The Role of Aged Organic Carbon in North Atlantic Fjord Sediments

Fjords are recognised as important hotspots for the burial and storage of organic carbon (OC) within their sediment, which potentially provides a long-term climate regulation service. Annually, it is estimated that 18 Mt of OC is buried within fjord sediments with between 55 – 62% of the OC originating from the terrestrial environment. The transfer of OC from the terrestrial environment to the fjord sediments is likely a significant pathway for aged OC to reach the coastal ocean. By estimating the quantity and mapping the spatial distribution of aged OC within the fjord sediments, we can develop a better understanding of the processes that govern the transfer of terrestrial OC from the catchment to the sediment of fjords, further constraining their role in long-term climate regulation.

Here we bring together radiocarbon analysis with isotopic and biomarker measurements to investigate the age of the surficial sediments within 46 fjords across the North Atlantic. The fjords in this study range from Scottish systems with catchments dominant with OC rich peat to the glaciated systems of Svalbard and Greenland.  The results from this analysis highlight that a multiple natural and anthropogenic processes govern the quantity and distribution of aged OC across North Atlantic fjords ranging between glacial input of fossil OC to the erosion of aged terrestrial material facilitated by deforestation.  This study highlights the fundamental need to understand the processes that govern the transfer of OC across the land-ocean interface to allow the role these marine sedimentary systems play in long-term climate regulation to be constrained.