A profile of samples taken across the Fram Strait from the east coast of Greenland to the west coast of Svalbard passes through the East Greenland Current that transports organic matter from Russia down, along the east coast of Greenland. The current is cold (temperature shown in the top graph), fresh (salinity shown in the middle graph), and full of organic matter from Siberia (shown in the bottom graph). (Illustration: Colin Stedmon).
Back on board, Stedmon (background) analyses the water on a spectrophotometer to characterise the organic matter and trace its origins. (Photo: Colin Stedmon)
A water sampling rig loaded with cannisters is lowered into the sea. On-board sensors measure temperature and pressure so that Stedmon and his team know when they have reached the desired depth for sampling. They then close the canisters and raise the rig. (Photo: Thomas Juul Pedersen)
The Technical University of Denmark’s research vessel R/V Dana heads out to the North Atlantic for a field campaign (Photo: Colin Stedmon)
Stedmon and his colleagues sampled ocean water throughout the North Atlantic, shown here by black and red dots. The different colour denotes separate field campaigns. Red dots depict samples taken across the Fram Strait that intercept the East Greenland Current. (Illustration: Colin Stedmon)
Dissolved organic matter from Siberian rivers (light blue arrows) enters the Arctic Ocean and is carried by ocean currents (dark blue and red arrows) into the Fram Strait (dashed line). Here, the East Greenland Current carries it into the Atlantic Ocean. (Illustration: Paul Dodd)
Siberian dissolved organic matter in the Lena River (brown water). The Lena drains the vast plains of Siberia and carries with it lots of organic matter--the remains of plants and soil. (Photo: Rafael Gonçalves-Araujo)
The Lena River is one of the longest rivers in the world at 2,800 miles long. It is the easternmost of the three great Siberian rivers that flow into the Arctic Ocean. (Photo: NASA)

Greenlandic fjords get their organic matter from Russia

GREENLAND: A simple chemical technique sheds new light on ocean circulation in the Arctic and could help improve computer models of ocean circulation.


Take a cup of water from a fjord on the east coast of Greenland and it will contain the traces of soil from Russia. It may sound strange, but this is exactly what scientists discovered when they sampled ocean water along the east coast of Greenland.

They were testing a new method to trace the sources of freshwater--water from rivers, glacial melt, or from the atmosphere in the form of rain or snow--in the Atlantic ocean.

“It’s a weird thought that you can take a sample of water on the Greenland shelf and trace it all the way back to Siberia. That’s a long distance!” says lead-author Colin Stedmon, from the Technical University of Denmark, DTU.

Stedmon and his colleagues from the Norwegian Polar Institute discovered a tell tale chemical signature of forest soil that is pumped into the Arctic Ocean via massive rivers along the Siberian coast as dissolved organic matter.

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“We discovered that we can use organic matter from Siberia as a tracer in the Arctic Ocean,” says Stedmon. “And when we measure water the Fram Strait off the coast of East Greenland, the terrestrial signal that we measure is essentially from Siberia and not from Greenland.”

The results are published in the Journal of Geophysical Research: Oceans.

Simple chemical technique can improve computer models

Each year, Siberian rivers pump vast quantities of fresh water into the Arctic Ocean. And together with other sources of fresh water around the Arctic, they could disrupt vital ocean circulation that drive weather systems throughout Europe and North America. (See side story)

While computer models can simulate these ocean circulation systems, they need observations to validate their results and to identify where the fresh water has come from--glaciers, sea ice, or rivers. And this is important if you want to understand how these various contributions of fresh water into the north Atlantic might change in the future.

This is where Stedmon’s technique comes in.

“It’s basically forensics--we’re trying to trace the signature of different water masses, and their chemical composition is a way of doing that. It’s like a finger print,” says Stedmon.

Traditional salinity measurements are often used to trace freshwater in the ocean. But this new technique allows Stedmon and his colleagues to go a step further and work out the relative proportions of Siberian river water, glacial melt, or sea ice melt of this freshwater in the Arctic Ocean.

Read More: Melting Greenland ice has not slowed down ocean circulation

Siberian soil in Greenlandic fjords

Stedmon traced the dissolved organic matter in the waters around Greenland by measuring the water colour.

“Organic matter is humic material. You can look at it like tea. When you make a cup of tea, it changes from clear water to brown because you dissolved some leaves in it. That’s the same process that you see in a forest lake,” says Stedmon.

This dissolved organic matter is carried out to sea by the large rivers along the Siberian coast, where it is diluted and transported around the Arctic to Greenland via the East Greenland Current (see the gallery above). Stedmon measured the amount of organic material in the water by seeing how much light was absorbed by the water and in which part of the spectrum using a spectrophotometer.

“Basically a little bit of the soil and the degradation of living plants and animals produce this organic matter. And we use this colour, like the colour of your tea, as a tracer,” he says.

Read more: Fjords catch loads of carbon

Mapping fresh water sources in the Arctic

While Stedmon wasn’t surprised that dissolved soil made it all the way from Russia to Greenland, he was surprised by just how easy it was to detect and measure.

“Now we’ve developed this technique that hadn’t been used before, we need to return each year and repeat our measurements,” says Stedmon, who has already collected more water samples from further north in the Arctic Ocean and will return to the Fram Strait in August this year to continue sampling.

Eventually he plans to gather enough data to map the organic matter content of ocean water over a larger area in the north Atlantic to see not only how much fresh water is entering the ocean, but specifically where it is coming from.

“We’re now working with a cruise from the Davis Strait, between Greenland and Canada, to see if we can trace it all the way round Greenland: Can we see the same patterns, or at least use the same approach? We have no idea!” says Stedmon.

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