Dynamics of structural and functional characteristics of zooplankton in the Northern Sea of Okhotsk in the “Warm” and “Cold” years

An analysis of the structural and functional characteristics of zooplankton community and their coupling with the synoptic situation was carried out for the spring period in the northern Sea of Okhotsk. The years of 2000 and 2001 may be referred to as “cold” type due to the significant extent of the ice-covered area. Based on the ice cover extent, the years of 2004 and 2005 may be referred to as “warm” years due to the decreased extent of the ice-covered area. The “cold” and “warm” years did not significantly differ from each other in terms of the total zooplankton biomass. In the northeast Sea of Okhotsk, the zooplankton abundance increased during the “cold” years, while, in its northwestern part, the zooplankton abundance increased during the “warm” years. The different types of years significantly differ in the species structure of the macrozooplankton community. The abundance of copepods was higher in the “warm” years, whereas the chaetognath abundance increased in the “cold” ones. These features of the dynamics and distribution of zooplankton in the northern part of the Sea of Okhotsk also affected its productivity. The higher production of the elements of the zooplankton community that was revealed in the “warm” years was caused by the increase in the seasonal P/B ratio of both nonpredatory and predatory species. In the “warm” years, the production of nonpredatory zooplankton was higher in the northwest, while, in the “cold” years, it was higher in the northeast of the area.     

Enhanced concentrations of dissolved gaseous mercury in the surface waters of the Arctic Ocean

During an almost three months long expedition in the Arctic Ocean, the Beringia 2005, dissolved gaseous mercury (DGM) was measured continuously in the surface water. The DGM concentration was measured using an equilibrium system, i.e. the DGM in the water phase equilibrated with a stream of gas and the gas was thereafter analysed with respect to its mercury content. The DGM concentrations were calculated using the following equation, DGM = Hg_eq / k_H' where Hg_eq is the equilibrated concentration of elemental mercury in the gas phase and k_H' is the dimensionless Henry's law constant at desired temperature and salinity. During the expedition several features were observed. For example, enhanced DGM concentration was measured underneath the ice which may indicate that the sea ice acted as a barrier for evasion of mercury from the Arctic Ocean to the atmosphere. Furthermore, elevated DGM concentrations were observed in water that might have originated from river discharge. The gas-exchange of mercury between the ocean and the atmosphere was calculated in the open water and both deposition and evasion were observed. The measurements showed significantly enhanced DGM concentrations, compared to more southern latitudes.     

Statistical analysis and forecasts of long-term sandbank evolution at Great Yarmouth, UK

A data-driven model has been developed to analyse the long-term evolution of a sandbank system and to make ensemble predictions in a period of 8 years. The method uses a combination of empirical orthogonal function (EOF) analysis, (to define spatial and temporal patterns of variability), jack-knife resampling, (to generate an ensemble of EOFs), a causal auto-regression technique, (to extrapolate the temporal eigenfunctions), and straightforward statistical analysis of the resulting ensemble of predictions to determine a ‘forecast’ and associated uncertainty. The methodology has been applied to a very demanding site which includes a curved shoreline and a group of mobile nearshore sandbanks. The site is on the eastern coast of the UK and includes the Great Yarmouth sandbanks and neighbouring shoreline. A sequence of 33 high quality historical survey charts reaching back to 1848 have been used to analyse the patterns and to predict morphological evolution of the sandbank system. The forecasts demonstrate an improved skill relative to an assumption of persistence, but suffer in locations where there are propagating features in the morphology that are not well-described by EOFs.     

Pteropods in Southern Ocean ecosystems

To date, little research has been carried out on pelagic gastropod molluscs (pteropods) in Southern Ocean ecosystems. However, recent predictions are that, due to acidification resulting from a business as usual approach to CO₂ emissions (IS92a), Southern Ocean surface waters may begin to become uninhabitable for aragonite shelled thecosome pteropods by 2050. To gain insight into the potential impact that this would have on Southern Ocean ecosystems, we have here synthesized available data on pteropod distributions and densities, assessed current knowledge of pteropod ecology, and highlighted knowledge gaps and directions for future research on this zooplankton group.Six species of pteropod are typical of the Southern Ocean south of the Sub-Tropical Convergence, including the four Thecosomes Limacina helicina antarctica, Limacina retroversa australis, Clio pyramidata, and Clio piatkowskii, and two Gymnosomes Clione limacina antarctica and Spongiobranchaea australis. Limacina retroversa australis dominated pteropod densities north of the Polar Front (PF), averaging 60 ind m⁻³ (max = 800 ind m⁻³) and 11% of total zooplankton at the Prince Edward Islands. South of the PF L. helicina antarctica predominated, averaging 165 ind m⁻³ (max = 2681 ind m⁻³) and up to >35% of total zooplankton at South Georgia, and up to 1397 ind m⁻³ and 63% of total zooplankton in the Ross Sea. Combined pteropods contributed <5% to total zooplankton in the Lazarev Sea, but 15% (max = 93%) to macrozooplankton in the East Antarctic. In addition to regional density distributions we have synthesized data on vertical distributions, seasonal cycles, and inter-annual density variation.Trophically, gymnosome are specialist predators on thecosomes, while thecosomes are considered predominantly herbivorous, capturing food with a mucous web. The ingestion rates of L. retroversa australis are in the upper range for sub-Antarctic mesozooplankton (31.2-4196.9 ng pig ind⁻¹ d⁻¹), while those of L. helicina antarctica and C. pyramidata are in the upper range for all Southern Ocean zooplankton, in the latter species reaching 27,757 ng pig ind⁻¹ d⁻¹ and >40% of community grazing impact. Further research is required to quantify diet selectivity, the effect of phytoplankton composition on growth and reproductive success, and the role of carnivory in thecosomes.Life histories are a significant knowledge gap for Southern Ocean pteropods, a single study having been completed for L. retroversa australis, making population studies a priority for this group. Pteropods appear to be important in biogeochemical cycling, thecosome shells contributing >50% to carbonate flux in the deep ocean south of the PF. Pteropods may also contribute significantly to organic carbon flux through the production of fast sinking faecal pellets and mucous flocs, and rapid sinking of dead animals ballasted by their aragonite shells. Quantification of these contributions requires data on mucous web production rates, egestion rates, assimilation efficiencies, metabolic rates, and faecal pellet morphology for application to sediment trap studies.Based on the available data, pteropods are regionally significant components of the Southern Ocean pelagic ecosystem. However, there is an urgent need for focused research on this group in order to quantify how a decline in pteropod densities may impact on Southern Ocean ecosystems.     

The fate of terrestrial organic matter in two Scottish sea lochs

Sea lochs are zones of rapid organic matter (OM) turnover. Most of this OM is of allochthonous origin, being introduced into the lochs via freshwater input. In this study the behaviour of terrestrially derived OM was elucidated using a combination of parameters which indicate OM diagenesis in the near surface sediments from two Scottish sea lochs, Loch Creran and Loch Etive. Alkaline CuO oxidation was used to determine lignin phenols which serve as biomarkers for terrestrial OM in sediments. Stable carbon isotope, total carbon and nitrogen and total OM (including the labile and refractory fractions) compositions were also determined.     

Isotopic,trace element and nutrient characterization of coastal waters from Ubatuba inner shelf area,south-eastern Brazil

Stable isotopes, tritium, radium isotopes, radon, trace elements and nutrients data were collected during two sampling campaigns in the Ubatuba coastal area (south-eastern Brazil) with the aim of investigating submarine groundwater discharge (SGD) in the region. The isotopic composition (δD, δ¹⁸O, ³H) of submarine waters was characterised by significant variability and heavy isotope enrichment. The stable isotopes and tritium data showed good separation of groundwater and seawater groups. The contribution of groundwater in submarine waters varied from a few % to 17%. Spatial distribution of ²²²Rn activity concentration in surface seawater revealed changes between 50 and 200 Bq m⁻³ which were in opposite relationship with observed salinities. Time series measurements of ²²²Rn activity concentration in Flamengo Bay (from 1 to 5 kBq m⁻³), obtained by in situ underwater gamma-spectrometry showed a negative correlation between the ²²²Rn activity concentration and tide/salinity. This may be caused by sea level changes as tide effects induce variations of hydraulic gradients, which increase ²²²Rn concentration during lower sea level, and opposite, during high tides where the ²²²Rn activity concentration is smaller. The estimated SGD fluxes varied during 22–26 November between 8 and 40 cm d⁻¹, with an average value of 21 cm d⁻¹ (the unit is cm³/cm² per day). The radium isotopes and nutrient data showed scattered distributions with offshore distance and salinity, which implies that in a complex coast with many small bays and islands, the area has been influenced by local currents and groundwater–seawater mixing. SGD in the Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater), which claims for potential environmental concern with implications on the management of freshwater resources in the region.     

The onset of fish colonization in a coastal defence structure (Chioggia,Northern Adriatic Sea)

Coastal defence structures constitute the most extensive hard substrates of the Northwestern Adriatic Sea and are known to sustain rich benthic and nektonic communities. To appreciate the pattern of colonization, we studied the fish assemblage of a recently deployed breakwater. We compared observations from two years, the different sides (landward and seaward) of the barrier, and the two fringes, characterized by timing of work completion. The results indicate that colonization, still in process, follows different patterns among species. Benthic and necto-benthic species presented a striking increase in abundance and richness in the second year of colonization, while more mobile species did not evince any variation between years. Differences in mobility among species suggest that the latter group may have reached the breakwater from nearby artificial substrates, whereas the former colonized the new structure as recruits. In addition, fish assemblages differed between the two sides, likely due to variation in the environmental characteristics, and according to depth, reflecting species preferences.     

Lagrangian measurements and modelling of fluid advection in the inner surf and swash zones

New laboratory and field data are presented on fluid advection into the swash zone. The data illustrate the region of the inner surf zone from which sediment can be directly advected into the swash zone during a single uprush, which is termed the advection length. Experiments were conducted by particle tracking in a Lagrangian reference frame, and were performed for monochromatic breaking waves, solitary bores, non-breaking solitary waves and field conditions. The advection length is normalised by the run-up length to give an advection ratio, A, and different advection ratios are identified on the basis of the experimental data. The data show that fluid enters the swash zone from a region of the inner surf zone that can extend a distance seaward of the bore collapse location that is approximately equal to half of the run-up length. This region is about eight times wider than the region predicted by the classical swash solution of Shen and Meyer [Shen, M.C., Meyer, R.E., 1963. Climb of a bore on a beach. Part 3. Runup. Journal of Fluid Mechanics 16, 113–125], as illustrated by Pritchard and Hogg [Pritchard, D., Hogg, A.J., 2005. On the transport of suspended sediment by a swash event on a plane beach. Coastal Engineering 52, 1–23]. Measured advection ratios for periodic waves show no significant trend with Iribarren number, consistent with self-similarity in typical swash flows. The data are compared to recent characteristic solutions of the non-linear shallow water wave (NLSW) equations and both finite difference and finite volume solutions of the NLSW equations.     

ATON型Hall推力器缓冲区预电离问题研究

ATON是20世纪90年代新提出的一种Hall推力器设计方案,其中的缓冲区是ATON新采用的一种结构.本文对缓冲区的作用进行分析,在此基础上提出了采用附加电源提高缓冲区预电离率的方法.并采用PIC(Particle-in-cell)粒子模拟方法对这种设计方式的等离子体分布进行数值模拟.结果表明,通过增加缓冲区内的附加电压,能够有效地提高缓冲区预电离率.     

Management of the coastal-sea-zone-ecosystem model

We present a model of the processes of development in the ecosystem of the coastal zone of the sea constructed by the method of adaptive balance of causes (ABC-method). The model contains nine variables (phyto- and zooplankton, fish larvae, fishes, oxygen, carbon dioxide, salinity, biogenic elements, and detritus) affected by the solar radiation, surface wind, sea temperature, and river discharge. The equations of the model contain control agents governing the dependences of the elements of the food chain on the vitally important resources and environmental conditions. The scenarios of the processes of development are constructed for the simulated annual courses of external actions. The possibility of management of fish resources by regulating the flows of biogenic elements and detritus with river discharge is discussed. A mechanism of management based on the monitoring of the concentration of dissolved oxygen in seawater is proposed. The numerical experiments show that the ABC-model of the processes of development in the ecosystem of the coastal zone of the sea makes it possible to simulate the scenarios of regulation of the flows of biogenic elements and detritus into the sea with an aim of preservation of of fish resources. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 36–49, January–February, 2009.