Research On Front Features And The Influence Of Deep Water Structure And Deep Circulation On Overflow Of GIN Seas

The variances of climatology in the GIN seas which connect the Arctic Oceanand North Atlantic Ocean, influence the northern hemisphere even the global climate.The spatial distribution and seasonal variations of the main fronts in GIN seas isanalyzed by grid data of monthly mean of temperature and salinity. The suitableapplication methodfor monthly data in frontal study is discussed. As the fronts oftenmoves or swings, the front information in monthly data has been blurred and thefronts obtained by monthly mean temperature and salinity sometimes showsinterrupted front and multi-front phenomena. However, the blurry fronts are just theaveraged status of fronts, which can only be revealed by monthly data. The frontsshow significant diversity in their characteristics and seasonal variations.The EastGreenland Polar Front (EGPF) is mainly a salinity front, being evidentand continuousin summer and weak and interrupted in winter. The EGPF is also a temperature frontin summer. The obvious temperature gradient and uninterrupted shape appeared inSeptember, being attributed to the maximum temperature difference between the EastGreenland Current and the return currents at that time, which keeps the location ofEGPF relatively stationary. The Arctic Front (AF) has a seasonallyspatial variationwith "dumbbell" shape--the seasonal displacement nearthe northern and southernparts of the front is much larger than that in the middle part, showing the largerswinging amplitude there. AF near the Mohn Ridge was addressed as a no-motion part,however, AF by this study is revealed to move northwestward in winter because theflux of Norwegian Current reaches the maximum then and induces thebroadestwidthof the current nearthe Mohn Ridge area. A special characteristic of the Iceland-Faroe Front is that the interface of the front appears more southward andstronger in deep part, which is caused by the overflow above the ridge.The overflow on the Greenland-Scotland Ridge is regarded as main power forthe thermalhaline circulation, origin of which is from deep waters in GIN seas. It isimportant to study deep water masses construction, deep current system and theirimpact on overflow. Grid data of monthly mean of hydrography is used to analyze thecharacteristics of deep waters in the main three basins. Although deep waters in GINseas seem constant, area averaged density below2000m in basins varies greatly. Deepwater formed by cooling and convection in the Greenland basin is the densest whileNorwegian basin is the lightest. Densities in the Greenland, Lofoten and Norwegianbasins are28.440,28.425and28.411respectively. In addition, those in basin below3000m are28.445,28.429and28.411. The averaged densities in basins below1400msimilarly vary and0.2is the difference. The statistical analysis of waters denser than28.38shows volume of waters in Greenland basin is largest, in which waters denserthan28.42are dominant. On the contrary, the Norwegian basin is the lightest and thedominant densities are less than28.41. Volumes of dense waters in the Lofoten basinappear normal distribution with mean value of28.41. Seasonal variance is little whendensity is not less than28.42. Volume variance in the Greenland basin is obvious.Volume anomaly is generally negative in winter as deep water formed by convectionin Greenland basin, while summer is generally positive. In the Lofoten basin, anomalyis larger in the volume dominant densities. No seasonal regulation is found inNorwegian basin. Diagnostic sections and depths of dense waters indicate isopycnalsat variant depths in basins. Deep circulations can be deduced by equations ofgeostrophic current and strongly restricted by topography. Deep circulations arecyclonic as the surface circulation in the Lofoten and Norwegian basins. However,circulation is anticyclonic in Greenland basin, different from surface circulation. It iscirculations that prevent water exchange between basins. There are three gaps on theGreenland-Scotland ridge as main passages for overflow. Faroe Bank Channel, through Faroe-Shetland channel, and overflow. Overflow also occur over ridge insmaller density. Waters of density less than28.40could occur overflow, which lies atdifferent depth in basins. The GIN seas could be generally divided into4layers. Theyare surface circulation layer, overflow layer, deep circulation layer and bottom layer.