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: Plant Succession, Glacier Surges and Organic Pollutants

Phosphorus, Not Nitrogen, Limits Primary Succession

From Science Advances: “Current models of ecosystem development hold that low nitrogen availability limits the earliest stages of primary succession, but these models were developed from studies conducted in areas with temperate or wet climates. We combine field and microcosm studies of both plant and microbial primary producers and show that phosphorus, not nitrogen, is the nutrient most limiting to the earliest stages of primary succession along glacial chronosequences in the Central Andes and central Alaska. We also show that phosphorus addition greatly accelerates the rate of succession for plants and for microbial phototrophs, even at the most extreme deglaciating site at over 5000 meters above sea level in the Andes of arid southern Peru.”

Read more about the factors affecting plant succession in cold-arid regions here.

Plant succession occurring after the retreat of the Exit Glacier, Alaska (Source: National Park Service).

 

Tidewater Glacier Surges Initiated at the Terminus

From Journal of Geophysical Research: “There have been numerous reports that surges of tidewater glaciers in Svalbard were initiated at the terminus and propagated up‐glacier, in contrast with downglacier‐propagating surges of land‐terminating glaciers. We present detailed data on the recent surges of two tidewater glaciers, Aavatsmarkbreen and Wahlenbergbreen, in Svalbard. High‐resolution time series of glacier velocities and evolution of crevasse patterns show that both surges propagated up‐glacier in abrupt steps. Geometric changes near the terminus of these glaciers appear to have led to greater strain heating, water production, and storage at the glacier bed. Water routing via crevasses also likely plays an important role in the evolution of surges.“

Find out more about this proposed mechanism of glacier surges here.

Profile of a glacier during normal conditions (left) and during a surge event (right) (Source: Jean-Louis Etienne).

 

Hexachlorobenzene Accumulation in Svalbard Fjords

From Springer: “In the present study, we investigated the spatial and historical trends of hexachlorobenzene (HCB) contamination in dated sediments of three Svalbard fjords (Kongsfjorden, Hornsund, Adventfjorden) differing in environmental conditions and human impact. HCB concentrations ranging from below limit of quantification (6.86 pg/g d.w.) to 143.99 pg/g d.w. were measured… In case of several sediment cores, the HCB enrichment in surface (recent) sediments was noticed. This can indicate importance of secondary sources of HCB, e.g., the influx of HCB accumulated over decades on the surface of glaciers. Detected levels of HCB were generally low and did not exceed background concentration levels; thus, a negative effect on benthic organisms is not expected.”

Discover more about organic pollutions in Norway here.

The Arctic fox and other living organisms in Svalbard could be affected by hexachlorobenzene contamination (Source: Natalie Tapson/Flickr).
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