Points and dates of tagging and recapture of mature cod in the southern Barents Sea in 1937-1955

Barents cod spawn in the Motovsky Bay during the periods of warming in the Arctic when proportion of mature fish in the population is high enough. Cod spawning is most likely to occur in the Motovsky Bay when large cod forage in southeastern waters, and prespawning fish migrate close by the Murmansk coast. Under such conditions cod spawn in the Motovsky Bay, but low water temperature and slow egg drift toward Murmansk coastal waters delay development of cod eggs. As a result the eggs remain at the first stage for a long time; this causes high egg mortality before hatching. Larvae that survive and become pelagic and then bottom juveniles nevertheless have little chance to survive in winter because they are not biologically ready for overwintering. Thus, delay in egg development at the first stage delays subsequent stages of fish ontogeny, and strongly impairs survival of cod juveniles from the Motovsky Bay.

Planktonic foraminifera in Core ML2_66, North Atlantic

Evolution of approaches and methods for reconstruction of paleoenvironmental conditions from microfossils contained in bottom sediments is assessed. Authors elaborated a new actualistic basis for such reconstructions, consisting of a database on contents of tests of planktonic foraminifers in the surface layer of Atlantic sediments and a package of mathematical tools for computer data processing. Structure of the database is described. It contains data on test contents for 29 species and varieties of planktonic foraminifers in 381 samples. A mathematical model designed for reconstructions is based on factor analysis and multidimensional spline interpolation. The model allows one to deduce Quaternary hydrological parameters (paleotemperature, paleosalinity) for standard hydrological levels down to depth of 250 m for the four seasons of the year. Reconstructions are illustrated by an example of a sedimentary core from the North Atlantic representing a period of 300 ky. During the next to last and the last maxima of continental glaciation (oxygen isotope stages 8, 6, 4, and 2), the subarctic water mass was spread here. Winter and summer surface water temperatures comprised 1-5° and 5-7°C, respectively. During interglacials and in Holocene the conditions were close to present ones: winter and summer surface water temperatures comprised 10-12 and 15-17°C, respectively. Vertical paleohydrological profiles compiled for peaks of climatostratigraphic intervals suggest that during cold intervals water stratification was stronger than during the warm ones. At depth 50 m seasonal salinity oscillations did not exceed 0.4 per mil and commonly salinity was minimum in winter and maximum in summer.

Noble gases sampled from three cruises in the eastern tropical Atlantic

Oceanic upwelling velocities are too small to be measured directly. Deviations of the He-3/He-4 ratio in the mixed layer from solubility equilibrium provide an indirect means to infer vertical velocities at the base of the mixed layer. This method is applied to the Mauritanian upwelling region for data from three cruises in summer 2006 and winter 2007 and 2008. Diapycnal mixing coefficients are estimated from microstructure measurements, reaching from 10**-3 m**2/s over the shelf break to 10**-5 m**2/s in the open ocean. The resulting upwelling velocities in the onshore region (upto 50 km from the 50 m isobath) are of the order of 2 x 10**-5 m/s}, in agreement with Ekman theory. Further offshore, in some cases the vertical velocities inferred from the helium isotope disequilibrium exceed the values derived from the wind stress curl by one order of magnitude. The Mauritanian coastal area as part of the Canary Current upwelling system belongs to the most productive ocean regions in the world. Nutrient fluxes into the mixed layer (both advective and diffusive) are equivalent to a net community production of about 1 g C/d, and associated heat fluxes vary between 183 +/- 62 W/m**2 in summer and 97 +/- 25 W/m**2 in winter. Regarding the flux into the mixed layer, the contribution of diffusion and advection are of similar magnitude for both heat and nutrients. The upwelling, however, provides the supply of cold and nutrient rich water from below. The large offshore vertical velocities inferred from the helium method are associated with nutrient fluxes of the same order as for the onshore region, and may be responsible for observed patches of high productivity in that area. The offshore heat fluxes due to upwelling and diapycnal mixing are smaller than 70 W/m**2 for all cruises.