Subglacial Meltwater Boosts Greenland Ecosystems and Locks Carbon

Following news of the arrival of a Manhattan-sized iceberg from a retreating glacier next to a village in Greenland, a recent paper published in the Journal of Geophysical Research has unveiled new research on how subglacial meltwater in Greenland is pumping nutrients and carbon from the deep sea to drive a boom of microorganisms in the upper layers. This effect fuels the ecosystems around it and impacts carbon cycling within the fjords and ocean close to the glaciers, further increasing the carbon uptake from the atmosphere.

Since 2002, Greenland has lost around 270 billion tons of ice per year. The glaciers and ice sheets of Greenland are key to the magnitude of future sea level rise, prompting scientists and researchers from around the globe to travel to the glacier-laced land to study and measure the physics of glacier melting and retreat. A team of researchers from Hokkaido University, led by Naoya Kanna and Shin Sugiyama, found a new perspective to understand the interactions of glaciers with ecosystems under a changing climate.

Bowdoin Glacier and Fjord. Bowdoin is a tidewater glacier in northwestern Greenland (Source: Shin Sugiyama).

Since 2012, the team’s focus has been measurements of the ice in the region, with specific interest in the mechanisms of the Bowdoin glacier’s rapid retreat. Shin Sugiyama, the second author of the paper, wrote to GlacierHub, “We recognized the glacier-ocean interaction as the key process and expanded our activity to the ocean.”

The researchers moved from geophysical measurements to geochemical measurements over time. They started to camp in the nearby village of Qaanaaq beginning in the summer of 2016, surveying the water temperature, salinity, ocean currents and other physical properties.

A researcher collects water samples from the front of Bowdoin Glacier using a fishing rod (Source: Shin Sugiyama).

They collected biogeochemical samples from the top of Bowdoin Glacier, the plume along the glacier front, and nearby fjords. They found that the plume water is more turbid, and its chemical composition is significantly different from waters in other locations due to a higher concentration of nutrients and salts. At the same time, phytoplankton blooms were also detected.

They then found an underwater nutrient and carbon transfer route that may explain these observations. Sugiyama describes the transfer as a “nutrient pump.”

At the bottom of the sea, due to the gravity and ocean currents, there are water flows from the fjord moving toward the glacier front. These flows carry a lot of descended nutrients and dissolved carbon. There is also subglacial freshwater discharge that is turbid because of the subglacial weathering. The two flows meet at the deep sea and create massive fluxes of sediments along the glacier fronts.

When the sediment-laden upwell water reaches the sea surface, it forms an opaque layer below the relatively fresher sea surface water. During the upwelling process, the mixture of subglacial discharge water and flows from the fjord pumps nutrients and carbon from the deep water to the upper layers.

Schematics of the nutrient and carbon rich subsurface plume water formation at the front of Bowdoin Glacier (Source: Kanna et al.).

Later, phytoplankton blooms were observed in between the sea surface and the near surface plume water. Phytoplankton are plant-like marine microorganisms at the base of the ocean’s food pyramid. These tiny organisms absorb nutrients and carbon to fuel their growth. Some of the nutrients and carbon fall to the bottom with the phytoplankton when they wither. Other portions of the nutrients and carbon further pass into the food web through organisms that graze on the phytoplankton.

The growth burst of the phytoplankton went unnoticed until recent years. Through their analysis of samples from supraglacial meltwater, proglacial stream discharge, fjord surface water, and plume surface water, the authors identify a distinct vertical distribution of nutrients and carbon along the centerline of the fjord. The data prove that the upwelling associated with the subglacial discharge has been pumping the nutrients and carbon from the deep water toward the surface, catalyzing the formation of phytoplankton blooms.

As the planet warms, glacier melting is increasing in Greenland. For its implication on their findings, Sugiyama said, ”Our study implies that nutrient supply to fjord surface water is enhanced by an increase in meltwater discharge under the warming climate. This results in higher primary production [of microorganisms]. On the other hand, turbid plume water also disturbs the production by limiting light availability in water.” He noted the team will continue their research to understand how these positive and negative impacts counterbalance.

The researcher conduct measurements near the Bowdoin Glacier front with a boat operated by a local hunter (Source: Shin Sugiyama).

The study not only showed a critical role of freshwater discharge in the primary productivity of microorganisms in front of the glaciers, but it also indicated that changes in glacier melt might impact the fjord ecosystems.

“Tidewater glacier front is a biological ‘hot spot.’ We see many birds and sea mammals near the front of Bowdoin Glacier. Change in the ecosystem is not clear at this moment, but we suspect such a highly productive ecosystem is sensitive to the warming Arctic climate,” Sugiyama said.

The ocean also acts as an immense carbon sink, which scientists need to explore. This finding may provide ideas for how carbon transfers within the marine ecosystem.

Sugiyama added, “A possible influence on the carbon cycle is more carbon storage in the ocean when primary production is enhanced by increasing amount of upwelling meltwater. Nevertheless, the plume process is not directly related to the intake of carbon from the atmosphere.”

Bowdoin Glacier is smaller than other rapidly retreating glaciers in Greenland, such as the Jakobshavn and Helheim glaciers. The team hopes to find out if the processes observed in Bowdoin Fjord resemble the situations in the fjords of larger glaciers.

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Roundup: Ice Streams, Carbon Sequestration and Glacier Recession

Instability of Northeast Greenland Ice Stream

From Nature: “The sensitivity of the Northeast Greenland Ice Stream (NEGIS) to prolonged warm periods is largely unknown and geological records documenting such long-term changes are needed to place current observations in perspective. Using cosmogenic surface exposure and radiocarbon ages, the magnitude of NEGIS margin fluctuations over the last 45  kyr (thousand years) was determined. The NEGIS experienced slow early Holocene ice-margin retreat of 30–40  meters per year, likely as a result of the buttressing effect of sea-ice or shelf-ice. This retreat was smaller than present for approximately half of the last ~45 kyr and is susceptible to subtle changes in climate, which has implications for future stability of this ice stream.”

Discover more about ice stream and melting in Greenland here.

Aerial Image of Greenland Ice Sheet showing ice streams (Source: NOAA).

 

Sea Ice, Blue Carbon and Antarctic Climate Feedbacks

From The Royal Society: “Sea ice, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-ice losses around West Antarctica’s continental shelf generate longer phytoplankton blooms (less sea ice increases phytoplankton blooms, benthic growth, seabed carbon and sequestration) but also make it a hotspot for coastal iceberg disturbance. Significant benthic communities establish where ice shelves have disintegrated (giant icebergs calving), and rapidly grow to accumulate blue carbon storage. When 5000 km2 giant icebergs calve, we estimate that they generate approximately 106 tonnes of immobilized zoobenthic carbon per year (t C yr−1).”

Read more about the physical, chemical and biological processes of carbon sequestration here.

Fauna growth in Antartica on places exposed due to melting
Fauna growth in Antarctica on places exposed due to melting (Source: Biomes of the World).

 

Analysis of Mt. Kenya’s Glacial Recession

From the American Journal of Environmental Science and Engineering: “In a bid to discover what has been causing the retreat of glaciers of Mount Kenya, Optical Landsat data for 1984 to 2017 and climatic data of the same years were used. Glaciers and forest coverage were extracted from Landsat images and its thermal band was used to extract temperature data. Correlation with the respective year’s climatic data and forest cover area were done to justify the assumption that the shrinkage in the glaciers coverage has been caused by changes in climate and/or deforestation… Mt Kenya glaciers are likely to have still completely disappeared by the year 2100.”

Explore more about the modelling of Mount Kenya’s glaciers here.

Mount Kenya's Lewis Glacier
Photo of Mount Kenya’s largest glacier – the Lewis Glacier (Source: Earth Day Network/ Pinterest).
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When Rivers Meet the Sea: Carbon Cycling in the Gulf of Alaska

The Gulf of Alaska has numerous glacial inputs (Source: Jennifer Questel).

When rivers meet the sea, the sediment they carry becomes mixed into the ocean, where it makes quite a splash, biogeochemically speaking. In the subarctic North Pacific Ocean, for example, iron-rich sediment delivered from the continental margin spurs a wintertime phytoplankton bloom over 900 kilometers offshore. The presence of these terrigenous particles is felt up the food chain— the higher levels of iron in the water support larger diatom populations, which means more snacking for copepods, a type of zooplankton.

In the Gulf of Alaska, glacial meltwater is an important source of terrestrial particles. A recent study by Jessica Turner, Jessica Pretty, and Andrew McDonnell optically measured particles in the northern Gulf of Alaska, an area with extensive glacial inputs. This technique allowed the researchers to collect massive amounts of data with minimal lab work, maximizing the area they could survey, Jessica Pretty told GlacierHub. Their instrument measured a range of particle sizes, from some too small to be seen by the naked eye to others as large as paper clips.

Researcher Jessica Turner works with the optical profiling instrument (Source: Jennifer Questel).

Pretty and her coauthors found that in the Gulf of Alaska, particle concentrations are denser in two main places: where glaciers and rivers flow into the Gulf, and offshore, near the continental shelf break, where they are buoyed by waves, currents and tidal action. These small particles wield great influence, increasing biological productivity at the shelf break.

“The Gulf of Alaska is an interesting region,” said Pretty. “It has major freshwater input seasonally from melting glaciers and river runoff that eventually joins with Pacific waters and makes its way toward the Arctic.” The recent findings illuminate particle distribution in the northern Gulf of Alaska, yielding clues about how climate change may affect carbon cycling in the Gulf and parallel ocean systems.

Beyond local significance to the Gulf of Alaska ecosystem, the influence of these river-borne terrestrial particles scales up— globally, such sediment inputs impacts the carbon cycle, which regulates climate. The bits of rock Pretty tracked in the Gulf of Alaska are essentially tiny bundles of carbon, and when these bundles sink in the ocean, they drive what scientists have termed the “biological pump,” the process by which the ocean cycles organic and inorganic carbon, and sequesters carbon dioxide in the deep ocean.

Jessica Pretty observes an instrument deployment during a research cruise (Source: Jennifer Questel).

Because carbon dioxide is constantly exchanged between the upper layers of the ocean and lower levels of the atmosphere, concentrations become equal in the shallow ocean and low atmosphere over time. However, sinking particles remove carbon from this exchange. “The biological pump allows the ocean to store more carbon than it would be able to just from equilibration,” explained Pretty.

The ocean absorbs a quarter of the carbon dioxide released into the atmosphere each year, and so as carbon is pumped into the atmosphere, levels in the ocean increase in tandem. This leads to ocean acidification, which threatens many marine species. However, terrestrial carbon sequestration practices, like soil conservation and wildfire suppression, may be an important element of climate change mitigation.

Particle concentrations are high near glacial inputs, such as from the Fourpeaked Glacier (Source: Jennifer Questel).

As global climate warms and glaciers melt, higher glacial inputs will carry more sediment to the Gulf of Alaska and analogous ecosystems around the world. These minute particles will ramp up the global biological pump, increase carbon sequestration, and lead to a myriad of impacts yet unknown. In addition, seasonal changes, like an earlier springtime, may also spur earlier phytoplankton blooms, changing the dynamics of life in the sea. Through the movement of minuscule specks of rock, the Gulf of Alaska, and ultimately the whole ocean, will change.

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Roundup: Carbon Sinks, Serpentine Syndrome and Migration Dynamics

Roundup: Carbon, Serpentine, and Migration

 

Dwindling Glaciers Lead to Potential Carbon Sinks

From PLOS ONE: “Current glacier retreat makes vast mountain ranges available for vegetation establishment and growth. As a result, carbon (C) is accumulated in the soil, in a negative feedback to climate change. Little is known about the effective C budget of these new ecosystems and how the presence of different vegetation communities influences CO2 fluxes. On the Matsch glacier forefield (Alps, Italy) we measured over two growing seasons the Net Ecosystem Exchange (NEE) of a typical grassland, dominated by the C3 Festuca halleri All., and a community dominated by the CAM rosettes Sempervivum montanum L… The two communities showed contrasting GEE but similar Reco patterns, and as a result they were significantly different in NEE during the period measured. The grassland acted as a C sink, with a total cumulated value of -46.4±35.5 g C m-2 NEE, while the plots dominated by the CAM rosettes acted as a source, with 31.9±22.4 g C m-2. In spite of the different NEE, soil analysis did not reveal significant differences in carbon accumulation of the two plant communities, suggesting that processes often neglected, like lateral flows and winter respiration, can have a similar relevance as NEE in the determination of the Net Ecosystem Carbon Balance.”

Learn more about the colonization of a deglaciated moraine here.

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Glacier National Park (Source: Ada Be/Flickr).

 

Vegetation and the Serpentine Syndrome

From Plant and Soil: “Initial stages of pedogenesis (soil formation) are particularly slow on serpentinite (a dark, typically greenish metamorphic rock that weathers to form soil). This implies a slow accumulation of available nutrients and leaching of phytotoxic (poisonous to plants) elements. Thus, a particularly slow plant primary succession should be observed on serpentinitic proglacial areas. The observation of soil-vegetation relationships in such environments should give important information on the development of the serpentine syndrome (a phrase to explain plant survival on serpentine)… Plant-soil relationships have been statistically analysed, comparing morainic environments on pure serpentinite and serpentinite with small sialic inclusions in the North-western Italian Alps….Pure serpentinite supported strikingly different plant communities in comparison with the sites where the serpentinitic till was enriched by small quantities of sialic rocks.”

Find out more about the serpentine syndrome here.

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Franz Josef Glacier, New Zealand (Source: André Pipa/Flickr).

 

Climate Changes Landscape of South American Communities

From Global Migration Issues: “Mountain regions are among the most vulnerable areas with regard to global environmental changes. In the Bolivian Andes, for example, environmental risks, such as those related to climate change, are numerous and often closely intertwined with social risks. Rural households are therefore characterized by high mobility, which is a traditional strategy of risk management. Nowadays, most rural households are involved in multi-residency or circular migratory movements at a regional, national, and international scale. Taking the case of two rural areas close to the city of La Paz, we analyzed migration patterns and drivers behind migrant household decisions in the Bolivian Andes… Our results underline that migration is a traditional peasant household strategy to increase income and manage livelihood risks under rising economic pressures, scarcity of land, insufficient local off-farm work opportunities, and low agricultural productivity… Our results suggest that environmental factors do not drive migration independently, but are rather combined with socio-economic factors.”

Read more about migration dynamics here.

View of the Bolivian Andes and the city of La Paz (Source: Cliff Hllis/Flickr).
View of the Bolivian Andes and the city of La Paz (Source: Cliff Hellis/Flickr).
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Krill Contribute to Ocean Carbon Storage in Patagonia

Waters in the sub-Antarctic region of Chilean Patagonia are fed by glaciers in one of the largest freshwater systems on Earth, the North and South Patagonian Icefields. A recent study published in Marine Ecology Progress Series found that Euphasia vallentini, the most abundant species of krill in Chilean Patagonian waters, play a key role in food webs. The study also discovered that this species of krill helps to sequester carbon in the oceansthey consume plankton, which take in carbon during photosynthesis, and discharge some of the carbon into deeper ocean waters through the production of fast-sinking fecal pellets. This is increasingly important as atmospheric carbon concentrations rise, as it contributes to the role of the oceans as a carbon sink.

The North Patagonian Icefield (Source: McKay Savage / Creative Commons).
The North Patagonian Icefield (Source: McKay Savage/Creative Commons).

Krill are small, shrimp-like crustaceans that are found in all of the world’s oceans. In an interview with GlacierHub, Humberto E. González, the lead author of the study from the Austral University of Chile, explained that krill form “a trophic [related to food and nutrition] bridge between the microbial community [bacteria, nanoplankton, microzooplankton] and the upper trophic layers [seals, whales, penguins, etc.]. Thus, they play a pivotal role in trophic flows.”

The study by González et al. focused on the region between the Magellan Strait and Cape Horn because of the unique biological, chemical and physical conditions created by the hydrological input from three different sources: nutrient-rich Pacific and Atlantic Sub-Antarctic Waters (waters that lie between 46°– 60° south of the Equator), and cold and nutrient depleted freshwater from Patagonian rivers and glaciers.

Waters that are more saline or that are colder have higher densities. However, as explained in the study, the effect of salinity exceeds the effect of temperature on density within this region, giving rise to strong saline stratification in the mixture of oceanic and freshwater terrestrial environments. This reduces the movement of important species between the benthic (the lowest level) and pelagic (open water) ecosystems in southern Patagonia.

The stratification also reduces upward and downward mixing of ocean water. This reduces carbon fluxes in the region, as the transport of carbon dioxide to deeper parts of the ocean through diffusion across layers occurs more slowly than the circulation of ocean waters with different carbon dioxide concentrations.

A map of the Strait of Magellan and the region where the study took place (Source: / Creative Commons).
A map of the region where the study took place. The icefields are located further north (Source: Creative Commons).

The team of scientists embarked on a research cruise in the region in October and November 2010, collecting chemical and biological samples at about forty different stations. Using a variety of techniques, they studied features such as the types and distribution of organic carbon in the waters, and the abundance and diet of E. vallentini. All this was done to better understand the role of E. vallentini in the region’s food web structures and in the transport of carbon to deeper layers of the ocean despite strong stratification.

In conversation with GlacierHub, González stated that “the species of the genus Euphausia (a functional group of zooplankton) play a paramount role in many disparate environments from high to low latitude ecosystems. Euphausia superba in the Southern Ocean and Euphausia mucronata in the Humboldt Current System are some examples.In this study, González et al. found that E. vallentini play a similarly important role in Southern Chilean Patagonia, consuming a range of plankton from nano- to phytoplankton and forming the dominant prey of several fish, penguin and whale species.

Krill, such as E. vallentini, form an important link in food chains between phytoplankton and larger animals (Source: Uwe Kils / Creative Commons)
Krill, such as E. vallentini, form an important link in food chains between phytoplankton and larger animals (Source: Uwe Kils/Creative Commons)

The study also found that E. vallentini play an important role in passive fluxes of carbon through the sequestration of carbon in fast-sinking fecal pellets, or poop. The plankton ingested by E. vallentini takes in carbon dioxide during photosynthesis, and about a quarter of the plankton ingested by E. vallentini is then passed out in fecal matter. These fecal pellets form the dominant component of particulate organic carbon (organic carbon particles that are larger than a certain size) fluxes in the region’s waters, helping to sequester carbon as they sink to the ocean floor.

This process is accelerated by E. vallentini’s vertical diurnal migrations, which occur despite the strong saline stratification of waters in southern Patagonia. Their vertical movements, from deeper parts of the ocean during the day to the surface of the ocean in search of food at night, occurs more quickly than the rate at which their fecal pellets sink, speeding up the transport of carbon to deeper ocean layers. As González explained, “the Patagonian krill [and] the squat lobster (Munida gregaria) are the main species responsible for the carbon export towards deeper layer of the fjords and channels (in southern Patagonia).”

Although scientists from the Commission for the Conservation of Antarctic Marine Living Resources estimate that the total weight of Antarctic krill exceeds that of humans on Earth, they may not be immune from the effects of anthropogenic climate change. Indeed, González stated that a greater input of freshwater to the ocean could reduce nutrient levels in upper layers of the ocean. This will reduce the productivity of fjords and channels, reducing the availability of food for krill, and creating serious implications for the marine ecosystems that they are part of. This research serves as a reminder that biological organisms play an important role in the effects of marine ecosystems on the world’s climate, as they do in terrestrial ecosystems. 

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