The Birthplace of Arctic Sea Ice
For the past several years, the expanse of sea ice in the Arctic has melted more and more intensively during the summer months. To determine whether, and if so how, this trend will continue, we have to first better understand the processes involved in the formation and disappearance of sea ice. With that goal in mind, AWI researchers like the sea-ice physicist Thomas Krumpen are now especially exploring a region considered to be the ice machine of the Arctic – the Laptev Sea in northeast Siberia.
When Thomas Krumpen flies over the Laptev Sea in springtime, the AWI researcher sees nothing but ice. The sea off the coast of Siberia looks like a splintered pane of frosted glass, a chaotic mosaic of jagged fragments in countless shades of grey and white. The Laptev Sea is essentially the birthplace of Arctic sea ice. Here, in the remote northeast reaches of Russia, during the winter the wind incessantly blows from land out to sea. It pushes against the ice floes in the water, driving them forward - away from the shore and due north. As a result, the ice cover near the coast is increasingly broken up, briefly leaving behind areas of open water referred to as polynyas. But when exposed to the wintry air, which can be as much as 40 degrees below zero Celsius, they quickly refreeze. A thin sheen of ice is created, only to be broken up and then blown onward by the wind... This process constantly produces new sea ice in the Laptev Sea, which then finds its way to the Arctic Ocean. The Arctic ice machine only shuts down in May, when even northeast Siberia grows warmer - and starts back up in early October, when the icy winter winds return.
Sea-ice researcher Thomas Krumpen knows this interplay of frost, wind and water inside and out. Together with peers from the GEOMAR Helmholtz Centre for Ocean Research (Kiel) and experts from Russia's Arctic and Antarctic Research Institute (AARI, St. Petersburg), he conducts experiments in the Laptev Sea area on a regular basis. One of Krumpen's goals is to find answers to the question of why Arctic sea ice is melting more and more each summer. Over the past 25 years, the summer ice cover has shrunk from 8 million to 5 million square kilometres. "Like many other researchers, we're convinced that the increased melting is due to climate change. Our current goal is to better grasp the physical interactions between the sea ice and the Arctic Ocean, those between the sea ice and the atmosphere, and how these processes will change in connection with global warming," explains Thomas Krumpen.
The retreat of the Arctic Sea Ice Cover over time
The ice's journey ends in the Fram Strait
Research efforts in the Laptev Sea offer clues as to how much new ice is formed each winter. But in order to assess the fate of the Arctic sea ice, the researchers also need to determine how much ice flows back out of the Sea. One of the most important outlets is the Fram Strait – the sea lane between Greenland and Svalbard. Each year, between 500,000 and 800,000 square kilometres of sea ice – an area roughly twice the size of Germany – flow through the strait from the Arctic Ocean to the northern Atlantic.
The motor of this ice transport is the transpolar drift, a major current that pushes ice from the Russian marginal seas of the Arctic Ocean over the North Pole and toward the Fram Strait like a giant conveyor belt. “We are working to better estimate the ice mass balance in the Arctic by examining two factors – how ice is created in the Laptev Sea, and how it is lost again via the Fram Strait – in relation to one another,” says Thomas Krumpen.
As a rule, it is only the sea ice formed in the Laptev Sea in the early winter that survives its first summer. Caught by the transpolar drift, it is transported to the central Arctic. Once there, it can remain two to three years, growing to several-metre-thick pack ice in the process, before passing through the Fram Strait and into the Atlantic, where it melts. In contrast, the ice formed in the late winter usually melts before it can flow out of the Laptev Sea.
Over the past several years, Thomas Krumpen and his colleague Stefan Hendricks have regularly taken part in plane or helicopter flights over the Laptev Sea and the Fram Strait. During these flights they rely on the EM-Bird, a device that can measure differences in electrical conductivity from the air, allowing it to determine how thick the ice is.
Old ice in Arctic vanishingly rare
Since the 1980s, the amount of perennial ice in the Arctic has declined. This animation tracks the relative amount of ice of different ages from 1987 through early November 2014. The oldest ice is white; the youngest (seasonal) ice is dark blue. Key patterns are the export of ice from the Arctic through Fram Strait and the melting of old ice as it passes through the warm waters of the Beaufort Sea. (Animation by NOAA Climate.gov team)
Early warning signs of the great melting
The AWI sea-ice physicist conducted one such measuring campaign in the much-cited record year 2012, in which the Arctic sea-ice cover shrank to only 3.4 million square kilometres, the smallest expanse recorded since the advent of satellite measuring in 1979.
In a sense, Thomas Krumpen had seen the negative record year coming: in March 2012 he and partners from the Russian-German research project “System Laptev Sea” had made flights over the Laptev Sea and discovered surprising quantities of thin ice. “In places where the sea ice had been up to 1.5 metres thick in the winter of 2007/2008, in the spring of 2012 we encountered stretches up to 400 kilometres across where the ice was only 50 centimetres thick. This allowed us to safely assume that above all the ice in the Laptev Sea region would largely melt away by the end of the summer,” he explains.
The amount of old, thick ice in the central Arctic has been dwindling for years thanks to global warming, which has increased the sea ice’s drift speed. As a result, more and more ice is flowing out of the Laptev Sea. When this is combined with strong offshore winds, like those in the winter of 2012, huge stretches of thin ice form, only to rapidly melt away come spring.
This melting is accelerated further by the fact that in summer the dark stretches of open water warm much faster than the sea ice. “This warm water intensifies the melting of the remaining ice, an effect we’ve been able to clearly observe since 2012. For example the Northeast passage, the shipping route leading from the northern Atlantic and along the Siberian coast to the Pacific, was free of ice relatively early in the year,” says Thomas Krumpen.
Sentinels on the seafloor
The sea-ice physicist and his colleague Polona Itkin have now succeeded in reconstructing observations of the Laptev Sea with the help of mathematical models and satellite data. By doing so, they have confirmed what had long been only a theory, namely that the ice formed in the Laptev Sea during the winter and early spring plays a key role in determining the fate of Arctic ice in the Northeast passage once the summer comes.
“Now we’re interested in how these processes in the Laptev Sea affect the overall volume of ice in the Arctic, because that volume, which depends on both the thickness and the area, is already in decline,” claims Thomas Krumpen. According to the AWI researchers’ models and measurements, the amount of ice exported from the Laptev Sea appears to be increasing, because the young, thin ice is quickly carried away.
In order to validate their model, the researchers need to gather additional data. With that goal in mind, in 2013 Thomas Krumpen and Stefan Hendricks installed buoys at two points in the Laptev Sea. Anchored to the seafloor, the buoys are equipped with an Upward-looking Sonar (ULS) system, which consists of a transmitter that sends acoustic signals up toward the water’s surface. If it encounters ice, the distance travelled by the signal is correspondingly shorter, making it possible to determine how thick the ice is. Unlike flights with the EM-Bird, this method allows the researchers to collect data on a single location for weeks or even months at a time.
Flying halfway around the globe: measuring sea-ice thickness in the Arctic
Anyone who wants to accurately predict the summer ice extent in the Arctic has to first know how thick the ice is at the end of the long winter, which is why the AWI sea-ice physicists set out each spring to measure major sections of the Arctic sea-ice cover. Their flight route usually begins in Svalbard, taking them west over Greenland and Canada and ending in Alaska. The following gallery presents a selection of snapshots taken during flights in the spring of 2015 as part of the NETCARE campaign.
In the air from Svalbard to Canada
As in the Laptev Sea, ice export is also increasing in the Fram Strait. This is indicated by satellite data, which can be used to determine ice drift and concentration. The AWI researchers have also observed that the thickness of sea ice in the Fram Strait has decreased significantly. Together with their American, Canadian and Norwegian peers, Thomas Krumpen and Stefan Hendricks are working to gather the requisite data in measuring flights for the project PAMARCMIP (Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project). For this research campaign, every spring the researchers fly a route starting in Svalbard, continuing over the Fram Strait to Greenland and ultimately to the western coast of Canada, measuring the ice thickness for spans measuring hundreds of kilometres. “But at this time, we still can’t say to what extent the increased ice export in the Fram Strait will be compensated for by the lower ice thickness,” says Thomas Krumpen.
A further open question is how the altered ice mass balance – the increased export from the Laptev Sea and the Fram Strait – will affect the Arctic as a whole. According to Thomas Krumpen: “The trend of summer ice loss can clearly be recognised – but whether the Arctic will be completely ice-free in the summer, and if so, in how many years, is something we’ll only be able to say once we better understand the sea ice.”