Kurzzeit-Änderungen des Dänemarkstraßen-Überstromes

• Main Author: Baumann, Till
• Format: Thesis
• Language: German
• Published: 2012
• Subjects: Faroe Bank; Greenland; Norwegian Sea; Denmark Strait; Greenland-Scotland Ridge; Iceland; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/16565/; https://oceanrep.geomar.de/id/eprint/16565/1/BA_Till_Baumann.pdf

Within the meridional overturning circulation, the water-masses produced in the northern seas (Greenland-, Iceland- and Norwegian Sea) head towards the south. On their way, they have to pass the Greenland-Scotland-Ridge. There are only two narrow passes that allow the water masses to cross the ridge: the Denmark Strait between Greenland and Iceland, and the Faroe-Bank-Channel. In this work the Denmark Strait is focused, but the principal phenomenon is the same in the Faroe-Bank-Channel. When the water-masses cross the sill, they form a plume that, basically obeying the geostrophic constrains, descends the slope following the topography. During this descent, strong mixing occurs and the entrainment of the ambient water almost doubles the downslope transport. Because of this, the Denmark Strait Overflow combined with the similar developed Faroe-Bank-Channel Overflow, constitute an important amount of Water to the new-built NADW (North Atlantic Deep Water). In 2011, about 170 km downstream the sill, high resolution measurements of the plume region were taken, while the ship remained stationary for about fourteen hours. These datas provide an interesting insight into the short time variation of the overflow plume. In this dataset, it is seen, that the plume comes to an near extinction within only 10 to 11 hours. This scale of variability is much shorter than the scales that are common mentioned in the literature (typically a few days). Unfortunately, the Ozmidovscales, that describe the length of the occurring turbulences, are smaller than the resolution provided by the data. Analyzing the Richardson number (or its reciprocal, the Froude number), it seems, that the processes of mixing and entrainment barely depend on the plume height. This leads to the assumption, that, on the scale the data can resolute, mixing through mesoscale eddies exceeds the turbulent mixing through Kelvin-Helmholtz-Instabilities.