The climatology of polar lows over the Nordic Seas has been investigated using infrared satellite images for the period between 2000 and 2009. The same region was studied in the 1980s using traditional weather charts for the period between 1972 and 1982. One motivation for the present study was to revisit this climatology, but using a different decade and taking advantage of the vastly improved coverage and dissemination of infrared satellite images since the 1980s. The fact that forecasters at the Norwegian Meteorological Institute had introduced a routine to register polar-low events systematically from 2000 and onward also provided a unique opportunity for extending the existing repository of subjectively identified polarlow observations. On average we found 12 polar-low events per year in the region of study. This is more than the earlier investigation, but we believe that this can be explained by the fact that the previous study relied almost uniquely on weather charts with very little information from ocean areas in the Nordic Seas. The largest numbers were found in January with an average of 2.8 polar-low events per year. The study reconfirms the February minimum found in previous studies, but on the basis of our data we could not show that this minimum is statistically significant. It is suggested that this may be explained as a manifestation of the coldest winter month, when a surface-pressure high over the Scandinavian mainland is common and the large-scale atmospheric flow is less favourable to polar-low formation. This hypothesis was tested by calculating the mean sea-level pressure (MSLP) anomaly for January, February and March from an atmospheric reanalysis. This revealed a positive anomaly over Scandinavia and northwest Russia not found in the pressure distributions for January and March.
The Upper Carboniferous deep-water rocks of the Shannon Group were deposited in the extensional Shannon Basin of County Clare in western Ireland and are superbly exposed in sea cliffs along the Shannon estuary. Carboniferous limestone floors the basin, and the basin-fill succession begins with the deep-water Clare Shales. These shales are overlain by various turbidite facies of the Ross Formation (460 m thick). The type of turbidite system, scale of turbidite sandstone bodies and the overall character of the stratigraphic succession make the Ross Formation well suited as an analogue for sand-rich turbidite plays in passive margin basins around the world. The lower 170 m of the Ross Formation contains tabular turbidites with no channels, with an overall tendency to become sandier upwards, although there are no small-scale thickening-or thinning-upward successions. The upper 290 m of the Ross Formation consists of turbidites, commonly arranged in thickening-upward packages, and amalgamated turbidites that form channel fills that are individually up to 10 m thick. A few of the upper Ross channels have an initial lateral accretion phase with interbedded sandstone and mudstone deposits and a subsequent vertical aggradation phase with thickbedded amalgamated turbidites. This paper proposes that, as the channels filled, more and more turbidites spilled further and further overbank. Superb outcrops show that thickening-upward packages developed when channels initially spilled muds and thin-bedded turbidites up to 1 km overbank, followed by thick-bedded amalgamated turbidites that spilled close to the channel margins. The palaeocurrent directions associated with the amalgamated channel fills suggest a low channel sinuosity. Stacks of channels and spillover packages 25-40 m thick may show significant palaeocurrent variability at the same stratigraphic interval but at different locations. This suggests that individual channels and spillover packages were stacked into channel-spillover belts, and that the belts also followed a sinuous pattern. Reservoir elements of the Ross system include tabular turbidites, channel-fill deposits, thickening-upward packages that formed as spillover lobes and, on a larger scale, sinuous channel belts 2AE5-5 km wide. The edges of the belts can be roughly defined where well-packaged spillover deposits pass laterally into muddier, poorly packaged tabular turbidites. The low-sinuosity channel belts are interpreted to pass downstream into unchannellized tabular turbidites, equivalent to lower Ross Formation facies.
The Cretaceous andPalaeogenesuccession inthe NorthSea andNorwegianSea basins show widely variabled eep-waters edimentary systems int erms ofprocesses,f acies,g eometries,scalea ndd istribution. The primary controls on the large-scalevariability arec onsidered to be source area size, basinandb asinm argin physiographyandb athymetry,tectonic history andresultingmorphologyo fd rainage andd elivery systems of sediments to deep-waterareas,andthe rateofsediment delivery. The NorthSea andNorwegianSea basins were comparabled uringthe earliest Cretaceous,b ut thereafterdeveloped inw idely different ways asaresponseto proximity to oncomingNorthAtlantic seafloor spreading.Int he NorthS ea Basin,the Cretaceous andP alaeogeneturbiditesystems werec ontrolled byaninherited structuralt emplatef rom LateJ urassic rifting, andb ys ource area size.Poorly developed or small drainage systems on the Norwegianm arginandthe broad Horda Platform gavelittlesandsupply from the east to the VikingG rabenarea.Sand-rich systems weresourced from arelatively large hinterlanda ndshallow marine staginga rea on the East ShetlandP latform. Northofthe Horda Platform,sandsupply wasabundant inv ery discreteperiods,particularly int he Early Eocene.Int he NorwegianSea basins,the LateJ urassic structuralt emplatec ontrolled Early Cretaceous deep-water sedimentary systems inamannersimilartothe NorthSea Basin. Generallysmall andpoorly developed drainage systems caused development ofmud-rich systems. Incontrast,inthe LateCretaceous,onsetofprecursor tectonic activity to sea-floor spreadingled to increased sandsupply from the west into the VøringB asin. Arelatively narrow palaeoshelfandalarge source area contributed to formingsand-rich systems. Smallerturbiditesystems developed alongthe Norwegianm argin,which weresourced from the east from smallerdrainage areas,a nd partially across broad shelves,such ast he Trøndelag Platform. Bothi nt he Cretaceous andP alaeogene, the sandiest systems aref oundonly to the southandthe northofthe inherited structuralfeatures.
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