Warm Atlantic waters wage a new assault on Arctic ice from below 
 
 A new enemy is undermining ice floating on the Arctic Ocean: heat from below. 
 
 Sensors that have plumbed the depths of Arctic seas since 2002 have found warm currents creeping up from the Atlantic Ocean and helping drive the dramatic retreat of sea ice there over the last decade. A new study shows this “Atlantification” of the Arctic Ocean as a new, powerful driver of melting, alongside losses due to rising air temperatures. 
 
 The paper shows “a massive shift” in the behavior of the Arctic Ocean over a short time, says Finlo Cottier, a physical oceanographer with the Scottish Association for Marine Science in Oban who was not part of the study team. “Here we’re seeing an ocean basin changing on a generational timescale—or less,” he adds. 
 
 Deep below the Arctic sits a ridge that splits the ocean roughly in half: The Amerasian basin sits on the North American side, whereas the Eurasian basin lies north of Europe and most of Asia. Both basins are losing ice fast. Across the entirety of the Arctic Ocean, it’s disappearing at an eye-popping rate of 13% per decade since satellite data was available. It has also thinned by 1.7 meters since the 1970s. 
 
 Warm Atlantic waters, delivered by an offshoot of the Gulf Stream, have long been known to prevent ice formation north of Scandinavia, on the western side of the Eurasian basin. Satellite data show that, in general, sea ice is much more prevalent in the eastern side of the basin, north of Siberia. But over the last decade, ice has also begun to disappear here, too. It used to persist through the sunny summers, allowing several years of ice growth to accumulate. Now, the ice melts in summer, causing the total time without floating ice in the region to jump from less than 1 month per year to more than three. 
 
 To understand this new trend, scientists in 2002 began installing sensors on lines tethered to the floor of the Eurasian basin, called moorings. The team relied on a total of nine moorings, augmented with satellite data and sensors bolted below drifting sea ice and along ice frozen to the shore. When they retrieved data from the moorings in 2015, they found that the ocean had experienced a dramatic change over the previous decade, especially during the winter. 
 
 Between Norway and Greenland in the western Eurasian basin, Atlantic currents flow into the Arctic at a depth of 200 to 250 meters, about 4°C warmer than the surface water. In winter, cold air cools surface waters until they fall and mix with the warm waters below. That creates an overall warmer, well-mixed ocean over the top 250 meters, and one with little sea ice. 
 
 On the eastern side of the basin, however, the warm Atlantic waters were kept at bay—until recently. The currents lurked at a depth of about 150 meters, but they didn’t mix much with surface layers, because of a barrier called the cold halocline layer (CHL)—a boundary between salty deep waters and fresher water on top. Summer ice, as it forms, rejects salt, leading to the creation of dense, salty waters just below the ice. Those waters are heavier, and as they fall they create a highly stratified ocean. “Previously this monster, Atlantic warm water, was well covered from the surface” by the CHL, says Igor Polyakov, a physical oceanographer at the University of Alaska in Fairbanks, who led the study. “The new data show this layer has disappeared in winter.” 
 
 The result, he says, is an increased “Atlantification” of the Arctic, where the eastern side of the Eurasian basin is becoming more like the western side, the team reports today in Science . The top of the Atlantic water, according to one mooring, had risen from a depth of 140 meters in the winter of 2003–04 to a depth of 85 meters just a decade later. Without summer sea ice forming to establish the CHL, he says, the ocean mixes more—and less ice forms. 
 
 On the eastern side of the Eurasian basin, say Polyakov and his colleagues, air temperatures were the main culprit for ice melting in the 2000s. Now, however, they believe air temperatures and warm waters share the blame about equally. Polyakov says a positive feedback loop is underway, in which less summer sea ice will lead to warmer winter waters and even less summer ice in subsequent years. One unknown is how the addition of massive flows of freshwater from Siberian rivers, bolstered by thawing permafrost, could affect the system, says study co-author Eddy Carmack, an oceanographer with Fisheries and Oceans Canada in Sidney. That new freshwater could encourage more sea ice to form on the basin, unless winds wash the new water away. ||||| The Arctic is undergoing an astonishingly rapid transition as climate change overwhelms the region. 
 
 New research sheds light on the latest example of the changes afoot, showing that parts of the Arctic Ocean are becoming more like the Atlantic. Warm waters are streaming into the ocean north of Scandinavia and Russia, altering ocean productivity and chemistry. That’s making sea ice recede and kickstarting a feedback loop that could make summer ice a thing of the past. 
 
 “2015 was a really anomalous year when we had problems finding a suitable ice flow to launch our drifting buoys,”Igor Polyakov, an oceanographer at the University of Alaska who led the new study, said. “(There was) nothing like that in the past, and it became a motivation to our analysis: why was ice in 2015 so rotten? What drives this huge change?” 
 
 The findings, published in Science on Thursday, show that while warming air has a role to play, processes are playing out in the ocean itself that are fundamentally altering the region. 
 
 Those changes will have impacts on the people, plants and animals that call the Arctic home. They could also create more geopolitical tension as resources previously locked under ice become available and shipping lanes open up. 
 
 In the east Arctic Ocean, the shift is manifesting itself in changing the layers of the ocean. There’s a cap of cold, less salty water that covers the eastern portion of the Arctic Ocean. Underneath it sits a pool of warm, salty Atlantic water that until recently hasn’t been able to find a way to surface. That stratification of layers has kept ice relatively safe from its warm grip. 
 
 The ocean has become gradually less stratified since the 1970s. Using data from buoys and satellites, Polyakov and his colleagues have found a more marked shift over the past decade and a half. Since 2002, the difference in water temperatures between the layers has dropped by about 2°F. 
 
 In winter from 2013-2015, the cap separating the deep water and surface water disappeared completely in some locations, allowing the warm Atlantic waters to reach the surface and cut further into sea ice pack. At the same time, warm air has further reduced sea ice, which is allowing still more mixing of the ocean layers. 
 
 The result is a feedback loop that is essentially turning roughly a third of the eastern Arctic Ocean into something resembling the ice-free Atlantic Ocean. 
 
 “Rapid changes in the eastern Arctic Ocean, which allow more heat from the ocean interior to reach the bottom of sea ice, are making it more sensitive to climate changes,” Polyakov said. “This is a big step toward the Arctic with seasonal sea-ice cover.” 
 
 The changes are already apparent in the region, which has largely been ice-free during the summer since 2011. The sea ice winter maximum, which has set a record low for three years running, has been largely driven by a lack of ice in the eastern Arctic. 
 
 Polyakov said he’s seen the rapid changes in ice firsthand. When they first put buoys in the eastern Arctic in 2002, researchers had to reach the sites on heavy icebreakers. 
 
 “Now we can reach them using an ice class ship,” he said. Ice class ships are not necessarily as reinforced as icebreakers. 
 
 The sea ice changes are having profound impacts outside of researchers’ ability to access more remote sites. Other research published earlier this week in Science Advances shows that thinning sea ice is allowing phytoplankton to bloom across the region. 
 
 Phytoplankton are tiny plants, and like your average potted plant, they need sunlight to bloom. Sea ice has been thick enough to prevent that from happening until very recently. The new findings show that over the past decade, up to 30 percent of the Arctic has become primed for summer blooms. 
 
 “Both of our results show the Arctic becoming a very different place than it has been in the past,” Christopher Hovart, an oceanographer at Harvard who led the plankton study, said. “Water pathways are changing, the ecology is changing, all driven by the declining sea ice field.” 
 
 This article is reproduced with permission from Climate Central. The article was first published on April 6, 2017. ||||| E. Baccega/age fotostock/Robert Harding Picture Library 
 
 Before indifferent satellite eyes, the top of the world is undergoing a transformation. The Arctic ice pack, a primary indicator of climate change, has shrunk in recent weeks to an extent that no computer model and few scientists had thought possible. 
 
 After five years that all saw less ice than previously documented in the 34-year satellite record, this year’s record loss has scientists questioning their models. They are also striving to understand the complex cascade of effects — from shifting weather patterns to displaced marine species — that the accelerating retreat could trigger. 
 
 The US National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, announced the record decline on 26 August, saying that the ice extent had dropped to 4.10 million square kilometres (see ‘Going, going...’). The figure is 70,000 square kilometres less than the previous record low, set in 2007, and it came at least two weeks before the annual low is typically reached. According to the NSIDC, by 9 September that figure had dropped by another 14%, to around 3.52 million square kilometres. 
 
 The massive melt has occurred in relatively normal weather conditions, with only one strong summer storm to hasten the break-up of the pack ice. Mark Serreze, director of the NSIDC, says that much of the Arctic pack is now thin first-year ice — frozen only last winter — which requires much less energy to break apart and disperse than multi-year ice. “We have entered a new regime,” he says. “The sea ice is in such poor health in spring that large parts of it can’t survive the summer melt season, even without boosts from extreme weather.” 
 
 National Snow and Ice Data Center 
 
 Computer models that simulate how the ice will respond to a warming climate project that the Arctic will be seasonally ‘ice free’ (definitions of this vary) some time between 2040 and the end of the century. But the observed downward trend in sea-ice cover suggests that summer sea ice could disappear completely as early as 2030, something that none of the models used for the next report by the Intergovernmental Panel on Climate Change comes close to forecasting1. 
 
 “There’s a tremendous spread between observations and model projections,” says Serreze. “It might be that natural variability is larger than assumed, or perhaps models don’t get the change in ice thickness right.” Uncertainty also remains over the strength of various natural ‘feedbacks’. For example, an exposed ocean is darker than an ice-covered surface and so absorbs more solar heat, causing yet more warming and melting. 
 
 A lack of fine detail about circulation patterns in the Arctic Ocean could also be throwing off the models. For example, a survey carried out in 2008 revealed 20 formerly unobserved eddies, each some 15 to 20 kilometres in diameter, in waters north of Canada. “Whether these are new features, and what role they might play for ocean-mixing processes, we don’t know yet,” says Yves Gratton, an oceanographer and Arctic researcher at the National Institute of Scientific Research in Montreal, Canada. 
 
 Ice loss could also accelerate if the ice pack’s underlying waters warm up. Unlike in most of the world’s oceans, the coldest water in the Arctic, at −1 °C to −2 °C, is at the surface; below a depth of 200–300 metres, saltier and warmer water of about 1 °C flows in from the Atlantic. The cold surface layer — called the halocline — isolates the sea ice from the warmer water below. 
 
 But the halocline is vulnerable to warming from above, says Henning Bauch, a marine geologist at the GEOMAR research centre in Kiel, Germany. A thinning halocline — something that has not yet been observed — would not only jeopardize the sea ice but could also melt the carbon-rich permafrost beneath shallow coastal waters2, releasing greenhouse gases into the atmosphere. 
 
 Meanwhile, Arctic biology is already changing, as the retreat and thinning of sea ice allows more sunlight to penetrate the upper ocean and deprives certain species of habitat, says Jørgen Berge, a marine biologist at the University of Tromsø in Norway. For example, the dominant Arctic zooplankton — the copepods Calanus hyperboreus and C. glacialis — are being replaced by Atlantic C. finmarchicus. Meanwhile, Arctic cod (Arctogadus glacialis) is increasingly being out-competed by its larger Atlantic cousin Gadus morhua3. 
 
 Other species are showing unexpected resilience. In January, a research cruise into the pack ice north of Svalbard, Norway, found evidence that Apherusa glacialis — amphipods, or small crustaceans, that feed on algae growing beneath the ice and are the main food source for many Arctic sea birds — are less dependent on extensive sea ice than previously thought. Just as some coastal organisms drift with the tide to retain their positions in river estuaries, these amphipods can sink to depths at which pole-ward ocean currents sweep them farther north, where they can find and colonize surviving sea ice4. 
 
 “This looks like an adaptive trait that allows key Arctic-ice fauna to persist in changing sea-ice environments,” says Berge, who led the study. He points out that the Arctic Ocean has been ice-free during the summer several times during the past 2.5 million years, and that as recently as 8,000–6,500 years ago, during a period known as the Holocene Thermal Maximum, much more of the Arctic was ice-free than it is today5 — with no mass-extinction events known to have occurred. 
 
 Farther afield, this year’s record sea-ice melt might foreshadow a harsh winter in parts of Europe and North America. Recent research, although preliminary, suggests a connection between late-summer Arctic sea-ice extent and the location of areas of high and low atmospheric pressure over the northern Atlantic. The highs and lows can remain relatively fixed for weeks, shaping storm tracks and seasonal weather patterns such as extended cold surges6. 
 
 Ralf Jaiser, a climate scientist at the Alfred Wegener Institute for Polar and Marine Research in Potsdam, Germany, found a significant correlation in 1989–2011 meteorological data between late-summer Arctic sea-ice extent and atmospheric-pressure anomalies that favour extreme weather such as prolonged cold snaps in winter7. He reasons that in autumn, the open Arctic Ocean sheds heat to the high-latitude atmosphere. The warming tends to reduce the large-scale atmospheric-pressure gradient and weakens the dominant westerly winds in the Northern Hemisphere. Those winds normally sweep warm, moist Atlantic air to western Europe; their weakening leaves the region more prone to persistent cold. 
 
 “The impacts will become more apparent in autumn, once the freeze-up is under way and we see how circulation patterns have influenced the geographical distribution of sea ice,” says Judith Curry, a climate researcher at the Georgia Institute of Technology in Atlanta. But, she adds, “We can probably expect somewhere in the mid/high latitudes of the Northern Hemisphere to have a snowy and cold winter.”
– The "Atlantification" of the Arctic Ocean is underway. And no, that doesn't mean we're about to get the polar bear version of Outkast, but rather that the Arctic Ocean is rapidly becoming more like the Atlantic Ocean, according to new research published Thursday. The Arctic Ocean has historically been separated into two layers: a cold, less salty layer on top with a salty, warmer layer of Atlantic water underneath, Scientific American reports. The barrier between the two is called the cold halocline layer, and it's been responsible for preserving Arctic sea ice, according to Science. But the separation between the layers has been quickly breaking down over the past decade or so. The temperature difference between the two layers has lessened by 2 degrees since 2002, and the top layer of cold water has gotten thinner in the past decade—possibly by as much as 180 feet. From 2013 to 2015, the layers merged completely in some areas. The loss of the cold halocline layer means sea ice in the Arctic is getting attacked from both sides. Warming air and warming surface ocean temperatures are creating a "positive feedback loop" that is decimating the ice. Sea ice in the Arctic is decreasing by 13% every decade, and soon the Arctic Ocean could be entirely ice-free during the summer. Between warmer water with more nutrients and no more ice to block the sun, it's unclear what will happen to the Arctic's ecosystem, Inverse reports. (One woman's desperation advanced Arctic exploration.)