Meltwater from the Arctic is a wild card in future climate

The freshwater bubble bursts

Saltwater is heavier than freshwater, so freshwater in the Arctic tends to gather in bubbles near the ocean’s surface, where it can accumulate over many years. The difference in density eventually sets the water in motion, and since a large part of the freshwater in the Arctic Ocean flows into the Atlantic, it can affect important ocean currents. Danish researchers Peter Ditlevsen and Susanne Ditlevsen predicted in a much-discussed study from 2023 that the ocean current AMOC (The Atlantic Meridional Overturning Circulation) could collapse as early as 2057, which would mean much colder winters in Northern Europe – up to 10 degrees colder.

However, the Ditlevsen study and several similar studies of ocean currents have been criticized for having significant uncertainties, partly because we do not know enough about the freshwater in the Arctic and what will happen to it in the future. While the Greenland ice sheet is well monitored, there is less overview of freshwater inflow from rivers and ice in places like Svalbard, Siberia, and Canada.

“There are theories, for example, that the cold climate in Denmark in the 1940s and 50s was due to a freshwater bubble in the Arctic bursting and the freshwater flowing into the North Atlantic. Is that the kind of situation we are heading into? That’s something we hope to better model in the future,” says Ole Baltazar Andersen.

Golden age of climate satellites

But how do you measure something as fluid as water that mixes with other water? The short answer is satellites. Ice covers much of the Arctic for most of the year, making physical measurements from ships or buoys nearly impossible, but with lasers and radars, satellites can measure everything from salinity to water temperature, as well as height measurements of water and ice that can be used to calculate how much freshwater flows into the ocean.

Satellites have been monitoring the climate in the Arctic for a long time, but it is only now that the technology is mature enough to map changes in freshwater content.

“Frankly, the uncertainties have been too great in previous measurements – and climate models can end up with huge fluctuations in their results when looking into the future,” says Carsten Bjerre Ludwigsen, a postdoc at DTU Space who manages the daily operations of the Arcfresh project.

“But so much has happened with satellite technology in the last 10 years that we can now trust the observations, even though we don’t have ground measurements to verify them. That’s why we are in a golden age of satellite technology,” he says.

The pieces come together

The Arcfresh project is expected to provide us with most of the missing pieces of the freshwater puzzle because although the Arctic Ocean only accounts for 1.4% of the world’s ocean mass, 10% of all freshwater flows into the Arctic Ocean – and this number will only increase in the future as enormous amounts of ice will melt and wash into the oceans.

“If we map the freshwater, we can more accurately predict the consequences of, say, increased melting of ice in Greenland or permafrost in Russia and Canada for the future climate,” says Ole Baltazar Andersen.