Resolving Shelf Break Exchange Around the European Northwest Shelf

Graham, Jennifer; Rosser, J.; O’Dea, Enda; Hewitt, Helene T.

doi:10.1029/2018gl079399

Cited by 37 publications

(43 citation statements)

References 35 publications

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“…The heads of many canyons incise the edge of the NWES (Harris and Whiteway, 2011) and they are known to enhance shelf-edge exchange through advection and mixing, and can act as major conduits of dissolved and particulate matter from shallow to deep water (Allen and Durrieu De Madron, 2009;Puig et al, 2014). A recent study found that reducing the grid spacing in the AMM (Atlantic Margin Model) from 7 km to 1.5 km allowed smaller scale features such as canyons to be resolved, which contributed to stronger downwelling circulation in the higher resolution model (Graham et al, 2018). The models used here to estimate crossshelf exchange do not resolve submarine canyons and this is clearly a priority for future work.…”

Section: Outputs To Benthic Storage and The Open Oceanmentioning

confidence: 99%

“…Models predict a weakening of the shelf edge current, especially in the eastward circulation in the northern North Sea (Holt et al, 2010;Tinker et al, 2016) and it is possible that this weakened circulation may reduce the strength of off-shelf carbon transport. However, recent work has highlighted that models with spatial resolutions of the order of 1 km are needed to resolve key processes controlling cross-shelf exchange (Graham et al, 2018), and there is a lack of suitable synoptic scale observations for verifying such models (Bôas et al, 2019).…”

Section: Changing Circulationmentioning

confidence: 99%

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

et al. 2020

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A carbon budget for the northwest European continental shelf seas (NWES) was synthesized using available estimates for coastal, pelagic and benthic carbon stocks and flows. Key uncertainties were identified and the effect of future impacts on the carbon budget were assessed. The water of the shelf seas contains between 210 and 230 Tmol of carbon and absorbs between 1.3 and 3.3 Tmol from the atmosphere annually. Offshelf transport and burial in the sediments account for 60-100 and 0-40% of carbon outputs from the NWES, respectively. Both of these fluxes remain poorly constrained by observations and resolving their magnitudes and relative importance is a key research priority. Pelagic and benthic carbon stocks are dominated by inorganic carbon. Shelf sediments contain the largest stock of carbon, with between 520 and 1600 Tmol stored in the top 0.1 m of the sea bed. Coastal habitats such as salt marshes and mud flats contain large amounts of carbon per unit area but their total carbon stocks are small compared to pelagic and benthic stocks due to their smaller spatial extent. The large pelagic stock of carbon will continue to increase due to the rising concentration of atmospheric CO 2 , with associated pH decrease. Pelagic carbon stocks and flows are also likely to be significantly affected by increasing acidity and temperature, and circulation changes but the net impact is uncertain. Benthic carbon stocks will be affected by increasing temperature and acidity, and decreasing oxygen concentrations, although the net impact of these interrelated changes on carbon stocks is uncertain and a major knowledge gap. The impact of bottom trawling on benthic carbon stocks Frontiers in Marine Science | www.frontiersin.org 1 March 2020 | Volume 7 | Article 143Legge et al.Carbon on the Northwest European Shelf is unique amongst the impacts we consider in that it is widespread and also directly manageable, although its net effect on the carbon budget is uncertain. Coastal habitats are vulnerable to sea level rise and are strongly impacted by management decisions. Local, national and regional actions have the potential to protect or enhance carbon storage, but ultimately global governance, via controls on emissions, has the greatest potential to influence the long-term fate of carbon stocks in the northwestern European continental shelf.

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Section: Outputs To Benthic Storage and The Open Oceanmentioning

confidence: 99%

Section: Changing Circulationmentioning

confidence: 99%

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

et al. 2020

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“…COAWST has also been implemented for a domain covering the north-west European shelf seas by Reza Hashemi et al (2015), similar to that used in this study, using a horizontal grid spacing of the order of 4 km (1/24 • ). Their analysis focused on the impact of coupling on the wave simulations for wave energy resource applications (Hashemi and Lewis, 2017). Lewis et al (2019) used the same COAWST system for the role of tidal dynamics on the wave climate of the Irish Sea.…”

Section: Introductionmentioning

confidence: 99%

Can wave coupling improve operational regional ocean forecasts for the north-west European Shelf?

et al. 2019

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Operational ocean forecasts are typically produced by modelling systems run using a forced mode approach. The evolution of the ocean state is not directly influenced by surface waves, and the ocean dynamics are driven by an external source of meteorological data which are independent of the ocean state. Model coupling provides one approach to increase the extent to which ocean forecast systems can represent the interactions and feedbacks between ocean, waves, and the atmosphere seen in nature. This paper demonstrates the impact of improving how the effect of waves on the momentum exchange across the ocean-atmosphere interface is represented through ocean-wave coupling on the performance of an operational regional ocean prediction system. This study focuses on the eddy-resolving (1.5 km resolution) Atlantic Margin Model (AMM15) ocean model configuration for the north-west European Shelf (NWS) region.A series of 2-year duration forecast trials of the Copernicus Marine Environment Monitoring Service (CMEMS) north-west European Shelf regional ocean prediction system are analysed. The impact of including ocean-wave feedbacks via dynamic coupling on the simulated ocean is discussed. The main interactions included are the modification of surface stress by wave growth and dissipation, Stokes-Coriolis forcing, and wave-height-dependent ocean surface roughness. Given the relevance to operational forecasting, trials with and without ocean data assimilation are considered.Summary forecast metrics demonstrate that the oceanwave coupled system is a viable evolution for future oper-ational implementation. When results are considered in more depth, wave coupling was found to result in an annual cycle of relatively warmer winter and cooler summer sea surface temperatures for seasonally stratified regions of the NWS. This is driven by enhanced mixing due to waves, and a deepening of the ocean mixed layer during summer. The impact of wave coupling is shown to be reduced within the mixed layer with assimilation of ocean observations. Evaluation of salinity and ocean currents against profile measurements in the German Bight demonstrates improved simulation with wave coupling relative to control simulations. Further, evidence is provided of improvement to simulation of extremes of sea surface height anomalies relative to coastal tide gauges.

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“…The simulated vertical profile of cross-shelf break transport during winter (DJFM) integrated along the 200 m isobath between 47 and 61.5 • N (Fig. 8a) shows the typical structure of a strong wind-driven on-shelf surface flow (0-40 m), an on-shelf flow in the interior of the water column (40-130 m) and an off-shelf Ekman drain at the bottom (130-200 m) due to basal stress of the slope current (Graham et al, 2018). Independent of the GIS melting rates, the net on-shelf winter transport through this section weakens under RCP8.5 by about 23 % (from 1.11 in 1971(from 1.11 in -2000(from 1.11 in to 0.86 Sv in 2101(from 1.11 in -2150.…”

Section: Changes In the Mean Ocean-shelf Nutrient Transportmentioning

confidence: 99%

The impact of meltwater discharge from the Greenland ice sheet on the Atlantic nutrient supply to the northwest European shelf

Mathis¹,

Mikolajewicz²

2020

Ocean Sci.

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Abstract. Projected future shoaling of the wintertime mixed layer in the northeast (NE) Atlantic has been shown to induce a regime shift in the main nutrient supply pathway from the Atlantic to the northwest European shelf (NWES) near the end of the 21st century. While reduced winter convection leads to a substantial decrease in the vertical nutrient supply and biological productivity in the open ocean, vertical mixing processes at the shelf break maintain a connection to the subpycnocline nutrient pool and thus productivity on the shelf. Here, we investigate how meltwater discharge from the Greenland ice sheet (GIS), not yet taken into account, impacts the mixed layer shoaling and the regime shift in terms of spatial distribution and temporal variability. To this end, we have downscaled sensitivity experiments by a global Earth system model for various GIS melting rates with a regionally coupled ocean–atmosphere climate system model. The model results indicate that increasing GIS meltwater discharge leads to a general intensification of the regime shift. Atlantic subpycnocline water masses mixed up at the shelf break become richer in nutrients and thus further limit the projected nutrient decline on the shelf. Moreover, the stronger vertical nutrient gradient through the pycnocline results in an enhanced interannual variability of on-shelf nutrient fluxes which, however, do not significantly increase variations in nutrient concentrations and primary production on the shelf. Due to the impact of the GIS meltwater discharge on the NE Atlantic mixed layer depth, the regime shift becomes initiated earlier in the century. The effect on the onset timing, though, is found to be strongly damped by the weakening of the Atlantic meridional overturning circulation. A GIS melting rate that is even 10 times higher than expected for emission scenario Representative Concentration Pathway (RCP) 8.5 would not lead to an onset of the regime shift until the 2070s.

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Resolving Shelf Break Exchange Around the European Northwest Shelf

Cited by 37 publications

References 35 publications

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

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

Can wave coupling improve operational regional ocean forecasts for the north-west European Shelf?

The impact of meltwater discharge from the Greenland ice sheet on the Atlantic nutrient supply to the northwest European shelf

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