With enough evidence, even skepticism will thaw



Opinion evolves with evidence

As nervous as he was about their equipment, Muenchow was much more in his element here than he had been in 2010, testifying before Congress. Then, Muenchow’s scientific caution and compunction for rigor didn’t translate very well for a political audience.
Petermann Ice Shelf, GREENLAND
Half a decade before he took this trip to the farthest reaches of the north, Andreas Muenchow had his doubts about whether warming temperatures were causing one of the world’s great platforms of ice to melt and fall apart.
He even stood before Congress in 2010 and balked on whether climate change might have caused a mammoth chunk of ice, four times the size of Manhattan, to break off from this floating, 300-square-mile shelf. The University of Delaware oceanographer said he wasn’t sure. He needed more evidence.

Petermann Glacier
Arctic Ocean
Ellesmere Island
ice sheet
But then the Petermann Ice Shelf lost another two Manhattans of ice in 2012, and Muenchow decided to see for himself, launching a project to study the ice shelf intensively.
He was back again in late August, no longer a skeptic. It was hard not to be a believer here at 81 degrees north latitude, where Greenland and Canada very nearly touch. The surface of the bumpy and misshapen ice was covered with pools and puddles, in some cases frozen over but with piercing blue water beneath. Streams carved through the vast shelf, swelling into larger ponds or even small lakes.
The meltwater was a sign the ice shelf was growing more fragile, moving closer to the day when it might give up more city-size chunks of ice.
The Petermann Ice Shelf serves as a plug of sorts to one of Greenland’s largest glaciers, lodged in a fjord that, from the height of its mountain walls down to the lowest point of the seafloor, is deeper than the Grand Canyon. There’s enough ice piled up behind Petermann to raise oceans globally by nearly a foot someday.
The question for Muenchow is no longer whether Petermann is changing — it’s how fast it could give up still more ice to the seas. That’s why he and British Antarctic Survey colleague Keith Nicholls ventured here by helicopter to take the measure of the Petermann shelf, which had been shifting and surging in a way that damaged the scientific instruments they had left behind a year earlier — behaving as though it didn’t want to be known.


Hard data, hard to reach

Greenland is the largest island on Earth and home to its second-largest ice sheet after East Antarctica. It’s pouring 281 billion tons of that ice into the ocean each year, a major contribution to rising seas. Much of the loss comes from some 200 outlet glaciers, which extend out to the sea like fingers of the larger ice sheet.
The great fear is that Greenland’s ice loss is accelerating, and that’s why much attention has been directed at Petermann. One expert has called it one of the island’s three major “floodgates,” and the only one that has not yet opened. In part, the Petermann Ice Shelf has been slower to disintegrate simply because it is in a much colder place.
But that is beginning to change, and Muenchow and Nicholls are trying to understand the mechanics of how it might break apart.
They are old-school scientists, focused on gathering hard data in the world’s most remote places. Each has a “great record in terms of publications,” says Marco Tedesco, a Greenland researcher at Columbia University’s Lamont-Doherty Earth Observatory.
Muenchow, who was born in Germany, traveled to the United States to pursue oceanography and got his PhD studying the Delaware River. But before long he became infatuated with the idea of probing places that few have reached before, despite the hardships of leaving family and the comforts of home. The search took him five times to the Nares Strait, a tiny ocean passageway between northwest Greenland and Canada near Petermann glacier.

How the ice shelf edge has
changed since 2008
Sea ice
shelf edge
Rift in ice
Ice moves
roughly one
kilometer a year
Greenland ice sheet
Composite satellite image from ESA Sentinel
“To me, this hardship is pleasure as it always shatters prior expectations,” he explained later. “The only constant, it feels, is change and new insights. This drives me. Perhaps I am addicted to it. . . . The field work gives me this chance or opportunity to ‘reset’ and take a new look at what I thought I knew or I knew I did not understand.”
Nicholls, meanwhile, is an expert in his own sort of extreme pursuit — using hot water to drill holes hundreds of feet through the enormous ice shelves of Antarctica and now Greenland, and then analyzing data from the ocean beneath them.
They first worked together in 2015 as part of a major National Science Foundation-sponsored ship voyage to Petermann, where Muenchow was taking ocean measurements and Nicholls was busy drilling through the ice. Now, they had returned as part of a much smaller mission to recover data and determine why their instruments had gone dead. Two Washington Post journalists accompanied them with the support of the foundation which, in keeping with its policies, provided transportation and accommodations.
Their expedition began a day earlier from the United States’ Thule Air Base and the small village of Qaanaaq, Greenland’s most northern permanent settlement. This time they sought to reach Petermann by helicopter. The 300-mile journey was so long they had to break it in stages, picking up fuel from caches they strategically placed a year earlier when they had visited aboard a foundation-supported icebreaker.
A deep gulley with rushing water feeds into a river on Petermann Glacier. The shelf has reached a record low size after losing pieces larger than Manhattan in recent years.. (Whitney Shefte / The Washington Post)


The data stopped coming

As they crossed the desolate landscape, their Air Greenland chopper finally emerged from a series of inland canyons into the air above the ice shelf, which was streaked with thick veins of blue ice amid a sea of white, the landscape covered with meltwater pools. It was as though a fly had suddenly buzzed in through the window of a cathedral. The ice shelf was its sprawling floor, and it was rimmed on either side by enormous, symmetrical mountain walls sculpted into shapes resembling flying buttresses.
Along the shelf’s central aisle ran one of Petermann’s most distinctive features — a 30-mile-long meltwater river. A year ago, Muenchow and Nicholls had established three scientific data-collection stations on its banks — drilling through the football-field-thick ice and extending ocean sensors, attached to a long cable, into the dark and half-mile-deep waters beneath the shelf. These were to detect whether warming ocean water was causing a double-whammy of damage to Petermann by melting it from below, even as the warm air temperatures melt it from above.
But the main station had stopped feeding back any data in February. Now, Muenchow and Nicholls were here to see what had happened.
Muenchow sat in the second row of seats in the helicopter with earphones on to muffle the noise.
His chief fear, he had explained before the trip, was that this might just be a mop-up mission: That the flowing ice might have damaged the stations beyond repair, snapping the cables extending into the ocean below, and that there would be no data to retrieve.
Muenchow said he had prepared himself to be devastated if the data was lost. But he said he would give himself about “15 minutes” to mourn before adjusting to see what could be salvaged.

Petermann glacier had just lost a chunk of its ice shelf, and NASA satellite images of the enormous ice “island” were circulating widely. At the hearing, Jay Inslee (D), then a congressman and now the governor of Washington, pressed Muenchow to be more outspoken about what was happening to the planet. The scientist demurred.
The evidence “does not conclusively prove that this specific event is global warming,” Muenchow testified. The logic was simple — breaking off large pieces might just be something Petermann glacier does occasionally, if you go back far enough in time.
But two years later, another vast island of ice cleaved from Petermann. That’s when Muenchow began to change his mind. The shelf had by then lost 23 miles of its prior length, reaching a record low in size.
“It’s two extreme events in six years, so something is happening,” Muenchow said.
In science — unlike in politics — being hesitant when you don’t know something, and being willing to change your mind in the face of new evidence, are virtues. He has since joined a growing wave of researchers working to learn more.
Climate change doubters have continued to suggest — from a distance — that Petermann’s huge ice losses are just normal glacier behavior. Muenchow himself, no dogmatist about the matter, can still entertain the case for skepticism, in part because the glacier has never been as well observed as it now, by scientists and satellites. Conceivably, it lost as much ice during previous periods as it has lost in the present. Muenchow doubts that – the idea that the glacier has shifted to a new state, he says, is supported by the “preponderance of the evidence.”
Petermann is looking suspicious again: At its front edge near the ocean, it features several additional cracks, including one that penetrates further toward the center than the others, arcing inward toward the central river and the shelf’s thinnest region.
“I already see the beginning of a third break-up,” Muenchow said.

When ice shelves break away, the ice that had once fed the shelf instead flows directly into the ocean, helping to raise sea levels throughout the world. In the case of Petermann, that plug runs about 30 miles in length, floating over the fjord, to a “grounding line.” This is where the shelf ends and the ice touches the sea floor in 2,000-foot-deep waters. Farther back, the ice gets thicker and deeper.
Scientists worry about possible “marine ice sheet instability” in the region, which would allow warm ocean water to melt the base of the glacier and chase it backward — hastening its losses along the way.
It’s not clear where the retreat would end. Oregon State University geologist Alan Mix said researchers have recently discovered that behind Petermann glacier lies an enormous, ancient canyon that is nearly 500 miles long and cuts all the way to the center of the Greenland ice sheet. It was probably carved by a river long ago.
So if the ice shelf collapses and Petermann glacier starts breaking off large icebergs and retreating backward, the ocean could someday gain access to this canyon.
“You can think about this as a huge drain of Greenland,” Mix said of the Petermann fjord. “This is where the water gets out.”
A pool of frozen water rests on the bumpy, often wet surface of Petermann Glacier. (Whitney Shefte / The Washington Post)


When warm and cold collide

As the helicopter circled the researchers’ central station, Nicholls spotted the non-responsive device first. Its weather beacon listed at a 30-degree angle, felled by the moving ice. That would explain why the station had not transmitted data in six months.
Nicholls turned to his partner in the helicopter and drew a finger across his neck in a sign recognized universally: dead.
Half an hour later, Muenchow was on the ice, busily using a hacksaw to cut through the weather station’s steel pole to try to free it. “I’m making progress,” he huffed, the temperatures at around 39 degrees in the early afternoon of an August day that, this far north, won’t ever lose its light.
Muenchow retrieved a memory card and plugged it into his computer. It was the moment of truth.
And also, it turned out, one of pure scientific joy — the data was there, and the sensors were still recording more.
After realizing that the last recording was just a few hours old, Muenchow was speechless. He covered his mouth with his hands.
“That’s good news,” Nicholls deadpanned.
Muenchow started clapping softly.
It would take weeks, after the scientists got back home, to analyze the data. But they already knew it would give them an unprecedented image of the behavior of ocean waters in the deep cavity beneath the ice.
There is still some mystery about how warm waters might be reaching and interacting with the Petermann Ice Shelf.
The Atlantic’s warm, salty waters reach this fjord through a convoluted route that takes them north off Greenland’s eastern coast, along a full circuit of the Arctic Ocean, and ultimately south through the Nares Strait. Here, warmer Atlantic-originating waters are found at the greatest depths because their saltiness gives them more density, while fresher and colder Arctic waters lie at the surface.
Sources: Andreas Muenchow and ESA Sentinel
The warm waters then penetrate beneath the ice shelf and to the base of the glacier, and are somehow managing to melt and thin it at a rate of 30 to 40 feet per year. And the Atlantic waters in the area are getting still warmer over time.
But the fundamental question is what’s pulling the Atlantic waters in and causing them to touch the shelf?
One key idea, Nicholls suspected, turns on all the wetness atop Petermann — a sign of ever-rising Arctic air temperatures. “Our major hypothesis,” he said, is that some of this water is running off somehow, entering the ocean, and in the process, helping to draw in the warm water that causes the most extensive melting.
It isn’t clear where the fresh water is spilling out, but it could be further up the fjord from here, at the grounding line. That would mean cold, fresh and buoyant water is suddenly pouring into warm, salty Atlantic-originating water at extreme, dark ocean depths. This interaction is probably very turbulent and dramatic, and it could be the key to growing melting.
“Because the base of the ice shelf is sloping upwards, this water flows quickly up the bottom of the ice shelf, and as it does that, it mixes and stirs in the warm water from beneath,” said Nicholls.
This may help explain the most dramatic feature atop Petermann — its central river. It has a frozen surface in some areas, but flowing water underneath. It’s noisy — constantly the source of cracking, crashing and sliding sounds. It’s fed by a seemingly endless network of ice-banked tributaries that, amid above-freezing temperatures on the second day of the team’s trip, were roaring with water.
But why is it here in the first place? The reason seems to be below the surface, where ocean waters have carved an undersea channel into the bottom of the shelf. That changes the surface of the shelf, too, because thinner ice won’t float as high above the surface of the water. The result is a depression or chasm at the surface, which meltwater, flowing downhill, naturally fills.
This river, and the channel beneath it, seems implicated in the ice shelf’s undoing. According to Muenchow, the previous major ice loss events seemed to occur whenever a crack in the shelf, coming in from the side, finally extends as far as the river.
From above Petermann Glacier, cracks are visible on its surface. (Whitney Shefte / The Washington Post)


Time to get out

After an intense 24 hours of work in near-freezing temperatures — tearing apart, rebuilding and reprogramming scientific stations, and consigning four out of nine ocean sensors to a watery oblivion — the researchers had one remaining quest to complete.
With their time on the ice dwindling, they wanted to install a radar that measures the ice’s thickness roughly a mile from the main station. This would let them compare the shelf’s thinning in different places.
The helicopter had dropped off equipment at the spot, but to save fuel and flying time, they decided to hike the distance, guided by a GPS device.
The hike was at a slight incline, out of Petermann’s riverine depression and into higher terrain. At one point, the trek required crossing a small, flowing tributary. Nicholls used the long bamboo poles and drill bits he was carrying to test the opposite ice bank, making sure it provided a good foothold, before they did so.
After three hours of work, trouble arose. A cold rain had arrived, turning the ice treacherously slick. “The one thing you do not want is rain on an ice shelf,” Nicholls said.
The water complicated the trip back to the helicopter. The team made it to within about a football field of the aircraft but could go no further, blocked by a rain-swollen series of streams flowing so fast that their roars were audible.
So with time running short before the pilots would start out to look for them, the researchers had to backtrack half a mile, where they found a crossing at higher ground.
Returning to the helicopter, they considered the expedition a success — while the scientists had to jettison two scientific stations, they repaired one and established another. Most of all, they retrieved key ocean data. But they acknowledge that in the vastness of the Petermann Ice Shelf, those are still just two small points taking measurements.
A month and a half later, as he was about to embark from Alaska on a research vessel bound for a different part of the Arctic, Muenchow told The Post what the data from beneath Petermann revealed.
A sensor in 3,000-foot-deep waters had found that in the warm, salty Atlantic layer, temperatures were even warmer than just a year earlier, in 2015. Those waters are likely flowing toward Petermann glacier’s grounding line and helping to melt the shelf from below.
“The temperatures at the bottom end of the array continue to increase,” said Muenchow. “It’s getting warmer.”
In a recent paper he and Nicholls pointed out that several other glaciers in Greenland have already lost their ice shelves. Their work suggests that Petermann is now following this path.


Crippled Atlantic currents triggered ice age climate change

Melting icebergs may have triggered or exacerbated ice age slowdowns to Atlantic Ocean currents.


By Eric Hand
The last ice age wasn’t one long big chill. Dozens of times temperatures abruptly rose or fell, causing all manner of ecological change. Mysteriously, ice cores from Greenland and Antarctica show that these sudden shifts—which occurred every 1500 years or so—were out of sync in the two hemispheres: When it got cold in the north, it grew warm in the south, and vice versa. Now, scientists have implicated the culprit behind those seesaws—changes to a conveyor belt of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC).
These currents, which today drive the Gulf Stream, bring warm surface waters north and send cold, deeper waters south. But they weakened suddenly and drastically, nearly to the point of stopping, just before several periods of abrupt climate change, researchers report today in Science. In a matter of decades, temperatures plummeted in the north, as the currents brought less warmth in that direction. Meanwhile, the backlog of warm, southern waters allowed the Southern Hemisphere to heat up.
AMOC slowdowns have long been suspected as the cause of the climate swings during the last ice age, which lasted from 110,000 to 15,000 years ago, but never definitively shown. The new study “is the best demonstration that this indeed happened,” says Jerry McManus, a paleo-oceanographer at Columbia University’s Lamont-Doherty Earth Observatory, and a study author. “It is very convincing evidence,” adds Andreas Schmittner, a climate scientist at Oregon State University, Corvallis. “We did not know that the circulation changed during these shorter intervals.”
To assess the strength of ancient ocean currents over the course of 35,000 years in the middle of the ice age, McManus and his colleagues examined a 10-meter section of a 38-meter sediment core drilled from the bottom of the Atlantic Ocean. The core came from an elevated patch of sea floor known as the Bermuda Rise, where sediments accumulate abnormally fast. The thick layer allows for a more detailed reading of chemical changes within the sediments when they were buried.

Circulation slowdown

Ice Age climate swings may have come from the weakening of powerful Atlantic currents, in which shallow, warm waters move north (red), and deep, cold waters move south (blue).

The researchers measured the ratio of two products of radioactive decay: protactinium-231 and thorium-230. These daughter isotopes come from trace amounts of uranium that are dissolved everywhere in seawater. If the ocean were as still as a bathtub, the two daughter isotopes would bind to sediment particles, settle downward, and become buried at a constant ratio. But thorium gloms on to particles more readily than protactinium. It is therefore buried more readily, whereas protactinium tends to be carried away by ocean currents for burial elsewhere. At places like the Bermuda Rise, where the Atlantic conveyor belt is typically strong, little protactinium ends up in the sediments—except for four instances when the ratio to thorium rose sharply in a matter of decades to centuries, indicating the AMOC’s sudden weakening.
A 2014 study of the AMOC, based on a core from a nearby spot on the Bermuda Rise, found that the currents maintained much of their strength throughout the last glacial period. But because that team took fewer samples from the core and missed the sharp swings in strength. “Now these [new] guys have increased incredibly the data resolution,” says Jörg Lippold, a paleo-oceanographer at the University of Heidelberg in Germany and the leader of the 2014 study. “They found the peaks we missed.”
Still unclear is what triggered the AMOC’s sudden slowdowns. Many of the drops correspond to so-called Heinrich events: rapid releases of icebergs from Canada’s ice sheet. These iceberg armadas often chugged through the Hudson Strait of Canada and may have discharged more ice into the Atlantic Ocean than contained in the entire ice cap of Greenland, raising ancient sea levels by 10 meters. The meltwater brought incredible amounts of freshwater to the North Atlantic, precisely where ocean currents cool off and sink. Because freshwater is less dense than saltwater, it can plug up the AMOC, preventing the overturning and deep water formation the fuels the circulation’s engine. The slowdowns persisted for 1500 years or so, then the AMOC would suddenly regain strength as freshwater melt dissipated and the currents reached a certain threshold, McManus says.
But weak AMOCs are not always accompanied by a Heinrich event, and the timing is fuzzy—some Heinrich events seem to occur after the AMOC already began to weaken. “The Heinrich events may be a response to the change in the overturning circulation rather than a cause,” Schmittner says.
Another question is whether the AMOC—currently known to be in decline—could drop off suddenly today, as depicted in the 2004 movie The Day After Tomorrow, causing temperatures to plummet across northwestern Europe. Schmittner says the past provides an eye-opener. “It’s evidence that this really did happen in the past, on short time scales.” But McManus says that studies looking deeper into the ice ages have found that the 1500-year climate oscillations tend not to be nearly as strong during interglacial periods. “It would suggest that this kind of thing isn’t so likely to happen today,” he says. On the other hand, he adds, “In most interglacials, Greenland didn’t melt … and Greenland is currently melting.”
Posted in: 
DOI: 10.1126/science.aaf5828

Gulf Stream Slowing Down Faster Than Ever, Scientists Say

Home  Climate Science 
Posted on April 12, 2016Kevin Hester 

The Gulf Stream that helps to keep Britain from freezing over in winter is slowing down faster now than at any time in the past millennium according to a study suggesting that major changes are taking place to the ocean currents of the North Atlantic.
Scientists believe that the huge volumes of freshwater flowing into the North Atlantic from the rapidly melting ice cap of Greenland have slowed down the ocean “engine” that drives the Gulf Stream from the Caribbean towards north-west Europe, bringing heat equivalent to the output of a million power stations.’
———- ———-

And similarly: ‘While you were distracted, this climate change warning arrived‘:  ‘With dire warnings of catastrophic sea level rise and superstorms capable of pitching 1,000 tonne mega-boulders onto shorelines, scientist James Hansen sounded an alarm over continued global warming.  
In a video, coinciding with a release of a revised version of paper Hansen wrote  with 18 other authors, Hansen warned of “feedbacks” between the oceans and ice sheets.’
[dk:  like him or not, he does have gravitas here.  He seems more urgent than a year ago…]

Is the Gulf Stream broken? NOAA satellite data sounds alarm

Natural News
Friday, January 29, 2016 by: Jennifer Lea Reynolds
Tags: global warminggulf streamNOAA

(NaturalNews) It's no secret that the weather is becoming more severe as time goes on. From places like Buffalo, New York, which recently got hit with a hefty 5 feet of snow during one storm, to other areas that experience extreme temperature fluctuations from one day to the next, it's obvious that the climate is changing.

National Oceanic and Atmospheric Administration(NOAA) satellite data and details from an animated map called the Earth Wind Map, show that it's not only changing, but that it's changing fast.

Data suggests rapid changes occurring in Gulf Stream temperature

November 2014 data suggests that the stream is exhibiting colder than normal conditions. On top of that, it's taking place in not just one area, but two, further demonstrating that climate changes are underway. For example, both sites showed that the North Atlantic was colder than average, but also that the Gulf itself is colder than normal, which was not the case just one month prior, in October 2014.

The information has many wondering if the Gulf Stream may be broken, something that surely is cause for concern as bizarre weather patterns continue to occur. Unfortunately, it would appear that it is indeed broken and that climate changes will become the norm.

In fact, according to 1000 climate experts who gathered at the World Meteorological Organization (WMO) conference earlier this year, people should prepare to brace themselves for weather changes of apocalyptic proportions in the coming years. Their observations and words of warning are nothing short of alarming, indicatingthat the atmosphere may bebeyond repair. Instead, it's now a matter of dealing with the consequences, much of which has occurred at the hands of humans.

Changing weather conditions "irreversible"

"It's irreversible and the world's population continues to increase, so we must adapt," says Jennifer Vanos, a professor of atmospheric sciences at Texas Tech University.

Experts are adamant that by 2050, airplane passengers will experience about twice as much in-flight air turbulence, ships will encounter gigantic ocean waves well over 130-feet (40 meters)-high and a two percent rise in average global temperature is expected.

What does this mean? It isn't good.

Simon Wang, assistant director of the Utah Climate Center, says "We'll see clouds forming faster and more easily, and more downpours" which he notes will create an influx of flash flooding.

The changes occurring in the Gulf Stream and the climate overall are attributed to many factors, and experts are not ruling our human disruption.

Natural processes as well as human activity responsible for severe climate changes

Experts from NOAA, for example, say that natural factors such as volcanic activity and changes in solar luminosity are behind climate changes. However, they aren't hesitant to suggest that the changes are also brought on by human actions, mainly regarding greenhouse gas emissions.

The Intergovernmental Panel on Climate Change (IPCC) agrees, stating in a recent news release that "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century."

Thomas Stocker, the IPCC co-chair says, "Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions." Stocker explains that heat waves will become more common and last longer, while dry areas will receive less rainfall and wet regions will likely experience more.

The IPCC notes that "Warming in the climate system is unequivocal" expressing that "Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850, and since 1950 many changes have been observed throughout the climate system that are unprecedented over decades to millennia."

While the changes noted in the Gulf Stream and the overall weather are disturbing, can we really say that they are surprising?

Sources for this article include:


Gulf Stream slowdown tied to changes in Southern Hemisphere



October 5, 2016

University of Washington
The ocean circulation that is responsible for England's mild climate appears to be slowing down. The shift is not sudden or dramatic, as in the 2004 sci-fi movie "The Day After Tomorrow," but it is a real effect that has consequences for the climates of eastern North America and Western Europe. Also unlike in that movie, and in theories of long-term climate change, these recent trends are not connected with the melting of the Arctic sea ice and buildup of freshwater near the North Pole. Instead, they seem to be connected to shifts at the southern end of the planet, according to a recent University of Washington study in the journal Geophysical Research Letters.
"It doesn't work like in the movie, of course," said Kathryn Kelly, an oceanographer at the UW's Applied Physics Laboratory. "The slowdown is actually happening very gradually, but it seems to be happening like predicted: It does seem to be spinning down."
The study looked at data from satellites and ocean sensors off Miami that have tracked what's known as the Atlantic overturning circulation for more than a decade. Together they show a definite slowdown since 2004, confirming a trend suspected before then from spottier data.
Looking at other observations to determine the cause, the researchers ruled out what had been the prime suspect until now: that massive melting and freshening in the North Atlantic could stop water from sinking and put the brakes on the overturning circulation, which moves warmer water north along the ocean's surface and sends cold water southward at depths.
"It appears that this 10-year slowdown is not related to salinity," Kelly said. In fact, despite more ice melt, surface water in the Arctic is getting saltier and therefore denser, she said, because of less precipitation. "That means the slowdown could not possibly be due to salinity -- it's just backwards. The North Atlantic has actually been getting saltier."
Instead, the authors saw a surprising connection with a current around the southern tip of South Africa. In what's known as the Agulhas Current, warm Indian Ocean water flows south along the African coast and around the continent's tip toward the Atlantic, but then makes a sharp turn back to join the stormy southern circumpolar current. Warm water that escapes into the Atlantic around the cape of South Africa is known as the Agulhas Leakage. The new research shows the amount of leakage changes with the quantity of heat transported northward by the overturning circulation.
"We've found that the two are connected, but I don't think we've found that one causes the other," Kelly said. "It's more likely that whatever changed the Agulhas changed the whole system."
She believes atmospheric changes may be affecting both currents simultaneously.
"Most people have thought this current should be driven by a salinity change, but maybe it's the [Southern Ocean] winds," Kelly said.
The finding could have implications for northern European and eastern U.S. climates, and for understanding how the world's oceans carry heat from the tropics toward the poles.
"I think it changes how we think about the whole Atlantic overturning circulation, of which the Gulf Stream is a part," said co-author LuAnne Thompson, a UW professor of oceanography. "It brings back the role of the atmosphere into what's controlling the climate in the high latitudes, that it's not all driven by what's happening in the oceans."
And while a slowdown of the Gulf Stream and broader overturning circulation, for whatever reason, would bring less warm water to eastern North America and Western Europe, any effects are overwhelmed by the overall warming due to global climate change.
"So that whole concept in the movie of New York harbor freezing doesn't make any sense," Kelly said. "If the Gulf Stream doesn't carry as much heat from the tropics, it just means that the North Atlantic is not going to warm up as fast as the rest of the ocean -- it's not going to cool down."

Story Source:
Materials provided by University of WashingtonNote: Content may be edited for style and length.

Journal Reference:
  1. Kathryn A. Kelly, Kyla Drushka, LuAnne Thompson, Dewi Le Bars, Elaine L. McDonagh. Impact of slowdown of Atlantic overturning circulation on heat and freshwater transportsGeophysical Research Letters, 2016; 43 (14): 7625 DOI: 10.1002/2016GL069789

Cite This Page:
University of Washington. "Gulf Stream slowdown tied to changes in Southern Hemisphere." ScienceDaily. ScienceDaily, 5 October 2016. .