Restoration of mean monthly thermohaline fields in Tatar Strait

Statistical modeling and GIS “Sakhalin Shelf” are used to restore the annual variations of water temperature and salinity at standard oceanographic stations in Tatar Strait, where observation series are about 45 years long. Numerical modeling techniques with the help of Bergen University model are used to restore the spatial fields of water temperature and salinity. Analysis of calculation results made it possible to identify new features of the hydrological regime in the strait, in particular, during winter, for which no generalizations have been made before.     

Specific features of water circulation and biogenic substance transformation and transport in Tatar Strait (Sea of Japan): Assessment based on the results of mathematical modeling

This study has no analogues in terms of methodology, as it uses three electronic instruments for studying the oceanographic regime of Tatar Strait. GIS “Sakhalin Shelf” was used to reconstruct annual variations in hydrological and hydrochemical characteristics of the marine environment at standard horizons of oceanographic stations in fixed geographic coordinates. An adapted version of the Oceanic Model created in Bergen University was used to reconstruct the spatial and temporal distribution of seawater temperature and salinity, to calculate the density and the circulation rate of water masses and water exchange parameters between the strait and nearby water areas and between regions within the strait. The hydroecological CNPSi-model was next used to assess the annual dynamics of concentrations of biogenic element compounds; the biomasses, biohydrochemical activity, and bioproductivity of microorganisms (heterotrophic bacteria, three phytoplankton and two zooplankton groups), involved in transformation of biogenic substances, as well as the internal fluxes of biogenic substances, governed by microorganism activity and the external load onto the marine ecosystem. Analysis of calculation results made it possible to reveal new features in water circulation in the strait (including those for winter) and, for the first time, to analyze the transport regime of biogenic substances through the external boundaries of Tatar Strait and through the boundaries of three regions identified within the strait.     

Estimation of biogenic substance transport by water masses in Tatar Strait

The conditions of transformations of biogenic substances and the redistribution of their concentrations in the shelf water of Sakhalin Island are studied. Preliminary works have given the results for the water area of La Perouse Strait and Aniva Bay (the Sea of Okhotsk), while this paper gives such results for Tatar Strait (the Sea of Japan). Three electronic instruments of oceanographic studies are applied: an adapted version of Bergen Oceanic Model (for the reconstruction of the space and time distribution of seawater temperature, salinity, and density; the circulation intensity of water masses; and water exchange parameters with nearby water areas and within the strait); GIS “Sakhalin Shelf” (for the reconstruction of annual variations in thermohaline characteristics on a standard grid and horizons of oceanographic stations, and the parameters of the aquatic environment); hydroecological CNPSi-model (for studying the annual dynamics of biogenic element compounds, the biomasses, biohydrochemical activity and bioproduction of microorganisms—bacteria, phytoplankton, and zooplankton, taking part in transformation of biogenic substances and petroleum hydrocarbons, as well as the internal fluxes of biogenic substances governed by the activity of microorganisms and the external load on the marine ecosystem). The results of modeling the spatial transport of biogenic substances through the outer boundaries of Tatar Strait water area and the boundaries of the three areas identified within it are presented and discussed.     

Numerical model studies on the generation and dissipation of the diurnal coastal-trapped waves over the Sakhalin shelf in the Sea of Okhotsk

To clarify the generation and dissipation mechanisms of diurnal coastal-trapped waves (CTWs) over the Sakhalin shelf, a series of numerical experiments were conducted using a three-dimensional tidal model of the Okhotsk Sea with density stratification. The tidal model used has good reproduction owing to the careful fitting to the recent observations. The numerical experiments suggested that diurnal CTWs are primarily (~60%) generated by the conversion of tidal energy at the northern corner of the Sakhalin shelf, and further amplified by vorticity generation due to the water column oscillation from Sakhalin Bay and the influence of Kashevarov Bank. From the observations, it was found that diurnal CTWs are effectively dissipated by the strong spin-down due to bottom friction. The conventional turbulent closure model cannot reproduce the observed damping of diurnal CTWs, which raises a caution in modeling the tidal fields in high-latitude regions where diurnal CTWs exist. To resolve this underestimation of the damping, the vertical eddy viscosity was parameterized using its dependence on the observed major axis length of the diurnal tidal current ellipses, which improves the model reproduction on the damping of diurnal CTWs. The model also suggests that the spin-down effects due to friction associated with the sea-ice cover play an important role in the tidal current reduction in the region where diurnal CTWs exist, as the observations suggested.     

Investigation of the 2006 Alexandrium fundyense bloom in the Gulf of Maine: In-situ observations and numerical modeling

In-situ observations and a coupled bio-physical model were used to study the germination, initiation, and development of the Gulf of Maine (GOM) Alexandrium fundyense bloom in 2006. Hydrographic measurements and comparisons with GOM climatology indicate that 2006 was a year with normal coastal water temperature, salinity, current and river runoff conditions. A. fundyense cyst abundance in bottom sediments preceding the 2006 bloom was at a moderate level compared to other recent annual cyst survey data. We used the coupled bio-physical model to hindcast coastal circulation and A. fundyense cell concentrations. Field data including water temperature, salinity, velocity time series and surface A. fundyense cell concentration maps were applied to gauge the model's fidelity. The coupled model is capable of reproducing the hydrodynamics and the temporal and spatial distributions of A. fundyense cell concentration reasonably well. Model hindcast solutions were further used to diagnose physical and biological factors controlling the bloom dynamics. Surface wind fields modulated the bloom's horizontal and vertical distribution. The initial cyst distribution was found to be the dominant factor affecting the severity and the interannual variability of the A. fundyense bloom. Initial cyst abundance for the 2006 bloom was about 50% of that prior to the 2005 bloom. As the result, the time-averaged gulf-wide cell concentration in 2006 was also only about 60% of that in 2005. In addition, weaker alongshore currents and episodic upwelling-favorable winds in 2006 reduced the spatial extent of the bloom as compared with 2005.     

Evaluating Mineral Phosphorus Fluxes in Eutrophic Waters of the Northwestern Black Sea

Water Resources - Many-year data have been used to construct the spatial distributions of water salinity and calculate the seasonal and normal annual occurrence areas of transformed river waters in...     

Transformations of biogenic substances in Tatar Strait water (the Sea of Japan): Analysis of mathematical modeling results

The state of the marine environment (the temperature, light intensity, transparency, biogenic load) in Tatar Strait was assessed based on mean annual data from literary sources and with the use of GIS “Sakhalin Shelf.” The entire strait was divided into three regions (northern, southwestern, and southeastern), and water exchange between them for each month was estimated by using Bergen Oceanic Model. The information about the state of the marine environment and water exchange characteristics was used as input data for a hydroecological model, which enabled the assessment of annual variations of biogenic substance concentrations and biomasses of microorganisms (heterotrophic bacteria, three groups of phytoplankton, and two groups of zooplankton) in the strait regions chosen. The development conditions of microorganism biomasses within the year can be characterized by their activity indices (specific growth rates), the values of internal fluxes of biogenic substances, and calculated bioproductivity values. The calculated biogenic substance concentrations and phytoplankton bioproductivity values showed good agreement with the estimates for the Sea of Japan and Tatar Strait available from the literature.     

An overview of hydrometeorological datasets from a small agricultural catchment (Nučice) in the Czech Republic

We introduce the freely available web-based Water in an Agricultural Landscape—NUčice Database (WALNUD) dataset that includes both hydrological and meteorological records at the Nučice experimental catchment (0.53 km²), which is representative of an intensively farmed landscape in the Czech Republic. The Nučice experimental catchment was established in 2011 for the observation of rainfall–runoff processes, soil erosion processes, and water balance of a cultivated landscape. The average altitude is 401 m a.s.l., the mean land slope is 3.9%, and the climate is humid continental (mean annual temperature 7.9°C, annual precipitation 630 mm). The catchment is drained by an artificially straightened stream and consists of three fields covering over 95% of the area which are managed by two different farmers. The typical crops are winter wheat, rapeseed, and alfalfa. The installed equipment includes a standard meteorological station, several rain gauges distributed across the basin, and a flume with an H-type facing that is used to monitor stream discharge, water turbidity, and basic water quality indicators. Additionally, the groundwater level and soil water content at various depths near the stream are recorded. Recently, large-scale soil moisture monitoring efforts have been introduced with the installation of two cosmic-ray neutron sensors for soil moisture monitoring. The datasets consist of observed variables (e.g. measured precipitation, air temperature, stream discharge, and soil moisture) and are available online for public use. The cross-seasonal, open access datasets at this small-scale agricultural catchment will benefit not only hydrologists but also local farmers.     

Biotransformation of Organogenic Substances in the Aniva Bay Waters: Assessment with the Use of Mathematical Modeling

Mathematical modeling is used to study the conditions of natural biotransformation of biogenic element compounds (containing C, N, P, Si) in five areas within Aniva Bay. The input data for the model are evaluated with the use of GIS “Sakhalin Shelf” and the available reference literature on the bay oceanography. Water masses that transferred through the boundaries between the areas were evaluated based on the values of water level, river runoff, atmospheric precipitation, evaporation, and the volume of water in the bay, all of which vary as a result of water heating. The model was used to evaluate annual variations in the concentrations of organic and mineral fractions of these elements and the biomasses of planktonic organisms for the five areas in the bay. Modeling results also allowed the assessment of biogenic substance input with river runoff into Lososei Bay. Based on the internal fluxes of substances, the monthly and annual aquatic animal production was evaluated.     

Studying the Ecosystem Functioning Conditions in Aniva Bay–La Perouse Strait

An atlas of oceanographic data on the shelf zone of Sakhalin Island and a mathematical model describing the transformations of nutrient compounds (N, P, Si, C) are used to study the biotransformation and transport of organic and mineral components of these elements in the La Perouse Strait. To make the analysis more convenient, the area under examination was divided into four zones, which differ in the conditions of transport of matter in water flows. Transport calculations are made using a complex graphic method with geostrophic approximation, which takes into account the results of instrumental observations of flow velocities, sea level variations, and annual variations in the water volumes. The obtained patterns of dynamics of nutrient compounds are compared with the results of modeling of internal and external fluxes of those components. Calculated fluxes of the elements were used to assess the rate of chemicals and biomass transport through the boundaries of water areas (in particular, between the Seas of Japan and Okhotsk).     

Hydrographic variability on a coastal shelf directly influenced by estuarine outflow

Hydrographic variability on the Alabama shelf just outside of Mobile Bay, a major source of river discharge into the Gulf of Mexico, is examined using time series of water column temperature and surface and bottom salinity from a mooring site with a depth of 20 m in conjunction with a series of across-shelf CTD surveys. The time series data show variability in a range of time scales. The density variation is affected by both salinity and temperature, with its relatively strong annual signal mostly determined by temperature and its year to year variability mostly determined by salinity. Seasonal mean structures of temperature, salinity, and density show a transition from estuarine to shelf conditions in which three regions with distinct seasonal characteristics in their horizontal and vertical gradient structures are identified. Correlation analysis with the available forcing functions demonstrates the influence of Mobile Bay on the variability at the mooring site. At low frequencies, river discharge from Mobile Bay has a varying influence on salinity, which is absent during the periods with unusually low discharge. At shorter synoptic time scales, both the estuarine response to the across-shelf wind stress and the shelf response to the along-shelf wind stress are significantly correlated with temperature/salinity variability: the former becoming important for the surface layer during winter whereas the latter for the bottom layer during both winter and summer. These forcing functions are important players in determining the estuarine-shelf exchange, which in turn is found to contribute to the shelf hydrographic structure.     

Formation of Vertical Thermal Structure in Lakes in Northwestern Russia and Finland

Vertical distribution of average annual temperature of water in lakes in the period of maximum water heating is analyzed as a function of zonal climatic factors and lake morphometry. Regression analysis is applied to hydrometeorological data on water temperature measurements at standard horizons made from 1958 to 1989 in 58 lakes in northwester Russia and eight lakes in Finland. The temperature of the top five-meter layer is found to depend mainly on the latitude. The major factors at a depth of 10 and lower are the lake morphometry and river water inflow.     

Natural sources of methane and carbon dioxide on Sakhalin Island and their role in the formation of ecological gas-geochemical zones

Two major groups of the lithosphere sources of methane are distinguished, i.e., the lithosphere sources proper (metamorphism, and serpentinization and spreading zones) and organic fuel deposits in the Earth’s crust. Hydrocarbon deposits, mud volcanoes, geothermal systems, and mineral sources are located on Sakhalin Island. All investigated objects are associated with large tectonic faults: the Yuzhno-Sakhalinsky and Main Pugachiovsky mud volcanoes are controlled by the Central Sakhalin fault; the Shakhterskoe coal deposit is confined to the West Sakhalin fault, while the Daginskaya geothermal system and the studied oil- and-gas fields are associated with the Hokkaido-Sakhalin fault. The authors’ studies of natural gases allow allocating two basic zones on the Sakhalin island with different types of hydrocarbon-carbon dioxide sources: Oil-and-gas (mostly methane; north-east) area and Coal-Gas area (carbon-dioxide-methane; west, south-west). Those areas differ in both chemical and isotope composition of natural gases. Some gashazardous areas have also been identified along tectonic faults, where they are due to gas release on the land surface. The populated localities on Sakhalin are shown to be situated near fault zones; therefore, the problem of gas hazard control is of critical importance.     

Using Self-Organising Maps to investigate long-term changes in deep Adriatic water patterns

The paper attempts to document long-term changes in deep Adriatic water patterns by applying the Self-Organising Maps (SOM) method to temperature, salinity, dissolved-oxygen content, orthophosphate and total inorganic nitrogen profiles sampled at a single deep station in the South Adriatic Pit (SAP) over a half century (1957-2009). Seasonality observed in upper layers has been removed by the least-squares fitting of the annual and semi-annual sinusoidal functions. The sensitivity of the SOM to various parameter combinations reveals the importance of temperature, salinity and dissolved oxygen for mapping different water patterns, while nutrients have less influence on quality and applicability of SOM solutions to the extraction of characteristic SAP water profiles. The quality of fit obtained for different combination of the measured parameters introduced to a SOM suggests that the incomplete combinations of input parameters increase an imperfection in the applicability of SOMs to the dataset. Two modes of long-term changes in the SAP obtained by the SOM analyses are discussed with respect to the processes that drive the variability in the area, e.g., the Adriatic-Ionian Bimodal Oscillation: where the first mode is characterised by rapid changes in the transition of SAP water masses, observed before 1980s (less adoptable by the SOMs), and the second mode is characterised by steady transitions (better adoptable by the SOMs), observed in the 1990s and the 2000s. The SOM method is found to have certain advantages when compared to other methods that have previously been used to distinguish the Adriatic water masses, as it does not depend on predefinition of water mass sources and allows for gaps in series.     

The mechanism of Lake Kinneret salinization as a linear reservoir

The salinity of Lake Kinneret, Israel, is significantly higher than the salinity of the water from surface streams that flow to the lake. The relatively high salinity is a result of the activity of saline springs located at the bottom of the lake.The purpose of this work is to establish a general model for the salinization mechanism of Lake Kinneret. The model is based on the main components of the annual water and solute balance. Changes in time of the solute mass of the lake were described as a differential equation of a linear reservoir on an annual time scale. The model assumes that under any long-term operation policy of the lake, the components of the annual solute and water balance stay nearly constant in time.The model was tested for both steady-state conditions, and during changes in time, against measured lake salinity over the years 1968-2000. It was found that the major changes of lake salinity throughout the years were described well, despite the variety of rainfall amounts. Predictions of the expected lake salinity changes were proposed for the cases of controlled increase or decrease of saline springs discharge to the lake; for the changes of water quantity allowed to flow into or pumped out of the lake; and for various initial salinities. Predictions agree well with previous predictions made by statistical models.     

A three-dimensional variational ocean data assimilation system:Scheme and preliminary results

A new 3DVAR-based Ocean Variational Analysis System (OVALS) is developed. OVALS is capable of assimilating in situ sea water temperature and salinity observations and satellite altimetry data. As a component of OVALS, a new variational scheme is proposed to assimilate the sea surface height data. This scheme considers both the vertical correlation of background errors and the nonlinear temperature-salinity relationship which is derived from the generalization of the linear balance constraints to the nonlinear in the 3DVAR. By this scheme, the model temperature and salinity fields are directly adjusted from the altimetry data. Additionally, OVALS can assimilate the temperature and salinity profiles from the ARGO floats which have been implemented in recent years and some temperature and salinity data such as from expendable bathythermograph, moored ocean buoys, etc. A 21-year assimilation experiment is carried out by using OVALS and the Tropical Pacific circulation model. The results show that the assimilation system may effectively improve the estimations of temperature and salinity by assimilating all kinds of observations. Moreover, the root mean square errors of temperature and salinity in the upper depth less than 420 m reach 0.63℃ and 0.34 psu.     

Toward a global ocean data assimilation system based on ensemble optimum interpolation: altimetry data assimilation experiment

A global ocean data assimilation system based on the ensemble optimum interpolation (EnOI) has been under development as the Chinese contribution to the Global Ocean Data Assimilation Experiment. The system uses a global ocean general circulation model, which is eddy permitting, developed by the Institute of Atmospheric Physics of the Chinese Academy of Sciences. In this paper, the implementation of the system is described in detail. We describe the sampling strategy to generate the stationary ensembles for EnOI. In addition, technical methods are introduced to deal with the requirement of massive memory space to hold the stationary ensembles of the global ocean. The system can assimilate observations such as satellite altimetry, sea surface temperature (SST), in situ temperature and salinity from Argo, XBT, Tropical Atmosphere Ocean (TAO), and other sources in a straightforward way. As a first step, an assimilation experiment from 1997 to 2001 is carried out by assimilating the sea level anomaly (SLA) data from TOPEX/Poseidon. We evaluate the performance of the system by comparing the results with various types of observations. We find that SLA assimilation shows very positive impact on the modeled fields. The SST and sea surface height fields are clearly improved in terms of both the standard deviation and the root mean square difference. In addition, the assimilation produces some improvements in regions where mesoscale processes cannot be resolved with the horizontal resolution of this model. Comparisons with TAO profiles in the Pacific show that the temperature and salinity fields have been improved to varying degrees in the upper ocean. The biases with respect to the independent TAO profiles are reduced with a maximum magnitude of about 0.25°C and 0.1 psu for the time-averaged temperature and salinity. The improvements on temperature and salinity also lead to positive impact on the subsurface currents. The equatorial under current is enhanced in the Pacific although it is still underestimated after the assimilation.     

青海湖意外湖花介(Limnocythere inopinata Bird)壳体稳定氧同位素组成对盐度的可能响应

介形类壳体的氧同位素组成已成为恢复湖区古气候/古环境的有效代用指标,而其氧同位素分馏及环境意义目前还缺乏研究.为评价青海湖介形类壳体氧同位素分馏及其环境意义,在青海湖进行系统的表层沉积物和水样的采集,测定表层沉积物中的意外湖花介(Limnocythere inopinata Bird)和相应水样的氧同位素组成.结果表明:意外湖花介壳体的氧同位素组成主要受控于水体的氧同位素组成,除温度的影响外,还可能受到盐度的影响,随着盐度变化,该种壳体与水体之间的同位素分馏呈减小趋势,而两者的氧同位素组成均呈偏正趋势.青海湖意外湖花介壳体的氧同位素组成在一定程度上可能间接反映水体盐度的变化,值得进行更深入的研究.     

Salt-Finger convection in the surface discharge of heated saline jets

Abstract

Experimental investigations of the surface discharge of two-dimensional heated saline jets into surroundings with stable, constant salt gradients were carried out. The discharge conditions were parameterized with the densimetric Froude number, and the Reynolds number. The evolution of the discharge was monitored by flow visualization methods, and by the measurements of temperature and salinity distributions. For comparison, experiments of the surface discharge of heated water into homogeneous surroundings at the corresponding discharge conditions were also conducted. The results clearly showed that while in the former case, the region away from the vicinity of the discharge manifold was marked by the presence of salt-finger convection, in the latter case this region exhibited stable thermal stratification. Furthermore the occurrence of salt-finger convection considerably retarded the motion of the jet, and increased the penetration depth of temperature and salinity fields.     

Biohydrochemistry of marine environment and transformations of biogenic substances and oil hydrocarbons on the southeastern Sakhalin shelf

Mathematical simulation is used to study the biotransformation conditions of compounds of organogenic elements (C, N, P, Si) and oil hydrocarbons in the water of southeastern Sakhalin shelf. The input data for calculations were evaluated with the use of Sakhalin Shelf GIS or taken from the reference literature and materials of expedition studies. The values of water discharges through the boundaries of the zones chosen within the shelf water area and through the interface with the Sea of Okhotsk were derived from the characteristics of currents estimated by means of Bergen University oceanic model based on normal long-term monthly thermohaline parameters obtained from the Sakhalin Shelf GIS. The intraannual variations of the concentrations of organic and mineral compounds of C, N, P, and Si, as well as oil hydrocarbons because of biotransformation of substances by organisms of the community (bacteria, phytoand zooplankton) were evaluated in calculations with CNPSi-model. The results of calculations, revealing the features of the dynamics of substances, the biomass of organisms, and their activity in matter biotransformations were analyzed.