Future projections of Northwest European Shelf sea dynamics and exchange processes with the North Atlantic

Many shelf seas are regions of high marine productivity and intense anthropogenic use. In standard earth system models, the representation of shelf sea dynamics is inadequate due to the coarse grid resolutions and the negligence of tides in the ocean component. We study the impact of large-scale climate and circulation changes in the Northwest European Shelf (NWES) running the global ocean model MPIOM on a stretched grid configuration (Fig. 1). To account for ocean-atmosphere feedback mechanisms, MPIOM is coupled with REMO over the European region. The water cycle is closed using the hydrological discharge model HD. Biogeochemical processes are simulated by the ocean carbon cycle model HAMOCC.  Outside the coupling domain, MPIOM is driven by the output of the IPCC AR4 A1B simulation of the global coupled atmosphere-ocean model ECHAM5/MPIOM. For details on the coupling we refer to Sein et al. (2015) and Elizalde (2011).

 

Fig. 1: Stretched grid configuration of the global ocean model MPIOM (black lines), providing a higher horizontal grid resolution in the North Atlantic and NWES. Green lines represent the boundaries of the regional atmosphere domain, which corresponds to the standard EuroCORDEX area

A set of sensitivity experiments was performed to estimate the impacts of climate warming, rising atmospheric pCO2 and anthropogenic eutrophication on the physical and biogeochemical state of the North Sea. In Fig. 2 annual time series are shown for primary production and CO2 uptake integrated over the North Sea as well as PO4 inflow north of Scotland

Fig. 2: Time series of model data for the experiments climate warming only (black), climate warming with rising pCO2 (blue), climate warming with pCO2 and euthrophication (red), preindustrial control (black dotted): annual mean primary production in the North Sea in MtC (top), CO2 uptake of the North Sea from the atmosphere in MtC (middle) with an estimate from observations (triangle), import of phosphate from the Atlantic north of Scotland in winter in kmol/s (bottom)

The greenhouse gas-induced warming in the 21. century leads to a reduction of the nutrient import into the North Sea in winter. The consequences are a reduction in both primary production and carbon uptake. However, sensitivity experiments show that the effectivity of the shelf carbon pump is only 20%, as most of the water leaving the North Sea stays close to the surface and is thus exposed to gas exchange with the atmosphere. Therefore the net effect is lower than suggested by other studies.

 

More details can be found in:

Gröger, M., E. Maier-Reimer, U. Mikolajewicz, A. Moll and D. Sein (2013). NW European shelf under climate warming: implications for open ocean-shelf exchange, primary production, and carbon absorption. Biogeosciences 10, 3767-3792 (link)

 

Reference:

Elizalde Arellano A. (2011) The water cycle in the Mediterranean region and the impacts of climate change. Reports on Earth System Science (PhD thesis) (link)

Sein et al. (2015). Regionally coupled atmosphere-ocean-sea ice- marine biogeochemistry model ROM: 1. description and validation, J. Adv. Model. Earth Syst., 7, 268-304, doi:10.1002/2014MS000357 (link)