One may assume that the find more vertical clines separating the water masses and nutrient pools make a major contribution as sources of ‘foreign’ water upwelled to the surface layer. Nevertheless, the exact contribution of the different layers in the water column to the transport of nutrients is hard to detect from direct measurements, but this is possible from model- based estimates. In topographically asymmetrical regions, like the Gulf of Finland, one may assume a different contribution at different shores under upwelling-favourable wind conditions with the same magnitude. The objective of this paper was to study and estimate the nutrient transport from different depths to the surface

layer during coastal upwelling events along opposite coasts of an elongated basin such as the Gulf of Finland. For this purpose we used a series of numerical experiments in which the initial tracer (simulating short-term nutrient behaviour) source is put at different depths for each experiment. The results of the experiments are summarized as time and depth maps of cumulative nutrient mass transported to the upper layer from a layer of unit

thickness at a certain depth in the Gulf of Finland. We applied the Princeton Ocean Model (POM), which is a primitive equation, Epigenetics inhibitor σ-coordinate, free surface, hydrostatic model with a 2.5 moment turbulence closure sub-model embedded ( Mellor & Yamada 1982, Blumberg & Mellor 1983, 1987). The model domain included the whole Baltic Sea closed at the Danish Straits. The digital topography of the sea bottom was taken from Seifert et al. (2001). We used a horizontal resolution of 0.5 nautical miles within the Gulf of Finland and 2 nautical miles in the rest of the Baltic Sea ( Figure 1); in the vertical direction we used 41 equally spaced σ-layers, which in the Gulf gave the lowest vertical resolution of Δz = 3 m at a Ureohydrolase point of depth 120 m. A model resolution of 0.5 nautical miles allows good resolution of mesoscale phenomena,

including upwelling filaments/squirts ( Zhurbas et al. 2008) controlled by the internal baroclinic Rossby radius, which in the Gulf of Finland varies within 2–5 km ( Alenius et al. 2003). We chose the simulation period from 20 to 29 July 1999, which represents an intensive upwelling event along the northern coast and is well covered by high-resolution observations including CTD, biological and chemical measurements along with the SST from satellite imagery (Vahtera et al. 2005). Atmospheric forcing (wind stress and heat flux components) for the simulation period was calculated from a meteorological data set of the Swedish Meteorological and Hydrological Institute (SMHI). The 10 m wind components were calculated from the SMHI geostrophic wind vectors by turning the latter 15° counterclockwise and multiplying by a factor of 0.6. The components and other meteorological parameters obtained were afterwards interpolated in space from the 1° resolution to our 2 and 0.5 nautical mile model grid.