Simulations of interactions between shelf ecosystem – open ocean – atmosphere

Models are tools to explore interactions between physical, chemical and biological components of the coastal upwelling system and their sensitivity to changes in external forcing. Models also serve to evaluate our grasp on the relevant processes. Simulations create consistent data sets to enable statistical analysis of the system, and its dependence on variability of external factors. Scenaric models further help to anticipate the range of possible future developments. In this theme, GENUS will use/ adapt/improve existing model components and create new components to gauge the range of natural variations in the upwelling shelf pump for CO₂ and nutrients under natural and man-made climate variability.

Central goal of this theme is a quantitative estimate of natural ranges in mass fluxes between the shelf system and the adjacent mesopelagic ocean, as well as ocean-atmosphere fluxes of CO₂ and methane. This requires a differentiation between variability in structures and functioning of the upwelling ecosystem attributable to climate forcing, and to fisheries. Time windows for retrospective simulations are the period 1960-2008 AD, for which observational data exist for all ecosystem components, as well as two extremes in global climate of the last 1000 years: The Little Ice Age (LIA) during the Maunder sunspot minimum (1670-1710 AD) and the Medieval Warm Period (MWP; 1130-1170 AD).

In these experiments, synthetic climate forcing is simulated by a regional climate model (REMO) downscaled from a global Earth System Model (the Millennium simulation of MPI for Meteorology in Hamburg) and is passed on to a regional setup of MOM4/ERGOM, which will also use oceanic boundary conditions from the Millennium simulation. The modelled patterns of primary producers simulated by ERGOM are used to drive ECOPATH/ECOSIM energy balances of the higher trophic levels, which then are used to modify ERGOM in order to gauge effects of changing trophic structures on material cycles.