Terrestrial dissolved organic matter distribution in the North Sea

Area of Science:

• Environmental Science
• Oceanography
• Biogeochemistry

Background:

• Terrestrial carbon flow to aquatic systems is crucial for the global carbon cycle.
• The efficiency of terrestrial organic carbon transfer through coastal filters to the ocean is unknown.
• Understanding this flux is vital for assessing the role of terrestrial carbon in climate regulation.

Purpose of the Study:

• To investigate the spatial distribution of terrestrial dissolved organic matter (tDOM) in the North Sea.
• To test the hypothesis of quantitative tDOM transfer from the North Sea to the North Atlantic.
• To identify sources and pathways of tDOM within the North Sea.

Main Methods:

• Utilized fluorescent and chromophoric dissolved organic matter (FDOM and CDOM) as proxies for tDOM.
• Employed excitation emission matrix fluorescence and parallel factor analysis (EEM-PARAFAC).
• Analyzed spatial distribution and salinity relationships of FDOM and CDOM.

Main Results:

• Identified a single terrestrial humic-like FDOM class, primarily in coastal areas and linked to riverine inputs.
• Detected two distinct sources of fluorescent humic-like material from major river outflows and the Baltic Sea.
• Found insignificant tDOM flux from the North Sea to the Atlantic, with potential export via unsampled Norwegian waters.

Conclusions:

• The majority of tDOM from Northwest Europe and Scandinavia is buried or remineralized within estuarine and coastal systems.
• Residence time in these systems significantly controls tDOM fate and atmospheric carbon loss.
• Current models may overestimate the oceanic storage of terrestrial carbon due to limited transfer efficiency.