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International audience; Climate change is rapidly modifying marine fish assemblages in the Arctic. As fish eggs and larvae have a narrower thermal tolerance than nonreproductive adults, their response to increasing temperatures is likely one of the main drivers of these changes. In this study, we described ichthyoplankton assemblages in West Greenland between 62 and 73 °N, during summers 2017–2019, and investigated the relationship between sea surface temperature in the spring and summer and the survival of Arctic cod (Boreogadus saida (Lepechin, 1774)) early life stages over the hatching season. Warm years were associated with partial recruitment failures resulting from thermal stress to the eggs and larvae hatched late in the season. Using past environmental conditions, we forecasted an imminent decline in Arctic cod recruitment in the regions of Uummannaq and Disko Bay. Observations from fjords suggested that glacial meltwater could create a subsurface thermal refuge allowing Arctic cod larvae to survive despite very high summer sea surface temperature (ca. 10 °C). As the Greenland ice sheet is melting at an unprecedented speed, the mechanism underlying the “glacial meltwater summer refuge hypothesis” could curb some of the negative effects of ocean warming on the survival of young Arctic cod in West Greenland and other Arctic fjord systems.

In this thesis is presented mathematical model of stratified 2D flow of viscous incopressible fluid and its program realization. Basic equations of fluid flow in Boussinesq approximation were solved by finite volume method on structured nonortogonal grid. Discretization was done by the principle of semi-discretisation. The space derivative was solved by AUSM me- thod with MUSCL velocity reconstruction. The viscid terms were solved through auxiliary grids. During time discretization artificial compressibility method was used in dual time. The resulting system of ODEs is integrated in time by a suitable Runge-Kutta multistage scheme. Numerical experiments were calculated for flow with Reynolds number equals 1000. Further 3 numerical experiments are presented with different boundary conditions. 1