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

Craig Smeaton,William R Turrell,William E N Austin,Corallie A Hunt

doi:10.3389/feart.2021.593324

Craig Smeaton, William R Turrell + Show 2 more

Open Access

https://doi.org/10.3389/feart.2021.593324

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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 CO2to 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.

Highlights

Marine sediments accumulating on the ocean floor are well known as traps and stores of large quantities of carbon (C) over long timescales
Over the 29 selected areas, we observed that the area coverage of rock and boulders, coarse sediment and mixed sediment classes are more commonly underestimated, while the mud to muddy sand and sand classes are more often overestimated by the point observation approach compared to the backscatter-based mapping (Supplementary Table S3)
The normalized mean errors for the sediment classes were calculated as Coarse Sediment (5.57%), Mud and muddy Sand (5.23%), Sand (5.17%), Mixed Sediment (4.99%), Rock and Boulders (3.48%); these errors are broadly comparable to those observed from similar analyses undertaken in the Scottish fjords that estimated errors between 0.52% and 5.07% (Smeaton and Austin, 2019)

Summary

Introduction

Marine sediments accumulating on the ocean floor are well known as traps and stores of large quantities of carbon (C) over long timescales. For example, have been established as long-term stores of both OC and inorganic carbon (IC) (Smeaton et al, 2017) and, globally, are estimated to bury 18 Mt OC yr−1 (Smith et al, 2015), Smeaton and Austin (2019) suggest that 18 Mt OC yr−1 may very well represent an overestimation due to the complex spatial heterogeneity of fjord sediments These sedimentary environments are believed to play an important role in the global C cycle (Bauer et al, 2013; Bianchi et al, 2018) with an increasing number of proponents suggesting that these sedimentary systems provide a natural climate solution that mitigates climate change and requires management (Atwood et al, 2020; Avelar et al, 2017; Legge et al, 2020; Luisetti et al, 2019; Luisetti et al, 2020)

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