J.I. Allen

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 ,

Primary and bacterial production in the Mediterranean Sea: a modelling study

Abstract Relationships between bacterial and primary production in the eastern and western basins of the Mediterranean Sea are different. In this study, a 1D coupled ecosystem model is used to simulate primary and bacterial production along the west–east trophic gradient and to ascertain the physical and biogeochemical controls that determine regional variations in production. Simulations demonstrate differences in ecosystem function between the western and eastern basins of the Mediterranean Sea at the level of bacterial and primary production. Vertical mixing processes (deep mixing and convection), particularly in late winter, are crucial in determining total annual production in both basins, and the dissolved organic carbon pool, from which bacteria obtain their carbon, is derived from autotrophic rather than heterotrophic activity. Bacterial production is nutrient limited in the east, and may be grazer controlled in the west. The dissolved organic nutrient pools are derived from heterotrophic rather than autotrophic activity. The eastern basin is characterised by strong competition between phytoplankton and bacteria for nutrients whereas the western basin is characterised by relatively high levels of heterotrophic activity. Nitrogen and phosphate uptake by phytoplankton is biologically important in both basins, whereas bacterial uptake of these is only important in the eastern basin. A generic model parameterisation produces simulation results which concur with recent observations although simulated production rates are very sensitive to the initial conditions upon which those simulations are based.

The Mediterranean pelagic ecosystem response to physical forcing

The effects of physical forcing on pelagic ecosystem are studied using numerical models, in which ecological and physical processes are coupled. The implications of the mathematical formulation of coupling are discussed, outlining the different parameterisation in combining spatial and temporal scales. Existing 3D and 1D numerical models of the Mediterranean Sea are presented. The results are used to assess the respective roles of light and nutrients in limiting phytoplankton growth and to suggest that the East‐West trophic gradient in Mediterranean is the result of the superposition of biological pump and estuarine inverse circulation.

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.

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.

A numerical simulation study of dissolved organic carbon accumulation in the northern Adriatic Sea

The leading author of this paper was supported by a Ph.D. fellowship given to the Environmental Science graduate program of the University of Bologna at Ravenna and by the VECTOR project funded by the Italian Ministry of Research and University. N. Pinardi and M. Zavatarelli were partially supported by the MFSTEP project (EU contract EVK3-CT-2002-00075) and the ADRICOSM Project (funded by the Italian Ministry of Environment and Territory, Division of Environmental Research and Development). Icarus Allen and Marcello Vichi acknowledge the support by the EUR-OCEANS network of excellence (contract 511106).

Decadal reanalysis of biogeochemical indicators and fluxes in the North West European shelf‐sea ecosystem

This paper presents the first decadal reanalysis simulation of the biogeochemistry of the North West European shelf, along with a full evaluation of its skill, confidence, and value. An error-characterized satellite product for chlorophyll was assimilated into a physical-biogeochemical model of the North East Atlantic, applying a localized Ensemble Kalman filter. The results showed that the reanalysis improved the model simulation of assimilated chlorophyll in 60% of the study region. Model validation metrics showed that the reanalysis had skill in matching a large data set of in situ observations for 10 ecosystem variables. Spearman rank correlations were significant and higher than 0.7 for physical-chemical variables (temperature, salinity, and oxygen), ∼0.6 for chlorophyll and nutrients (phosphate, nitrate, and silicate), and significant, though lower in value, for partial pressure of dissolved carbon dioxide (∼0.4). The reanalysis captured the magnitude of pH and ammonia observations, but not their variability. The value of the reanalysis for assessing environmental status and variability has been exemplified in two case studies. The first shows that between 325,000 and 365,000 km2 of shelf bottom waters were vulnerable to oxygen deficiency potentially threatening bottom fishes and benthos. The second application confirmed that the shelf is a net sink of atmospheric carbon dioxide, but the total amount of uptake varies between 36 and 46 Tg C yr−1 at a 90% confidence level. These results indicate that the reanalysis output data set can inform the management of the North West European shelf ecosystem, in relation to eutrophication, fishery, and variability of the carbon cycle.

What can ecosystem models tell us about the risk of eutrophication in the North Sea

Eutrophication is a process resulting from an increase in anthropogenic nutrient inputs from rivers and other sources, the consequences of which can include enhanced algal biomass, changes in plankton community composition and oxygen depletion near the seabed. Within the context of the Marine Strategy Framework Directive, indicators (and associated threshold) have been identified to assess the eutrophication status of an ecosystem. Large databases of observations (in situ) are required to properly assess the eutrophication status. Marine hydrodynamic/ecosystem models provide continuous fields of a wide range of ecosystem characteristics. Using such models in this context could help to overcome the lack of in situ data, and provide a powerful tool for ecosystem-based management and policy makers. Here we demonstrate a methodology that uses a combination of model outputs and in situ data to assess the risk of eutrophication in the coastal domain of the North Sea. The risk of eutrophication is computed for the past and present time as well as for different future scenarios. This allows us to assess both the current risk and its sensitivity to anthropogenic pressure and climate change. Model sensitivity studies suggest that the coastal waters of the North Sea may be more sensitive to anthropogenic rivers loads than climate change in the near future (to 2040).

Assimilation of Ocean‐Color Plankton Functional Types to Improve Marine Ecosystem Simulations

We assimilated plankton functional types (PFTs) derived from ocean colour into a marine ecosystem model, to improve the simulation of biogeochemical indicators and emerging properties in a shelf sea. Error-characterized chlorophyll concentrations of four PFTs (diatoms, dinoflagellates, nanoplankton and picoplankton), as well as total chlorophyll for comparison, were assimilated into a physical-biogeochemical model of the North East Atlantic, applying a localized Ensemble Kalman filter. The reanalysis simulations spanned the years 1998 to 2003. The skill of the reference and reanalysis simulations in estimating ocean colour and in situ biogeochemical data were compared by using robust statistics. The reanalysis outperformed both the reference and the assimilation of total chlorophyll in estimating the ocean-colour PFTs (except nanoplankton), as well as the not-assimilated total chlorophyll, leading the model to simulate better the plankton community structure. Crucially, the reanalysis improved the estimates of not-assimilated in situ data of PFTs, as well as of phosphate and pCO2, impacting the simulation of the air-sea carbon flux. However, the reanalysis increased further the model overestimation of nitrate, in spite of increases in plankton nitrate uptake. The method proposed here is easily adaptable for use with other ecosystem models that simulate PFTs, for, e.g., reanalysis of carbon fluxes in the global ocean and for operational forecasts of biogeochemical indicators in shelf-sea ecosystems.