Polar Push & Bounce Back -Trends at the Extremes NEW ZT

On January 2018, methane levels as high as 2764 ppb (parts per billion) were recorded. The solid magenta-colored areas near Greenland indicate that this very high reading was likely caused by methane hydrate destabilization in the sediments on the seafloor of the Arctic Ocean.

The state of the sea ice is behind this. On January 1, 2018, Arctic sea ice extent was at record low for the time of the year. The smaller the extent, the less sunlight gets reflected back into space and is instead absorbed in the Arctic.

At this time of year, though, hardly any sunshine is reaching the Arctic. So, what triggered this destabilization? As the image below indicates, year-to-date average Arctic sea ice volume has been at record low in 2017, which means that there has been very little sea ice underneath the surface throughout 2017.

Warm water will melt the sea ice from below, which keeps the water at greater depth cool. However, when there is little or no sea ice underneath the surface, little or no heat will be absorbed by the process of melting and the heat instead stays in the water, with the danger that it will reach sediments at the bottom of the Arctic Ocean, as illustrated by the image below.

[ image from: Warming is accelerating ]

The image on the right shows warm water from the North Atlantic arriving near Svalbard. How warm is the water beneath the surface of the Arctic Ocean? The image below gives an indication, showing how much warmer the water was from October 1, 2017, to December 30, 2017, at selected areas near Svalbard, where warm water from the North Atlantic dives under the sea ice of the Arctic Ocean, carried by the Gulf Stream.

[ click on images to enlarge ]

In 1981-2011, temperatures were gradually falling by more than one degree Celsius from October 1 to the December 21 Solstice, then started to rise again in line with the change in seasons (blue line).

https://theconversation.com/warm-waters-melting-antarctic-ice-shelv...

The vast expanse of the Antarctic is a region of the world particularly vulnerable to climate change, where ice loss has the potential to significantly increase sea levels.

Now, for possibly the first time in 7,000 years, a phenomenon known as “upwelling” (the upward flow of warmer ocean water to the surface), is thought to have caused recent ice shelf collapse around the continent – and the glacial thinning associated with it.

Ice shelves floating on water are the oceanic extension of land glaciers and ice sheets, and the primary region for ice loss. As these shelves break apart, the flow of continental ice held up behind them accelerates.

The ocean surrounding Antarctica is extremely cold, but water over 300m deep, Circumpolar Deep Water (CDW), is about 3⁰C above the melting point of ice. Normally, the very cold water above keeps this away from ice shelves. But in some areas, CDW is spilling onto the shallow Antarctic continental shelf, causing the ice to thin.

Ice shelf thinning has accelerated in recent decades, but the picture is not the same everywhere. While the east of the Antarctic has shown modest gains in ice thickness, the west has outstripped this with significant ice loss – up to 18% in vulnerable areas like the Amundsen and Bellingshausen Seas.

The pattern of ice loss and other observations indicate that warmer water upwelling beneath these ice shelves is driving it. But what has caused this upwelling? Is it related to human activity? And how concerned should we be?

Two teams led by scientists from the British Antarctic Survey, both of which I have been working with, set out to tackle these precise questions by focusing on two vulnerable areas. One site is in Pine Island Bay, in the Amundsen Sea, and the other is in Marguerite Bay, in the Bellingshausen Sea.

The aims of the studies are similar – to monitor the extent of upwelling warm water onto the continental shelf over the past 10,000 years, in order to understand when this last occurred and what the impact was.

This involves collecting and sampling “cores” of sediment up to 10m long from the sea bed at a range of depths up to 900m. Obtaining suitable cores is particularly challenging in these remote locations, where glacial dynamics often disturb the sediment.

Core evidence

Much of the evidence for past oceanography comes from tiny shells of amoeboid organisms called foraminifera. A huge variety of species colonise habitats on the sea floor and make up much of the sediment collected. There can be hundreds of shells in just one gram of sediment.

Electron microscope images of planktonic foraminifera N. pachyderma from Pine Island Bay. Scale bar: 100µm equals 0.1mm. Nature Publishing Group

Forams are extremely valuable, as their shells are made of calcium carbonate precipitated from the ocean water in which they lived. Examining these shells allows us to reconstruct the chemistry of ocean water.

There were two geochemical tracers used for warm CDW in Pine Island Bay – the proportion of carbon isotopes, and the magnesium to calcium ratio controlled by water temperature. Both of these showed CDW was last on the inner shelf over 7,500 years ago.

In Marguerite Bay, shells of another plankton group called diatoms were also analysed. These indicate past productivity and sea surface temperatures. They showed that CDW was persistently on the shelf here over 7,000 years ago, and more sporadically since then.

Tellingly, the enhanced upwelling of warm CDW in both locations negatively impacted the local extent of ice.

Winds of change

Both studies suggest that the cause of the CDW upwelling before 7,000 years ago was a more southerly position of the southern hemisphere westerly winds (SHWW). These winds are thought to drive circulation of the warmer deep water. A recent shift in the position of the SHWW towards the poles could be the cause of greater CDW upwelling in Pine Island Bay since the 1940s.

Data llustrating the apparent link between winds and ocean around western Antarctica. The migration of the southern hemisphere westerly winds (SHWW) coincide with upwelling of Circumpolar Deep Water (CDW) in the Amundsen Sea.

This coincidence of timing with the onset of industrialisation shows it is possible that human made greenhouse gasses, thought to cause atmospheric warming, are having an impact on the position of the winds, the increase in warm water reaching the surface, and ultimately the melting of more ice in the Antarctic.

Irrespective of the causes of past changes in SHWW positions, the link between winds and ocean upwelling is cause for concern, as future projected global warming may shift SHWW belts and promote further upwelling and melting. More research is now needed to fully understand the link between CDW and past climate, and to estimate the strength of upwelling since the 1940s compared to upwelling before 7,000 years ago. But the emerging picture is one of the potentially increased vulnerability of West Antarctic ice sheets, and possible future sea level rise.

Comment by SongStar101 on February 28, 2018 at 11:23am: The polar vortex just split in two. Get ready for some wild weather from Europe to the U.S.

https://mashable.com/2018/02/15/polar-vortex-split-stratospheric-wa...

The polar vortex, the notorious swirl of winds around a low pressure area in the upper atmosphere over the Arctic, has split in two. Since the polar vortex tends to be associated with some of the coldest air during the winter, the split — which is more like a temporary separation than a lasting divorce — means that ultra cold air is on the move.

A split in the polar vortex may sound like a complicated weather concept, but it has huge consequences for weather patterns from Canada to Eurasia. The latest split is likely to put Western Europe and much of Eurasia into the deep freeze for the rest of February, and will offer glimpses of hope for snow lovers along the U.S. East Coast.

Figuring out where the coldest air will go and how it will affect worldwide weather patterns for the next several weeks is a key task facing weather forecasters now.

Helping matters is that most computer models appear to agree on the broad scenario that's likely to play out. Indications are that in the near-term, colder and stormier conditions than average are likely for Western Europe and much of Eurasia during the rest of February into early March.

During that same period, the Eastern U.S. will experience something of a spring thaw, with temperatures as much as 20 to 25 degrees Fahrenheit above average for this time of year.

Highs in the 70s Fahrenheit are possible during the closing days of February in Washington, D.C. and New York City, areas that saw record cold at the start of the winter.

Ski areas in the western part of the country, particularly in the Northern Rockies, could see heavy snowfall and ideal snowmaking conditions during the next two weeks.

Models are indicating very impressive early Spring warmth across the eastern U.S. next week... the West/Rockies will have some cold air to deal with, however. pic.twitter.com/nddbOhrHGd

— Michael Ventrice (@MJVentrice) February 15, 2018

Back to the polar vortex, though. One piece of the vortex is sliding southwest, out of the Arctic and into western Canada and the Pacific Northwest, where frigid conditions and above average snowfall is favored for the next few weeks. Another is spinning out of the Arctic and over Eurasia.

Caught in between is the Arctic Ocean, which should have some of the coldest air of any region in the Northern Hemisphere right now, but instead has seen yet another unusually mild winter. The polar vortex's split means that the ultra-cold air is being siphoned away from the Arctic, leaving unusually mild conditions in its wake.

Don't be surprised if Arctic sea ice sets yet another record low for the winter season.

This split occurred in the stratosphere

The main polar vortex exists in the stratosphere, which is the layer of air above where most of our weather occurs. A sudden warming of the stratosphere over the Arctic, appropriately known as a "sudden stratospheric warming event," took place in early-to-mid February, and this has caused the splitting of the stratospheric polar vortex.

Sudden stratospheric warming events occur when large atmospheric waves send energy upward, into the stratosphere, setting in motion a complex process that results in the temporary breakdown of the polar vortex. This February's stratospheric warming event was particularly extreme, possibly setting records for how sharply temperatures spiked in the upper atmosphere.

The polar vortex split isn't the only factor favoring a cold snap in Europe, warmup in the Eastern U.S., and cool down in the West. There's also a cycle of atmospheric pressure over the North Atlantic Ocean, known as the North Atlantic Oscillation (NAO), that can increase the odds of colder and snowier weather in some of these areas.

GFS predicting textbook example of #warm #Arctic/#cold #Eurasia pattern to end the month. Can't recall such a strong and extensive #cold forecast for the Eurasian continent! pic.twitter.com/V6F3ccMdML

— Judah Cohen (@judah47) February 13, 2018

Computer models are projecting the NAO will become strongly negative during the next few weeks in response to the polar vortex split and stratospheric warming event, and this also favors cold and snow in Western Europe. (It also ups the odds of similar weather in the eastern U.S., but that may not happen right away.)

"A significant PV [polar vortex] disruption is often followed by widespread cold temperatures across northern Eurasia and the Eastern US. However the cold is more certain across northern Eurasia following these type of PV disruptions," meteorologist Judah Cohen, who specializes in seasonal weather forecasting and tracking the polar vortex for AER, a Verisk Analytics company, wrote on his blog.

The negative mode of the NAO typically features an area of strong high pressure over Greenland, which blocks the progression of weather systems moving in from the southwest, and causes the jet stream to plunge southward over Europe, allowing cold air to flow in from the Arctic and Scandinavia. Sudden stratospheric warming events tend to cause the NAO to switch into negative mode shortly after they occur.

The rest of February should feature a colder than average Western U.S., coupled with a milder than average East Coast. However, the negative NAO phase could bring a return of winter weather to the East in early March, depending where exactly that Greenland block sets up. There's often a delay between when the polar vortex is disrupted, and when the cold air arrives in parts of the U.S., if at all.

Snow lovers will be watching upcoming forecasts anxiously, because the deeper into March we go, the less likely widespread snows along the East Coast become.

Comment by M. Difato on February 22, 2018 at 7:30pm: Arctic temperatures soar 45 degrees above normal, flooded by extremely mild air on all sides

https://www.washingtonpost.com/news/capital-weather-gang/wp/2018/02...

(The temperature difference from normal over the Arctic averaged over the next five days in the GFS model forecast. (University of Maine Climate Reanalyzer)

While the Eastern United States simmers in some of its warmest February weather ever recorded, the Arctic is also stewing in temperatures more than 45 degrees above normal. This latest huge temperature spike in the Arctic is another striking indicator of its rapidly transforming climate.

On Monday and Tuesday, the northernmost weather station in the world, Cape Morris Jesup at the northern tip of Greenland, experienced more than 24 hours of temperatures above freezing according to the Danish Meteorological Institute. “How weird is that?” tweeted Robert Rohde, a physicist at the University of California at Berkeley. “Well it’s Arctic winter. The sun set in October and won’t be seen again until March. Perpetual night, but still above freezing.”

This thaw occurred as a pulse of extremely mild air shot through the Greenland Sea.

Warm air is spilling into the Arctic from all sides. On the opposite end of North America, abnormally mild air also poured over northern Alaska on Tuesday, where the temperature in Utqiaġvik, previously known as Barrow, soared to a record high of 31 degrees (minus-1 Celsius), 40 degrees (22 Celsius) above normal.

The warmth over Alaska occurred as almost one-third of the ice covering the Bering Sea off Alaska’s West Coast vanished in just over a week during the middle of February, InsideClimateNews reported. Brian Brettschneider, a climatologist based in Alaska, posted that the overall sea ice extent on Feb. 20 was the lowest on a record by a long shot.

The lack of ice has real consequences for villages along the Bering Sea whose shores are normally protected from big storms and their giant waves. Without the ice as a buffer, waves can hammer the coastline and damage homes and buildings, as this video from the village of Diomede, Alaska, shot on Feb. 20 illustrates:

https://www.facebook.com/B00p5y/videos/489533644777458/

“Scary stuff, on many levels,” tweeted Rick Thoman, an Alaskan meteorologist.

Temperatures over the entire Arctic north of 80 degrees latitude have averaged about 10 degrees (6 Celsius) above normal since the beginning of the calendar year, sometimes spiking over 25 degrees (14 Celsius) above normal (the normal temperature is around minus-22, or minus-30 Celsius)..."

Comment by Stanislav on January 8, 2018 at 10:52am: The levels of radium-228 have almost doubled over the last decade in the middle of the Arctic Ocean

Diminishing sea ice near the Arctic coast leaves more open water near the coast for winds to create waves. The increased wave action reaches down and stirs up sediments on shallow continental shelves, releasing radium and other chemicals that are carried up to the surface and swept away into the open ocean by currents such as the Transpolar Drift. A new study found surprising evidence that climate change is rapidly causing coastal changes in the Arctic that could have significant impacts on Arctic food webs and animal populations. Credit: Natalie Renier, Woods Hole Oceanographic Institution. Image source: phys.org

3 January, 2018. "Scientists have found surprising evidence of rapid climate change in the Arctic: In the middle of the Arctic Ocean near the North Pole, they discovered that the levels of radium-228 have almost doubled over the last decade.

<...> To their surprise, the research team found that radium-228 concentrations in the central Arctic Ocean had increased substantially since measurements had last been made in 2007. What was its source and why had it increased?

<...> They concluded that the excess radium had to have come from sediments in the East Siberian Arctic Shelf off Russia, the largest continental shelf on Earth. It is relatively shallow, with an average depth of 170 feet, but it extends 930 miles off shore and contains a vast reservoir of radium and other chemical compounds."

Reference:

Woods Hole Oceanographic Institution (2018, January 3). Scientists find surprising evidence of rapid changes in the Arctic. Retrieved January 08, 2018, from https://phys.org/news/2018-01-scientists-evidence-rapid-arctic.html

Journal reference:

Kipp, L. E., Charette, M. A., Moore, W. S., Henderson, P. B., & Rigor, I. G. (2018). Increased fluxes of shelf-derived materials to the central Arctic Ocean. Science Advances, 4(1). doi:10.1126/sciadv.aao1302

Link [Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).]

Comment by SongStar101 on January 3, 2018 at 11:39pm

Unfolding Arctic Catastrophe

http://arctic-news.blogspot.co.nz/2018/01/unfolding-arctic-catastro...

In 2017, temperatures were rising in October. On October 25, 2017, the sea surface was as warm as 17.5°C or 63.5°F, i.e. a 14.1°C or 24.5°F anomaly. On average, it was 12.96°C or 23.35°F warmer during the period from October 1 to December 30, 2017 (red line), compared to the same days in 1981-2011.

Comment by SongStar101 on December 14, 2017 at 11:58am: The Arctic Is Warming Faster Than at Any Point in the Past 1,500 Years

http://www.motherjones.com/environment/2017/12/arctic-climate-chang...

The Arctic is warming faster than at any point in the past 1,500 years, according to a federal government report released Tuesday. The report, led by scientists at the National Oceanic and Atmospheric Administration, also found that maximum winter sea ice coverage in the Arctic was the smallest ever recorded.

The peer-reviewed annual report card, presented at the American Geophysical Union fall meeting, compiled the work of 85 scientists from 12 nations.
“The Arctic is going through the most unprecedented transition in human history.”

“The Arctic is going through the most unprecedented transition in human history,” said Jeremy Mathis, director of NOAA’s Arctic Research Program, during a press conference.

In 2017, maximum winter sea ice area, measured each March, was the lowest ever observed. Permafrost, the layer of soil that remains frozen in the Arctic, also thawed faster than ever before.

A section of the report based on geological records found that sea ice is now declining, and temperatures warming, at a faster rate than at any other time in the last 1,500 years.

2017 was the second warmest year in the Arctic since 1900, when instrumental recordkeeping began. The all-time record was set last year. While fewer records were shattered this year than in 2016, the Arctic shows no sign of returning to the reliably frozen region it was decades ago, the report says.

The Arctic is warming about twice as rapidly as anywhere else on Earth, affecting people in the region, the fish and wildlife they depend on for food, and their environment.

“The Arctic has traditionally been the refrigerator of the planet,” Mathis said. “But the door to that refrigerator has been left open.”

Overall, the Arctic has reached a “new normal,” the report finds, characterized by declines in sea ice cover, winter snow cover, and the mass of the Greenland Ice Sheet and Arctic glaciers. The Arctic Ocean is also warming.

“The unprecedented rate and global reach of these changes highlight the pressing need to prepare for and adapt to the New Arctic,” the report says.

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https://youtu.be/MvoFDZQKJHc

Comment by SongStar101 on November 15, 2017 at 11:40am: "There is now less sea ice globally than at any other time since satellite records began in 1978."

'Daunting' Antarctic sea ice plummet could be tipping point

http://www.newshub.co.nz/home/world/2017/11/daunting-antarctic-sea-...

A dramatic drop in the amount of sea ice around Antarctica has scientists wondering if the continent has hit a tipping point.

There has been a record 30 percent decrease in the total amount of sea ice, and this summer it's disappearing from the Ross Sea at a rate not seen in more than 30 years.

The rapidly changing conditions are having a major impact on this year's scientific research at Scott Base, with scientists describing the changes as "unusual", "unprecedented" and "daunting".

One of the affected scientists is Antarctic oceanographer Dr Natalie Robinson, who studies sea ice and what lies beneath it.

"We had about 200km of sea ice to play with last year, but this year we're down to about 25-30km, so it's certainly a very different ball game," she told Newshub.

The team's plan to drill holes through the sea ice has proved impossible this season, with some of their sites now just open water.

It's also affected their camping plans. The team usually bring eight modified shipping containers onto the ice to live and work from for several weeks, but Scott Base checked the ice and it was deemed too thin or weak for heavy vehicles to travel on.

Photo credit: NASA Icebridge

The Antarctic sea ice growth in winter and melt in summer is the biggest annual change on the planet. Dr Robinson describes it as the heartbeat or pulse of Earth, and it affects everybody because it drives global weather.

"It basically doubles the size of Antarctica each year and where that sea ice sits determines where the storms go, and when and where they might hit New Zealand," she said.

But the big changes occurring in Antarctica impact not only weather, but the health of the world's oceans too, delivering oxygen and nutrients.

During November the sea ice edge is usually around 100km further north of where it is this year. For it to have broken out this early is a significant change and it's causing alarms bells to ring.

"This is my 30th trip into the Southern Ocean and Antarctica," climate scientist Professor Gary Wilson told Newshub.

"Of all the visits I've made down here, we haven't seen the sea ice break out as much as it has this early."

Photo credit: Newshub.

This graph shows the normal range of sea ice in November since 1978. In 2016, there was a sudden and dramatic drop.

This year looks to be following suit.

"We're seeing the ice shelves break up around the peninsula, we're seeing sea ice extent change," Prof Wilson said.

"It dropped rapidly last year and we're seeing now early break-up of the sea ice. Many of these things coming together certainly don't bode well."

The sea ice is not only melting ahead of schedule, there's a lot less of it to begin with. Last year there was 30 percent less ice - a drop of around 1 million square kilometres.

Climate scientists believe Antarctica may have hit a tipping point.

Photo credit: Newshub.

"This could be the moment that Antarctica is catching up with the Arctic," Prof Wilson said.

"Geologically we know that's the case that both poles warm equally, but it hasn't been the case yet with the Antarctic. But maybe this is the moment."

There is now less sea ice globally than at any other time since satellite records began in 1978. Last year, when it reached a record low, was also the hottest year on record.

"The impacts that we're having on the planet, it wouldn't surprise me if we are going to some sort of step change in how the Antarctic sea ice system operates," Dr Robinson said.

"We're really in a critical position I think... We're actually in a race because we know changes are coming, and it's just whether we're ahead of the changes to understand them and predict them better."

Prof Wilson said the abrupt change is "exciting" but troubling.

"In one sense it's exciting we're starting to see signs, in another sense it's daunting because when ice melts it tends to melt rapidly," he said.

The scientists and staff at Scott Base have been forced to adapt to the changes in sea ice this season. They can't traverse as far north on it and it needs to be regularly checked for safety when the large vehicles are driving over it.

At least one expedition has had to be cancelled, while cracks have made some regular routes impassable for vehicles carrying scientific equipment.

Climate scientists will be watching closely over the next few years to establish whether this is a one-off event, or the moment Antarctica began to succumb to a rapidly warming planet.

Comment by SongStar101 on November 1, 2017 at 6:33pm: Update: Satellites measuring Earth’s melting ice sheets go dark

http://www.sciencemag.org/news/2017/09/satellites-measuring-earth-s...

Artist’s conception of the GRACE spacecraft orbiting Earth.

Update, 27 October, 11:25 a.m.: NASA announced today that it has ended GRACE's science operations earlier than expected, after determining that its remaining battery capacity would not be sufficient for one last run that was previously planned to last from October into early November. Its early demise leaves what could be close to a half-year gap in its records before its successor mission, GRACE Follow-On, launches early next year.

Here is our earlier story from 15 September:

A sentinel of Earth’s climate is going dark. After running for a decade beyond its planned life, the Gravity Recovery and Climate Experiment (GRACE) is nearly out of fuel and will soon make its final science run, NASA announced late yesterday. The tandem of satellites—called GRACE-1 and GRACE-2—measure minute shifts in Earth’s gravity to chart flows of mass across the planet, such as the unexpectedly rapid melt of polar ice sheets and the drawdown of underground water reservoirs called aquifers.

Scientists had hoped GRACE would operate until its successor, the $550 million GRACE Follow-on (GRACE-FO) mission, reached orbit. But troubles securing a ride to space have delayed GRACE-FO’s launch until early 2018. Meanwhile, the battery in GRACE-2 used to store solar power has been deteriorating rapidly, forcing the satellite to burn through fuel. Engineers turned off an accelerometer last year to keep it running, but the satellite’s data have continued to degrade.

On 4 September, scientists lost contact with GRACE-2 after another of its battery cells stopped operating. Four days of feverish work followed, with scientists steeling themselves for the mission’s end. But finally, engineers bypassed the satellite’s flight software, successfully rebooting it. NASA has now put GRACE-2 on standby until mid-October, when it will run until early November in full sun on its final planned science collection.

However small, a gap between the missions will make it more challenging to stitch their records together into a seamless whole, says Eric Rignot, a glaciologist at NASA’s Jet Propulsion Lab in Pasadena, California. There are alternative ways to calculate some of the measures GRACE provides, so stopgaps are possible. For example, changes in the mass of the ice sheets can be estimated by using other satellite data to compare discharges of peripheral ice to snowfall accumulations. But there is no comparable method to monitor changes in the mass of glaciers or ice caps, let alone the measures of Earth’s groundwater and soil moisture that hydrologists derive from the satellites. “It would be an impossible task to fill the gap,” Rignot says.

A dynamic duo

A joint U.S.-German effort, GRACE has provided an unprecedented view of the planet’s water and ice since its launch in 2002. The experiment relies on measuring changes in the tug of gravity as the two satellites orbit the Earth. Flying 220 kilometers apart, the GRACE satellites constantly monitor their distance from each other with microwave pulses, down to microns. When the satellites approach a more massive feature, such as an ice sheet, the enhanced gravity of that region tugs a little bit more on the first satellite—briefly widening the distance between the pair—before the second satellite catches up. The changes in distance can be translated into mass.

This data revolutionized entire disciplines, such as hydrology, allowing scientists to document the loss of groundwater due to human exploitation. GRACE showed that the melting polar ice sheets are contributing more to sea level rise than the demise of mountain glaciers. Greenland, it found, is losing 280 gigatons of ice a year on average, while Antarctica is shedding 120 gigatons—rates that both seem to be accelerating. GRACE also inspired a similar mission, NASA’s Gravity Recovery and Interior Laboratory, which probed the moon’s interior.

There’s much that can still be done with GRACE’s archival data, says Isabella Velicogna, a geophysicist at the University of California, Irvine. For example, Velicogna and her colleagues recently used GRACE data to observe for the first time a strange, c...: Melting ice sheets in Greenland and Antarctica are pouring water into the oceans and adding to sea level rise. But the lost ice also means lost gravity—and so sea levels in the immediate vicinity of the ice sheets actually drop, while ocean levels half a world away are goosed. The dynamic, called sea level fingerprints, had wide acceptance in the field, but GRACE provided the first direct confirmation that it was happening.

Although the data gap is unfortunate, it was never a sure bet that GRACE would hold out, Velicogna says. And GRACE-FO, essentially a replication of the first mission, will provide finer mass resolutions by measuring the distance between the two satellites not just with microwaves, but with an experimental laser ranging in.... It’s the same technology that could one day help a planned satellite constellation capture gravitational waves.

Comment by SongStar101 on November 1, 2017 at 6:27pm: Warm waters melting Antarctic ice shelves may have appeared for the first time in over 7,000 years

https://theconversation.com/warm-waters-melting-antarctic-ice-shelv...

The vast expanse of the Antarctic is a region of the world particularly vulnerable to climate change, where ice loss has the potential to significantly increase sea levels.

Now, for possibly the first time in 7,000 years, a phenomenon known as “upwelling” (the upward flow of warmer ocean water to the surface), is thought to have caused recent ice shelf collapse around the continent – and the glacial thinning associated with it.

Ice shelves floating on water are the oceanic extension of land glaciers and ice sheets, and the primary region for ice loss. As these shelves break apart, the flow of continental ice held up behind them accelerates.

The ocean surrounding Antarctica is extremely cold, but water over 300m deep, Circumpolar Deep Water (CDW), is about 3⁰C above the melting point of ice. Normally, the very cold water above keeps this away from ice shelves. But in some areas, CDW is spilling onto the shallow Antarctic continental shelf, causing the ice to thin.

Ice shelf thinning has accelerated in recent decades, but the picture is not the same everywhere. While the east of the Antarctic has shown modest gains in ice thickness, the west has outstripped this with significant ice loss – up to 18% in vulnerable areas like the Amundsen and Bellingshausen Seas.

The pattern of ice loss and other observations indicate that warmer water upwelling beneath these ice shelves is driving it. But what has caused this upwelling? Is it related to human activity? And how concerned should we be?

Two teams led by scientists from the British Antarctic Survey, both of which I have been working with, set out to tackle these precise questions by focusing on two vulnerable areas. One site is in Pine Island Bay, in the Amundsen Sea, and the other is in Marguerite Bay, in the Bellingshausen Sea.

The aims of the studies are similar – to monitor the extent of upwelling warm water onto the continental shelf over the past 10,000 years, in order to understand when this last occurred and what the impact was.

This involves collecting and sampling “cores” of sediment up to 10m long from the sea bed at a range of depths up to 900m. Obtaining suitable cores is particularly challenging in these remote locations, where glacial dynamics often disturb the sediment.

Core evidence

Much of the evidence for past oceanography comes from tiny shells of amoeboid organisms called foraminifera. A huge variety of species colonise habitats on the sea floor and make up much of the sediment collected. There can be hundreds of shells in just one gram of sediment.
Electron microscope images of planktonic foraminifera N. pachyderma from Pine Island Bay. Scale bar: 100µm equals 0.1mm. Nature Publishing Group

Forams are extremely valuable, as their shells are made of calcium carbonate precipitated from the ocean water in which they lived. Examining these shells allows us to reconstruct the chemistry of ocean water.

There were two geochemical tracers used for warm CDW in Pine Island Bay – the proportion of carbon isotopes, and the magnesium to calcium ratio controlled by water temperature. Both of these showed CDW was last on the inner shelf over 7,500 years ago.

In Marguerite Bay, shells of another plankton group called diatoms were also analysed. These indicate past productivity and sea surface temperatures. They showed that CDW was persistently on the shelf here over 7,000 years ago, and more sporadically since then.

Tellingly, the enhanced upwelling of warm CDW in both locations negatively impacted the local extent of ice.

Winds of change

Both studies suggest that the cause of the CDW upwelling before 7,000 years ago was a more southerly position of the southern hemisphere westerly winds (SHWW). These winds are thought to drive circulation of the warmer deep water. A recent shift in the position of the SHWW towards the poles could be the cause of greater CDW upwelling in Pine Island Bay since the 1940s.
Data llustrating the apparent link between winds and ocean around western Antarctica. The migration of the southern hemisphere westerly winds (SHWW) coincide with upwelling of Circumpolar Deep Water (CDW) in the Amundsen Sea.

This coincidence of timing with the onset of industrialisation shows it is possible that human made greenhouse gasses, thought to cause atmospheric warming, are having an impact on the position of the winds, the increase in warm water reaching the surface, and ultimately the melting of more ice in the Antarctic.

Irrespective of the causes of past changes in SHWW positions, the link between winds and ocean upwelling is cause for concern, as future projected global warming may shift SHWW belts and promote further upwelling and melting. More research is now needed to fully understand the link between CDW and past climate, and to estimate the strength of upwelling since the 1940s compared to upwelling before 7,000 years ago. But the emerging picture is one of the potentially increased vulnerability of West Antarctic ice sheets, and possible future sea level rise.

Comment by Stanislav on October 21, 2017 at 12:48pm: Giant, mysterious hole was formed in Antarctica

PHOTOGRAPH COURTESY OF MODIS-AQUA VIA NASA WORLDVIEW; SEA ICE CONTOURS FROM AMSR2 ASI VIA UNIVERSITY OF BREMEN. Source of image: news.nationalgeographic.com

18 October, 2017. "A rare phenomenon, this type of open water space was first observed on the ice continent in the 1970s and is referred to by the Russian word polynya.

Sometimes stretching to thousands of square mile, the holes are generally thought to be caused by the deep water in the Southern Ocean being warmer and saltier than the surface water. Therefore, when warmer currents are brought upwards by currents, blankets of ice are melted despite continually low temperatures.

What makes this hole particularly remarkable, however, is that it has occurred "deep in the ice pack", as atmospheric physicist Kent Moore explained to Motherboard. Considering its position, scientists have concluded that it must have been formed by other processes that are not yet clear.

As Moore explains, a polynya was found in the area four decades years ago but only just reappeared last year when it stayed around for a few weeks before disappearing once more. As he says: "This is now the second year in a row it's opened after 40 years of not being there. We're still trying to figure out what's going on."

References: Pouget, J. (2017, October 18). Scientists Are Looking Into A Giant Hole That's Opened Up In Antarctica. Retrieved October 21, 2017, from http://www.konbini.com/us/lifestyle/giant-hole-opened-antarctica/

Source: NOAA Sea Ice Index Data; D3.js multi; csv: data4.csv (Based on this example: https://bl.ocks.org/mbostock/3884955) (Released under the GNU General Public License, version 3.)

Comment by jorge namour on October 2, 2017 at 7:48pm: Antarctic loses another piece

28 September 2017,

http://www.wikistrike.com/2017/09/l-antarctique-perd-encore-un-morc...

https://translate.google.com/translate?sl=fr&tl=en&js=y&...

Breaking news from Pine Island Glacier, which lost 267km2 of icebergs today, after the internal crack resulted in a large calving event 1/n

The Antarctic has again lost a giant iceberg. This time it is an iceberg that has detached itself from the Pine Island glacier and is nearly the size of the New York City borough of Manhattan.

A gigantic iceberg with an area of about 115 square kilometers has broken away from Antarctica, CBC News reported quoting the statement of the National Ice Center in the United States.

This iceberg is the third in the last four years to detach from the Pine Island glacier. In 2013 the glacier lost an iceberg with an area of 652 square kilometers and in 2015 another 582 square kilometers.

"It's not the size of the iceberg that matters. This is the frequency, "said Ian Howat, a glaciologist at Ohio State University, quoted by CBS News.

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