The Great London:
Greenland

The ice sheet covering Greenland is four times bigger than California -- and holds enough water to raise global sea-level more than twenty feet if most of it were to melt. Today, sea levels are rising and the melting of Greenland is a major contributor. Understanding how fast this melting might proceed is a pressing question for policymakers and coastal communities.

To make predictions about the future of the ice sheet, scientists have tried to understand its past, hoping to glean what the ice was doing millions of years ago when the Earth was three or more degrees Fahrenheit warmer than it is now. But our understanding of the ice sheet's complex behavior before about 125,000 years ago has been fragmentary at best.

Now, two first-of-their-kind studies provide new insight into the deep history of the Greenland Ice Sheet, looking back millions of years farther than previous techniques allowed. However, the two studies present some strongly contrasting evidence about how Greenland's ice sheet may have responded to past climate change -- bringing new urgency to the need to understand if and how the giant ice sheet might dramatically accelerate its melt-off in the near future.

The two new studies were published in the journal Nature, including one led by University of Vermont geologist Paul Bierman.

Ice On the East

In >the first study Bierman and four colleagues -- from UVM, Boston College, Lawrence Livermore Laboratory, and Imperial College London -- examined deep cores of ocean-bottom mud containing bits of bedrock that eroded off of the east side of Greenland. Their results show that East Greenland has been actively scoured by glacial ice for much of the last 7.5 million years -- and indicate that the ice sheet on this eastern flank of the island has not completely melted for long, if at all, in the past several million years. This result is consistent with existing computer models.

Their field-based data also suggest that during major climate cool-downs in the past several million years, the ice sheet expanded into previously ice-free areas, "showing that the ice sheet in East Greenland responds to and tracks global climate change," Bierman says. "The melting we are seeing today may be out of the bounds of how the Greenland ice sheet has behaved for many millions of years."

Since the data the team collected only came from samples off the east side of Greenland, their results don't provide a definitive picture of the whole Greenland ice sheet. But their research, with support from the National Science Foundation, provides strong evidence that "an ice sheet has been in East Greenland pretty much continuously for seven million years," says Jeremy Shakun, a geologist at Boston College who co-led the new study. "It's been bouncing around and dynamic -- but it's been there nearly all the time."

Contrasting Results

The >other study in Nature -- led by Joerg Schaefer of Lamont-Doherty Earth Observatory and Columbia University, and colleagues -- looked at a small sample of bedrock from one location beneath the middle of the existing ice sheet and came to what appears to be a different conclusion: Greenland was nearly ice-free for at least 280,000 years during the middle Pleistocene -- about 1.1 million years ago. This possibility is in contrast to existing computer models.

"These results appear to be contradictory -- but they may not be," UVM's Bierman says. He notes that both studies have "some blurriness," he says, in what they are able to resolve about short-term changes and the size of the ancient ice sheet. "Their study is a bit like one needle in a haystack," he says, "and ours is like having the whole haystack, but not being sure how big it is."

That's because Schaefer and colleagues' data comes from a single point in the middle of Greenland, pointing to a range of possible scenarios of what happened in the past, including several that challenge the image of Greenland being continuously covered by an extensive ice sheet during the Pleistocene. In contrast, Bierman and colleagues' data provides a record of continuous ice sheet activity over eastern Greenland but can't distinguish whether this was because there was a remnant in East Greenland or whether the ice sheet remained over the whole island, fluctuating in size as the climate warmed and cooled over millions of years.

"It's quite possible that both of these records are right for different places," Bierman says. "Both of these studies apply a similar innovative technique and let us look much farther into the past than we have been able to before."

New Method

Both teams of scientists used, "a powerful new tool for Earth scientists," says Dylan Rood, a scientist at Imperial College London and a co-author on the Bierman-led study: isotopes within grains of quartz, produced when bedrock is bombarded by cosmic rays from space. The isotopes come into being when rock is at or near Earth's surface -- but not when it's buried under an overlying ice sheet. By looking at the ratio of two of these cosmic-ray-made elements -- aluminum-26 and beryllium-10 caught in crystals of quartz, and measured in an accelerator mass spectrometer -- the scientists were able to calculate how long the rocks in their samples had been exposed to the sky versus covered by ice.

>Paul Bierman, a geologist at the University of Vermont and his colleagues --f rom UVM, Boston College, 
>Lawrence Livermore Laboratory, and Imperial College London--wanted to develop a better understanding 
>of the ancient history of the huge ice sheet that covers Greenland, like this portion of the ice sheet shown from 
>a helicopter on a Bierman-led expedition there. The team studied deep cores of ocean-bottom mud containing 
>bits of bedrock that eroded off of the east side of Greenland. Their results show that East Greenland has been 
>actively scoured by glacial ice for much of the last 7.5 million years--and indicate that the ice sheet on the 
>eastern flank of the island has not completely melted for long, if at all, in the past several million years. Their 
>field-based data also suggest that during major climate cool-downs in the past several million years, the ice sheet 
>expanded into previously ice-free areas, "showing that the ice sheet in East Greenland responds to and tracks
> global climate change," Bierman says. "The melting we are seeing today may be out of the bounds of how 
>the Greenland ice sheet has behaved for many millions of years." [Credit: Joshua Brown/UVM]
This isotope technique has been used for several decades for measuring land-based erosion, but this is its first application to ocean core samples, said Lee Corbett, a postdoctoral researcher at UVM and co-author with Bierman. "This has never been attempted with marine sediments," she says. Their results overcome a basic problem of trying to discern the deep history of ice from bedrock: every time an ice sheet retreats and then grows back, it scours away the bedrock and the isotope record of its own past. "It's hard to discern an ice sheet's cycles on land because it destroys the evidence," she says, "but it dumps that evidence in the oceans, archived in layers on the bottom."

Now Corbett, Shakun, and others are applying this isotope technique to additional cores taken from around the coast of Greenland to get a more complete and in-focus picture of the whole ice sheet's long history. And they have already applied the new isotope technique far beyond Greenland -- particularly in exploring the much larger, more mysterious ice sheets covering Antarctica.

"These two apparently conflicting -- but not necessarily conflicting -- studies in Nature really force the issue that we don't know enough about how ice sheets work over deep time," Bierman says. "We must recognize the importance of advancing polar science to understand how our world works. And, right now, because we're pumping huge plumes of greenhouse gases into the atmosphere, we really need to know how our world works."

The dynamics of Antarctica's giant ice sheet is full of questions and the disastrous potential. "But there's enough sea-level rise tied-up in Greenland alone to put a lot of cities and long stretches of coastline underwater," says Paul Bierman, "including Donald Trump's property in Florida."

Source: University of Vermont [December 07, 2016]

The traditional diet of Greenland natives — the Inuit — is held up as an example of how high levels of omega-3 fatty acids can counterbalance the bad health effects of a high-fat diet, but a new study hints that what’s true for the Inuit may not be true for everyone else.

The study, which appears in the Sept. 18 issue of the journal Science, shows that the Inuit and their Siberian ancestors have special mutations in genes involved in fat metabolism. The mutations help them partly counteract the effects of a diet high in marine mammal fat, mostly from seals and whales that eat fish with high levels of omega-3 polyunsaturated fatty acids.

Those genetic mutations, found in nearly 100 percent of the Inuit, are found in a mere 2 percent of Europeans and 15 percent of Han Chinese, which means that these groups would synthesize omega-3 polyunsaturated fatty acids differently from the Inuit.

“The original focus on fish oil and omega-3s came from studies of Inuit. On their traditional diet, rich in fat from marine mammals, Inuit seemed quite healthy with a low incidence of cardiovascular disease, so fish oil must be protective,” said project leader Rasmus Nielsen, a UC Berkeley professor of integrative biology. “We’ve now found that they have unique genetic adaptations to this diet, so you cannot extrapolate from them to other populations. A diet that is healthy for the Inuit may not necessarily be good for the rest of us.”

These genetic mutations in the Inuit have more widespread effects. They lower “bad” LDL cholesterol and fasting insulin levels, presumably protecting against cardiovascular disease and diabetes. They also have a significant effect on height, because growth is in part regulated by a person’s fatty acid profile. The researchers found that the mutations causing shorter height in the Inuit are also associated with shorter height in Europeans.

“The mutations we found in the Inuit have profound physiological effects, changing the whole profile of fatty acids in the body, plus it reduces their height by 2 centimeters: nearly an inch,” said Ida Moltke, a University of Copenhagen associate professor of bioinformatics who is joint first author on the study. “Height is controlled by many genes, but this mutation has one of the strongest effects on height ever found by geneticists.”

Personalized diets

Nielsen noted that this is some of the clearest evidence to date that human populations are actually adapted to particular diets; that is, they differ in the way they physiologically respond to diets. Just as genome sequencing can lead to personalized medicine tailored to an individual’s specific set of genes, so too may a person’s genome dictate a personalized diet.

“People ask themselves whether they should be on a Stone Age diet, for example. The response may well depend on their genome,” Nielsen said.

Nielsen and his colleagues at UC Berkeley and in Greenland and Denmark came to their conclusions after analyzing the genomes of 191 Greenlanders with a low admixture of European genes (less than 5 percent) and comparing them to the genomes of 60 Europeans and 44 Han Chinese. They looked for mutations occurring in a large percentage of Inuit individuals but in few or no other groups, which indicates that the mutation spread throughout the Inuit because it was somehow useful to their survival while not essential in other groups.

One cluster of mutations — in genes that code for enzymes that desaturate carbon-carbon bonds in fatty acids — stood out strongly, said Anders Albrechtsen, an associate professor of bioinformatics at the University of Copenhagen and a joint project leader. Fatty acids are the fat in our diet, and occur in saturated, polyunsaturated and unsaturated forms, depending on whether the molecules’ carbon atoms are linked together with no, some or all double bonds. Saturated fats are considered bad because they raise levels of cholesterol in the blood and lower the “good” high-density lipoproteins (HDL), all of which leads to plaque formation and clogged arteries. Diets rich in polyunsaturated and unsaturated fats are linked to lower heart disease. Desaturase enzymes convert dietary fatty acids into fatty acids stored and metabolized by the body.

The mutations common in the Inuit, once known as Eskimos, decrease the production of both omega-3 and omega-6 polyunsaturated fatty acids, presumably to account for the high amount of these fatty acids coming from the diet. Changing production of one fatty acid affects all fatty acids, however, since they regulate one another in a complex way, Albrechtsen said.

Thus, while it’s not clear which specific gene or genes within the cluster is responsible for the alteration in fatty acid metabolism, he said that “when you change the genes that are involved in fatty acid synthesis, you change the whole conversation among fatty acids, and that has a lot of downstream effects.”

Adaptation to Ice Age living

The mutations seem to be at least 20,000 years old, and may have helped many groups of humans adapt to high-meat, high-fat, hunter-gatherer diets from large land and marine mammals high in certain types of omega-3 and omega-6 fatty acids, said Matteo Fumagalli, a researcher at University College London, who is joint first author of the study. They may have arisen among the original Siberians, who have lived in the Arctic for more than 20,000 years and arrived in Greenland when Inuit settled there about 1,000 years ago.

“We think it is a quite old selection that may have helped humans adapt to the environment during the last Ice Age, but the selection is far stronger in the Inuit than anywhere else,” said Fumagalli. “It’s fascinating that Greenlanders have a unique genetic makeup that lets them better use their traditional food sources.”

The researchers discovered another common mutation in a gene that is involved in the differentiation of brown, subcutaneous fat cells and brite fat cells, the latter of which generate heat. This may also have helped the Inuit adapt to a cold environment.

Author: Robert Sanders | Source: University of California, Berkeley [September 18, 2015]

An ancient basin hidden beneath the Greenland ice sheet, discovered by researchers at the University of Bristol, may help explain the location, size and velocity of Jakobshavn Isbræ, Greenland's fastest flowing outlet glacier.

The research also provides an insight into what past river drainage looked like in Greenland, and what it could look like in the future as the ice sheet retreats.

Michael Cooper and colleagues from Bristol's School of Geographical Sciences and Cabot Institute, and Imperial College London, studied the bedrock in Greenland using data collected mainly by NASA (through Operation Ice Bridge), as well as various researchers from the UK and Germany, over several decades. This data is collected by aircraft using ice penetrating radar, which bounces back off the bedrock underneath the ice (as ice is mostly transparent to radio waves at certain frequencies).

Mr Cooper said: "The drainage basin we discovered shows signs of being carved by ancient rivers, prior to the extensive glaciation of Greenland (i.e. before the Greenland Ice Sheet existed), rather than being carved by the movement of ice itself. It has been remarkably well preserved – and has not been eroded away by successive glaciations. The channel network has never been seen before by humans – it was last uncovered around 3.8 million years ago."

The size of the drainage basin the team discovered is very large, at around 450,000 km2, and accounts for about 20 per cent of the total land area of Greenland (including islands).

This is comparable to the size of the Ohio River drainage basin, which is the largest tributary of the Mississippi. The channels the team mapped could more appropriately be called 'canyons', with relative depths of around 1,400 metres in places, and nearly 12km wide, all hidden underneath the ice.

As well as being an interesting discovery of great size, the channel network and basin was instrumental in influencing the flow of ice from the deep interior to the margin, both now and over several glacial cycles, as well as influencing the location and speed of the Jakobshavn ice stream.

The study is published in >Geophysical Research Letters.

Source: University of Bristol [June 14, 2016]