Coastal Upwelling Systems

Coastal upwelling systems are directly driven by atmospheric forcing and vary significantly in their geographical location, intensity of upwelling, CO2 and nutrient budgets, and ecosystem structure on higher trophic levels. Upwelling regions also constitute a crucial climate bias in coupled atmosphere-ocean models. Small- and meso-scale variability of upwelling systems creates steep gradients in concentrations of all radiatively and/or biologically relevant sea water constituents. The resolution of both the model and the surface forcing is critical to correctly estimate fluxes of materials. Current models differ both in sign and in upwelling quantity in scenario models of the future, but coastal upwelling is likely to intensify due to enhanced land-sea pressure gradients.

Central questions

  1. Do coupled global models show coherent responses of individual coastal and oceanic upwelling systems to changes in atmospheric forcing within the last decades and on millennial scales, i.e. are there large-scale teleconnections between individual upwelling systems?
  2. Do regional and global atmospheric and coupled models support the hypothesis of upwelling intensification as a response to altered circulation and how is this likely to affect individual marine systems in terms of water-mass make-up?
  3. What is the role of upwelling areas as CO2 sources and sinks and on what time scales is the budget balanced/unbalanced? Is the re-sequestration capacity affected by materials coming from land?
  4. Is the observed decrease in CO2 uptake by the subtropical ocean, caused by enhanced stratification, balanced by enhanced nutrient supply from coastal upwelling systems?

To answer these questions existing model experiments will be evaluated (ECHO-G long integration, MPI-OM+HAMMOCC, 0.4°) and dedicated model experiments with forthcoming model configurations will be performed (STORM-HAMOCC; ICON; "global downscaling"). Two regions will be investigated: SE Atlantic (SE Trade) and Arabian Sea (SW Monsoon), which differ in the underlying atmospheric forcing. Additional research on land-sea-interactions, on emission of halocarbons and methane, on dynamics of oxygen supply and its control on nutrients and on ecosystem dynamics will be done in upwelling systems.