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.
An important Arctic fish might be in trouble. A recent study in Greenland examines changes in the feeding ecology of capelin, a small forage fish in the smelt family. Melting glaciers are affecting its diet, and this change in diet can heavily influence its growth and reproduction. This could spell trouble for the other animals that eat capelin.
Found in the Arctic, Capelin are an important food source for marine mammals such as whales and seals. Atlantic cod, a major commercial fish species, are one of its major predators. Atlantic puffin also like to feed on them, along with other sea birds.
Capelin enjoy feeding on plankton, microorganisms that float in the sea and on freshwater. Krill, small shrimp-like crustacean, are also crucial in the diet. Capelin seem to migrate less than other species, making them extremely dependent on the food that’s readily available to them. Any major changes in food availability can ripple through the Arctic food web.
The Godthåbsfjord in West Greenland was sampled at a number of sites, all the way from the mouth where it opens to the ocean to the furthest inland basin. Capelin were sampled by the researchers during the months of May and August, when increased meltwater from summer heating flows into the fjord. The fish were then divided into 2-cm interval size groups, assessing for differences in age. Researchers carefully dissected the stomachs and intestines, preserving them so that they could later examine their contents to determine diets over different locations and times.
Lorenz Meire talks about the framework of the study in an interview with GlacierHub. Meire is a marine scientist at the Royal Netherlands Institute for Science Research and one of the scientists behind this study. “By trawling in a sub-Arctic fjord impacted by glacial meltwater, we aimed to assess the change in capelin size distribution and its diet throughout the season,” he says. Meire adds that scientists tried to link diet with observed changes in zooplankton biomass and environmental conditions.
What are some observed environmental changes?
Studies show a shift in abundance of krill from freshwater-influenced regions toward the oceans. We see similar shifts with large plankton. GlacierHub spoke with Kristine Engel Arendt, a marine biologist from the University of Copenhagen. Her research on plankton community structure is referenced in the study. She provides some insight on how runoff from the exit glacier and high up ice sheets affect the ecosystem ecology, looking particularly at smaller plankton species.
Arendt told GlacierHub that the fjord typically experiences a bloom of algae in the spring, which is a food source for plankton. The addition of freshwater from the late summer runoff initiates a second bloom of algae, driven by an upwelling of nutrients. “The marine food web is closely linked to the energy source from the algae bloom, and therefore zooplankton species that can utilize food over the entire summer period are favored,” she says. These smaller species of plankton benefit from the nutrients. They use this extra algae bloom during the summer to grow and reproduce. This observation indicates an abundance of smaller plankton at the inner basin region in August. Stomach examinations show a clear increase of small plankton in the diet of fish from this area of the fjord.
Arendt points out that climate change effects such as melting glaciers are not always negative. We see that this inflow of freshwater is in fact beneficial to these smaller plankton. But how might this change affect capelin?
A Disadvantage to Younger Capelin
It’s important to look at the migration and reproductive pattern of capelin to understand the impacts. Maturing adult capelin spawn from April to June in the fjord, from the inner basin to near-coastal regions. Studies show that all male capelin and some females die off with connection to spawning. Researchers can then presume that the May sample will consist of both mature and immature capelin, and August will be dominated by young capelin. This is reflected in the findings of the study.
The quality of the available food sources must also be examined. It differs with plankton size. Larger plankton species are relatively richer in fat per unit of weight. This makes them more ideal for energy intake and growth than the smaller plankton species. Energy intake and growth is particularly critical for young capelin. Meire told GlacierHub, “If smaller copepods (plankton) become more abundant, they will form a more important food source for capelin. Though this can impact the energy transfer as small copepods in the diet cannot compensate for the absence of larger copepods and krill.”
Lack of the more favored species in the inner regions can negatively affect nutrition of capelin. Younger capelin here are at risk. They will need to feed on the larger, fat-rich plankton to receive enough nutrients to effectively grow and reproduce. This can greatly affect the Arctic food web.
In this week’s Video of the Week, watch two poets from two different walks of life unite to call attention to climate change. Aka Niavana is from Greenland, and she reflects on the way life is changing as the glaciers around her melt. Kathy Jetnil-Kijner is from the Marshall Islands, where her home is threatened by the melting ice and rising seas. In a joint expedition to the remote fjords of southern Greenland, the two activists perform their poetry, hoping to inspire action on climate change.
The story, published in The Guardian, is written by Bill McKibben, co-founder of 350.org.
One year has elapsed since the successful GEUS expedition to Camp Century to establish instrumentation in the summer of 2017. Three automated instruments were deployed, 175 m of ice core was drilled, and nearly 100 km of ice-penetrating radar imagery was collected on the expedition.
This video describes the expedition.
Data from the First Year
Ice and climate data are satellite-transmitted from stations on the ice-sheet several times per day and the daily averages are shown in real time online here.
The minimum average daily air temperature measured in the first year of the programme was -47.2°C on 10 March 2018. The maximum average daily air temperature was -0.8°C on 31 July 2017. The average temperature for the first year was -24°C.
The minimum average daily wind speed measured in the first year of the programme was 0.6 m/s on 31 August 2017. The maximum average daily wind speed was 16.0 m/s on 25 October 2017.
The instruments were in complete darkness – polar night – for approximately three and half months. During this time, the solar-powered instruments relied on their battery reserves and transmitted measurements less frequently.
New scientific article
The scientific article, “Initial field activities of the Camp Century Climate Monitoring Programme in Greenland,” has been published in the Geological Survey of Denmark and Greenland Bulletin 41 – Review of Survey Activities 2017. Read the article here.
The article documents that surface melt briefly occurred – less than one week – in both summer 2017 and 2018. Additional refrozen melt layers from the past decade are identifiable in the ice cores. When Camp Century was built in 1959, no summer melt occurred at the site.
Plans for 2019 and Beyond
The next fieldwork at Camp Century is scheduled for summer 2019. Existing instruments will be raised above the accumulating snow, and a fourth instrument to measure the speed of ice flow will be installed. This year’s maintenance was postponed due to bad weather and logistical issues in Northwest Greenland.
Analysis of radar imagery to map the precise extent and depth of the Camp Century debris field and active layer footprint is ongoing. A complete site map is expected to be published in 2019.
The refined knowledge of the sub-surface debris field and data on the overlying snow and ice will form the basis for modelling of the likelihoods of meltwater interacting with abandoned materials at the Camp Century site over the next century. The first updated preliminary projections based on the new data are expected at the end of 2019. In time, this will lay the foundation for a science-based discussion of the future of Camp Century.
Between 2003 and 2010, the Greenland Ice Sheet and its associated glaciers experienced a mean annual mass loss of 186 Gt, double the rate between 1983 and 2003. Though this mass loss has been linked to global sea-level rise through meltwater discharge, heightened glacial runoff has also been hypothesized to have another important effect: increasing marine primary productivity through nutrient fertilization. This hypothesis was the focus of a recent study published in Nature Communications, which reports that the upwelling of nitrate-rich deep seawater driven by subglacial discharge— not the meltwater itself— is likely the main driver of the increased productivity.
This question about the impact of heightened glacial runoff is important both for academic research on marine ecosystems and for assessing the future of oceans to serve as carbon sinks. The photosynthesis represented by primary productivity is one of the key mechanisms through which carbon dioxide dissolved in seawater can be captured and retained in the oceans.
During the spring, marine primary productivity off the coast of Greenland increases as phytoplankton bloom. Then, in the summer, productivity usually diminishes. Recently, however, there have been summer phytoplankton blooms accounting for up to half of annual primary productivity. The goal of the study was to examine these changes to summer productivity and see how they relate to nutrient availability during the meltwater season.
The researchers first assessed which nutrient deficiency limits summer primary productivity off of Greenland. In most parts of the high-latitude Atlantic, summer primary productivity is limited by iron or nitrate deficiencies. However, in Greenland, few studies had previously examined the nutrient limits to phytoplankton blooms.
The researchers found that iron values were the most positive near the coasts, while offshore values were close to zero. On the other hand, nitrate values were deficient near the coasts and offshore. These results indicate that iron may help trigger the summer blooms while also inhibiting the drawdown of nitrate by plankton, leading the researchers to conclude that the availability of nitrate is likely the constraint on summer primary productivity.
Is heightened glacial runoff supplying more iron and nitrate, contributing to the summer phytoplankton blooms? Iron concentrations from glacial runoff were comparatively low, unlikely to trigger the blooms given the already iron-rich waters, the authors concluded. Furthermore, in Greenland, glacial runoff supplying iron can have a negative impact on primary production. It has this effect by reducing the availability of other nutrients and by creating cloudy sediment plumes from glacial flour composed of fine-grained rock particles created by glaciers grinding over underlying bedrock. These cloudy plumes limit light availability, says lead author Mark Hopwood, who spoke with GlacierHub about the paper. In contrast, he said, nitrate concentrations were found to be even lower than iron ones, only enough to have a very small effect on phytoplankton blooms.
While the meltwater from glacial runoff is unlikely to be the trigger of the summer plankton blooms off Greenland, the researchers determined marine-terminating glaciers to represent another aspect of glacial discharge.
Unlike their land-terminating counterparts, marine-terminating glaciers discharge meltwater through sub-glacial plumes. This discharge, once injected into the water at the glacial grounding line, entraps nutrient-rich deep seawater in a rising plume. This upwelling, if it occurs at the right depth, takes nitrate-rich waters to the photic zone where light is sufficient for photosynthesis, driving the phytoplankton blooms.
The researchers found four scenarios through which plume upwelling affects nutrient delivery near marine-terminating glaciers, with glacial grounding line depth the primary influence on the efficacy of this delivery. Under the first scenario, a nutrient-rich plume is generated by sub-glacial discharge. However, the glacier is too deep, and the plume is unable to reach the photic zone. In the second scenario, the glacier is in the optimum depth zone, and the nutrient-rich deep sea water is upwelled to the photic zone, enhancing the phytoplankton bloom. In the third scenario, the grounding line depth shallows because of glacial retreat. This shallowing limits the amount of seawater entrapped by the sub-glacial discharge. The seawater that is entrapped lacks the nutrients of deeper waters, thereby lessening the positive effects of the upwelling on phytoplankton blooms. In the final scenario, the glacier has retreated inland and no longer ends in the ocean, so no upwelling is generated.
After delineating these four scenarios, the researchers next simulated the plume upwelling effect to find the optimum conditions for peak nitrate flux to be upwelled to the photic zone. According to Hopwood, each fjord-glacier system in Greenland has unique physical characteristics, such as fjord depth and annual discharge volume.
This means that the optimum conditions for each system varies regionally. As a general rule of thumb, shallow glacier grounding line depths below 100 m will likely lead to low productivity, while grounding line depths between 400 and 600 m will likely be linked with high productivity, according to Hopwood. Other factors also affect summer marine productivity including turbidity and the depth of the photic zone. However, the plume upwelling of nutrients appears to be the dominant factor.
The future of marine productivity off Greenland under climate change will be determined by glacier grounding line depths, which may remain as they currently are or migrate into the optimum zone for subglacial discharge, triggering the upwelling of nitrate nutrients. Shallow glacier grounding line systems are likely to have already experienced peak nitrate supplies, while the peak for deeper systems will likely occur in the future if current retreats continue. For the 243 Greenland glaciers that have been mapped for bed topography, 55 percent will retreat onto land in the future, reducing the ice sheet-to-ocean nutrient fluxes driving summertime phytoplankton blooms.
What happens to the plume upwelling of nutrients in Greenland ultimately depends on climate change and subsequent glacier retreats. One subject for future study that could help improve understanding of marine productivity is the influence of icebergs, says Hopwood. The largest icebergs usually extend far below the ocean surface, hypothetically allowing them to “act as miniature nutrient ‘pumps’ as they melt,” Hopwood told GlacierHub. This is similar to what occurs with glaciers on a larger scale. Yet icebergs are more difficult to study and will require interdisciplinary work between both physicists and chemists to examine how icebergs affect the water column and phytoplankton.
Taken together, this research on the effects of different kinds of glaciers on phytoplankton blooms is key to a better understanding of marine ecosystems, helping scientists to assess the ability of the oceans to serve as sinks for the carbon dioxide that we humans continue to release.