J.C. Blackford

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 analysis of benthic biological dynamics in a North Sea ecosystem model

Abstract This paper presents an overview and analysis of the benthic biological submodel of the European Regional Seas Ecosystem Model II (ERSEM II). This submodel consists of a detailed model description of the benthic system which is integrated with a marine ecosystem model which attempts to address the full range of pelagic and benthic biogeochemical and physical processes. The submodel simulates the seasonal dynamics of a number of functional groups, ranging from decomposers to predators and their interaction with detrital matter in the sediments. The improvements and extensions to the benthic biology submodel compared with the previous published version of the European Regional Seas Ecosystem Model are described. The improvements comprise: the reformulation of turbation and irrigation as functions of faunal activity, the inclusion of oxygen stress limitations and mortalities, a refinement of the description of detritus, additions to the diet of the filter feeders in line with the extensions to the primary production module and an extensive re-parameterisation. Using the 1° × 1° North Sea application, the submodel predictions are compared with data and the performance of the submodel assessed. Using the results of the submodel, the relation between benthic biological dynamics and its principal determinants, depth and overlying production is examined. The model is found to give qualitatively correct results. The transition in community type from anaerobe/deposit feeder in the south to a more mixed community in the north, involving aerobes and meiobenthos is also correctly predicted by the model. The biology is demonstrated to have a strong influence on nutrient efflux. The lack of resuspension/deposition processes is identified as the most significant omission from the current model.

Nutrient fluxes and budgets for the North West European Shelf from a three-dimensional model.

A three-dimensional ecosystem model of the NW European continental shelf is used to simulate the seasonal cycle of nutrients (N, P, Si) and primary and secondary production during 1995. Nutrient budgets within areas of the shelf are calculated and their component parts (advective, benthic, pelagic, riverine, recycling) are examined. Nutrient fluxes across sections of the continental shelf are also calculated and compared with previous modelled/observed flux values.

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 1-D vertically resolved modelling study of the ecosystem dynamics of the middle and southern Adriatic Sea

Abstract In order to investigate the regional variations in the physical controls upon the Adriatic Sea ecosystem the European Regional Seas Ecosystem Model (ERSEM) has been coupled to an 1-D vertically resolved water column model. It has been set-up and run to simulate climatological seasonal cycles at two sites, in the open waters of the middle and southern Adriatic Sea. Climatological seasonal cycles of temperature and salinity have been simulated and validated for these sites. On a qualitative level, the response of the biochemical submodels to physical forcing of the type observed in this region is good. They reproduce the deep chlorophyll maxima (DCM) during the summer and show phosphate to be the limiting nutrient for primary production. The comparison of seasonal cycles of chlorophyll, oxygen and nutrients with data shows that the climatological seasonal cycle in the Adriatic Sea can be reproduced.

Planktonic community structure and carbon cycling in the Arabian Sea as a result of monsoonal forcing: the application of a generic model

The Arabian Sea exhibits a complex pattern of biogeochemical and ecological dynamics, which vary both seasonally and spatially. These dynamics have been studied using a one-dimensional vertical hydrodynamic model coupled to a complex ecosystem model, simulating the annual cycle at three contrasting stations. These stations are characterised by seasonally upwelling, mixed-layer-deepening and a-seasonal oligotrophic conditions, respectively, and coincide with extensively measured stations on the two JGOFS ARABESQUE cruises in 1994. The model reproduces many spatial and temporal trends in production, biomass, physical and chemical properties, both qualitatively and quantitatively and so gives insight into the main mechanisms responsible for the biogeochemical and ecological complexity. Monsoonal systems are typified by classical food web dynamics, whilst intermonsoonal and oligotrophic systems are dominated by the microbial loop. The ecosystem model (ERSEM), developed for temperate regions, is found to be applicable to the Arabian Sea system with little reparameterisation. Differences in in-situ physical forcing are sufficient to recreate contrasting eutrophic and oligotrophic systems, although the lack of lateral terms are probably the greatest source of error in the model. Physics, nutrients, light and grazing are all shown to play a role in controlling production and community structure. Small-celled phytoplanktons are predicted to be dominant and sub-surface chlorophyll maxima are robust centers of production during intermonsoon periods. Analysis of carbon fluxes indicate that physically driven outgassing of CO2 predominates in monsoonal upwelling systems but ecological activity may significantly moderate CO2 outgassing in the Arabian Sea interior.

Coupled Marine Ecosystem Modelling on High-Performance Computers

Simulation of the marine environment has become an important tool across a wide range of human activities, with applications in coastal engineering, offshore industries, fisheries management, marine pollution monitoring, weather forecasting and climate research to name but a few. Hydrodynamic models have been under development for many years and have reached a high level of sophistication. However, sustainable management of the ecological resources of coastal environments demands an ability to understand and predict the behaviour of the marine ecosystem. Thus, it is highly desirable to extend the capabilities of existing models to include chemical, bio-geo-chemical and biological processes within the marine ecosystem. This paper describes the development of a high-resolution threedimensional coupled transport/ecosystem model of the Northwest European continental shelf and explores the particular problems encountered in its implementation on high-performance computer systems. We present preliminary results from the coupled model. We also discuss the performance levels achieved and the parallelization and optimization strategies employed.

13 – Environmental risks and performance assessment of carbon dioxide (CO2) leakage in marine ecosystems

Abstract: This chapter describes the state of the current understanding of the potential for CO 2 leaked from carbon dioxide (CO 2 ) capture and storage (CCS) to impact the marine ecosystem. This is a complex problem as it requires an understanding of physical dispersion, the behaviour of plumes, marine chemistry, organism physiology and ecological relationships. Aside from predicting the likelihood of a leak event, the key issue is to understand the spread, persistence and impact of a hypothetical CCS derived leak and contrast this with, for example, trawling impacts and the global long-term consequences of climate change and the uptake of anthropogenically created atmospheric CO 2 (ocean acidification), which CCS seeks to mitigate. Excess CO 2 in the marine system is undoubtedly harmful to many organisms. In the vicinity of a leak event, it is likely that significant ecological alteration would occur. Initial research indicates that only persistent leaks of a significant proportion of reservoir capacities would cause widespread and unacceptable impacts. However, much more research is required to determine critical leak magnitudes, within sediment interactions and ecosystem recovery before any comprehensive risk assessment of CCS can be delivered.

Best Practice Guidance for Environmental Risk Assessment for offshore CO2 geological storage

Carbon dioxide (CO2) separated from natural gas has been stored successfully below the seabed off Norway for almost two decades. Based on these experiences several demonstration projects supported by the EU and its member states are now setting out to store CO2 captured at power plants in offshore geological formations. The ECO2 project was triggered by these activities and funded by the EU to assess the environmental risks associated with the sub-seabed storage of CO2 and to provide guidance on environmental practices. ECO2 conducted a comprehensive offshore field programme at the Norwegian storage sites Sleipner and Snohvit and at several natural CO2 seepage sites in order to identify potential pathways for CO2 leakage through the overburden, monitor seep sites at the seabed, track and trace the spread of CO2 in ambient bottom waters, and study the response of benthic biota to CO2. ECO2 identified a rich variety of geological structures in the broader vicinity of the storage sites that may have served as conduits for gas release in the geological past and located a seabed fracture and several seeps and abandoned wells where natural gas and formation water are released into the marine environment. Even though leakage may occur if these structures are not avoided during site selection, observations at natural seeps, release experiments, and numerical modelling revealed that the footprint at the seabed where organisms would be impacted by CO2 is small for realistic leakage scenarios. ECO2 conducted additional studies to assess and evaluate the legal framework and the public perception of CO2 storage below the seabed. The following guidelines and recommendations for environmental practices are based on these experiences.