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The role of Greenland's marine forests in supporting carbon sequestration in marine sediments

New publication by Sarah Bachmann Ørberg


In the Arctic, macroalgae (seaweed) forests and seagrass meadows are expanding due to warming and reduced sea ice cover and, as a result Arctic blue carbon (C) sinks may increase. This thesis used a bottom-up approach to evaluate Greenland’s marine forests in supporting C sequestration and the potential for a growing Arctic blue C sink, presenting a case study for the Arctic. First, barcoding tools for tracing C from marine forests in marine sediments using environmental DNA (eDNA) were developed and tested. Then, a large-scale set of marine surficial sediment samples from off the coast of Greenland and Svalbard were analyzed using eDNA and stable isotopes, to quantify and evaluate the presence-absence of C derived from marine forests along spatial gradients. Finally, sediment cores from off the west coast of Greenland were used as historical archives to document C sequestration from macroalgae and evaluate potential changes related to changes in climate over the past ca. 2600 years. Conclusively, macroalgae are prevalent C contributors to marine sediments along the coast of Greenland and Svalbard, while the contribution from seagrasses is confined mostly to the meadows. Further, macroalgae contribute to C sequestration in Greenland’s marine sediments thousands of years back in time, but we found no definitive evidence for a growing Arctic blue C sink. Lastly, eDNA-based methods add greatly to the C tracing toolbox for marine forests, but quantification of C sources needs further development and testing.