What is known: Vikings sailed to Greenland. They homesteaded there for a few hundred years, and likely experienced multiple famines. Many died. Some returned to European shores. And all of this happened during a time in Europe known to geoscientists as the Medieval Warm Period. The warmer, milder conditions that defined this time eventually ended too.
For many years, scientists have pondered if the Vikings' diaspora to Greenland was made easier by the warmer temperatures of the Medieval Warm Period. Climate data extracted from shells had indicated that this warm period extended to Greenland, but new research looking at glacial movements and using isotope data from terminal moraines suggests this may not necessarily be so.
Greenland's glaciers are retreating quickly, and a new study shows in historical terms just how quickly: over the past century, at least twice as fast as any other time in the past 9,500 years. The study also provides new evidence for just how sensitive glaciers are to temperature, showing that they responded to past abrupt cooling and warming periods, some of which might have lasted only decades.
To track how glaciers grew and shrank over time, the scientists extracted sediment cores from a glacier-fed lake that provided the first continuous observation of glacier change in southeastern Greenland. They then compared the results to similar rare cores from Iceland and Canada's Baffin Island for a regional view.
"Two things are happening," said study co-author William D'Andrea, a paleoclimatologist at Columbia University's Lamont-Doherty Earth Observatory. "One is you have a very gradual decrease in the amount of sunlight hitting high latitudes in the summer. If that were the only thing happening, we would expect these glaciers to very slowly be creeping forward, forward, forward. But then we come along and start burning fossil fuels and adding carbon dioxide to the atmosphere, and glaciers that would still be growing start to melt back because summer temperatures are warmer."
A new study questions the popular notion that 10th-century Norse people were able to colonize Greenland because of a period of unusually warm weather. Based upon signs left by old glaciers, researchers say the climate was already cold when the Norse arrived--and that climate thus probably played little role in their mysterious demise some 400 years later. On a larger scale, the study adds to building evidence that the so-called Medieval Warm Period, when Europe enjoyed exceptionally clement weather, did not necessarily extend to other parts of the world.
"It's becoming clearer that the Medieval Warm Period was patchy, not global," said lead author Nicolás Young, a glacial geologist at Columbia University's Lamont-Doherty Earth Observatory. "The concept is Eurocentric--that's where the best-known observations were made. Elsewhere, the climate might not have been the same." Climate scientists have cited the Medieval Warm Period to explain anomalies in rainfall and temperature in far-flung regions, from the U.S. Southwest to China. The study appears today in the journal Science Advances.
Norse, or Vikings, led by Erik the Red, first sailed from recently settled Iceland to southwestern Greenland around 985, according to Icelandic records. Some 3,000 to 5,000 settlers eventually lived in Greenland, harvesting walrus ivory and raising livestock. But the colonies disappeared between about 1360 and 1460, leaving only ruins, and a longstanding mystery as to what happened. The native Inuit remained, but Europeans did not re-inhabit Greenland until the 1700s.
The Greenlandic Vikings' apogee coincided with the Medieval Warm Period (also known as the Medieval Climate Anomaly), generally dated from about 950-1250; their disappearance followed the onset of the Little Ice Age, which ran from about 1300-1850. Both periods are firmly documented in European and Icelandic historical records. Thus, popular authors and some scientists have fixed on the idea that nice weather drew the settlers to Greenland, and bad weather froze and starved them. But there are no early historical climate records from Greenland. Recently, historians have proposed more complex factors in addition to, or instead of, climate: hostilities with the Inuit, a decline in ivory trade, soil erosion caused by the Vikings' imported cattle, or a migration back to Europe to farms depopulated by the Black Plague.
In the new study, the scientists sampled boulders left by advancing glaciers over the last 1,000-some years in southwest Greenland, and on neighboring Baffin Island, which the Norse may also have occupied, according to newly uncovered evidence. Glacial advances during the Little Ice Age have wiped out most evidence of where the glaciers were during the Norse settlement. But Young and his colleagues were able to find traces of a few moraines--heaps of debris left at glaciers' ends--that, by their layout, they could tell predated the Little Ice Age advances. Using newly precise methods of analyzing chemical isotopes in the rocks, they showed that these moraines had been deposited during the Viking occupation, and that the glaciers had neared or reached their later maximum Little Ice Age positions between 975 and 1275. The strong implication: it was at least as cold when the Vikings arrived as when they left. "If the Vikings traveled to Greenland when it was cool, it's a stretch to say deteriorating climate drove them out," said Young.
Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution
Authors:
Luo et al
Abstract:
As one of the earliest-known mammaliaforms, Haramiyavia clemmenseni from the Rhaetic (Late Triassic) of East Greenland has held an important place in understanding the timing of the earliest radiation of the group. Reanalysis of the type specimen using high-resolution computed tomography (CT) has revealed new details, such as the presence of the dentary condyle of the mammalian jaw hinge and the postdentary trough for mandibular attachment of the middle ear—a transitional condition of the predecessors to crown Mammalia. Our tests of competing phylogenetic hypotheses with these new data show that Late Triassic haramiyids are a separate clade from multituberculate mammals and are excluded from the Mammalia. Consequently, hypotheses of a Late Triassic diversification of the Mammalia that depend on multituberculate affinities of haramiyidans are rejected. Scanning electron microscopy study of tooth-wear facets and kinematic functional simulation of occlusion with virtual 3D models from CT scans confirm that Haramiyavia had a major orthal occlusion with the tallest lingual cusp of the lower molars occluding into the lingual embrasure of the upper molars, followed by a short palinal movement along the cusp rows alternating between upper and lower molars. This movement differs from the minimal orthal but extensive palinal occlusal movement of multituberculate mammals, which previously were regarded as relatives of haramiyidans. The disparity of tooth morphology and the diversity of dental functions of haramiyids and their contemporary mammaliaforms suggest that dietary diversification is a major factor in the earliest mammaliaform evolution.
Researchers who are building the highest-resolution map of the Greenland Ice Sheet to date have made a surprising discovery: two lakes of meltwater that pooled beneath the ice and rapidly drained away.
One lake once held billions of gallons of water and emptied to form a mile-wide crater in just a few weeks. The other lake has filled and emptied twice in the last two years.
New perspectives on the Late Triassic vertebrates of East Greenland: preliminary results of a Polish−Danish palaeontological expedition
Authors:
Sulej et al
Abstract:
The Fleming Fjord Formation (Jameson Land, East Greenland) documents a diverse assemblage of terrestrial vertebrates of Late Triassic age. Expeditions from the turn of the 21st century have discovered many important fossils that form the basis of our current knowledge of Late Triassic Greenlandic faunas. However, due to the scarcity and incompleteness of the fossils and their insufficient study, our understanding of the taxonomic diversity of the Fleming Fjord Formation is hindered. Here, we report the preliminary findings of a Polish-Danish expedition to the Fleming Fjord Formation that took place in 2014. Three areas were visited – the fairly well known MacKnight Bjerg and Wood Bjerg and the virtually unexplored Liasryggen. MacKnigth Bjerg and Liasryggen yielded fossils which promise to significantly broaden our knowledge of vertebrate evolution in the Late Triassic. Stem-mammal remains were discovered at Liasryggen. Other fossils found at both sites include remains of actinopterygians, sarcopterygians, temnospondyl amphibians and various archosaurs (including early dinosaurs). Numerous vertebrate trace fossils, including coprolites, pseudosuchian footprints, theropod and sauropodomorph dinosaur tracks, were also discovered. Newly discovered skeletal remains as well as abundant trace fossils indicate higher tetrapod diversity in the Late Triassic of Greenland than previously thought. Trace fossils also allow inferences of early theropod and sauropodomorph dinosaur behaviour.
Exhumation rates in the Archean from pressure–time paths: Example from the Skjoldungen Orogen (SE Greenland)
Authors:
Berger et al
Abstract:
The discussions on the orogenic evolution during Earth's history converge to the question of a different thermal structure in the Archean compared to the Phanerozoic and the applicability of the plate tectonic paradigm. However, geothermal structures are transient in orogens and are difficult to translate into large-scale tectonics and exhumation rates. Therefore, we propose depth–time data in the Archean Skjoldungen Orogen (SE Greenland, North Atlantic Craton) that allow for reconstruction of an exhumation rate independent of geothermal gradients. The resulting exhumation rate of ca. 0.4 km/Ma is similar to exhumation rates during erosion-controlled processes in modern orogens. These exhumation rates can only be established by erosion time constants similar to modern orogens. The occurrence of erosion-controlled exhumation is best explained by a stiff foreland promoting localized deformation in the orogen. Therefore, a switch from magmatic-dominated processes to localized deformation is proposed in the Skjoldungen Orogen area. This is supported by a change in magma composition and volume, from widespread granodiorite to localized alkaline intrusions. In addition, the involved metasedimentary rocks include detrital zircons of the only 50 Ma older foreland, which also correspond to erosion and tectonics as in modern orogens, i.e. flysh-type sediments. Relatively fast exhumation rates and the structural-magmatic evolution of the Neoarchean Skjoldungen Orogen thus indicate modern-style tectonic processes where stiff Mesoarchean continental crust forms a foreland to a collisional orogen instead of typical accretionary tectonics of weak island arc-like terranes in granite-greenstone terranes.
Less than half a decade ago, Greenlanders were imagining the riches that would follow an oil bonanza as the price of crude approached $150 a barrel. That wealth was supposed to buy the island independence from Denmark.
Today, with oil trading at less than $75, well below levels that would make exploration off the world’s largest island profitable, Greenlanders are casting their votes for a new home-rule government after the previous administration collapsed amid an expenses scandal.
“People in Greenland always ponder how to achieve economic independence from Denmark,” Ulrik Pram Gad, a post doctoral political scientist at the University of Copenhagen, said in an interview. “People are just realizing that things will take longer; nobody knows how to fund the economy without oil and mining.”
Ancient DNA unravels the truth behind the controversial GUS Greenlandic Norse fur samples: the bison was a horse, and the muskox and bears were goats
Authors:
Sinding et al
Abstract:
The Norse Greenlandic archaeological site known as ‘the Farm Beneath the Sand’ (GUS) has sourced many well-preserved and unique archaeological artefacts. Some of the most controversial finds are tufts of hair, which previous morphological-based examination concluded derive from bison, black bear, brown bear and muskox, all species whose natural presence in South Greenland is unlikely. If true, the consequences are potentially significant, as they could imply Viking trading with, or hunting within, North America. To validate these previous findings, we genetically profiled the samples, through mitochondrial 16S DNA analysis. The results revealed that the putative bison was, in fact horse, while the bears and muskox were goat. The results demonstrate the importance of using genetic analyses to validate results derived from morphological analyses on hair, in particular where such studies lead to sensational claims.
An international research team's field work, drilling and measuring melt rates and ice sheet movement in Greenland is showing that things are, in fact, more complicated than we thought.
"Although the Greenland Ice Sheet initially speeds up each summer in its slow-motion race to the sea, the network of meltwater channels beneath the sheet is not necessarily forming the slushy racetrack that had been previously considered," said Matthew Hoffman, a Los Alamos National Laboratory scientist on the project.
A high-profile paper appearing in Nature this week notes that observations of moulins (vertical conduits connecting water on top of the glacier down to the bed of the ice sheet) and boreholes in Greenland show that subglacial channels ameliorate the speedup caused by water delivery to the base of the ice sheet in the short term. By mid summer, however, the channels stabilize and are unable to grow any larger. In a previous paper appearing in Science, researchers had posited that the undersheet channels were not even a consideration in Greenland, but as happens in the science world, more data fills in the complex mosaic of facts and clarifies the evolution of the meltwater flow rates over the seasons.
In reality, these two papers are not inconsistent - they are studying different places at different times - and they both are consistent in that channelization is less important than previously assumed, said Hoffman.
A new model developed by researchers at the University of Cambridge has shown that despite its apparent stability, the massive ice sheet covering most of Greenland is more sensitive to climate change than earlier estimates have suggested, which would accelerate the rising sea levels that threaten coastal communities worldwide.
In addition to assessing the impact of the increasing levels of meltwater created and spilled into the ocean each year as the climate continues to warm, the new model also takes into account the role that the soft, spongy ground beneath the ice sheet plays in its changing dynamics. Details are published today (29 September) in the journal Nature Communications.
The Greenland Ice Sheet, which is the second-largest ice sheet in the world, covers 1.7 million square kilometres - an area roughly eight times the size of the United Kingdom - and contains enough ice to raise sea levels by more than seven metres if it were to be lost altogether.
Currently, due to surface melting alone, it is losing ice at a net annual rate of 200 gigatonnes, equating to 0.6 millimetres of sea level rise. A similarly large, but ultimately more uncertain source of sea level rise is tied to a net annual ice loss caused by increased movement of the ice sheet, which results in more ice being discharged into the ocean. Globally, sea levels are rising at three millimetres annually.
Large ice sheets such as in Greenland are far from stationary. Different parts of the ice often move at different speeds, causing ice to shear, a phenomenon known as ice flow.
"When these large ice sheets melt, whether that's due to seasonal change or a warming climate, they don't melt like an ice cube," said Dr Marion Bougamont of Cambridge's Scott Polar Research Institute, who led the research. "Instead, there are two sources of net ice loss: melting on the surface and increased flow of the ice itself, and there is a connection between these two mechanisms which we don't fully understand and isn't taken into account by standard ice sheet models."
Whereas other models of the Greenland Ice Sheet typically assume the ice slides over hard and impermeable bedrock - an assumption which is largely practical and based on lack of constraints - this study incorporates new evidence from ground-based surveys, which show soft and porous sediments at the bed of the ice sheet, more like the soft and muddy bottom of a lake than a sheet of solid rock. The new study specifically identifies the intake and temporal storage of water by weak sediment beneath the ice sheet as a crucial process in governing the ice flow.
Using a three-dimensional ice sheet model, together with an observational record of surface melting produced by collaborators at Aberystwyth University, Dr Bougamont and Dr Poul Christoffersen were able to accurately reproduce how the ice sheet's seasonal movement changes in response to the amount of surface meltwater being delivered to the ground below.
Lakes which form on the surfaces of glaciers, known as supraglacial lakes, are often created during the melt season, and typically last from early June to late August. Co-author Professor Alun Hubbard of Aberystwyth University studied these lakes and found that many empty in just a matter of hours, when hydrofracturing opens up water-filled crevasses, resulting in huge amounts of water entering and flooding the subglacial environment. In warmer years, these high-discharge drainage events are expected to become even more frequent.
"Not only is the ice sheet sensitive to a changing climate, but extreme meteorological events, such as heavy rainfall and heat waves, can also have a large effect on the rate of ice loss," said Dr Christoffersen. "The soft sediment gets weaker as it tries to soak up more water, making it less resistant, so that the ice above moves faster. The Greenland Ice Sheet is not nearly as stable as we think."
While complete loss of all ice in Greenland is judged to be extremely unlikely during this century, the record extent of surface melting in the past decade clearly shows that the ice sheet is responding to Earth's changing climate.
Early Ordovician (Skullrockian) trilobites of the Antiklinalbugt Formation, northeast Greenland, and their biostratigraphic significance
Authors:
McCobb et al
Abstract:
The Antiklinalbugt Formation of northeast Greenland comprises peritidal to subtidal carbonate sediments, deposited in shallow shelf settings during an early Tremadocian transgressive-regressive megacycle. The succession of shales and microbial, muddy and grainy limestone, with minor dolostone at the base and top, terminates at the cryptic Fimbulfjeld disconformity. The formation has yielded trilobites collected on Ella Ø, Albert Heim Bjerge, and Kap Weber by C. Poulsen (1920s and 1930s), J. W. Cowie and P. J. Adams (1950s), and during recent field studies in 2000 and 2001. The fauna includes dimeropygids Tulepyge cowiei and T. tesella n. spp., hystricurids Millardicurus and Hystricurus, and several species of Symphysurina. Micragnostus chiushuensis (Kobayashi, 1931) is rare, as are Chasbellus sp., Clelandia sp., and Lunacrania?. The presence of several Symphysurina species places the Antiklinalbugt Formation within the Symphysurina Zone. Chasbellus indicates the upper (lower Ordovician) part of the Symphysurina Zone for the lower upper Antiklinalbugt Formation. Conodonts place the middle lower formation in the Cordylodus intermedius conodont Biozone, the lower upper part in the Cordylodus angulatus conodont Biozone and the uppermost part in the Rossodus manitouensis conodont Biozone. This combined fauna is characteristic of the upper Skullrockian Stage of the Ibexian Series, with the lower part of the Antiklinalbugt Formation lying within the uppermost Cambrian of North America, and the upper part within the lower Ordovician. The entire formation lies within the global Tremadocian Stage of the early Ordovician.
A new study of three ice cores from Greenland documents the warming of the large ice sheet at the end of the last ice age – resolving a long-standing paradox over when that warming occurred.
Large ice sheets covered North America and northern Europe some 20,000 years ago during the coldest part of the ice age, when global average temperatures were about four degrees Celsius (or seven degrees Fahrenheit) colder than during pre-industrial times. And then changes in the Earth's orbit around the sun increased the solar energy reaching Greenland. Beginning some 18,000 years ago, release of carbon from the deep ocean led to a graduate rise in atmospheric carbon dioxide (CO2).
Yet past analysis of ice cores from Greenland did not show any warming response as would be expected from an increase in CO2 and solar energy flux, the researchers note.
In this new study, funded by the National Science Foundation and published this week in the journal Science, scientists reconstructed air temperatures by examining ratios of nitrogen isotopes in air trapped within the ice instead of isotopes in the ice itself, which had been used in past studies.
Not only did the new analysis detect significant warming in response to increasing atmospheric CO2, it documents a warming trend at a rate closely matching what climate change models predict should have happened as the Earth shifted out of its ice age, according to lead author Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the Science article.
"The new elevation maps are snapshots of the current state of the ice sheets. The elevations are very accurate, to just a few metres in height, and cover close to 16 million km2 of the area of the ice sheets. This is 500,000 square kilometres more than any previous elevation model from altimetry", says lead-author Dr. Veit Helm, glaciologist at the Alfred Wegener Institute in Bremerhaven.
For the new digital maps, the AWI scientists had evaluated all data by the CryoSat-2 altimeter SIRAL. Satellite altimeter measure the height of an ice sheet by sending radar or laser pulses in the direction of the earth. These signals are then reflected by the surface of the glaciers or the surrounding waters and are subsequently retrieved by the satellite. This way the scientists were able to precisely determine the elevation of single glaciers and to develop detailed maps.
On the basis of further CrysoSat-2 the scientists also documented how the elevation has changed over the 2011-2014 period. Ice sheets gain mass through snowfall and lose it due to melting and accelerating glaciers, which carry ice from the interior of the ice sheet to the ocean. "We need to understand where and to which extent the ice thickness across the glaciers has changed. Only then can we can analyse the drivers of these changes and find out how much ice sheets contribute to global sea level rise", says Veit Helm.
The team derived the elevation change maps using over 200 million SIRAL data points for Antarctica and around 14.3 million data points for Greenland. The results reveal that Greenland alone is reducing in volume by about 375 cubic kilometres per year. "When we compare the current data with those from the ICESat satellite from the year 2009, the volume loss in Greenland has doubled since then. The loss of the West Antarctic Ice Sheet has in the same time span increased by a factor of 3. Combined the two ice sheets are thinning at a rate of 500 cubic kilometres per year. That is the highest rate observed since altimetry satellite records began about 20 years ago," says AWI glaciologist Prof. Dr. Angelika Humbert, another of the study's authors.
The Finnefjeld domain, Maniitsoq structure, West Greenland: Differential rheological features and mechanical homogenisation in response to impacting?
Authors:
Garde et al
Abstract:
The 35 by 50 km large, Mesoarchaean Finnefjeld domain near Maniitsoq in the North Atlantic craton of southern West Greenland constitutes the central part of the previously proposed, deeply eroded Maniitsoq impact structure with an age of 3.0 Ga. The Finnefjeld domain is an exceedingly homogeneous, quartzo-feldspathic rock mass which superficially appears to be a late-orogenic, deep-crustal, intrusive granitoid pluton, and which was described as such for decades. However, new observations confirm and qualify the first observations from 1962 of these rocks as ‘cataclastic’. The Finnefjeld domain is characterised by a highly unusual, mixed rheological behaviour. Plagioclase displays brittle behaviour with cataclasis, quartz was ductilely deformed, and K-feldspar was melted. The deformation and homogenisation of the Finnefjeld domain was caused by an intense event of heating and deformation, which was coseismic in nature and comprised numerous increments of pure shear strain. This type of intense, brittle, regional deformation and concomitant direct mineral melting in the deep crust is unknown from endogenic orogenic events and is ascribed to deep-crustal effects of impacting.
Greenland’s white snow is getting darker. Scientists have generally attributed that darkening to larger, slightly less white snow grains caused by warmer temperatures. But researchers have found a new source of darkening taking hold: impurities in the snow.
“It can increase the speed of melting,” says Marie Dumont, a remote sensing scientist at Météo France in Grenoble, who publishes today with her colleagues in Nature Geoscience.
Scientists have known for years that Greenland’s snow is getting darker, based on satellite observations that have revealed lower albedos, or reflectivity. That’s a problem because the darker the snow is, the more sunlight it absorbs, and the faster it melts. Greenland’s melting ice sheets are already predicted to raise sea levels by 20 centimeters by 2100.
But Dumont and her colleagues have found that, since 2009, there has been a darkening that cannot be explained by larger snow grain size alone. Using satellite observations, they found lower albedos at elevations and at times of the year that are too cold for larger snow grains to form.
Beneath the barren whiteness of Greenland, a mysterious world has popped into view. Using ice-penetrating radar, researchers have discovered ragged blocks of ice as tall as city skyscrapers and as wide as the island of Manhattan at the very bottom of the ice sheet, apparently formed as water beneath the ice refreezes and warps the surrounding ice upwards.
The newly revealed forms may help scientists understand more about how ice sheets behave and how they will respond to a warming climate. The results are published in the latest issue of Nature Geoscience.
"We see more of these features where the ice sheet starts to go fast," said the study's lead author, Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory. "We think the refreezing process uplifts, distorts and warms the ice above, making it softer and easier to flow."
The structures cover about a tenth of northern Greenland, the researchers estimate, becoming bigger and more common as the ice sheet narrows into ice streams, or glaciers, headed for the sea. As meltwater at the bottom refreezes over hundreds to thousands of years, the researchers believe it radiates heat into the surrounding ice sheet, making it pick up its pace as the ice becomes softer and flows more easily.
Since the 1970s, and as recently as 1998, researchers flying over the region mistook radar images of these structures for hills. Newer instruments flown during NASA's IceBridge campaign to map ice loss at both poles found the hills to be made of ice instead of rock. Bell, who had discovered similar ice features at the base of the East Antarctic ice sheet, recognized them immediately.
While mapping Antarctica's ice-covered Gamburtsev Mountains in 2008 and 2009, Bell and colleagues discovered extensive melting and refreezing along ridges and steep valley walls of the range. Though researchers had long known that pressure and friction can melt the bottom of ice sheets, no one knew that refreezing water could deform the layer-cake structure above. In a 2011 study in Science, Bell and colleagues proposed that ice sheets can grow from the bottom up, not just from the top-down accumulation of falling snow.
The current study builds on the findings from Antarctica by linking the bottom features to faster ice sheet flow. The researchers looked at Petermann Glacier in the north of Greenland, which made headlines in 2010 when a 100-square mile chunk of ice slipped into the sea. They discovered that Petermann Glacier is sweeping a dozen large features with it toward the coast as it funnels off the ice sheet; one feature sits where satellite data has shown part of the glacier racing twice as fast as nearby ice. The researchers suggest that the refreeze process is influencing the glacier's advance hundreds of miles from where Petermann floats onto the sea.
The first ecological study of an entire glacier has found that microbes drastically reduce surface reflectivity and have a non-negligible impact on the amount of sunlight that is reflected into space.
The research, led by the University of Leeds and published today [12 June] in the journal FEMS Microbiology Ecology, will help improve climate change models that have previously neglected the role of microbes in darkening the Earth's surface.
Observing how life thrives at extreme cold temperatures also has important implications for the search for life on distant worlds, such as Jupiter's icy moon Europa.
Stefanie Lutz, a PhD student at the School of Earth and Environment at the University of Leeds, and lead author of the study, said: "Our three-week field trip revealed a 'microbial garden' of life forms flourishing in this cold environment, including snow algae, bacteria, fungi and even invertebrates.
"Skiers may have seen snow algae before, but not been able to identify it. They are visible to the naked eye as coloured snow – most often red – and are frequently referred to as 'watermelon snow'."
The study was carried out on the Mittivakkat Glacier in south east Greenland during the summer of 2012, which was the hottest summer and thus the fastest melting season recorded for 150 years.
"Our timing was serendipitous, as it meant we were able to see changes in microbial processes over an extremely fast melting season and observe a process from start to end across all habitats on a glacier surface. This is the most comprehensive study of microbial communities living on a glacier to date," said Lutz.
The research showed that, compared to pure snow and ice, the reflectivity of the glacier (known as the "albedo") can be reduced by up to 80% in places where coloured microbial populations are extremely dense, leading to the darkening of the glacier surface.
Greenland's icy reaches are far more vulnerable to warm ocean waters from climate change than had been thought, according to new research by UC Irvine and NASA glaciologists. The work, published today in Nature Geoscience, shows previously uncharted deep valleys stretching for dozens of miles under the Greenland Ice Sheet.
The bedrock canyons sit well below sea level, meaning that as subtropical Atlantic waters hit the fronts of hundreds of glaciers, those edges will erode much further than had been assumed and release far greater amounts of water.
Ice melt from the subcontinent has already accelerated as warmer marine currents have migrated north, but older models predicted that once higher ground was reached in a few years, the ocean-induced melting would halt. Greenland's frozen mass would stop shrinking, and its effect on higher sea waters would be curtailed.
"That turns out to be incorrect. The glaciers of Greenland are likely to retreat faster and farther inland than anticipated – and for much longer – according to this very different topography we've discovered beneath the ice," said lead author Mathieu Morlighem, a UCI associate project scientist. "This has major implications, because the glacier melt will contribute much more to rising seas around the globe."
To obtain the results, Morlighem developed a breakthrough method that for the first time offers a comprehensive view of Greenland's entire periphery. It's nearly impossible to accurately survey at ground level the subcontinent's rugged, rocky subsurface, which descends as much as 3 miles beneath the thick ice cap.
