Tracking freshwater browning and coastal water darkening from boreal forests to the Arctic Ocean

• Main Authors: Opdal, Anders Frugård, Andersen, Tom, Hessen, Dag Olav, Lindemann, Christian, Aksnes, Dag L.
• Format: Other/Unknown Material
• Language: unknown
• Published: 2023
• Subjects: CDOM; coastal darkening; greening; browning; Forest cover; light attenuation; freshwater; Baltic Sea; Skagerrak; Norwegian Coastal Water; Arctic; Arctic Ocean; Barents Sea; Norway; Kattegat; Browning
• Online Access: https://zenodo.org/record/7701266; https://doi.org/10.5281/zenodo.7701266

The forest cover of Northern Europe has been steadily expanding during the last 120 years. More terrestrial vegetation and carbon fixation leads to more export to surface waters. This may cause freshwater browning, as more degraded plant-litter ends up as chromophoric (coloured) dissolved organic matter. Although most freshwater ultimately drains to coastal waters, the link between freshwater browning and coastal water darkening is poorly understood. Here, we explore this relationship through a combination of centennial records of forest and coastal water clarity, contemporary optical measurements in lakes and coastal waters, as well as an ocean drift model. We suggest a link between forest cover in Northern Europe and coastal water clarity in the Baltic, Kattegat and Skagerrak Sea and show how brown coloured freshwater from Northern European catchments can dictate coastal water clarity across thousands of kilometres, from the Baltic lakes to the Barents Sea. Funding provided by: Norges ForskningsrådCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100005416Award Number: 287490 The forest cover data was retrieved from the Historic Land Dynamics Assessment (HILDA) database provided by the Department of Geoinformation Science and Remote Sensing, Wageningen University, Netherlands (http://www.geo-informatie.nl/fuchs003/#), and the FAO Global Forest Resources Assessment database (https://fra-data.fao.org/WO/fra2020/home/). For Norway, which is not part of the EU, forest cover was drawn from Norway's national forest inventory available at https://landsskog.nibio, and described in https://doi.org/10.1186/s40663-020-00261-0 Data on Secchi disk measurements and salinity were available from 1) The International Council for the Exploration of the Sea, https://data.ices.dk; 2) Swedish Meteorological and Hydrological Institute, https://www.smhi.se/data; 3) Norwegian Environment Agency, https://vannmiljo.miljodirektoratet.no; 4) Secchi disk archive www.ices.dk/data/ (Aarup 2002); 5) World Ocean Database, ...