http://hdl.handle.net/1956/1023 Search the Channel search http://bora.uib.no/simple-search http://hdl.handle.net/1956/2393 Title: On the Nordic Seas’ role in the Atlantic Meridional Overturning Circulation <br/> <br/>Authors: Iovino, Doroteaciro <br/> <br/>Abstract: In the present climate, the North Atlantic thermohaline circulation (THC) plays a fundamental role in the global transport of heat at high latitudes. The response of the North Atlantic Ocean-Nordic Seas THC to surface forcing and basin geometries in an idealized one-hemisphere basin is analyzed to better understand the processes that are fundamental to the modeled circulation. Focusing on the dynamics of the Nordic Seas, analytical and numerical modeling highlight the relevance of a sill (Greenland-Scotland Ridge) in setting the properties of the water masses formed in and exported from a marginal sea. Finally, the influence of the convective activity in the Greenland Sea for the overflow, and thus the overturning, is assessed using hydrographic data (from 1950 to present), a regional ocean model, and a unique tracer release experiment. Greenland Sea Gyre water is estimated to contribute less than 1 Sv, and there is no evidence for causality between changes in the Greenland Sea and the overflow. http://hdl.handle.net/1956/2176 Title: The Atlantic Water flow along the Vøring Plateau: Detecting frontal structures in oceanic station time series <br/> <br/>Authors: Nilsen, Jan Even Øie; Nilsen, Frank <br/> <br/>Abstract: The topographic steering of the baroclinic western branch of the Norwegian Atlantic Current (NwAC) determines the extent of Atlantic Water and location of the Arctic Front in the Nordic Seas. In this paper the geographical spread of hydrographic measurements at the Ocean Weather Station M (OWSM, 66°N 2°E) is utilised to create mean sections across the Vøring Plateau Escarpment in the Norwegian Sea. In concert with a theoretical framework involving the impact of low pressure systems on frontal jets over steep bathymetry, the behaviour of the front-current system at this location is described. It is shown that the halocline and thermocline are sloped from about 200 m in the west and down to 400 m in the east over 40 km centred on the station, indicating that the western branch of the NwAC is located here. The horizontal gradients introduced by this slope are 2°C and 0.1 for salinity. The frontal slope is not seen to change its inclination on seasonal, multi-annual, nor decadal timescales, indicating that the dynamic control of this frontal slope does not change appreciably. Further supported by the theoretical framework it is shown that the subsurface part of this front and the associated western branch of the NwAC is strongly locked by topography along the Vøring Plateau also on short timescales. From large scale bathymetry it is also shown how this kind of frontal locking can be expected over most of the ridges and continental slopes in the Nordic Seas. http://hdl.handle.net/1956/2116 Title: Change and variation in a hyer-arid cultural landscape: a merhodological approach using remote sensing timeseries (Landsat MSS and TM, 1973-1996) from the Wadi vegetation of the eastern desert of Egypt <br/> <br/>Authors: Andersen, Gidske L. <br/> <br/>Abstract: Nine wadi localities in a hyper-arid environment have been registered in the field and studied using earth observation data. Branch height, crown – and trunk – diameter, and indicators of land-use such as present traces of browsing, lopping and charcoal production were registered for arboreal vegetation, mostly Acacia tortilis and Balanites aegyptiaca. A point mapping (GPS) was selected to optimise subsequent integration with raster data and to facilitate a detailed interpretation of change images. Field data and change images are interpreted according to two gradients, one cultural and one hydrological. Derived tree maps are overlaid referenced TM data in order to detect differences between pixels with and without vegetation. The Red band is the most consistent spectral band in its content of vegetation information. Nevertheless it is apparent that several methodological and technical factors constrain the possibilities to register vegetation in this environment of very scarce vegetation cover. Similar problems are also recognised in the change analysis which is based on the difference between Red bands of the years compared. Four different datasets are part of the analysis: 1973, 1979, 1984 (all Landsat MSS images) and 1996 (TM). Field data indicate that changes are taking place in the cultural landscape of the Eastern Desert, and the change is primarily due to processes that both in causes and consequences is associated with ‘deforestation’. Although several sources of errors introduce variations in the change images, the images do reflect the field observations. http://hdl.handle.net/1956/2115 Title: North Sea circulation: Atlantic inflow and its destination <br/> <br/>Authors: Winther, Nina Gjerde; Johannessen, Johnny A. <br/> <br/>Abstract: This study investigates the Atlantic inflow to the North Sea; its variabil- ity, pathways and destination. Results from a numerical model show that the variability of Atlantic inflow is dependent on the inflow location. The inflow between Orkneys and Shetland and in the Shetland shelf area show a strong connection to the strength in westerly winds in winter and spring on a weekly time scale, while the inflow in the Norwegian Trench has a longer response time to the large scale wind pattern. About 50% of the Atlantic water that enters the North Sea is mixed with fresher water before it leaves the North Sea as the Norwegian Coastal Current. This illustrates the important role of estuarine processes within the North Sea and Skagerrak area, and their interaction with the Atlantic water. http://hdl.handle.net/1956/2106 Title: Passive tracers and active dynamics - a model study of hydrography and circulation in the northern North Atlantic <br/> <br/>Authors: Mauritzen, C.; Hjøllo, S.S.; Sandø, Anne Britt <br/> <br/>Abstract: A long-standing problem in oceanography has been to understand the relationship between what can be measured in the ocean, such as hydrography, and what cannot, such as the strength and structure of the complete Meridional Overturning Circulation (MOC) of the world oceans, commonly considered the main oceanic long-term modifier of Earth’s climate. With the aid of a 50 year simulation from a numerical ice-ocean model we have investigated this relationship in the area of the northernmost extension of the MOC, in the Subpolar and Nordic Seas, on interannual timescales. We find that variability in the northward flux of salt and temperature in this region is controlled almost entirely by the volume flux, confirming that a knowledge of the variability of the circulation strength proper is necessary. The simulated hydrographic anomalies are within the range observed in the 20th century, thus fundamental changes to the circulation were not expected nor found. It is seen that variability in either temperature or salinity does contain some information about the variability in current strength, because hydrography and circulation generally respond to the same atmospheric forcing in the North Atlantic sector. Whether it is temperature or salinity that contains the information is related to the parameter range of the equation of state at the location in question: if density depends primarily on temperature then a salinity anomaly will tend to survive and vice versa. The oceanic response involves hydrographic changes and propagation of these, gyre strength changes, and changes in the MOC. http://hdl.handle.net/1956/2090 Title: Magnitude and Origin of the Anthropogenic CO2 Increase and the 13C Suess Effect in the Nordic Seas since 1981 <br/> <br/>Authors: Olsen, Are; Abdirahman, Omar M.; Bellerby, Richard G. J.; Johannessen, Truls; Ninnemann, U. S.; Brown, Kelly R.; Olsson, K. Anders; Olafsson, Jon; Nondal, Gisle; Kivimäe, Caroline; Kringstad, Solveig; Neill, Craig; Olafsdottir, Solveig <br/> <br/>Abstract: This study evaluates the anthropogenic changes of CO2 (∆Cant) and δ13C (∆δ13Cant) in the Nordic seas, the northern limb of the Atlantic Meridional Overturning Circulation, that took place between 1981 and 2002/03. The changes have been determined by comparing data obtained during the Transient Tracers in the Ocean, North Atlantic Study (TTO-NAS) with data obtained during the Nordic seas surveys of R/V Knorr in 2002 and R/V G.O. Sars in 2003 using an extended multi-linear regression approach. The estimated ∆δ13Cant and ∆Cant and their relationship to each other and to water mass distribution suggest that the Polar Water entering the Nordic seas from the north is undersaturated with respect to the present atmospheric anthropogenic CO2 levels and promotes a local uptake of Cant within the Nordic seas. In contrast, the Atlantic Water entering from the south appears equilibrated. It carries with it anthropogenic carbon which will be sequestered at depth as the water overturns. This pre-equilibration leaves no room for further uptake of Cant in the parts of the Nordic seas dominated by Atlantic Water. The upper ocean pCO2 in these regions appears to have increased at a greater rate than the atmospheric pCO2 over the last two decades; this is reconcilable with a large lateral advective supply of Cant. http://hdl.handle.net/1956/2089 Title: Towards a more saline North Atlantic and a fresher Arctic under global warming <br/> <br/>Authors: Bethke, Ingo; Furevik, Tore; Drange, Helge http://hdl.handle.net/1956/2088 Title: Inception of the Northern European Ice Sheet due to contrasting ocean and <br/> <br/>Authors: Risebrobakken, B.; Dokken, Trond M.; Otterå, Odd Helge; Jansen, E.; Gao, Yongqi; Drange, Helge <br/> <br/>Abstract: About 115,000 years ago the last interglacial reached its terminus and nucleation of new ice sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined with minimum Northern hemisphere insolation, introduced a strong sea-land thermal gradient that together with a strong wintertime latitudinal insolation gradient increased the storminess and moisture transport to the high northern European latitudes, at a time when the Northern hemisphere summer insolation approached its minimum.