PhD defence on the quantification and fate of terrestrial organic matter in the Arctic Ocean

With accelerating global warming, there will be increasing river discharge and erosion of riverbanks and coastlines around the Arctic. This will result in more terrestrial carbon being transported from land to sea in the future. This is a cause of concern as it represents a mobilization of carbon from being stored on land as organic matter to being potentially mineralized to CO2 at sea and eventually contributing to rising CO₂ in the atmosphere.

In his PhD project, Anders Dalhoff Bruhn, DTU Aqua, has studied the fate of terrestrial dissolved organic carbon in the Arctic Ocean. The studies show that the processing and remineralization to CO₂ of carbon from coastal erosion is greatly dependent on which permafrost soil type will erode into coastal waters. 

However, he found that most of the terrestrial carbon is likely refractory to rapid mineralization and may survive passage through the coastal zone and be exported to the open ocean. Here, the ocean currents will carry the carbon into the Atlantic Ocean, where it may be sequestered into the deep ocean and kept away from interaction with the atmosphere for centuries.

Besides, Anders Dalhoff Bruhn has developed an analytical method to quantify and characterize terrestrial dissolved organic carbon. The method measures the seawater's content of lignin, which only exists in terrestrial plants. When found in the ocean, lignin reflects the distribution of terrestrial dissolved organic matter. With this new method, he has analyzed seawater from the Fram Strait and documented import and export of water masses and where they come from.

Furthermore, Anders Dalhoff Bruhn has developed a model for determining the lignin content in seawater based on measurements of fluorescence. Fluorescence measurements are cheaper and easier to perform, and the perspective is that fluorescence sensors on drones or buoys can be used to monitor the effect of climate change on the ocean's carbon budget.

About the PhD defence

Anders Dalhoff Bruhn will defend his PhD thesis "Terrestrial and coloured dissolved organic matter in Arctic waters: Towards in-situ sensor based monitoring of Arctic-Atlantic organic carbon exchange at major Arctic gateways” on Tuesday 18 April 2023, 13:00 on Zoom (find link below) and at DTU, Anker Engelunds Vej, building 101, room S09, 2800 Kgs. Lyngby. 

Supervisors

• Principal supervisor: Professor Colin Stedmon, DTU Aqua
• Co-supervisor: Professor Christopher Osburn, NC State University, USA

Examiners

• Senior Researcher, Dr. Techn. Sigrun Jonasdottir, DTU Aqua (chair)
• Professor Peter Hernes, University of California, USA
• Associate Professor Nikoline Juul Nielsen, University of Copenhagen, Denmark

Chairperson at defence

• Head of Section Karen Edelvang, DTU Aqua

Learn more

A copy of the thesis is available by e-mail on request. Please contact Karin Stubgaard, stub@aqua.dtu.dk