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.

High Altitude Plants Discovered in the Himalayas

Melting glaciers in the Himalayas have exposed land underneath, allowing new forms of life to migrate to deglaciated landscapes. Recently, these glacial changes have led to the discovery of the world’s highest altitude vascular plants, made possible by the early colonization of microbes in the space left by retreating glacier ice, according to a recent report in the journal Microbial Ecology.

A mountain in the Himalaya range (Source: Adarsh Thakuri/Creative Commons).
A mountain in the Himalaya range (Source: Adarsh Thakuri/Creative Commons).

It was during a 2012 expedition that researchers first recorded six plants at an unprecedented altitude in India, 6,150 meters above sea level. The plants were growing in a small patch of undeveloped soil. The glaciers in the region had rapidly receded since the 1990s due to a spike in temperatures in the region. As a sparsely populated, cold desert with limited rainfall, the northwestern Himalayas present arid and highly stressful conditions to plants. Still, the six plants seemed to be in stable condition, according to the researcher’s report.

Based on the monitored temperature and snow cover, there were only a few weeks per year that these plants could use for growth. The researchers emphasize that these are vascular plants, with tissues that contain vessels that conduct water and dissolved nutrients.

But how does plant life first reach these deglaciated landscapes once the glaciers have receded? By definition, subnival zones are places where plants and microorganisms can grow and refers to the altitudinal zone between the nival zone of permanent snow (nival) and the alpine zone, the highest area of extensive vegetation, characterized by low shrubs, grasses, and cushion plants. Microorganisms such as bacteria and some types of fungi colonize subnival zones within a few years of glacial recession, making way for plants and other life forms.

A glacier region in the Himalayas (Source: Pradeep Kumbhashi).
A glacier region in the Himalayas (Source: Pradeep Kumbhashi/Creative Commons).

Bacteria and fungi typically arrive first to the deglaciated landscape because they disperse more easily and are more stress-tolerant. They disperse spores that travel in the wind to reach remote places high in mountainous regions. Because the glaciers have receded from the section of the Himalayas visited by the researchers, an opportunity arrives for microorganisms to live in the soil that was once buried underneath the ice and snow.

There are several biological processes by which these microorganisms help develop the soil and allow plants to grow. For one, many bacteria can carry out photosynthesis, using sunlight to synthesize food from carbon dioxide and water. Some bacteria and fungi can also carry out nitrogen fixation, which is the process of converting nitrogen in the atmosphere to ammonia, more readily absorbed by plants. The nitrogen, in turn, can be used by other organisms. These biological processes help cultivate the soil in deglaciated landscapes by depositing nutrients, which ultimately allow plants to grow. Plant seeds and spores, also dispersed by the wind, make their way to high elevation areas. But once there, the plants rely on microorganisms to supply minerals and fix nitrogen.

Rooey Angel, a coauthor of the report on the high altitude plants, talked to GlacierHub about his team’s findings. “Indeed, microbial colonisation of glacial forefield is crucial for starting soil development processes, release of minerals from soil particles, accumulation of organic carbon and nitrogen fixation,” he said. “However, with respect to nitrogen, it is important to remember that there’s a large effect of atmospheric nitrogen deposition on the forefield ecosystem, which makes nitrogen fixation less crucial.”

Once plants arrive up the mountain, they further enrich the soil in deglaciated landscapes with organic matter and nutrients through a process of rhizodeposition (in which roots release organic compounds into the environment) and by weathering the bedrock. The soil surrounding the plant and containing its roots, known as the rhizosphere, is high in microbial activity. The plants use microorganisms to supply minerals and fix nitrogen, making it impossible for plants to precede microorganisms in colonization. Lack of nitrogen is one of the only biological reasons plants cannot arrive first in newly deglaciated soils.

Six plant species found over 6000 meters in the Indian Himalayas (Source: Microbial Ecology).

The specimens located by the researchers included five perennial herbs and one perennial grass, ranging in color and structure. All of the plants were found at high altitudes formerly covered in glaciers, often at elevations from 5,000 to 6,000 meters above sea level. Of the four plants where age could be determined, three were less than 10 years old and one, Ladakiella klimesii, was approximately 15 years old.

The L. klimesii, also known as Alyssum klimesii, is a plant in the mustard family and a close relative of sweet alyssum, a plant commonly grown in gardens for its hardiness and drought tolerance as well as for its profuse white blooms and rich fragrance. The specimen of L. klimesii resembles a tiny gray bush and is 1-3 cm tall and 2-10 cm in diameter. The species is endemic to the Tibetan Plateau and grows in subnival zones. In Ladakh these plants are found in 5,350 to 6,150 meters, with optimum altitudes at 5,800 meters. The researchers emphasize that this new specimen provides evidence of the recent upward migration of plants and rapid changes affecting the western Himalayan slopes.

In addition, the researchers discovered that the roots of the plants harbored several hundred types of microbes; these are termed OTUs or operational taxonomic units, and correspond to species. Other harsh climates like the patches of soil in coastal and interior Antarctic environments have similar OTUs, which demonstrates the remarkable resilience of these microbes.

Thanks to microorganisms cultivating land that had once been covered by glacier ice, researchers have discovered the highest-ever elevation plants, a surprising side effect of climate change. This new record offers testimony both to the profound effects of climate change on ecosystems and to the vigor of the diverse organisms on our planet.