Ice has weighed heavy on the Arctic for at least two million years. And now it´s rapidly retreating. Present studies of ice sheets in Greenland and Antarctica help us unravel the past. The past provides perspective on the future.
Text: Maja Sojtaric
We are just coming out of an ice age, as remarkable as it may sound.
The Quaternary period, as geologists call it, has also been called The Great Ice age and it is the period that we currently live in. It started 2,7 million years ago and has sporadically covered the higher latitudes with ice. Culminating in the last glacial maximum, some 25.000 years ago, when Northern Europe and America were covered with ice sheets up to 4 km thick.
Just imagine that somebody smacked Mont Blanc on top of Denmark.
The Barents Sea in the Arctic, now deep and secretive, was covered by just such a massive ice sheet 25 millennia ago. This ice soaked up the water: The levels of all of Earth´s oceans dropped by 120 metres.
Ice sheets and their outlet glaciers forever changed the face of the Earth. Deep fjords of Norway were bulldozed. Other mega terraforming also took place: Submerged on the continental shelf in the Barents Sea are enormous troughs carved by ice streams, large fast-moving tongues of ice draining from these ice sheets.
This phenomenal power of ice is on going today in Antarctica and Greenland. No wonder it is attractive to scientists and adventurers alike. Professor Alun Hubbard at CAGE is both.
The berg that sank Titanic
On the west coast of Greenland is the outlet glacier that once gave birth to the most famous iceberg of all, the one that sank the luxury ship Titanic. In that same fjord Hubbard’s humble boat Gambo spent several winters 100 years later.
Looking at images of Gambo, a small vessel with the red Welsh dragon on the bow, you could rightfully ask what had possessed the glaciologist to let this seemingly fragile thing spend the winter next to a giant, groaning wall of ice. You could easily fit hundreds of Gambos in the famous vessel praised as unsinkable.
“On a small boat you can do whatever you want. Such as observe Greenland´s glaciers in the frigid winter months, which nobody else does.” says Hubbard.
No only did Gambo stay afloat, but also provided the basecamp for the collection of new winter data.
The melting Greenland
Greenland´s ice sheet is melting at a record rate and is the largest contributor to global sea level rise. In 2014 it lost 500 cubic kilometres of ice to the ocean, much of which was in the form of calving bergs.
The scene of Gambo´s frosty endeavour was Store Glacier, one of the largest and fastest moving marine terminating glaciers in West Greenland. But as opposed to its many neighbours, it doesn´t serve as a good example of retreating ice sheet due to climate change: It´s 500 meter calving front has been in the same position for close to 50 years.
“The stability of Store glacier is what makes it interesting. It allows us to calibrate the natural processes that make glaciers tick. We then incorporate this knowledge into our models at CAGE to better understand natural systems that glaciers are a part of.” Hubbard explains.
What makes glaciers calve and melt in Greenland is the violent encounter with another force of nature: The North Atlantic Current. This tropical warm water is attributed to up to 50% of the loss of mass from the marine edges of Greenland ice sheet.
When two forces collide
It seems logical that tropical ocean water carried around by the North Atlantic Current can melt ice. But it is not that simple, the warm water runs deep.
You need a catalyst that brings it to the glacier front, and the glacier itself provides that. If you look carefully at the seawater at the front of a glacier it will often appear as if it is boiling. Plumes of fresh water shooting out from the ice cause this bubble bath effect. The reaction between salinity and density of the warm and cold water create prefect conditions for the upwelling of warm Atlantic water from depths of 400 metres.
“ The ocean is doing most of damage to the front of the glacier. And it is happening in the winter too, even though we can´t see it because the fjords are frozen.”
The source of the fresh water is the surface melting of the ice sheet, which is prevalent in the summer with warm temperatures. But it also comes from the friction created by glacier´s movement, heating up the base. And that continues throughout the winter months.
“Ocean water contains much more energy than air. The atmosphere cools in winter, but the deep ocean waters keep warm to fuel continued melting of the glacier front even throughout long frigid months. ”
The end of the ice age
The very same processes undermined the massive ice sheet in the Barents Sea. For much of the Quaternary the ice sheet weighed heavy on what is now the sea bottom. Then it started retreating rapidly by the same violent encounter with warm, salty water conveyed by the North Atlantic Current.
(This is supported by several paleontological studies from CAGE professor Tine Rasmussen and her group. See link)
Professor Karin Andreassen at CAGE leads the team of modellers, glaciologists, and geologists that Alun Hubbard is a part of.
The team looks at 3D seismic records of the seabed, paleontological discoveries and present day processes to discern what happened to the Barents Sea ice sheet from its maximum extent to complete demise.
“Field data of today are integrated in modelling experiments that help us create snapshots, time slices of the past.” says Andreassen.
What happened to methane?
Professor Andreassens group is particularly interested in what happened to the methane hydrates, a solid ice form of the greenhouse gas under the ocean floor. Under the immense pressure and cold temperatures of the ice sheet this volatile structure was created and remained stable for millions of years under the Barents Sea bottom.
But then ice sheet collapsed. Now the stability zones are constrained to narrow slivers of deepest ocean. (see figures)
“When the ice disappeared, the enormous pressures exerted by the ice sheet were released. The floor became warmer as the ocean once again occupied the basin. This destabilized the methane hydrates. And when they melt, we get explosive flares that release a very potent greenhouse gas into the ocean.” says Andreassen.
Why does it matter?
The present helps us understand the past. And that could be more important to our future than we know. We don´t know enough about the events of deglaciation in the Barents Sea, says Andreassen. But we better learn. Because the planet´s ice sheets are still retreating. And under all that pressure, there is methane hydrate.
“Barents Sea during the last glacial maximum is much like the ice sheet in West Antarctica today. There are several studies that suggest that there are large methane hydrate reservoirs under West Antarctica. That makes it very important to learn why the Barents Sea ice sheet varied through time and what happened to the methane hydrate in the past.”