Dynamics and Ecology of Shelf Sea Systems
The interdisciplinary investigation of shelf sea dynamics at our institute deals with the development of marine ecosystem models and their application for the investigation of interactions between physical and biogeochemical processes. The main focuses of our work are the North and Baltic Sea. However, our models are applied to other shelf regions, coastal waters and estuaries in cooperation with foreign partners.
Shelf regions play among other things an important part in the coupling between the north-west European main land and the North Atlantic. This concerns fresh water, carbon and other substances that are transported and modified on their way from the continent to the open ocean over the shelf seas. An important role plays the exchange and turnover of nutrition salts on the shelf during the turnover of material cycles. The state of the shelf seas thereby depend highly on the input from the atmosphere and continental rivers. The repercussions of coastal management measures on the marine ecosystem material cycles are, next to the yearly environmental monitoring, included and analyzed in mathematical models. Hence, model scenarios of these measures are calculated and their repercussions estimated with indicators.
Modelling the marine ecosystem
An interesting aspect of these investigations concerns the functioning of the marine ecosystem under influence of its physical environment. So, for the first time it was possible to parameterize the influence of the winter convection on the primary production in the model ECOHAM (see below). The model predicts a winter stock of oceanic phytoplankton comparable to the biomass of the summer bloom. This biomass could not have been modelled without the new parameterization of convection. First, the impact of the convection on the primary production was proven on the shelf and later transferred on to the ocean, where it was confirmed by observations. Our future work will include the role of the winter plankton stock as part of the export production and hence the climate relevant CO2 balance of the ocean.
HAMSOM and ECOHAM
The HAMSOM (Hamburg Shelf Ocean Model) model belongs to the existing model systems for the simulation of shelf sea circulation on time scales from hours to centuries. It is maintained at our institute since 1985 and used in numerous partner institutions worldwide, although it has many younger competitors. A coupled version resulted from the combination of HAMSOM with an ecosystem model for plankton and nutrition dynamics ECOHAM (ECOsystem Model HAMburg). Ongoing model developments in ECOHAM include modules for zooplankton, coupled inorganic and organic carbon dynamics as well as oxygen balances and suspended matter dynamics. The VOM model (Vector-Ocean-Model), also developed in our institute, is the younger sister of HAMSOM and allows a process oriented increase of vertical resolution at topographic slopes and the ocean bottom. Hence, boundary currents and the exchange between the shelf and the ocean can be simulated realistically without a coordinate transformation. One version of the model, VOM-SW (SW: Shallow Water), allows a three dimensional simulation in the Wadden Sea where the whole grid can fall dry. This is a requirement for the modelling of the matter and heat fluxes at the border between sediment, water and atmosphere.