed/corroborated in proxies. There are several obliquity swings recorded in their design. (I have also tested the design in model form and it is very precise).
So you’re relying on calendars that are thousands of years old, instead of modern astronomy.
Why would the tilt angle change abruptly? What would cause that?
crackers345, this may help you with your question. Warming polar regions but simultaneous cooling in tropics. All seismic events. Megalithic calendar design during that period records earth tilt. https://www.facebook.com/melitamegalithic/photos/a.689655294542612.1073741862.430211163820361/689655301209278/?type=3&theater
crackers345, no reply button after your question above. An answer is here. Note the subject of this thread. We rely many times on proxy evidence, because there are no direct answers to questions. The calendars happen to point to a clear answer to something the effect of which appears in many proxies, and in astronomical observation of the past. It has been noticed that ancient measurements of obliquity do not match modern calculations for that age. That has never been explained (except some attempts to deny, which is wrong). The ancient calendars tell clearly otherwise.
As to why the abrupt change, ????,; however, first it has to be acknowledged. Present thinking deny it can happen, the result of a wrong assumption from the past.