Abstract
The potential response of the marine ecosystem of the northwest European continental shelf to climate change under a medium emissions scenario (SRES A1B) is investigated using the coupled hydrodynamics-ecosystem model POLCOMS-ERSEM. Changes in the near future (2030–2040) and the far future (2082–2099) are compared to the recent past (1983–2000). The sensitivity of the ecosystem to potential changes in multiple anthropogenic drivers (river nutrient loads and benthic trawling) in the near future is compared to the impact of changes in climate. With the exception of the biomass of benthic organisms, the influence of the anthropogenic drivers only exceeds the impact of climate change in coastal regions. Increasing river nitrogen loads has a limited impact on the ecosystem whilst reducing river nitrogen and phosphate concentrations affects net primary production (netPP) and phytoplankton and zooplankton biomass. Direct anthropogenic forcing is seen to mitigate/amplify the effects of climate change. Increasing river nitrogen has the potential to amplify the effects of climate change at the coast by increasing netPP. Reducing river nitrogen and phosphate mitigates the effects of climate change for netPP and the biomass of small phytoplankton and large zooplankton species but amplifies changes in the biomass of large phytoplankton and small zooplankton.
Highlights
Marine ecosystems are in continual adjustment responding to changes in the climate, both from natural variability and long term anthropogenic climate change
Initial ecosystem fields for CNTRL are from a spin-up simulation where homogeneous initial values corresponding to the average bulk properties of the shelf have been spun up for five years; for BASE and A1B the nutrient fields in the CNTRL initial data are perturbed by the fractional change in nutrients in the PISCES ecosystem model
In order to study the integrated response of the ecosystem to changes in forcing, mean values of biomass and net primary production are calculated for each simulation
Summary
Marine ecosystems are in continual adjustment responding to changes in the climate, both from natural variability and long term anthropogenic climate change. We investigate the relative and combined effects of climate change and changes in the direct anthropogenic drivers of benthic fishing and river nutrients, and study the impacts on the LTL ecosystem over the northwest European shelf. Lacroix et al (2007) used a 3D model of the southern North Sea and showed that reducing river nitrogen loads led to an increase in diatom biomass, whereas decreasing river phosphate reduced both diatom and Phaeocystis biomass; in addition, changes in open-ocean nutrient concentrations transported eastwards through the English Channel. In this paper we use the Proudman Oceanographic Laboratory Coastal Ocean Modelling System, POLCOMS (Holt and James, 2001), coupled to the European Regional Seas Ecosystem Model, ERSEM (Baretta et al, 1995; Blackford et al, 2004) to examine the effects of changes in climate, benthic fishing in the North Sea and river nutrient loads on the ecosystem of the European shelf. The cumulative effects of the direct drivers and climate change are studied to investigate whether the impact of changing the direct drivers amplifies or mitigates the effects of climate change
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