Global Warming Slows Antarctica’s Coldest Currents

March 5, 2014 by admin  
Filed under Global Warming

A shift from briny to fresh in Antarctica’s ocean waters in recent decades could explain the shutdown of the Southern Ocean’s coldest, deepest currents, a new study finds.

The cold currents, called the Antarctic Bottom Water, are chilly, salty rivers that flow from the underwater edge of the Antarctic continent north toward the equator, keeping to the bottom of the seafloor. The currents carry oxygen, carbon and nutrients down to the deepest parts of the ocean. Previous studies have found this deep, dense water is disappearing, though researchers aren’t sure if the shrinkage is part of a long-term trend linked to global warming, or a natural cycle.

The new study suggests that Antarctica’s changing climate is to blame for the shrinking Antarctica Bottom Water. In the past 60 years, the ocean surface offshore Antarctica became less salty as a result of melting glaciers and more precipitation (both rain and snow), researchers reported Sunday (March 2) in the journal Nature Climate Change. This growing freshwater layer is the key link in a chain that prevents the cold-water currents from forming, the study finds.

“Deep ocean waters only mix directly to the surface in a few small regions of the global ocean, so this has effectively shut one of the main conduits for deep-ocean heat to escape,” said Casimir de Lavergne, an oceanographer at McGill University in Montreal.

Holey ice

The linchpins linking freshwater and cold currents are polynyas, or natural holes within sea ice. These persistent regions of open water form when upwellings of warm ocean water keep water temperatures above freezing, or when winds drive sea ice away from the coast.

Polynyas are one of the main sources of Antarctica Bottom Water. Polynyas act like natural refrigerators, letting frigid temperatures and cold winds chill seawater and send it sinking down to the ocean bottom. As the cold water sinks, warmer ocean water comes up to take its place, maintaining the polynya’s open water. [Album: Stunning Photos of Antarctic Ice]

But as Antarctica’s ocean surface water has freshened, fewer polynyas have appeared, the researchers found. That’s because the fresher water is less dense. Even if the water is very cold, it doesn’t sink as readily as saltier water, de Lavergne explained. The freshwater acts like a lid, shutting down the ocean circulation that sends cold water to the seafloor, and brings up warm water into the polynyas.

“What we suggest is, the change in salinity of the surface water makes them so light that even very strong cooling is not sufficient to make them dense enough to sink,” de Lavergne told Live Science. “Mixing them gets harder and harder.”

Trapped heat

In addition to warming and shrinking the Antarctic Bottom Water currents, the reduction in polynyas could be trapping extra heat in the Southern Ocean, de Lavergne said.

“If the warm waters aren’t able to release their heat to the atmosphere, then the heat is waiting in the deep ocean instead,” he said. “This could have slowed the rate of warming in the Southern Hemisphere.”

De Lavergne cautioned that the heat-storage effect is localized and not related to the so-called global warming “hiatus” — the recent slowdown in the rise of global surface temperatures.

“Our study is still a hypothesis,” he added. “We say that climate change is preventing convection from happening, but we do not know how frequent it was in the past, so that’s a big avenue for future research.”

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Article source: http://www.scientificamerican.com/article/global-warming-slows-antarcticas-coldest-currents/

Greenland ice sheet future ‘grim’

December 28, 2010 by admin  
Filed under Global Warming

Dr Alun Hubbard and his team camped about 70 miles (112km) up the ice sheet in Greenland

A glaciologist is warning that the Greenland ice sheet is “retreating and thinning extensively” after a year of record-breaking high temperatures.

Dr Alun Hubbard on Aberystwyth University says its future is “grim” but disputes claims by other experts that it could collapse within 50 years.

He maintains it would be at least 100 to 1,000 years before it “potentially passes any point of no return leading to any widespread collapse”.

Dr Hubbard and his team have been analysing the results of a summer-long expedition.

His team of 15 from Aberystwyth and Swansea universities spent five months on the ice sheet from the beginning of May.

The group camped about 70 miles (112km) up the sheet, and measured the thickness, speed, climate, and other vital statistics using radar, seismic and geophysical equipment.


Large melt lakes form on the Greenland ice sheet

They found rising temperatures had caused extensive melting in new upper parts of the ice sheet in this “very sensitive polar region of the planet”.

This has generated at least double the quantity of melt water, compared with 2009, which runs off the ice sheet into the Atlantic and Arctic oceans.

There are fears the melting of the entire sheet could raise sea levels globally by about 7m (20ft), and a study last year found it was losing its mass faster than in previous years.

Dr Hubbard said his expedition had proved enhanced melting was more than just replenishing the oceans, it was now “directly contributing to global sea-level rise”.

He said global warming - at least local Greenland warming - was “worse than ever”.

“This year was another record-breaking year marked by very warm temperatures across Greenland and the Arctic,” he said.

“This warming enhanced and extended melting into new northern and upper parts of the ice sheet generating huge quantities - at least double that compared with the previous year - of melt water which runs off the ice sheet into the ocean.”

Dr Hubbard has spent four years researching the effects of climate change on the country. He has also worked on other glaciers and spent five years working in Antarctica before the Greenland project started.

It’s much like the ice is suddenly aquaplaning or slipping on a banana skin  -Alun Hubbard

The team of scientists and students monitored the build up and drainage of a series of large melt lakes - up to five miles (8km) across - which form on the ice sheet surface during the summer and can drain rapidly to the bed through more than 1000m of ice.

He said the effect of this rapid drainage was to “lubricate and hydraulically lift up” the base of the ice sheet, “overcoming friction with underlying rock”, thereby allowing the sheet to flow much faster.

“It’s much like the ice is suddenly aquaplaning or slipping on a banana skin,” he explained.

“What we observed using methods borrowed from earthquake monitoring, is that the ice sheet slides and accelerates massively when these lakes drain, but the effect is relatively short lived and that the flow does regulate as further melt water drains to the bed.”

His work is part of a wider project involving researchers from Bristol, Cambridge, Edinburgh, Denmark, Sweden, the Netherlands, Germany and the United States.

Dr Hubbard and his team plan to return to the Greenland ice sheet next year to study the effect that reduced winter sea ice has on ice sheet flow and ice berg calving.

Funding for the research has come from the Natural Environment Research Council.

Article source: http://www.bbc.co.uk/go/rss/int/news/-/news/uk-wales-mid-wales-11993455

Melting sea ice blamed for UK Arctic weather

December 25, 2010 by admin  
Filed under Global Warming

Scientists are claiming melting sea ice in the Arctic Ocean is the cause of the bitter polar weather causing chaos across Europe.

Recent meteorological reports claim a high pressure area over the Atlantic resulting in the repositioning of the jet stream combined with the influence of La Nina are responsible for the current bleak midwinter. Scientists in Germany, however, are forming a complementary theory, with climate experts at the Potsdam Institute suggesting melting sea ice could be the cause.

The institutes Vladimir Petoukov believes the big freeze is a result of global warming causing sea ice in the Arctic to melt, changing wind patterns across the northern hemisphere and bringing icy blasts of freezing air across the UK. He expects the trend to continue, with Britain shivering in the grip of longer and colder winters.

Petoukov states the disappearing sea ice will have an unpredictable effect on the climate in the northern hemisphere due to a complex and powerful feedback mechanism detected in the Barents-Kara Sea. He adds that colder winters are not disproving the global warming theory, but are supplementing it.

The Arctics floating ice cover is though to have diminished by around 20 per cent in recent years, with temperatures rising at up to three times the global average. As the ice melts, the comparatively warm sea water loses its heat to the atmosphere, causing an area of high pressure to form. This creates clockwise Arctic winds which sweep southwards over northern Europe and the UK.

Although the climate research institute states its too early to link the last two years bitter winters to changes in the Arctic, it believes the theory resulting from the research is strong. and predicts freezing winters will continue for around 50 years, after which warmer winter conditions will develop.

Article source: http://news.carrentals.co.uk/melting-sea-ice-blamed-for-uk-arctic-weather-34230354.html

As the Arctic Ocean Melts

December 22, 2010 by admin  
Filed under Global Warming

22 Dec 2010: Interview

With the Arctic Ocean heading toward a largely ice-free state in summer, scientists are looking for areas that may help preserve ice-dependent creatures. In an interview with Yale Environment 360, geologist Stephanie Pfirman talks about the need for a refuge north of Canada and Greenland that researchers say could be a kind of Noahs Ark in the age of global warming.

As scientists from around the world tracked the rapid decline of Arctic sea ice in recent years, they couldnt help but notice that one part of the Arctic basin is a repository for the oldest and thickest polar ice. Stetching across northern Greenland and the Canadian Arctic Archipelago, this band of reasonably sturdy ice forms as prevailing wind and ocean currents drive sea ice from Siberia, across the Arctic, and up against the opposite shore.

Stephanie PfirmanStephanie Pfirman

Leading Arctic sea ice specialists believe that this strip of ice could become a crucial ice refuge as summer sea ice all but disappears in most other parts of the Arctic by mid- to late-century. One of those researchers is Stephanie Pfirman, co-chair of the Environmental Science Department at Barnard College in New York City, who, along with several colleagues, presented the concept of the Arctic sea ice refuge at the recent meeting of the American Geophysical Union.

In an interview with Yale Environment 360, Pfirman described how the refuge could become a key habitat for polar bears, ringed seals, and other ice-dependent Arctic creatures. While these species are likely to suffer major population declines in other parts of the Arctic, the ice refuge zone could harbor substantial numbers of these creatures until the end of the 21st century and, possibly, beyond.

The good news, says Pfirman, is that if humanity begins to significantly reduce its emissions of greenhouse gases, the ice refuges could preserve Arctic species and enable them to repopulate the region if ice levels recover in the future.

Yale Environment 360: Can you tell me where the concept of the Arctic sea ice refuge came from?

Stephanie Pfirman: With the summer sea ice projected to decline, the more we looked at the models, the more we realized that in the latter half of this century most models project that there will still be some ice. And so that got us thinking. Where will that ice be? And where would it come from? The observations show that right now the oldest ice is right up along the northern flank of Canada and Greenland. The oldest ice has been there for a long time, and we know that from our analysis of the way the ice moves. And it makes sense that its there because the winds come from Siberia. They blow across the Arctic, and the Russian currents do, too, and it basically piles up ice in northern Canada and Greenland. So in the future, as you continue to freeze the ocean during the wintertime, the winds will blow that winter ice over toward Canada and Greenland. So its likely that youll continue to have ice there even when you have less and less ice in the summertime.

Then we looked at the model projections and they were showing the same thing. So theres a real scientific consensus saying that this is likely to be the place thats going to have the most persistent ice into the future. So then once you know that, then you say, well, what does that mean?

e360: I want to get into the details of this so-called refuge, but could you first describe the rate of melting, both in terms of extent and thickness, that is driving the necessity to even think about having an ice refuge?

Pfirman: When I first started working on ice up in the Arctic back in 1980 or so, ice tended to be in equilibrium and was around three meters thick. Thats at least twice as thick as it is now.

e360: Throughout the Arctic basin?

Pfirman: Yes, but even more so in this [refuge] area. When you ridge the ice, when you deform it, you pile it up and then you have much, much thicker ice. Ice would form and then it would get transported in this big gyre, the Beaufort Gyre, kind of like a whirlpool, to the one side of the Arctic. And the ice just circulates around and around in that area and can stay there for over a decade.Then on the other side theres the Transpolar Drift Stream that goes from the middle of Siberia, sweeps all the way across and over the North Pole. So you had these two systems and right in the middle of the two is kind of this dead zone where the ice is very slow and sluggish and its up against the Canadian Arctic archipelago and Greenland. And thats the likely place of the refuge.

e360: And one of your colleagues said that based on the rate of melt and the continued pouring of greenhouse gases into the atmosphere, that in the 2030s and 2040s you could see a really precipitous drop of Arctic sea ice?

Pfirman: Yes. So the [steep] drop that we saw in 2007, something like that had actually been projected by Marika Holland, Cecilia Bitz, and Bruno Tremblay, who had done some work earlier where they had said that theres no reason why, with the warming that were having, the decline of ice has to happen gradually. It could happen precipitously. And those are

A new study says if we do act to reduce greenhouse gas emissions, then it looks like the sea ice can come back.

called rapid ice loss events. They were analyzing a lot of models and they said, you know, there is potential for this to happen and it could result in much diminished ice cover. Theres a really neat new study that just came out [in Nature], which shows that if we do act to reduce greenhouse gas emissions, then it looks like the sea ice can come back. Its kind of a bookend on our refuge analysis, because what were saying is, if we dont act, whats the base case? Where is the most persistent ice likely to be? What are the sources of it? But what they did was they said,

Article source: http://e360.yale.edu/feature/as_the_arctic_ocean_melts_can_refuge_save_polar_bears/2355/

Nanoparticles from melting glaciers could trap carbon

December 10, 2008 by admin  
Filed under Global Warming

by Catherine Brahic from http://www.newscientist.com

The increasing number of icebergs breaking off Antarctica may have an unexpected benefit. According to one team of scientists, the bergs could feed carbon-loving plankton. If they are right, melting icebergs could - theoretically - slow global warming. Just how great an effect this would have remains to be seen.

Rob Raiswell of the University of Leeds, UK and colleagues trained high-resolution microscopes on ice sampled from icebergs in the Southern Ocean and the Antarctic glaciers from which they are born.

They found nano-sized particles of iron, between five and 10 millionths of a millimetre across. The team believe that because of the size and structure of the particles, the iron could be assimilated by phytoplankton.

“Most of the ground-up rock carried by icebergs is thought to be inert,” says Raiswell. “However, the high resolution microscopy shows there are small amounts of iron nanoparticles. They simply could not be seen except by these techniques.”

Phytoplankton need iron in order to grow, and the Southern Ocean is generally thought to be low on iron. But there is evidence that some Antarctic glaciers are flowing into the ocean faster because of climate change. This means more icebergs. If Raiswell’s findings are correct, more icebergs would mean more dissolved iron, therefore more phytoplankton, and more carbon dioxide sucked out of the atmosphere and into the oceans.

Plankton boost

“Dust has been thought to be the main outside source of iron to the Southern Ocean,” says Raiswell. He and his colleagues calculated that existing icebergs could double the supply of iron to the region.

The researchers will need to prove that the nano-iron can indeed boost plankton growth. Ken Denman of the Canadian Centre for Climate Modelling and Analysis says there is some debate over what form of iron phytoplankton can use. “For example, only a few percent of air-borne iron deposited in the oceans is believed to be readily utilisable by phytoplankton,” he says.

Denman also points out that climatologists think there is typically less iron in the oceans during warm inter-glacial periods. “Why would human-induced warming increase the iron supply whereas recent natural warming occurred at the same time as decreased iron and southern Ocean [phytoplankton], as far as we can tell from the ice cores?”

It is too early to say how much of an impact more icebergs will have. One problem is that not all plankton sinks to the bottom of the ocean and contributes to the deep-ocean carbon sink. Part of it is eaten by marine animals and returned to the water column in their excrement. Geochemists have only a poor idea of the amount of carbon that is cycled in this way.

Journal reference: Geochemical Transactions (DOI: 10.1186/1467-4866-9-7)