Determining the age of water and long-term transport timescale of the Chesapeake Bay

The concept of age of water (AW) is applied to the Chesapeake Bay to investigate the long-term transport properties for dissolved substances. A real-time calibrated hydrodynamic Chesapeake Bay model in 3 Dimensions (CH3D), employing a boundary-fitted curvilinear grid, is used for the study. The long-term transport properties, represented by AW, are investigated under the conditions of low river inflow of 1995 and high river inflow of 1996, as well as for constant mean inflows. The influences of freshwater, density-induced circulation, and wind-induced transport on age distribution have been investigated. Model results show that river inflows, wind stress, and density-induced circulation play important roles in controlling the long-term transport in the Bay. The model results shows that it requires 120–300 days for a marked change in the characteristics of the pollutant source discharged into the Bay from the Susquehanna River to affect significantly the conditions near the mouth under different hydrodynamic conditions. An increase of river discharge results in increases of downstream residual current and gravitational circulation, and thus reduces AW. The density-induced circulation contributes to the transport substantially. The dissolved substances discharged into the Bay are transported out of the Bay more rapidly when the estuary becomes more stratified. Southeasterly and southwesterly winds have strong impacts on the transport compared to the northeasterly and northwesterly winds. The former increases lateral and vertical mixing significantly. Consequently, the gravitational circulation is reduced and the transport time is increased by 50%. The model results provide useful information for understanding the long-term transport processes in the Bay.     

Population dynamics of Callichirus major (Say, 1818) (Crustacea, Thalassinidea) on a beach in northeastern Brazil

We describe the structure, reproductive cycle, fecundity, growth, and mortality of a harvested population of the ghost shrimp Callichirus major. Samples were collected at monthly intervals from September 1999 to October 2000 on an urban sandy beach (08°11′S 34°55′W) in northeastern Brazil. During this period the sex ratio did not differ significantly from 1:1 (0.98 M: 1 F). Minimum and maximum sizes of the Dorsal Oval were 2.59 and 12.19 mm for males and 4.46 and 12.62 mm for females, respectively. Ovigerous females were found throughout the period, except between August and September 2000. Maximum lifespan was estimated as 3.3 and 3.4 years for females and males, respectively. This northeastern population differed from others previously studied in southern and southeastern Brazil, in regard to sex ratio, maximum attained size, maturation size, period and duration of the reproductive cycle, and fecundity. We interpret these regional differences as evidence for over-fishing at the study site, and suggest that large-scale management plans for callianassid populations should use regional population parameters.     

Estimation of changes in characteristics of the climate and carbon cycle in the 21st century accounting for the uncertainty of terrestrial biota parameter values

ensemble simulations with the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS) climate model (CM) for the 21st century are analyzed taking into account anthropogenic forcings in accordance with the Special Report on Emission Scenarios (SRES) A2, A1B, and B1, whereas agricultural land areas were assumed to change in accordance with the Land Use Harmonization project scenarios. Different realizations within these ensemble experiments were constructed by varying two governing parameters of the terrestrial carbon cycle. The ensemble simulations were analyzed with the use of Bayesian statistics, which makes it possible to suppress the influence of unrealistic members of these experiments on their results. It is established that, for global values of the main characteristics of the terrestrial carbon cycle, the SRES scenarios used do not differ statistically from each other, so within the framework of the model, the primary productivity of terrestrial vegetation will increase in the 21st century from 74 ± 1 to 102 ± 13 PgC yr⁻¹ and the carbon storage in terrestrial vegetation will increase from 511 ± 8 to 611 ± 8 PgC (here and below, we indicate the mean ± standard deviations). The mutual compensation of changes in the soil carbon stock in different regions will make global changes in the soil carbon storage in the 21st century statistically insignificant. The global CO₂ uptake by terrestrial ecosystems will increase in the first half of the 21st century, whereupon it will decrease. The uncertainty interval of this variable in the middle (end) of the 21st century will be from 1.3 to 3.4 PgC yr⁻¹ (from 0.3 to 3.1 PgC yr⁻¹). In most regions, an increase in the net productivity of terrestrial vegetation (especially outside the tropics), the accumulation of carbon in this vegetation, and changes in the amount of soil carbon stock (with the total carbon accumulation in soils of the tropics and subtropics and the regions of both accumulation and loss of soil carbon at higher latitudes) will be robust within the ensemble in the 21st century, as will the CO₂ uptake from the atmosphere only by terrestrial ecosystems located at extratropical latitudes of Eurasia, first and foremost by the Siberian taiga. However, substantial differences in anthropogenic emissions between the SRES scenarios in the 21st century lead to statistically significant differences between these scenarios in the carbon dioxide uptake by the ocean, the carbon dioxide content in the atmosphere, and changes in the surface air temperature. In particular, according to the SRES A2 (A1B, B1) scenario, in 2071–2100 the carbon flux from the atmosphere to the ocean will be 10.6 ± 0.6 PgC yr⁻¹ (8.3 ± 0.5, 5.6 ± 0.3 PgC yr⁻¹), and the carbon dioxide concentration in the atmosphere will reach 773 ± 28 ppmv (662 ± 24, 534 ± 16 ppmv) by 2100. The annual mean warming in 2071–2100 relatively to 1961–1990 will be 3.19 ± 0.09 K (2.52 ± 0.08, 1.84 ± 0.06 K).     

Far fields of internal gravity waves from oscillating sources of disturbances

We considered the problem dealing with the far field of internal gravity waves generated by the source oscillating in the vertical. It is shown that, at a fixed observation point, we first record the arrival of the main wave front of a separate mode followed by the arrival of two fronts of an additional field of this wave mode, which is caused by the oscillations of the source, the asymptotics near the additional wave front being expressed via Airy function.     

Deep-sea suprabenthos assemblages (Crustacea) off the Balearic Islands (western Mediterranean): Mesoscale variability in diversity and production

The composition of suprabenthic crustacean assemblages, their diversity, production (P) and production/biomass (P/B) ratios, were analyzed at species level along two transects situated to the north (N) and south (S) of Mallorca (Balearic Islands, western Mediterranean) at depths between 134 m and 760 m, based on a ca. bi-monthly sampling performed between August 2003 and June 2004. Differences with depth and season in assemblage composition and diversity were analyzed as a function of the contrasting environmental features (e.g. water mass dynamics) of the two areas. We identified 187 species (18 decapods, 5 euphausiids, 16 mysids, 76 gammaridean amphipods, 13 hyperiids, 1 caprellid, 21 isopods and 37 cumaceans). Substantial mesoscale variability in the deep-sea suprabenthic assemblages coupled with diversity trends between the N and S transects were found. Seasonality was the most important gradient influencing the dynamics of suprabenthos over the upper (350 m) and middle (650–750 m) slope in the N area. Conversely, the S area appeared to be more stable temporally with depth as the main gradient inducing assemblage differences. Different depth-related patterns were observed both for diversity and P/B. To the north diversity was very low at the shelf-break, increasing on the upper-slope (H′ > 3.00) and then decreasing again on the middle-slope. To the south diversity increased smoothly downward, reaching the highest values on the middle-slope. Regarding productivity, P/B was highest at intermediate depths to the north (over ca. 450–500 m), while to the south highest P/Bs were found deeper (over ca. 600–650 m). The higher P/B at intermediate depths found along N are likely due to higher % of organic matter (OM) in sediments, a product of oceanographic frontal systems. In particular, P/B was higher along N among omnivores and detritus feeders (e.g. Andaniexis mimonectes, Lepechinella manco and combined cumaceans), coupled to enriched OM in sediments, while along S mesoplanktonic carnivores (Rhachotropis spp.) had higher P/Bs. We conclude that on the north slope the influence of frontal systems and more active flow dynamics of different water masses (WIW and LIW) increases natural disturbance in the area, increasing productivity and diversity of suprabenthic peracarids in the Benthic Boundary Layer. Also, species showed a displacement of their average distributions (their Centres of Gravity, CoG) to shallower depths along N, which is another indicator of more favorable habitat conditions for suprabenthos in the 400–500 m range at N.     

Development of the summer breeze circulation in the west part of the Black Sea

On the basis of the results of regional reanalysis of the atmospheric circulation presented with a resolution of 9 km, the process of formation of breezes is studied for the case of weak synoptic background activity in the rectilinear part of the west coast of the Black Sea for the period 01–04.07.2007. It is shown that the gravitational currents, breeze fronts, and intense internal waves are formed under these conditions in the troposphere during the daytime. The Hovm?ller diagrams of the wind velocity and the maps of the vertical sections of potential temperature, vertical velocity of the air masses, and other parameters are presented. On the basis of these diagrams and maps, we obtain quantitative estimates of the wind velocity in the breeze and of the velocity of propagation of the breeze front and compare these estimates with the available literature data.     

Information-and-measuring drifter system for the monitoring of currents in the coastal zone of the sea

The autonomous drifting buoys equipped with satellite link turn into one of the most important components of the global system of operative observations of the ocean and the surface layer of the atmosphere. However, on the regional level, the problem of analysis of the surface circulation of waters in the coastal zone and sea straits remains quite urgent because the available drifters cannot be used in this case due to their sizes and long intervals between measurements. We present the results of development and testing of a new drifter system aimed at measuring currents. The system is based on the use of buoys operating at depths less than 1 m. To improve the space-and-time resolution of measurements, the buoys are equipped with receivers of the global positioning system (GPS) and GSM modems for the data transfer via cellular communication networks. The drifter system guarantees the possibility of determination of the coordinates of buoys with a resolution of 3 min in time and 14 m in space. We describe the specific features of the design of the proposed information-and-measuring drifter system and present the first results of application of new buoys called “minidrifters” for the pilot monitoring of currents in the Kerch Strait.