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Organic matter in the Arctic Ocean

In the late 19th century, Norwegian explorers learned about the transpolar drift in the Arctic Ocean during an attempt to cross the northernmost point on earth.  

Today, scientists are still venturing to the top of the world, but each with different goals in mind.  

“The transpolar drift moves water from the Siberian shelf out through the Fram Strait and out through the east side of Greenland,” said marine chemist Heather Reader. 

Reader, an assistant professor in the department of chemistry at Memorial University of Newfoundland, visited Dalhousie University on Nov. 2 as part of Science Atlantic’s Women in Science speaker tour. Reader’s interest lies in the dissolved organic matter (DOM) in the Arctic Ocean, and she worked with many other scientists on board the Polarstern as part of the 2015 TRANSARC II expedition exploring the subject. 

“I’m interested in understanding what kind of carbon [there] is and how it’s participating in the marine carbon cycle,” continued Reader.  

She explained the ocean’s important role in the carbon cycle: it’s a major carbon source and sink, meaning it both produces and stores large amounts of carbon.  

Understanding the ocean’s role in the carbon cycle is becoming more important as the Arctic Ocean undergoes extreme change as the climate crisis intensifies, she said. 

The DOM in the Arctic Ocean is a particularly large pool of carbon, amassing to almost as much carbon as there is in CO2 in the atmosphere.  

The way this carbon ends up in the Arctic Ocean is a result of six large watersheds flowing into the arctic ocean, carrying large amounts of organic matter. Reader made the comparison between the ocean picking up organic matter, and steeping a cup of tea.  

The organic matter in this case is similar to the tea bag. The leaves, soil and other organic matter in the water eventually leech organic compounds into the water, which changes the colour of the water, said Reader. 

Because of this change in colour, Reader looked into whether the carbon could be characterized using the absorbance of light and the fluorescence of the DOM across the UV invisible spectrum. Using these optic techniques in tandem with the chemical characterization, Reader hoped to create a better understanding of the chemistry that’s happening in the oceans.  

By figuring out the characteristics of this carbon, they will hopefully be able to determine how the river water moves via the transpolar drift.  

Iron was another focus of the research done onboard the Polarstern. Like carbon, iron is an extremely important component of the ocean. Iron is a micronutrient that phytoplankton rely on to fix nitrogen and photosynthesize. Because iron precipitates into its mineral form in regular ocean conditions, phytoplankton have different strategies to access the iron they need. One of these strategies, Reader explained, is to “put organic molecules out into the water that will capture the iron and keep it in solution.”   

There’s evidence that organic terrestrial materials have some capability of doing this as well, “so it’s coming from an outside source rather than phytoplankton in the system,” said Reader.  

Working alongside scientists from the Netherlands, Reader characterized the carbon using optics alongside their chemical characterization methods. In this way, they were able to figure out how much of the terrestrial materials were capturing the iron.  

The environment is changing. This much has become clear in the last few years.  

“The Arctic Ocean in general is experiencing a lot of change,” said Reader. “The increases in carbon are projected to be quite great over the next century, so there will be more terrestrial matter in the arctic ocean. [This] has the potential to change how the carbon cycle is balanced.”  


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