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Besøksadresse: Allég. 70
In the present climate, all deep oceans are filled with cold water originating at high latitudes. Cooling and salinification through freezing and brine rejection in polar regions produce cold, dense water masses that sinks and eventually flow equatorward at depth. Meanwhile, light and warm surface water flows poleward, cloosing the (much simplified) loop that is commonly referred to as the thermohaline circulation (THC). The THC transports heat poleward, and has a central role in climate. Dense water "spilling over" from one ocean basin to another, will flow out along the continental slope as a dense plume. These overflow sites are regions of major water mass transformation, since lighter, ambient water is entrained into the plume, and important links in the THC. Despite their importance, much of the internal physics and dynamics of these flows are unknown. An understanding of overflows, plumes, and the related processes is an necessity if one seeks to understand and predict our changing climate.
In my work, I combine in situ observations with laboratory experiments and numerical models to explore e.g. mesoscale variability, secondary circulation, topographic steering, turbulence and mixing.
Faroe Bank Channel Overflow; The Faroe Bank Channel (840m) is the deepest connection between the Nordic Seas in the north and the Atlantic in the south. One third of the southflowing water passes through the channel. Energetic eddies or waves with a period of 3-5 days are observed in the plume downstream of the sill, effecting mixing and downslope transport, and in the channel secondary circulation influences the flow. In the project FAROE BANK CHANNEL OVERFLOW - DYNAMICS AND MIXING, we will deploy moorings and do an extensive fieldstudy combining traditional CTD and LADCP profiling with turbulence measurements and gliders to address questions on eddy generation, mixing and the role of secondary circulation.
Filchner Overflow, Antarctica; The Filchner Overflow was detected in 1977, when hydrographic sections from the continental slope in the southwestern Weddell Sea revealed a plume of dense, supercooled water emerging from the Filchner depression. The plume consists of Ice Shelf Water (ISW) originating from the Filchner-Ronne Ice Shelf cavity, where it has been cooled from contact with glacial ice at great depth. On the continental slope, the ISW mixes with the ambient water to form Weddell Sea Bottom Water and evenually Antarctic Bottom Water (AABW). AABW occupies a major part of the deep ocean. In my PhD, I analysed data from current meter moorings in the outflow region. We focussed on small-scale variability, and revealed oscillations in the velocity and temperature records with periods of 1.5, 3 and 6 days, that existent theories are unable to explain. We also synthesised all available CTD-data. In the current project WEDDELL we are returning to the Filchner overflow, to deploy new moorings and collect turbulence data.
Topographic Steering; Due to the earth'r rotation (the Coriolis force), dense plumes will tend to flow along the slope in geostrophic balance. Canyons - and as shown in my PhD-thesis - also ridges cross-cutting the slope, may break this balance and steer plume water down the slope. In my PhD I applied an analytical model to describe the dynamics of these flows, and I further explored flow in canyons/along ridges in laboratory experiments, which I performed at the Geophysical Fluid Dynamics Laboratory, University of Washington and at the rotating Coriolis platform in Grenoble, France.
Darelius, E., I.Fer and D. Quadfasel (2011), ”Faroe Bank Channel Overflow: Meso-scale variability”, Journal of Physical Oceanography, Vol 41(11), p. 2137-2154.
Darelius, E., L.H. Smedsud, S. Østerhus, A.Foldvik and T. Gammelsrød (2009), ”On the structure and variability of the Filchner Overflow Plume”, Tellus A , Vol 63(3), p. 446-464Darelius, E. (2008) “Topographic steering of dense overflows: Laboratory experiments with V-shaped ridges and canyons”, Deep Sea Research I, doi: 10.1016/j.dsr.2008.04.008
Wåhlin, A.K., E. Darelius, C. Cenedese and G. Lane-Serff (2008) “Mixing in density currents induced by submarine canyons and ridges”, Deep Sea Research I, doi:10.1016/j.dsr.2008.02.007
Darelius, E and A.K. Wåhlin (2007) “Downward flow of dense water leaning on a submarine ridge” Deep Sea Research I, Vol 54 (7), p. 1173-1188
GEOF335: Polar oceanography
FAROE BANK CHANNEL OVERFLOW: DYNAMICS AND MIXING