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.
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.
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.
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 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.