For millions of years, mountains, valleys, rocks and riverbeds have been buried deep under the Greenland Ice Sheet. When glaciers melt, nutrients, minerals and other remains from the prehistoric landscapes are washed into fjords and from there into the seas via an underwater flow of meltwater.
It is not yet known how the introduction of increasing amounts of sediments from the so-called marine-terminating glaciers affects the marine environment as the climate gets warmer. But new research from the Geological Survey of Denmark and Greenland (GEUS) may be important for the understanding of it.
The GEUS researchers have created a formula for how large a sediment footprint a single glacier leaves on the fjord it melts into. The formula, which has just been published in the journal Nature Communications, is based on sediment cores that have been collected over several years.
“Originally, we collected sediment cores to reconstruct changes over the past millennia in the glaciers around Greenland that flow into the seas. Gradually, we got so much data that we could make a solid comparison between the different glaciers and their sediment production over the past decades,” says Camilla Snowman Andresen, Senior Researcher at GEUS, who has done the study in collaboration with several colleagues, including Nanna B. Karlsson from GEUS.
Sediment and melting follow each other
The researchers’ analyses show that there is a direct correlation between the amount of meltwater from a glacier and the amount of sediment it leaves behind in the fjord it flows into. That means that they can calculate how much sediment is discharged and how it is distributed in a fjord, based on how much meltwater comes from a nearby glacier.
“The connection is not surprising – it makes sense that sediment supply and melting from glaciers follow each other. What is interesting is that we have collected enough observations to start putting numbers on it,” says Camilla Snowman Andresen and continues:
“The sediment is not evenly distributed. There is far more sediment deposited near the glacier than 80 kilometres from the glacier. We also take this distribution downstream into account in our formula.”
The numbers are the basis for more knowledge
The numbers are important for several reasons:
Knowledge of how much sediment from glaciers ends up in the oceans is necessary if the marine life around Greenland and in the North Atlantic benefits from the sediment – for instance if the sediment contains nutrients in a form that the organisms in the oceans can absorb.
Another possibility is that marine life is harmed – for instance if sediments flowing out from the Greenlandic fjords block sunlight and thus prevent photosynthesis below sea level.
“Knowledge of sediment also plays a role in our understanding of the dynamics of the Greenland Ice Sheet. Some scientists believe that the sediment under the ice, together with water, causes the ice to flow faster towards the coasts. Other researchers suggest that the sediment that is deposited at the foot of the glacier edge can form high sediment hills, which actually protect the ice from warm seawater and thus further melting,” explains Senior Researcher Camilla Snowman Andresen.
The future – and more research – will show whether increasing amounts of sediment in the oceans is good, bad or both. But according to Camilla Snowman Andresen, the new observations are an important piece in the efforts to be one step ahead and adapt to the changes.