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Content available remote Unusual Baltic inflow activity in 2002-2003 and varying deep-water properties
The unusual sequence of inflow events into the Baltic Sea that occurred in 2002 and 2003 includes the first ever important baroclinic inflow to be described (August 2002), the Major Baltic Inflow (January 2003), which gave rise to the highest oxygen levels in the Gotland Deep since the 1930s, and the baroclinic inflow (August 2003) that elevated the Gotland Basin deep water salinity to values last observed in 1977, and caused the surface salinity to rise again. From these trend changes, salt residence times were estimated at about 20 years in the deep waters and 30 years above the pycnocline. Ventilation of the remote Karlsö Deep took until 2005, two years after the inflow event responsible, at a time when the Bornholm and Eastern Gotland Basins were already returning to stagnation.
Content available remote Temporal and spatial evolution of the Baltic deep water renewal in spring 2003
In January 2003, a deep-water renewal process in the Baltic Sea commenced with an inflow of about 200 km3 of cold and well oxygenated water from the Kattegat, half of which was of salinity >17 PSU; it is considered to be the most important inflow since 1993. Related front propagation and the ventilation of anoxic waters between the western and the central Baltic were recorded by the Darss Sill measuring mast, the Arkona Basin buoy, a subsurface mooring in the Eastern Gotland Basin, and hydrographic research cruises conducted in January, February, March, May and August 2003. Already in May, the central Gotland Basin was reached by water with near-bottom oxygen concentrations among the highest ever recorded there. A comprehensive review of the observed spatial and temporal structures together with additional background data is presented. Estimates of the intensity of the present inflow are discussed.
The paper describes the hydrographic-hydrochemical development in the eastern Gotland Basin between the major saltwater inflows into the Baltic Sea in 1993 and 2003. This period is characterised by only low inflow activity. The most important hydrographic events were the effects of the very strong inflow in 1993 and the weak inflows in 1993/1994 and 1997. The 1993/1994 inflows led to deep-water renewal, a steep fall in deep-water temperatures, and increasing salinity. The effects of the inflow of very warm, saline and oxygen-rich water in autumn 1997 were observed in the deep water in 1998, resulting in temperatures rising to 7°C. The recent renewal in spring 2003 is reflected in the decreasing temperature, higher salinity and improved ventilation of the bottom water. Changes in the redox conditions exert a considerable influence on the nutrient distribution. During stagnation periods, there is enrichment of phosphate and ammonium, while nitrate is absent. Thus, around 31 žmol l-1 ammonium and 7 žmol l-1 phosphate were measured prior to the water renewal in 2003. Deep-water ventilation results in lower phosphate concentrations of around 2 žmol l-1, the nitrification of ammonium and the occurrence of nitrate. For the observation period, an estimate of nutrients stored in the deep water was done for the eastern Gotland Basin. During the recent stagnation period, there was an increase of up to 150% in the phosphate pool below the halocline, whereas the pool of inorganic nitrogen compounds decreased to 80% compared with 1992 when the previous stagnation period had ended. Under specific circumstances, these unbalanced nutrients can be made available to the upper water layers and can induce large-scale blooms of algae, especially of cyanobacteria.
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