Parameterisation of oxygen dynamics in the bottom water of the Baltic Sea-North Sea transition zone

摘要

An organic carbon budget for the Kattegat and Belt Seas in the North Sea-Baltic Sea transition zone was used to parameterise the pelagic and benthic respiration in a new oxygen model, OXYCON, which describes the influence of temperature-dependent pelagic and benthic respiration on bottom water oxygen conditions. The significance of respiration versus physical mixing and advection processes for the bottom water oxygen concentration was analysed through a sensitivity study where the OXYCON model was implemented in 2 transport models: a Lagrangian model of bottom water transport, based on an age-tracer of the bottom water transit-time through the area, and a 3-dimensional circulation model of the transition zone. The solutions of both models were in accordance with the observed spatial and temporal distribution of oxygen in the area during the period 2001 to 2003. In particular, the temporal and spatial dynamics of a severe hypoxic event in 2002 were well described. The inter-annual variability of hypoxia during this period could therefore be explained by changes in physical mixing and ventilation of the bottom layer with oxygen-rich surface water and by the bottom water temperature. Variability in the sources of organic material available for remineralisation in the bottom water seems to have less influence on the inter-annual variation in hypoxia but instead determines the background conditions and the long-term trend in oxygen dynamics.