Jason T. Holt

An s coordinate density evolving model of the northwest European continental shelf: 1. Model description and density structure

The Proudman Oceanographic Laboratory Three-Dimensional Baroclinic B grid model (POL3DB) has been developed to incorporate features suitable for the modeling of baroclinic processes on the shelf, at the shelf slope, and in ocean regions to allow long-term coupled ocean-shelf simulations. We test the model on the northwest European continental shelf in the period November 1988 to October 1989 against satellite sea surface temperature measurements, against CTD sections both on and off the shelf, and (in summary) against the whole of the North Sea Project CTD data set. The model accurately reproduces the seasonal cycle in the shelf-wide spatial temperature structure seen in the observations. Spatial correlations range from r = 0.92 in December to 0.79 in July, and the overall rms errors range from 0.8°C in April to 1.6°C in July. We demonstrate that the increase in the errors during the summer is due to uncertainties in modeling the vertical temperature structure. Compared with a climatology, the large-scale sea surface salinity structure is also well modeled (r = 0.80), but there is a tendency for the model to overestimate the salinity in the Norwegian Trench and underestimate it in the Kattegat. The s coordinates (a modified sigma-coordinate system) allow the formation of a seasonal mixed layer across the shelf break and into the northeast Atlantic with a modest vertical resolution. The accuracy to which this deep water region is modeled is limited by the initial and boundary conditions and by the extent of the model domain.

Impacts of climate change on marine ecosystem production in societies dependent on fisheries

iesonmarinefisheries 3 .Predictedchanges in fish production indicate increased productivity at high latitudes and decreased productivity at low/mid latitudes, with considerable regional variations. With few exceptions, increases and decreases in fish production potential by 2050 are estimated to be<10% (meanC3.4%) from present yields. Among the nations showing a high dependency on fisheries 3 ,

A highly spatially resolved ecosystem model for the North West European Continental Shelf

Abstract This paper outlines an approach to complex spatio-temporal marine ecosystem modelling as applied to the North Western European Continental Shelf. The model presented here goes further than previous work, as we combine a higher resolution hydrodynamic model, the POL-3DB baroclinic model with the European Regional Seas Ecosystem Model. This combination of models includes many of the processes (benthic-pelagic coupling, dynamic zooplankton and nitrogen, phosphorous and silicate cycling) previous authors have identitied as missing from their models and partially responsible for the inadequacies of their simulations. Spatial distributions of key physical and ecological variables taken from the three dimensional high resolution hydrodynamic/ecological simulations are presented to illustrate how spatial and temporal variations in physical processes determine the onset of the spring bloom in the North Sea. A basic validation of these simulations is presented, which indicates the model reproduces many of the features of the seasonal cycles of nutrients and phytoplankton, but fails to simulate mesozooplankton biomass in a convincing manner. The reasons for this are discussed along with potential new research directions.

An initial assessment of the potential environmental impact of CO2 escape from marine carbon capture and storage systems

Abstract If carbon capture and storage is to be adopted as a CO2 mitigation strategy, it is important to understand the associated risks. The risk analysis consists of several elements such as leakage probability, assessing the strength of environmental perturbation, and quantifying the ecological, economic, and social impacts. Here, the environmental perturbation aspect is addressed by using a marine system model of the North West European Shelf seas to simulate the consequences of CO2 additions such as those that could arise from a failure of geological sequestration schemes. Little information exists to guide the choice of leak scenario and many assumptions are required; for consistency the assumptions err towards greater impact and what would be in likelihood extreme scenarios. The simulations indicate that only the largest leakage scenarios tested are capable of producing perturbations that are likely to have environmental consequences beyond the locality of a leak event. It is shown that, given the available evidence, the chemical perturbation of a sequestration leak, regionally integrated, is likely to be insignificant when compared with that from continued non-mitigated atmospheric CO2 emissions and the subsequent acidification of the marine system. The potential ecological impacts of a large environmental CO2 perturbation are reviewed, indicating that the biogeochemical functioning and biodiversity are sensitive. The key unknowns that must be addressed in future research are identified; namely, the fine scale dispersion of CO2 and the ability of ecological systems to recover from perturbation.

An operational ocean forecast system incorporating NEMO and SST data assimilation for the tidally driven European North-West shelf

A new operational ocean forecast system, the Atlantic Margin Model implementation of the Forecast Ocean Assimilation Model (FOAM-AMM), has been developed for the European North West Shelf (NWS). An overview of the system is presented including shelf specific developments of the physical model, the Nucleus for European Modelling of the Ocean (NEMO), and the Sea Surface Temperature (SST) data assimilation scheme. Initial validation is presented of the tides and model SST. The SST skill of the system is significantly improved by the data assimilation scheme. Finally, an analysis of the seasonal tidal mixing fronts shows that these, in general, agree well with observation, but data assimilation does not significantly alter their positions.

Biomass changes and trophic amplification of plankton in a warmer ocean

Ocean warming can modify the ecophysiology and distribution of marine organisms, and relationships between species, with nonlinear interactions between ecosystem components potentially resulting in trophic amplification. Trophic amplification (or attenuation) describe the propagation of a hydroclimatic signal up the food web, causing magnification (or depression) of biomass values along one or more trophic pathways. We have employed 3-D coupled physical-biogeochemical models to explore ecosystem responses to climate change with a focus on trophic amplification. The response of phytoplankton and zooplankton to global climate-change projections, carried out with the IPSL Earth System Model by the end of the century, is analysed at global and regional basis, including European seas (NE Atlantic, Barents Sea, Baltic Sea, Black Sea, Bay of Biscay, Adriatic Sea, Aegean Sea) and the Eastern Boundary Upwelling System (Benguela). Results indicate that globally and in Atlantic Margin and North Sea, increased ocean stratification causes primary production and zooplankton biomass to decrease in response to a warming climate, whilst in the Barents, Baltic and Black Seas, primary production and zooplankton biomass increase. Projected warming characterized by an increase in sea surface temperature of 2.29 ± 0.05 °C leads to a reduction in zooplankton and phytoplankton biomasses of 11% and 6%, respectively. This suggests negative amplification of climate driven modifications of trophic level biomass through bottom-up control, leading to a reduced capacity of oceans to regulate climate through the biological carbon pump. Simulations suggest negative amplification is the dominant response across 47% of the ocean surface and prevails in the tropical oceans; whilst positive trophic amplification prevails in the Arctic and Antarctic oceans. Trophic attenuation is projected in temperate seas. Uncertainties in ocean plankton projections, associated to the use of single global and regional models, imply the need for caution when extending these considerations into higher trophic levels.

Modelling the global coastal ocean

Shelf and coastal seas are regions of exceptionally high biological productivity, high rates of biogeochemical cycling and immense socio-economic importance. They are, however, poorly represented by the present generation of Earth system models, both in terms of resolution and process representation. Hence, these models cannot be used to elucidate the role of the coastal ocean in global biogeochemical cycles and the effects global change (both direct anthropogenic and climatic) are having on them. Here, we present a system for simulating all the coastal regions around the world (the Global Coastal Ocean Modelling System) in a systematic and practical fashion. It is based on automatically generating multiple nested model domains, using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System coupled to the European Regional Seas Ecosystem Model. Preliminary results from the system are presented. These demonstrate the viability of the concept, and we discuss the prospects for using the system to explore key areas of global change in shelf seas, such as their role in the carbon cycle and climate change effects on fisheries.

Thermohaline circulation of shallow tidal seas

The mechanisms controlling the temperature and salinity structure of shallow continental shelf seas have been understood for over thirty years, yet knowledge of what drives their large-scale circulation has remained relatively unknown. Here we describe a decade long programme of measurements, using satellite-tracked drifting buoys on the northwest European shelf, to draw attention to a striking picture of highly organised thermohaline circulation consisting of narrow, near surface, fast flowing jets. These are ubiquitous above sharp horizontal gradients in bottom temperatures and/or salinities. The circulation phenomena we describe are likely to be prevalent on all similar, wide, tidally energetic continental shelves including those off north-eastern China, Argentina and parts of the Arctic. The robust, repeatable observation of the key role of jets above bottom fronts results in a fundamental reassessment of how we view the dynamics of shelf seas.

Regional scale impacts of distinct CO2 additions in the North Sea

A marine system model applied to the North West European shelf seas is used to simulate the consequences of distinct CO(2) additions such as those that could arise from a failure of geological sequestration schemes. The choice of leak scenario is guided by only a small number of available observations and requires several assumptions; hence the simulations reported on are engineered to be worse case scenarios. The simulations indicate that only the most extreme scenarios are capable of producing perturbations that are likely to have environmental consequences beyond the locality of a leak event. Tidally driven mixing rather than air-sea exchange is identified as the primary mechanism for dispersal of added CO(2). We show that, given the available evidence, the environmental impact of a sequestration leak is likely to be insignificant when compared to the expected impact from continued non-mitigated atmospheric CO(2) emissions and the subsequent acidification of the marine system. We also conclude that more research, including both leak simulations and assessment of ecological impacts is necessary to fully understand the impact of CO(2) additions to the marine system.

An s coordinate density evolving model of the northwest European continental shelf: 2. Seasonal currents and tides

The barotropic tides and the residual currents from a year long run of a three-dimensional baroclinic model (the Proudman Oceanographic Laboratory Three-Dimensional Baroclinic B grid model) applied to the northwest European shelf are investigated. M2 currents and elevations differ from observations by typically 0.114 m s−1 and 0.143 m; these errors are dominated by a number of large values at the coast. The density component of the residual currents is derived from the difference between the full model and wind and tide only model runs. This demonstrates the importance of density-driven currents in a number of regions, particularly in the Norwegian Trench, around the St. Georges Channel, to the east of the Shetland Isles, and in the river plumes. However, volume fluxes show the mass budget of the North Sea is primarily determined by the wind-driven circulation. Calculations of the dynamic balance in the model show the significance of friction and/or advective effects, on a timescale of days, at a number of locations (e.g., the Dover Strait and in the central North Sea). However, the monthly mean currents are in geostrophic balance over virtually the whole domain; ageostrophic components adjust the surface and isopycnal slopes to restore this balance on comparatively short timescales. Particular attention is given to the western boundary, and we demonstrate that variations in the imposed temperature and salinity here have only a limited effect on the shelf. Current meters on the Hebrides shelf show that the model produces reasonably accurate residual currents but also that this agreement is degraded by the boundary condition on Porcupine Bank.