World Meteorological Organization says sea level rise accelerating, fed by land ice melting
From the World Meteorological Organization: “The amount of ice lost annually from the Antarctic ice sheet increased at least six-fold, from 40 Gt per year in 1979-1990 to 252 Gt per year in 2009-2017.
The Greenland ice sheet has witnessed a considerable acceleration in ice loss since the turn of the millennium.
For 2015-2018, the World Glacier Monitoring Service (WGMS) reference glaciers indicates an average specific mass change of −908 mm water equivalent per year, higher than in all other five-year periods since 1950.”
The “dramatically changing landscape” of Mer de Glace
From New Scientist: “About a century ago, women with boaters and parasols sat near the Montenvers train station above the glacier, which then was almost level with a tongue of jagged ice snaking into the distance. Today, visitors are greeted by a slightly sad and largely grey glacier that is about 100 metres lower.”
An interdisciplinary analysis of changes in the high Andes
From Regional Environmental Change: “The high tropical Andes are rapidly changing due to climate change, leading to strong biotic community, ecosystem, and landscape transformations. While a wealth of glacier, water resource, and ecosystem-related research exists, an integrated perspective on the drivers and processes of glacier, landscape, and biota dynamics is currently missing. Here, we address this gap by presenting an interdisciplinary review that analyzes past, current, and potential future evidence on climate and glacier driven changes in landscape, ecosystem and biota at different spatial scales.
Our analysis indicates major twenty-first century landscape transformations with important socioecological implications which can be grouped into (i) formation of new lakes and drying of existing lakes as glaciers recede, (ii) alteration of hydrological dynamics in glacier-fed streams and high Andean wetlands, resulting in community composition changes, (iii) upward shifts of species and formation of new communities in deglaciated forefronts,(iv) potential loss of wetland ecosystems, and (v) eventual loss of alpine biota.”
Greenland and Iceland have been periodically reshaped by megafloods over thousands of years, a new paper in the journal Earth-Science Reviews has revealed.
British research duo Jonathan Carrivick
and Fiona Tweed have
provided the first evidence of gargantuan Greenlandic floods and extensively
reviewed the record of comparable events in Iceland. The researchers set out to
better understand what constituted a megaflood and find traces of them recorded
in the landscapes of these icy islands.
In media stories and even within the scientific literature the authors found that terms like “catastrophic flood,” “cataclysmic flood,” and “super flood” have been used indiscriminately and interchangeably. There are, however, strict definitions associated with each. A “catastrophic flood,” for instance, occurs when peak discharge exceeds 100,000 cubic meters per second — more than 18 times greater than the flow over Niagara Falls. Multiply that by ten (i.e. 1,000,000 cubic meters per second) and you get a sense of what constitutes a true megaflood.
Despite expressly seeking records of megafloods in the landscape
and literature, Carrivick and Tweed found that a more practical approach was to
identify events with “megaflood
attributes.” Scientists have recorded very few true megafloods since
those that cascaded off the Laurentide Ice Sheet, which
once mantled much of North America in the aftermath of the Last Glacial Maximum. While
there have been few recent floods that exceed one million cubic meters per
second, there have been several with comparable erosive power and lasting
Shaped by water
In Greenland, Carrivick and Tweed found 14 sites where huge floods had rampaged down fjords and across expansive “sandur,” or outwash plains. These have typically been outbursts from ice-dammed lakes, which have periodically unleashed inconceivably vast volumes. The glacial lake Iluliallup Tasersua empties every five to seven years and has a capacity of more than six cubic kilometers of water. At its peak, that flow would drown New York City’s Central Park in a column of water deeper than four Empire States Buildings.
Iceland, too, has experienced
its fair share of monstrous floods. Many of them have were triggered by
volcanic eruptions. Due to the unique setting of Iceland, where the active
fire-breathing mountains of the Mid-Atlantic island are blanketed with ice caps
and glaciers, erupting magma invariably explodes into the underside of a
quenching ice mass. This interaction, more often than not, results in an outburst
flood known locally as a “jökulhlaup,”
which produces tremendous amounts of power that is capable of reshaping and
inundating the island’s plains.
The region surrounding Öræfajökull, one of the most active
volcanoes in Iceland, is infamous for having suffered from devastation wrought
by both fire and ice.
“After it erupted in 1362, the
whole area was renamed as ‘Öræfi,’ which means ‘The Wasteland,” Tweed told
GlacierHub. “They renamed the area because it had been inundated by a grey
sludge, hyper-concentrated flow deposits and volcanic ash which had eradicated
the farmland and rendered it unusable.”
The eruption was the largest in Europe since Vesuvius immortalised
the communities of Pompeii and Herculaneum in AD79. The floodwaters rushed out
at over 100,000 cubic meters per second — qualifying as a “catastrophic flood.” The torrent was
so powerful that it was able to transport rocks weighing 500 metric tons, each
equivalent to four and a half blue whales. Despite not strictly meeting the
definition of a megaflood, the event certainly bore many of the hallmarks of
But the impacts of such deluges are not limited to their power to remold centuries-old landforms, toss about house-sized chunks of ice, or transport a beach-worth of sediment in a matter of hours.
Outbursts in Greenland can release as much as six billion metric tons of water within a matter of 7-10 days. This rapid draining of a glacier-lake basin radically changes the pressure atop the ice sheets, causing isostatic rebound, which can result in fractured shorelines, as localized sections of coast re-expand.
Water from an outburst flood often passes through a highly pressurized network of conduits within, beneath, and alongside ice. This can trigger a “seismic tremor.” So-called “glacier-derived seismicity” has been measured via seismometers since the early 2000s and experienced by eye-witnesses in the vicinity of Grænalón, one of the most famous jökulhlaup systems in Iceland. The authors note that while these events can be detected and felt, there is negligible impact from them.
Consequences for communities and corporations
Glacier floods also impact the communities living in the shadow of ice. Carrivick and Tweed’s previous work revealed that Iceland has experienced at least 270 glacier outburst floods across 32 sites, killing at least seven people. This makes Iceland among “the most susceptible regions to glacier floods” — and the economic costs that often result.
Icelanders are well acquainted with the natural dangers. Volcanic
eruptions, floods, and other geohazards are signature characteristics of their
Looking to the future, Tweed said: “We can expect to have jökulhlaups for another 200 years, until the ice
Such dire flood predictions are unlikely to rattle the stoic
Icelanders, who are more liable to fear the prospect of an Iceland bereft of
In even less populous Greenland, with people rarely situating
themselves in known flood paths, the impacts appear to be less disastrous. That
said, Carrivick noted: “When these big
outburst floods go into the fjords, and move out of the fjords and up and down
the coasts, you get these visible sediment plumes.”
The influx of sediment and freshwater changes the temperature,
salinity, and turbidity of the water in a fjord and the nearby ocean, which can
drive fish out the region. “It
basically shuts down the fishing industry for a couple of days at least,” Carrivick
Yet longstanding industries are not the only ones exposed to
the fickleness of Greenland’s glacier outbursts. As the ice sheet melts, a
number of resources are being eyed by extractive industries. Carrivick
recounted meeting teams of Swiss experts who had been commissioned by
Australian mining companies to set up rigs and conduct mineralogical
investigations in deglaciating regions.
He also remarked on the prospects of the hydropower industry, which has taken advantage of booms in other nations, like Nepal. “It might be an exaggeration, but I think it’s goldrush time,” he said. Regulators, he added, might struggle to keep up with monitoring and mitigating environmental impacts.
Whatever the future holds for Iceland and Greenland, Carrivick and Tweed’s research advances significantly scientific knowledge of the history of flooding on these two islands and makes a strong case for remaining attentive to the changes occurring on their diminishing ice masses.
“The extent of pre-Columbian land use and its legacy on modern ecosystems, plant associations, and species distributions of the Americas is still hotly debated. To address this gap, we present a Holocene palynological record (pollen, spores, microscopic charcoal, SCP analyses) from Illimani glacier with exceptional temporal resolution and chronological control close to the center of Inca activities around Lake Titicaca in Bolivia. Our results suggest that Holocene fire activity was largely climate-driven and pre-Columbian agropastoral and agroforestry practices had moderate (large-scale) impacts on plant communities. Unprecedented human-shaped vegetation emerged after AD 1740 following the establishment of novel colonial land use practices and was reinforced in the modern era after AD 1950 with intensified coal consumption and industrial plantations of Pinus and Eucalyptus. Although agroforestry practices date back to the Incas, the recent vast afforestation with exotic monocultures together with rapid climate warming and associated fire regime changes may provoke unprecedented and possibly irreversible ecological and environmental alterations.”
“Politicians have tussled for years over the fate of the Tongass, a massive stretch of southeastern Alaska replete with old-growth spruce, hemlock and cedar, rivers running with salmon, and dramatic fjords. President Bill Clinton put more than half of it off limits to logging just days before leaving office in 2001, when he barred the construction of roads in 58.5 million acres of undeveloped national forest across the country. President George W. Bush sought to reverse that policy, holding a handful of timber sales in the Tongass before a federal judge reinstated the Clinton rule.
“The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has measured ice-sheet elevation and thickness via repeat airborne surveys circumscribing the ice sheet at an average elevation of 1708 ± 5 m (Sørensen et al. 2018). We refer to this 5415 km survey as the ‘PROMICE perimeter’ (Fig. 1). Here, we assess ice-sheet mass balance following the input-output approach of Andersen et al. (2015). We estimate ice-sheet output, or the ice discharge across the ice-sheet grounding line, by applying downstream corrections to the ice flux across the PROMICE perimeter.”
Temperature records fell one after another in Europe last week with five countries—Great Britain, Belgium, the Netherlands, Germany, and Luxembourg—registering record highs.
A study conducted by World Weather Attribution concluded that temperatures during the hot spell would have been 1.5-3 degrees Celsius cooler if not for the additional warming brought about by human-caused climate change.
Video posted to Twitter shows how rising temperatures are impacting Europe’s alpine glaciers. Severe-weather.EU posted footage of a massive mudslide barreling down a mountainside on July 28th at the height of the heat wave. The group alleges the mudflow was brought about by melting glaciers in Mauvoisin, Switzerland.
A mudflow from the melting glaciers in Mauvoisin, Switzerland yesterday, July 28th. Thanks to Ilyes Ghouil for the report! Source: @Météo Franc-comtoise pic.twitter.com/SnSskjkD7A
The high pressure system that parked over Europe and brought about the record heat has since moved north, where it’s led to potentially record-breaking melt across Greenland’s ice sheet.
The familiar images of temperature anomalies that are produced by the world’s climate and weather agencies have inspired Philadelphia, Pennsylvania-based artist Diane Burko, who is currently working on a painting depicting the July heatwave in Europe.
From GlacierHub writer and environmentalist Tsechu Dolma: “China is hosting World Environment Day 2019, its mounting environmental crisis is endangering hundreds of millions and downstream nations, what happens on the Tibetan plateau has profound consequences on rest of Asia.”
Everest traffic jam blamed for climber deaths
From the New York Times: “Climbers were pushing and shoving to take selfies. The flat part of the summit, which he estimated at about the size of two Ping-Pong tables, was packed with 15 or 20 people. To get up there, he had to wait hours in a line, chest to chest, one puffy jacket after the next, on an icy, rocky ridge with a several-thousand foot drop.
This has been one of the deadliest climbing seasons on Everest, with at least 11 deaths. And at least some seem to have been avoidable.”
From Frontiers of Earth Science: “Kangerlussuaq Glacier is one of Greenland’s largest tidewater outlet glaciers, accounting for approximately 5% of all ice discharge from the Greenland ice sheet. In 2018 the Kangerlussuaq ice front reached its most retreated position since observations began in 1932. We determine the relationship between retreat and: (i) ice velocity; and (ii) surface elevation change, to assess the impact of the retreat on the glacier trunk. Between 2016 and 2018 the glacier retreated ∼5 km and brought the Kangerlussuaq ice front into a major (∼15 km long) overdeepening. Coincident with this retreat, the glacier thinned as a result of near-terminus acceleration in ice flow. The subglacial topography means that 2016–2018 terminus recession is likely to trigger a series of feedbacks between retreat, thinning, and glacier acceleration, leading to a rapid and high-magnitude increase in discharge and sea level rise contribution. Dynamic thinning may continue until the glacier reaches the upward sloping bed ∼10 km inland of its current position. Incorporating these non-linear processes into prognostic models of the ice sheet to 2100 and beyond will be critical for accurate forecasting of the ice sheet’s contribution to sea level rise.”
In this Video of the Week, watch an aerial view of the flow line at the Jakobshavn Glacier, in Ilulissat, Greenland. The video was posted on Twitter by Santiago de la Peña of Ohio State University’s Byrd Polar and Climate Research Center.
“This behemoth shreds into the ocean the equivalent of San Francisco’s water consumption,” he said.
Jakobshavn glacier is well known for likely producing the iceberg that sunk the Titanic.
It is also a very dynamic glacier. In the early 2000s, Jakobshavn was one of the fastest-flowing glaciers in the world, losing up to 20 meters in height each year. It is estimated that between 2000 and 2010, Jakobshavn alone contributed almost 1 millimeter to global sea level rise. In more recent years, however, Jakobshavn is actually growing again, now gaining about 20 meters in height per year.
Researcher Santiago de la Peña of Ohio State University’s Byrd Polar and Climate Research Center posted video on Twitter of raging streams of meltwater carving through the surface of Greenland’s Russell Glacier.
“Early May and melt season is already in full swing in western Greenland,” he wrote. “The amount of meltwater at Russell glacier for this time of year is staggering.”
The glacier is located on the west coast of Greenland.
Peña studies ice sheet dynamics and surface mass balance in Greenland and Antarctica.
In several tweets following his video of Russell Glacier, Peña described high temperatures and large amounts of meltwater.
“We serviced 2 stations at an elevation of 2300m and 1900m; the lower site was above freezing, the other at -4C. They are usually in the -20s and -30s this time of the year,” he wrote in a May 6 tweet.
From Geomorphology: “Ahora Gorge is a 400 m deep canyon located along the North Eastern flank of Mt. Ararat (Turkey), a compound volcanic complex covered by an ice cap. In the past, several diarists and scientific authors reported a calamitous event on July 2, 1840, when a landslide triggered by a volcanic eruption and/or an earthquake obliterated several villages located at the foot of the volcano. The reasons and effects of this Ahora Gorge Catastrophe (AGC) event have been obscure and ambiguous. To reappraise the 1840 catastrophe and the geomorphic evolution of the Ahora Gorge, we used high-resolution satellite images, remote sensing thermal data supplemented by observations collected during two field surveys.”
Albedo Effect in the Swiss Alps
From The Cryosphere: “Albedo feedback is an important driver of glacier melt over bare-ice surfaces. Light-absorbing impurities strongly enhance glacier melt rates but their abundance, composition and variations in space and time are subject to considerable uncertainties and ongoing scientific debates. In this study, we assess the temporal evolution of shortwave broadband albedo derived from 15 end-of-summer Landsat scenes for the bare-ice areas of 39 large glaciers in the western and southern Swiss Alps. […] Although a darkening of glacier ice was found to be present over only a limited region, we emphasize that due to the recent and projected growth of bare-ice areas and prolongation of the ablation season in the region, the albedo feedback will considerably enhance the rate of glacier mass loss in the Swiss Alps in the near future.”
Glacier Meltwater Impacts in Greenland
From Marine Ecology Progress Series: “Arctic benthic ecosystems are expected to experience strong modifications in the dynamics of primary producers and/or benthic-pelagic coupling under climate change. However, lack of knowledge about the influence of physical constraints (e.g. ice-melting associated gradients) on organic matter sources, quality, and transfers in systems such as fjords can impede predictions of the evolution of benthic-pelagic coupling in response to global warming. Here, sources and quality of particulate organic matter (POM) and sedimentary organic matter (SOM) were characterized along an inner-outer gradient in a High Arctic fjord (Young Sound, NE Greenland) exposed to extreme seasonal and physical constraints (ice-melting associated gradients). The influence of the seasonal variability of food sources on 2 dominant filter-feeding bivalves (Astarte moerchi and Mya truncata) was also investigated. Results revealed the critical impact of long sea ice/snow cover conditions prevailing in Young Sound corresponding to a period of extremely poor and degraded POM and SOM.”
In this week’s Video of the Week, watch a massive glacier calving event that occurred at Helheim Glacier in Greenland. The video was captured on 22 June 2018 by Denise Holland of New York University.
The calving event took place over a 30-minute time period, and was sped up into a time-lapse of about 90 seconds. During this time span, over four miles of the glacier’s edge broke off, flowing into one of the fjords that connects Helheim Glacier to the ocean. To put this in perspective, a calving event of this size would measure roughly the size of lower Manhattan, all the way to Midtown in New York City. In a warming world, glacier calving is a large force contributing to global sea-level rise.
The dynamics of climate and environment have a large and growing influence on our culture, practices and health. Climate change is expected to impact communities all over the world, requiring people to adapt to these changes. A recent study by Kirsten Hastrup in the journal Cross-Cultural Research looks at the history of health and environment of the Inuit people of Greenland’s Thule community. Global warming has impacted the hunting economy in the region, and increasing sea contamination is negatively affecting the Arctic ecosystems and human health. Kirsten Hastrup locates these recent changes in the context of earlier dynamics, identifying the social and environmental factors contributing to Inuit development over time.
Effects of Early Exploration and Trade
The Thule community is located in the far northern region of Qaanaaq, Greenland. It is called Avanersuaq, or “Big North,” in the Inuit language of Iñupiat. The Little Ice Age, which lasted from the 14th to 18th century, isolated this small population of 140 from other communities and regions in the south. Waters opened with melting sea-ice in the 19thcentury, allowing European explorers and whalers to contact the region and the Inuit people. The explorers engaged in trade with the Inuit, exchanging wood, guns, and utensils for fur. Unfortunately, trade and the arrival of whalers introduced new diseases to the community, leading to epidemics and population decline.
Hastrup explains that the Inuit also suffered from famine at the time due to the grip of the Little Ice Age. Expansion of inland ice and glaciers and persistent sea ice made it hard for the Inuit to hunt for food sources like whales, walruses and seals. A lack of driftwood used to make bows, sleds and build kayaks for hunting also contributed to the Inuit’s hardship and further population decline. Natural hazards from living in the Arctic environment led to the decline on a smaller scale. Some of these deaths were due to instabilities of the icy landscape, accidents while traveling across expanses of ice, and large animal attacks during hunting.
Cold War Implications on Health and Identity
Although the risk of disease was great, Hastrup recognizes the impacts of diseases. She also identifies the benefits of trade, which brought resources necessary for hunting and overcoming famine. Development of formal trading stations and greater access to wood allowed for increased hunting capability. Fur trade became quite profitable for the Inuit toward the early 20thcentury, much to the benefit of the local economy.
However, this did not last long, according to Hastrup. During the Cold War period, the Arctic became a sort of frontier between the U.S. and the Soviet Union. An American airbase was established in the early 1950s, and this had long-lasting effects on health and Inuit identity. Transport vessels, airplanes, and heavy activity at the airbase disturbed the Arctic animals, damaging important Inuit hunting grounds. The population had to relocate to make room for the airbase. This forced movement to new housing sites left a sense of dislocation among the Inuit community.
A new health risk was introduced in 1959 with the launch of Camp Century, a scientific military camp built under the ice cap. This nuclear-powered camp was also secretly designed to house missiles during the Cold War. The movement of the ice sheet led to an abandonment of the camp in 1966; however, the nuclear threat continued. In 1968, a plane carrying plutonium bombs crashed, going right through the sea ice outside of Thule. Three bombs were retrieved from the waters, although reports in European news media suggest a fourth bomb remains. A nearby fjord was also later revealed to be contaminated by nuclear radiation. According to Hastrup, the people in the region continue to fear risks from radiation-related illness and contaminated food.
Impacts of Changing Climate
These activities and the historical implications of outside contact have left a deep-rooted concern for health and well-being among the Thule community, one that is felt even today. According to Hastrup, many fear that changes in the environment may expose them to further ice-trapped radiation. Camp Century was eventually buried within a glacier, and continued warming is causing movement within the ice. Some Inuit worry that leftover radiation might be released if the glaciers were to retreat, harming the health of their community, Hastrup reports.
Warming trends impacting the Arctic regions are influencing Inuit practices in certain ways. No longer able to subsist as hunters, for example, the Inuit have adapted to halibut fishing for income. Hastrup argues that in its own way, this adaptation adds a sense of dislocation from tradition. Sharing of game was a longtime tradition among the community, which provided a feeling of unity.
Sherilee L. Harper, associate professor at the Public Health School of the University of Alberta, told GlacierHub about how changing climate might continue to affect the Inuit community. “Research, based on both Inuit knowledge and health sciences, has documented impacts ranging from waterborne and foodborne disease to food security to unintentional injury and death to mental health and wellbeing,” she said.
Despite shifts in traditional practices, Inuit appear ready to meet the challenges of their changing environment. As oceans continue to warm and threaten this Arctic ecosystem, Inuit residents continue to work with governments and climate scientists to monitor changes, deploy conservation efforts, and manage local development. Their openness to change is shown in their shifts to commercial fur collecting in the past to new forms of fishing in the present. Harper added that the Inuit have shown resilience to climate change and continue to be international leaders in climate change adaptation.
The discovery of an impact crater in remote northwestern Greenland may resolve a major climate history question: what caused the planet to suddenly cool around 12,800 years ago? In a new study published last month in the journal Science Advances, the researchers are careful not to make claims about the larger implications of the find. But details, including the size and approximate timing of the impact, offer much to consider about what triggered Earth’s last sudden climate change.
The impact crater was discovered beneath Hiawatha Glacier, under more than a kilometer of ice. Hiawatha is among the largest impact craters ever discovered on Earth, as well as the northernmost and first to be located under ice. Modern geospatial technology has enabled the Earth’s surface to be thoroughly mapped, leaving significant undiscovered features either deep under the sea or beneath ice, like Hiawatha. That a striking and visible geologic feature of Hiawatha crater’s magnitude had yet to be located makes the find even more remarkable.
The initiative to map the crater was led by the intuition of principal author, Kurt Kjær, a glacial geologist at the University of Copenhagen and curator at the Natural History Museum of Denmark. Kjær wondered whether a connection might exist between an anomalous circular ice pattern he observed in satellite images of the Greenland ice sheet and an iron meteorite on display at the museum where he parks his bicycle.
To pursue his hunch, Kjær needed to know what was under the ice. Joe MacGregor, a glaciologist with the NASA Goddard Space Flight Center, unearthed archival imagery from Operation IceBridge. The temporary mission collected critical data used to predict the response of the Earth’s polar ice to climate change and sea-level rise. NASA assembled the operation after an ice monitoring satellite malfunctioned in 2009, bridging the gap until the successor satellite could be launched in September 2018. The aircraft often operated out of Thule Air Base, near Hiawatha. It often activated its instruments in test mode and happened to overfly the impact site on its flight path to the polar ice cap, adding a layer of serendipity to Kjær’s discovery. “Without Operation IceBridge the crater might’ve gone undiscovered for even longer than it did,” MacGregor told GlacierHub. Lucky or not, Kjær had mounted enough evidence to make his case.
A foundation backed by Copenhagen brewery, Carlsberg, funded the mission. A Basler BT-67 aircraft with a state-of-the-art ice-penetrating radar made three flights in May 2016, to map the suspected location. Kjær’s hunch was correct. The radar revealed a massive crater under the ice, suggesting an extraterrestrial impact. Measuring over 31 kilometers in diameter, the imprint left by the impact is among the largest on the planet, big enough to comfortably hold the city of Paris. Most similar-sized craters on Earth have changed much over time, many eroded to the point of unrecognizability. While ice tends to preserve organic material well, the pressure and grinding weight of ice scours topography. Beneath Hiawatha, the disheveled ice still bore signs of the cataclysm. At the bottom of the crater, classic impact characteristics, like central uplift features, were also apparent.
Recognizing the need for conclusive evidence to solidify his impact finding, Kjær visited Hiawatha later in the summer of 2016. In the outflow of the glacier, he found what he was looking for; tektites, a natural glass formed by meteoric impacts, and shocked quartz. Shocked quartz is only found in post-nuclear blast craters or extraterrestrial impact sites, like the Yucatan’s Chicxulub crater, whose impactor caused the mass extinction that killed off the dinosaurs. The Hiawatha crater’s crisp impact features and disrupted ice indicate it collided with the Earth at a much more recent date, perhaps as recent as the last Ice Age.
Could the Impact Have Triggered Sudden Climate Change?
The potential timing of the impact might be the greatest significance of the discovery. The Earth’s climate fluctuates between glacial and relatively warm interglacial periods, like the present. But as the planet thawed from the last ice age, it abruptly stopped warming, and cooled for over a millennium. For decades, climatologists theorized possible causes for this return to near-glaciation, known as the Younger Dryas. The period is named for an Arctic-alpine flower, Dryas octopetala, whose pollen is found in abundance in ice cores from the era. Some scientists believe Younger Dryas climate reversal may have been triggered by an event around 13,000 years ago. But the lack of physical evidence to support an impact hypothesis left the door open for a variety of theories.
A popular hypothesis for the cause of the Younger Dryas period is a sudden influx of melt water into the North Atlantic Ocean. The fresh water would create a stable surface layer, that would both slow the ocean circulation and freeze easily. An impact like the one that caused the Hiawatha crater would turn enough ice into fresh water to suppress the North Atlantic cycle and halt the warming. The timing seems about right.
Wally Broecker, known as the “Grandfather of Climate Science,” is a geoscientist at Columbia University’s Lamont-Doherty Earth Observatory. Among many climate firsts, Broecker coined the term “global warming” and was the first to recognize the global Ocean Conveyor Belt, a temperature and salinity-driven cycling of deep ocean water. In a 1989 paper published in Nature, Broecker theorized that the Younger Dryas period, and other periods of cooling like it, was triggered by the reorganization of deep ocean circulation — a critical process for modulating the Earth’s climate.
James Kennett is a marine geologist at the University of California, Santa Barbara, and one of Broecker’s co-authors of the 1989 paper. Kennett told Science, “I’d unequivocally predict that this crater is the same age as the Younger Dryas.” The impact would align with Kennett’s theory that a cosmic event precipitated the Younger Dryas cooling period. But, according to Broecker, the slowdowns of the conveyor belt are the effect of internal oscillation of the ocean system, independent of any impact event. In other words, though a meteor collision may have pre-triggered a cooling period, the Younger Dryas would have happened with or without an impact.
Broecker explained to GlacierHub, “I’m not convinced this caused the Younger Dryas. If you look at the record of Greenland ice cores, they happen over and over again,” Broecker said, referring to the Earth’s cycles of glaciation. “You can say the Younger Dryas was unique — it was triggered by an impact and all the others were just an internal oscillation.”
The location of the crater on the edge of Greenland also gave Broecker reason to doubt the impact-trigger for Younger Dryas, “I don’t think it could have melted that much ice,” he said. There are also other uncertainties regarding the impact, for example, the lack of evidence in deep ice cores taken elsewhere in Greenland. “That’s a problem,” Broecker said, referring to the absence of ejecta in the ice cores.
Whether or not ejecta would be present, however, depends on the angle of impact. Jay Melosh, from Purdue University’s Department of Earth, Atmospheric and Planetary Sciences, approached the question with similar restraint. He cautioned against making conclusions about the impact before a core is drilled and recovered, telling GlacierHub, “It will only be proved by drilling through the ice and demonstrating that the basin contains impact metamorphosed rock.”
While the slowdown of ocean circulation may have occurred independent of an impact, effects on biodiversity and humans would be tied to an impact. The Paleo-Indian Clovis culture and megafauna, like the woolly mammoth, are believed to have disappeared around the onset of the Younger Dryas. Until a core can be taken from Hiawatha, down to the impact-melted rocks, uncertainty regarding the timing will remain.
The study remains silent on questions about ocean circulation, providing the more general conclusion, “based on the size of the Hiawatha impact crater, this impact very likely had significant environmental consequences in the Northern Hemisphere and possibly globally.” It hints at forthcoming research and potentially a global quest for further evidence of the Hiawatha impact. Referring to the Younger Dryas impact theorists, Broecker said, “now people will renew the hunt.” In the quest to cross-reference the impact crater with paleoclimate evidence around the world, Hiawatha glacier might become one of the planet’s most significant. As mankind pushes Earth’s system toward the brink, understanding the planet’s most documented, sudden climate change, the Younger Dryas, becomes ever more urgent.
Park Enlists Citizens to Track Changes in Teton Glaciers
From U.S. News: “The project aligns with one of Grand Teton’s fundamental duties, keeping tabs on its natural resources. Estimates vary, but with global temperatures increasing some studies suggest many glaciers could disappear within the next few decades.”
Fracturing Glacier Revealed by Ambient Seismic Noise
From AGU 100: “Here we installed a seismic network at a series of challenging high‐altitude sites on a glacier in Nepal. Our results show that the diurnal air temperature modulates the glacial seismic noise. The exposed surface of the glacier experiences thermal contraction when the glacier cools, whereas the areas that are insulated with thick debris do not suffer such thermal stress.”
From Science Direct: “Here, we use a multi-proxy approach that combines proglacial lake sediment analysis, cosmogenic nuclide surface-exposure dating (in situ10Be and 14C), and radiocarbon dating of recently ice-entombed moss to generate a centennial-scale record of Holocene GIC fluctuations in southwestern Greenland.”
Read more about holocene mountain glacier history here.