Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone

Abstract

Continental shelf sediments are recognized as long-term stores of globally significant quantities of carbon (C) and potentially provide an important, yet largely overlooked climate regulation service via the Earth’s C cycle. Current understanding of the spatial distribution of sedimentary C across continental shelves remains poor, inhibiting the targeted management and potential inclusion of these globally significant C stores into national C budgets. Further understanding of the spatial heterogeneity of continental shelf sediments and associated C provides a foundation to quantify the organic carbon (OC) stock and better understand the role that marine sediments play in regulating the global climate and the potential for CO2 to be released through anthropogenic disturbance of these C stores. Utilizing a spectrum of available marine data, we have created bespoke sediment maps that quantify the surficial (top 10 cm) OC stock and highlight significant spatial heterogeneity in the distribution of sediments and their associated C content across the United Kingdom’s Exclusive Economic Zone (EEZ). The surficial sediments within the UK EEZ are estimated to store 524 ± 68 Mt of organic carbon (OC) and 2,582 ± 168 Mt of inorganic carbon (IC). The spatial mapping of this C highlights well-defined OC accumulation hotspots in fjords, estuaries and coastal muds, while large accumulations of IC are found in the tidally swept areas around Orkney, Shetland and the South West of England. Within the well-defined OC hotspots, muddy sediments store the greatest quantity of OC; the muds offer potentially valuable opportunities for targeted future management and protection of sedimentary C stores within the UK EEZ. In the future, if areas of the seafloor were to be managed to include the protection of these valuable sedimentary C resources, we recommend an initial focus on hotspots of high sedimentary OC density.

The potential for mobile demersal fishing to reduce carbon storage and sequestration in seabed sediments

“…Further, due to their often biological origin, fine grained sediments such as silts and clays typically have higher concentrations of OC compared to habitats dominated by sand and coarse sediment (Burdige 2007, Paradis et al 2021, Smeaton et al 2021). As mobile demersal fishing generally exposes or suspends fine material, this would tend to reduce overall OC storage through resuspension, oxidation and remineralisation (Fig.…”

“…Standing stock of OC in global seabed sediments is relatively well resolved at a number of spatial scales (e.g. Seiter et al 2004, Lee et al 2019, Luisetti et al 2019, Atwood et al 2020, Legge et al 2020, Diesing et al 2021, Smeaton et al 2021). However, precise estimates of OC remineralisation, accumulation and burial rates are generally lacking (Berner 1982, Burdige 2007, Keil 2017, Wilkinson et al 2018, Luisetti et al 2019, Legge et al 2020, Diesing et al 2021).…”

“…It is important that future research into the impact of mobile demersal fishing on carbon storage is focused in areas which are expected to contain significant stocks of OC or have large future sequestration potential, based on their geographic projections (Atwood et al 2020), sediment characteristics (Smeaton et al 2021) and local hydrology (Lee et al 2019). Research should also focus on areas that overlap with significant mobile demersal fishing pressure (Amoroso et al 2018, Kroodsma et al 2018, Sala et al 2021), and where this can be compared to areas that could be considered truly “unfished”, either from well enforced protected areas or specific environmental settings.…”

“…That withstanding, subtidal marine sediments contain the ocean’s biggest OC store, estimated to hold ~87 Gt of OC in the upper 5 cm (Lee et al 2019) or ~2.3 Tt in the top 1 m (Duarte et al 2013, Atwood et al 2020). Quantification of annual sequestration rates in these sediments is relatively poorly constrained, however they have been estimated globally at approximately 126 - 350 Mt OC yr -1 (Berner 1982, Seiter et al 2004, Burdige 2007, Keil 2017, Lee et al 2019, Smeaton et al 2021).…”

“…In total these areas cover around 9% of the global seabed, yet they store an estimated 360 Gt in their top 1 m of sediment (Atwood et al 2020). Continental shelf sediments are also highly productive, estimated to sequester up to 86% of all OC that is buried annually in global subtidal sediments (Berner 1982, Seiter et al 2004, Atwood et al 2020, Smeaton et al 2021).…”