FJORD BASIN WATER EXCHANGE IN SILL NORWEGIAN FJORDS

The global change in climate is expected to have large ecological implications, although knowledge of such changes in fjords and coastal waters is sparse. In sill fjords the exchange of the basin water will only occur when the oceanic water at sill depth is denser than the fjord basin water. Between exchange episodes the fjord basin water density is continuously decreasing due to vertical mixing processes.To increase the knowledge of climatic alterations in the fjord basins, we have investigated how the environment is altered through warming, increased stratification and reduced water exchange resulting in less frequent re-oxygenation of the deep fjord basins in the last 50 years.This knowledge is essential for studying variability in and the potential changes to these ecosystems, and to evaluate the sustainability of aquaculture activity in sill fjords to obtain a predictable environmentally sustainable production that is demanded. Fjord basin exchange episodes was recognised in time series of salinity and oxygen from the historical fjord surveys containing observations of temperature, salinity, oxygen and more from 139 stations, in 32 fjords from south to north from the time period 1975 – 1997. The temperature in the upper 200 m has increased in the latter 30 years at all stations, with the increase largest close to the surface at the southern stations. During the last 30 years, the density at 20 m depth at Utsira has decreased one sigma unit, increasing the stability of the water column. It is likely that the increased stratification at the coast will impact the fjord basin exchange rate in sill fjords.