Organic carbon densities and accumulation rates in surface sediments of the North Sea and Skagerrak

Abstract

Abstract. Continental shelf sediments are places of both rapid organic carbon turnover and accumulation, while at the same time increasingly subjected to human-induced disturbances. Recent research suggests that shelf sediments might have a role to play as a natural climate solution, e.g. by storing organic carbon if left undisturbed from anthropogenic activity. However, we have an incomplete understanding about the centres of organic carbon accumulation and storage on continental shelves. To better constrain the rate of accumulation and the mass of organic carbon that is stored in sediments, we developed and applied a spatial modelling framework that allows us to estimate those quantities from sparse observations and predictor variables known or suspected to influence the spatial patterns of these parameters. This paper presents spatial distribution patterns of organic carbon densities and accumulation rates in the North Sea and Skagerrak. We found that organic carbon stocks and accumulation rates are highest in the Norwegian Trough, while large parts of the North Sea are characterised by low stocks and zero net accumulation. The total stock of organic carbon that is stored in the upper 0.1 m of sediments amounted to 230.5 ± 134.5 Tg C, of which approximately 26 % is stored in the Norwegian Trough. Rates of organic carbon accumulation in the Norwegian Trough are comparable with those reported from nearby fjords. We provide baseline datasets that could be used in marine management, e.g. for the establishment of “carbon protection zones”. Additionally, we highlight the complex nature of continental shelves with zones of rapid carbon cycling and accumulation juxtaposed, which will require further detailed and spatially explicit analyses to constrain sedimentary organic carbon stocks and accumulation rates globally.

Sounding Out the Carbon: The Potential of Acoustic Backscatter Data to Yield Improved Spatial Predictions of Organic Carbon in Marine Sediments

“…High-intensity backscatter is characteristic of coarse or poorly-sorted material (Collier and Brown, 2005;Biondo and Bartholomä, 2017), which are likely to result from dynamic or erosive processes, and therefore unimportant areas for C storage. This visual aid can help prioritise ground-truthing toward the finer-grained sediments associated with deposition and enrichment in organic matter (Diesing et al, 2021). The difficulties of the backscatter to delineate between finer materials could be due to a limitation of the MBES survey technology and post-processing methods employed over a decade ago, however, similar challenges have been identified in very recent studies, indicating that further development is still required within this field (Diesing et al, 2020).…”

“…In the past decade, a suite of toolboxes have been developed to enable researchers to derive geomorphological parameters from high-resolution bathymetry data (Lecours et al, 2016a). Further research including terrain attribute predictors for sediment deposition could prove invaluable for improving the picture of sedimentary OC on the shelf (Diesing et al, 2021).…”

“…The management of these activities, such as benthic trawling (Paradis et al, 2017), could be key to maintaining sediments as part of the suite of nature-based solutions for mitigating against climate change (Sala et al, 2021). Assessments of the spatial distribution of sedimentary OC are key to understanding the processes that influence how C is processed and where it is more likely to be accumulating, i.e., carbon hotspots (Diesing et al, 2021).…”

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

“…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). Any studies which aim to quantify the impact of demersal fishing on carbon storage and sequestration must therefore quantify both the before and after scenarios for robust conclusions to be drawn.…”

“…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.…”