The Arctic ice is melting into Nordic Seas but the Gulf Stream remains

Mosaic of images of the Arctic by MODIS on the Aqua satellite. 

Credit: NASA

The melting ice in the Arctic is not the source of reduced saline in Nordic Seas.

It is the Gulf Stream that has provided less salt.

A new study published Sunday in Nature Geoscience claims; the source of fresher Nordic Seas, since 1950, is rooted in the saline Atlantic, as opposed to an influx of Arctic freshwater, dispelling the common inference.

"This is an important finding as it shows that the Gulf Stream is not about to short circuit. A halting Gulf Stream has been a concern with ongoing climate change; its collapse was taken to the extreme in the Hollywood blockbuster The Day After Tomorrow," says Tor Eldevik, professor in oceanography at the University of Bergen and the Bjerknes Centre.

Reversing the chain of events
The Nordic Seas have freshened substantially since 1950. At the same time, there has been observed an increased river runoff and net ice melting in the Arctic.

The concurrence of a less saline ocean and Arctic freshwater input has given the climate research community reason for concern.

"It has been a concern that a layer of Arctic freshwater could impede the Gulf Stream's Arctic branch."

"Going back in time, into and through the ice ages, such a freshwater lid has been understood to reduce ocean circulation and thus the Gulf Stream's poleward heat transport," says Tor Eldevik.

Eldevik is co-author of the study where Mirjam Glessmer and colleagues at the Bjerknes Centre in Bergen, Norway, show that change in the Nordic Seas is at the receiving end of change in the more global climate system.

Southern freshwater
The researchers from the Bjerknes Centre have analysed the available observations back to 1950 and conclude that the changing salt content in the Nordic Seas is explained by the variable salinity of the Gulf Stream's Arctic branch entering the seas from the south.

The mode of operation is also realised in a numerical ocean model forced by the observed stated of the atmosphere during the period in question.

Although not part of the present study, it appears to be several reasons for the freshening of the Atlantic source waters.

A dominant explanation is a general increase in net precipitation over the North Atlantic Ocean (which may very well relate to global climate change).

The contribution is spread over the Gulf Stream system, and accordingly transported further northward.

The analysis of Glessmer and colleagues further shows, and in line with the above, that the salt deficit in the Nordic Seas is not related to a surface layer of freshwater.

The low-salinity anomaly since 1950 is distributed throughout the water column following the Gulf Stream's northern overturning from warm surface flow to cold deep water.

Potential for climate prediction
The study has important practical implications.

The Bjerknes Centre is presently developing the Norwegian Climate Prediction Model, with the aim of establishing a Norwegian operational system for climate prediction on seasonal to decadal time scale.

"Our study documents how large-scale changes in our marine climate propagate with the extension of the Gulf Stream into the Nordic Seas."

"This suggests that the marine climate could be predictable on the time scale that a climate signal is travelling north," concludes Tor Eldevik.

More information: Glessmer, M.S., T. Eldevik, K. Våge, J.E.Ø. Nilsen, and E. Behrens, 2014: "Atlantic origin of observed and modelled freshwater anomalies in the Nordic Seas." Advance online publication Nature Geoscience, dx.doi.org/10.1038/ngeo2259

Significant amount of methane is escaping from the East Siberian Arctic Shelf

Main bathymetric features of the Arctic Ocean, taken mainly from Weber 1983 'Maps of the Arctic Basin Sea Floor: A History of Bathymetry and its Interpretation' on a base of a screenshot taken from the Nasa WorldWind software. 

Credit: Mikenorton / Wikipedia

A combined team of U.S. and Russian researchers has found that large amounts of methane are bubbling up from the subsea permafrost along the East Siberian Shelf.

In their paper published in the journal Nature Geoscience, the team describes research they've conducted over several years from fishing vessels in the Laptev Sea and other areas along the shelf along with the results of measurements they've made.

North of Russia lies the Arctic Ocean, over time, parts of it have been given different names—one of those the Laptev Sea, lies north of Siberia, and is bounded by peninsulas on both sides.

The sea normally freezes in the winter and thaws in the summer, but the water remains so cold that the seafloor has, at least until recent years, remained frozen.

The researchers in this latest effort have been monitoring the amount of methane released into the sea as the subsea permafrost melts in the summer.

The melting of the subsea permafrost in the Arctic Ocean can't be blamed on modern humans—it's been slowly warming down there for thousands of years—it's just recently however, reached the point where it melts in the summer just enough to allow the methane in it to seep out and bubble up into the sea column above.

The researchers have been seeing record levels of methane in the both seawater and permafrost core samples they've been collecting over the past several years (they also use sonar to measure the density of bubbles emanating into the seawater).

Worse, they have found that methane levels drop dramatically during storms.

This means, the researchers report, that all that methane in the seawater is whipped into the atmosphere, adding to the other greenhouse gasses that are contributing to global warming.

The researchers note that their measurements contradict predictions by others that a massive "pulse" of methane will very soon add as much as 50 billion tonnes of methane to the atmosphere, causing a dramatic spike in global air temperatures.

Instead, they suggest, it appears more likely that the methane will continue to bubble up slowly, contributing to greenhouse gases much as is happening currently—though they do caution that its possible global warming could cause more or bigger storms in the Arctic Ocean, releasing methane on a bigger scale.

More information: Ebullition and storm-induced methane release from the East Siberian Arctic Shelf, Nature Geoscience (2013) DOI: 10.1038/ngeo2007

New Zealand's Southern Alps glaciers reducing rapidly

Hochstetter Icefall feeding the retreating Tasman Glacier in the Southern Alps of New Zealand's Southern Island.

Credit: Dr. Huw Horgan

Historic records show Franz Josef Glacier retreated three kilometres in the last century and mathematical modeling indicates it is likely to retreat even more this century.

Other glaciers in the region, including Fox Glacier, are declining at similar rates as a result of climatic change says Dr Brian Anderson, a senior research fellow at the Antarctic Research Centre, who is supported by a Marsden Fast Start research grant.

Dr Anderson says mathematical modelling helps him, and other researchers in the team, understand how glaciers have evolved since the last ice age.

It also helps them analyse what is occurring now and predict how many glaciers in the Southern Alps will fare in the future.

Brian Anderson

"It's important to see the long term picture to really understand what's going on. That's because many of our glaciers—Fox and Franz Josef particularly—change so quickly and, apparently, so erratically.

"In the 12 years we've been carrying out this study, we've seen them rapidly retreat and then rapidly advance."

"It's not until we look back over the past century that we see an overall pattern of retreat emerging," says Dr Anderson.

"Looking ahead, we are likely to see warmer and wetter weather, which means Franz Josef and Fox glaciers will retreat a lot—our best estimate is that they will be seven or eight kilometres shorter than present by 2100."

The research findings are being collated and published as part of the Antarctic Research Centre's glacier monitoring project which also involves Dr Ruzica Dadic, Dr Huw Horgan and Associate Professor Andrew Mackintosh.

Together, the researchers are observing and measuring three glaciers—the well-known Franz Josef and Tasman glaciers and the lesser-known Brewster Glacier.

Nicolas Cullen

Other collaborators on the Brewster Glacier project are Dr Nicolas Cullen at the University of Otago and Dr Andrew Lorrey at NIWA.

The data gathered is contributing to the University of Zurich's World Glacier Monitoring Service.

Dr Anderson says: "Already we are seeing issues at Franz Josef Glacier, where walking access has not been possible for more than a year, and tourists are now being flown onto the ice."

"These are the kinds of things being predicted to happen around the world as glaciers decline and temperatures continue to warm," he says.

Earlier this year, Dr Anderson says a 70-metre chunk of ice broke off the terminal face of Tasman glacier, releasing an estimated seven million cubic metres of ice into Tasman Lake.

"Tasman is undergoing rapid decline right now, with large chunks breaking off and falling into Tasman Lake.

We are using time-lapse photography to capture these 'calving' events as they happen and gather valuable information on ice loss and glacier behaviour at the same time."