Gotland Basin

Pohl, C., Loffler, A., and Hennings, U. (2004) A sediment trap flux for trace metals under seasonal aspects in the stratified Baltic Sea (Gotland Basin 57° 19.20 N 20°03.00/E). Mar. Chem. 84, 143-160. 

Volkov 1. L, Rozanov A. G., and Zhabina N. N. (1983) Sulfur compounds in sediments of the Gotland Basin (Baltic Sea). Lithology and Mineral Resour. 18(6), 584-598. 

In the Baltic Sea, the offshore scale for the transition of topography from the coast to the plain areas of the basins is commonly much larger than the baroclinic Rossby radius. Therefore, CTW can be used to analyze the dispersion and modal structure of sea level variations and quasi-geostrophic currents trapped at the basin rim. Some basins do not have well established plains, therefore, in these basins, the eigenvalue problem must be solved for the whole basin diameter, for example, the Eastern Gotland Basin. The CTW structures of both coasts splice each other in the center of the basin. Hence, CTWs are an effective mechanism for the communication between the rim and the center of the corresponding (e.g., Gotland) basin. 

Dissipation measurements in the Eastern Gotland Basin were performed by Lass et al. (2003) during winter stratification in April 1999 and during summer stratification in September 2000. Dissipation profiles were measured about every 10 min over a time interval of about 9 days. This provided a data set that enabled to estimate quite reliable averaged dissipation profiles given the huge intermittency of dissipation in stratified water, see Fig. 2.8. The dissipation decreases from the surface to a depth of about 50 m. Maximum dissipation is observed in the halocline, while it decreases below the halocline to an absolute... 

FIGURE 2.8 Averaged dissipation of turbulent kinetic energy measured in the Eastern Gotland Basin in April 1999 and September 2000. 

Hagen, E., Feistel, R., 2004. Observations of low-frequency current fluctuations in deep water of the Eastern Gotland Basin/Baltic Sea. Journal of Geophysical Research, 109, C03044, doi 10.1029/ 2003JC002017. 

Zhurbas, V. M., Paka, V. T., 1997. Mesoscale thermohaline variabihty in the Eastern Gotland Basin following the 1993 major Baltic inflow. Journal of Geophysical Research, 102(C9), 20,917-20,926. 

FIGURE 3.1 Monitoring station network of the IfM in 1980 and of the lOW in 2005, the first IfM buoy station in 1964, and the MARNET stations. Lower right comer bathymetric map of the central Eastern Gotland Basin with positions of the central BMP station (271) and moored subsurface strings between 1993 and 2005 used abbreviations and further details are compiled in Table 3.3. 

TABLE 3.3 lOW Current Measurements in the Eastern Gotland Basin between 1993 and 2005 Carried Out by Moored Current Meter Strings... 

Besides MB Is, baroclinic summer inflows of exceptionally warm and saline water affect the deeper layers of the central Baltic Sea (cf. Section 10.5). Such inflows do not fulfill the criteria for MB Is (cf. Section 10.3) but can effectively influence the deep water below the halocline in the Bornholm, Gdansk, and Eastern Gotland Basins (Feistel et al., 2003c, 2004a). 

The salinity of the Bornholm Basin below the permanent halocline is a measure for the estimation of the impact of weak inflows on the central Baltic deep water. During periods of low inflow activity, salinity and thus density decreases in the deep water of the Bornholm Basin. Depending on the volume of saline water and its density, inflows below the MBI magnitude — but sometimes even MBIs — fill up only that basin, and the saline water does not pass to a greater extent the Slupsk Sill downstream through the Slupsk Channel into the Gotland Basin (cf. Fig. 10.2). 

Fonselius (1962) started the detailed description of the effects of MBIs in the central Baltic deep water. He identified MBIs studying long-term variations, mainly of salinity in the Bornholm Basin. Fonselius described the dynamic processes between the Baltic deep basins after MBIs, the importance of the Bornholm Basin as buffer basin, and the overflow of the Eastern Gotland Basin in intermediate depths downstream into the Landsort Deep. 

The MBI in January 2003 and the temporal and spatial evolution of the Baltic deepwater renewal have been investigated in detail by Feistel et al. (2003b). The propagation of the saline and oxygen-rich water into the Baltic Sea and the ventilation of anoxic water between Bomhohn Basin and central Baltic were recorded by the Darss Sill measuring mast, the Arkona Basin buoy, a subsurface mooring in the Eastern Gotland Basin (cf. Chapter 3), and several research cruises. 

The Gotland Basin deep water does not show regular seasonal variations (cf. Matthaus, 1977, 1978), and the effects of MBls can be clearly identified. Three marked stagnation periods occurred during the past century—from 1922 to 1933-1934,1952-1961, and 1977-1992 identified by means of salinity (cf. Fig. 10.12). 

The strongMBI in December 1975/January 1976 (No. 15 in Table 10.2) was the beginning of the most significant stagnation period observed so far, lasting for 16 years in the Eastern Gotland Basin. The salinity decreased to the lowest values on record in the central Baltic deepwater, that is, from 13 psu in April 1977 to about 11 psu in January 1993 in the 200 m... 

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