Comparing benthic biogeochemistry at a sandy and a muddy site in the Celtic Sea using a model and observations

Abstract

Results from a 1D setup of the European Regional Seas Ecosystem Model (ERSEM) biogeochemical model were compared with new observations collected under the UK Shelf Seas Biogeochemistry (SSB) programme to assess model performance and clarify elements of shelf-sea benthic biogeochemistry and carbon cycling. Observations from two contrasting sites (muddy and sandy) in the Celtic Sea in otherwise comparable hydrographic conditions were considered, with the focus on the benthic system. A standard model parameterisation with site-specific light and nutrient adjustments was used, along with modifications to the within-seabed diffusivity to accommodate the modelling of permeable (sandy) sediments. Differences between modelled and observed quantities of organic carbon in the bed were interpreted to suggest that a large part ([90%) of the observed benthic organic carbon is biologically relatively inactive. Evidence on the rate at which this inactive fraction is produced will constitute important information to quantify offshore carbon sequestration. Total oxygen uptake and oxic layer depths were within the range of the measured values. Modelled depth average pore water concentrations of ammonium, phosphate and silicate were typically

Carbon on the Northwest European Shelf: Contemporary Budget and Future Influences

“…Recent data suggests that these fluxes can be highly variable seasonally and that POC burial may be greater than expected from our current modeling, depending on processes varying temporally and spatially (Snelgrove et al, 2018;Queirós et al, 2019). Furthermore, a substantial proportion of the empirical benthic carbon data is derived from cohesive sediment studies, with the exception of a few (e.g., Boudreau et al, 2001;Precht and Huettel, 2003;Rao et al, 2008;Burt et al, 2014;Aldridge et al, 2017), yet the wide spatial coverage of permeable sediments on the shelf means there is likely to be an underestimation of the influence of advective flow on the carbon dynamics within benthic stocks (Boudreau et al, 2001;de Beer et al, 2005). More data, from a range of sediment types across the shelf and a better coverage of seasonality (measurements of carbon fluxes as well as physical and biological process rates) are needed to better quantify the balance of POC deposition and DIC release throughout the year.…”

Bottom mixed layer oxygen dynamics in the Celtic Sea

“…The relative contribution of these processes is poorly known however (Breitburg et al 2018). Predicting the magnitude and spatial distribution of future oxygen loss is hampered by insufficient data and the lack of mechanistic understanding of oxygen dynamics at a variety of scales (Breitburg et al 2018;Aldridge et al 2017). This oxygen loss can lead to bottom-water hypoxia (Holte 1920) which has a variety of implications including: loss of marine life and reduced biodiversity (Breitburg et al 2018), altering the balance of nitrogen cycling (Neubacher et al 2013) and increased production of the potent green-house gas nitrous oxide (Kitidis et al 2017;Breitburg et al 2018).…”

“…Shelf seas can vary over short temporal and spatial scales, therefore long term and spatially broad averages do not well represent their dynamics. These knowledge gaps hinder our ability to design numerical models that can correctly reproduce the carbon dynamics of these regions, which limits their predictive potential (Aldridge et al 2017;Diesing et al 2017;Solan et al 2020).…”

Comparison of mechanical disturbance in soft sediments due to tickler-chain SumWing trawl vs. electro-fitted PulseWing trawl

“…Whereas both SumWing and PulseWing trawling reworked the top layers of the seabed, SumWing trawling also caused vertical mixing and homogenisation of sediment particles in deeper layers. The replacement of the oxidised layer by a homogenised layer may further retard organic matter cycling by the shift from surficial aerobic to subsurface, anaerobic respiration (Trimmer et al, 2005;Aldridge et al, 2017). This homogenisation does not occur in any natural processes and may have significant ecological implications to the stability of carbon mineralisation and nutrient cycles (Mayer et al, 1991;Duplisea et al, 2001;Sciberras et al, 2016).…”