Shelf-slope Zone Research Articles

Increase of Temperature and Salinity in the Active Layer of the North-Eastern Black Sea from 2010 to 2020

Purpose. The paper is aimed at assessing salinity and temperature variability in the upper 300-meter layer of the northeastern part of the Black Sea based on the analysis of the archival and modern expeditionary data. Methods and Results. The data on the cross-sections “coast – sea center” (with the length of 70–110 nautical miles) performed from 1999 to 2009, as well as the results of regular ship monitoring in the shelf-slope zone of the northeastern part of the Black Sea carried out in 2010–2020 were used. It was found that salinity was progressively increasing in the upper 200-meter layer during the last decade. Salinity increase, on the average, constituted annually about 0.05–0.06 PSU. An increase of temperature was also observed below the layer of temperature minimum (core of the cold intermediate layer). In particular, the lower 8.7 °C isotherm rose annually, on the average, by 11 m from its annual average depth 242 m in 2010 up to 121 m in 2020. Salinity growth led to the corresponding changes in water density that resulted in elevation of the lower boundary of the oxygen-containing layer (potential density is 15.8) from the depth of 143 m in 2010 to 124 m in 2020. Conclusions. Climatic changes have led to a noticeable salinity increase in the upper 200-meter layer of the northeastern Black Sea, as well as to a temperature increase in the layers situated below the temperature minimum layer. Though the measurements were carried out in a certain area of the shelf-slope zone, there are reasons to assume that the observed dynamics can be attributed to the entire Black Sea. Physical reasons for the observed changes require a detailed research.

Rost solenosti i temperatury v deyatel'nom sloye severo-vostochnoy chasti Chernogo morya s 2010 po 2020 god

Purpose. The paper is aimed at assessing salinity and temperature variability in the upper 300-meter layer of the northeastern part of the Black Sea based on the analysis of the archival and modern expeditionary data. Methods and Results. The data on the cross-sections “coast – sea center” (with the length of 70–110 nautical miles) performed from 1999 to 2009, as well as the results of regular ship monitoring in the shelf-slope zone of the northeastern part of the Black Sea carried out in 2010–2020 were used. It was found that salinity was progressively increasing in the upper 200-meter layer during the last decade. Salinity increase, on the average, constituted annually about 0.05–0.06 PSU. An increase of temperature was also observed below the layer of temperature minimum (core of the cold intermediate layer). In particular, the lower 8.7 °C isotherm rose annually, on the average, by 11 m from its annual average depth 242 m in 2010 up to 121 m in 2020. Salinity growth led to the corresponding changes in water density that resulted in elevation of the lower boundary of oxygen-containing layer (potential density 15.8) from the depth 143 m in 2010 to 124 m in 2020. Conclusions. Climatic changes have led to a noticeable salinity increase in the upper 200-meter layer of the northeastern Black Sea, as well as to a temperature increase in the layers situated below the temperature minimum layer. Though the measurements were carried out in a certain area of the shelfslope zone, there are the reasons to assume that the observed dynamics can be attributed to the entire Black Sea. Physical reasons for the observed changes require a detailed research

Implications of the depth profile on the functional structure of the fish community of the Perdido Fold Belt, Northwestern Gulf of Mexico

Studies have demonstrated that environmental conditions affect the richness, diversity, and abundance of fish communities. Depth is an important variable with many species showing preferences for specific depth ranges. Here, we present a functional analysis of the fish community in the Perdido Fold Belt (PFB), Gulf of Mexico. The sampling design was structured across a depth range of 40–3500 m, using 20 oceanographic stations. The aims of our study were: (1) to determine the functional arrangement of the fish community in the PFB; and (2) to describe the effect of the environmental variables on fish richness and functional diversity. A total of 232 species were identified; 195 were grouped into 42 functional groups (FGs). Thirty-seven species did not group with any others and are referred to as “functionally independent species” (FIS). According to our results, depth changes in physicochemical variables allow us to segregate three vertically stratified zones: shelf, slope, and deep. Temperature was the most important environmental variable constraining functional distribution of fishes. The highest FG diversity, species diversity, and biomass were found in the shelf/slope zone (SSo), while the highest diversity of FIS was found in the shelf zone. As the SSo displays its highest diversity, and since greater diversity has been linked with greater resilience and stability of fish communities, the SSo may be the most resilient zone of the PFB. Our study provides the first description of the diversity and resilience of the PFB fish community and helps our understanding of the factors constraining the distribution and functional diversity of fishes across depth gradients.

ФОРМИРОВАНИЕ ХОЛОДНОГО ПРОМЕЖУТОЧНОГО СЛОЯ В ШЕЛЬФОВО-СКЛОНОВОЙ ЗОНЕ СЕВЕРО-ВОСТОЧНОЙ ЧАСТИ ЧЕРНОГО МОРЯ

The paper presents an overview of the existing hypotheses about the formation areas and the distribution mechanisms of the cold intermediate layer (CIL) in the Black Sea. The testing of the statistical hypothesis about the relationship of the CIL parameters in the shelf-slope zone of the Black Sea Northeastern part with the temperature of the atmosphere surface layer in the central part of the eastern cyclonic gyre is performed. The obtained high values of the correlation coefficients (~0.98) confirmed the dependence of the CIL parameters during its formation period from the air temperature over the Northeastern part of the Black Sea. One of the concepts of the “convective-advective” hypothesis by Ovchinnikov and Popov (1987) about approximately 2 months time shift between the processes of cold air masses invasion into the water area of the Black Sea and the developed CIL waters appearance in the coastal zone of the Gelendzhik area is also confirmed.

Early Miocene sedimentary processes and their hydrocarbon implications in the Baiyun Sag of Pearl River Mouth Basin, northern south China sea

Abstract The shelf-slope zone has received considerable attention for hydrocarbon exploration due to its unique location, where the sediments are delivered to deep-water environment and deposited as hydrocarbon reservoirs that have been discovered around the world. However, it is realized that the sedimentary processes are very complex, and various depositional bodies develop in the shelf-slope zone. Constrained by 3D seismic, core and well log data, numerical simulations can be applied to better understand the sedimentary processes, and predict the distribution and characteristics of deposits as hydrocarbon reservoirs. Based on core-log-seismic integration, the Early Miocene shelf-margin delta and channelized submarine fan systems along the northern slope of Baiyun Sag in the Pearl River Mouth Basin are distinguished and they are mainly composed of debris, turbidites and slumps. The numerical model is built based on Early Miocene topography acquired by back-stripped well-tied seismic profiles, and the initial boundary conditions, including sediment concentration, velocity and, grain size, and so on, behaviors and structures of slope system are set according to the results of marine surveys around the world. The Computational Fluid Dynamic software ANSYS-FLUENT was applied for the modelling. As a results, the distributions and geometries of the simulated deposits are compared with the depositional bodies interpreted from seismic data. The hydrodynamic simulations of the two sedimentary systems indicate that depositional bodies converge to the downstream of the slope and the basin floor, and turn tractive current into turbidity current during the sedimentary processes, which result in obviously various sedimentary characteristics in different locations. The identification of sedimentary processes in the shelf-margin delta and channelized submarine fan systems has been beneficial for predicting reservoirs and exploring hydrocarbons in the Baiyun Sag, Pearl River Mouth Basin, which is also contributing to the understanding of sedimentary process and reservoir prediction in deep-water areas around the world.

Thermochains of the Southern Branch, Shirshov Institute of Oceanology, Russian Academy of Sciences: Design, Methods, and Results of Metrological Investigations of Sensors

Thermochains for Black Sea hydrophysical studies are described, and the features of their displacement at the moored buoy station with subsurface buoyancy are considered. A technique for calibrating the temperature sensors is described and their stability is estimated by comparing the obtained calibration coefficients with the values established in previous calibrations. The characteristics of the temperature sensors, including the time constant are specified, as well as their reading error with respect to the reference thermometer. The performed metrological studies prove that the temperature sensors used in the thermochains work rather stably and make measurements with an accuracy of ± 0.01 °C for several months of operation in marine conditions. This allows to determine adequately the temperature at various horizons in the water environment of the shelf-slope zone of the Black Sea and to study not only its short-period, but also long-term variability.

Sequence architecture and depositional evolution of the Late Miocene to quaternary northeastern shelf margin of the South China Sea

Based on an integrated analysis of seismic, well logging and paleontological data, the sequence architecture and depositional evolution of the northeastern shelf margin of the South China Sea since Late Miocene are documented. The slope deposits of the Late Miocene to Quaternary can be divided into two composite sequences (CS1 and CS2) bounded by regional unconformities with time spans of 3–7 Ma, and eight sequences defined by local unconformities or discontinuities with time spans of 0.8–2.3 Ma. Unconformities within CS1 feature shelf-edge channel erosion, while in CS2 they form truncations at the top of the shelf margin as prograding complexes and onlap contacts against the slope.Depositional systems recognized in the slope section include unidirectionally migrating slope channels, slope fans or aprons, shelf-edge deltas and large-scale slope clinoforms. CS1 (Late Miocene to Pliocene) is characterized by development of a series of shelf-margin channels and associated slope fan aprons. The shelf-margin channels, oriented mostly NW-SE, migrate unidirectionally northeastwards and intensively eroded almost the entire shelf-slope zone. Two types of channels have been identified: (1) broad, shallow and unconfined or partly confined outer-shelf to shelf-break channels; and (2) deeply incised and confined unidirectionally migrating slope channels. They might be formed by gravity flow erosion as bypassing channels and filled mostly with along-slope current deposits. Along the base of the shelf slope, a series of small-scale slope fans or fan aprons are identified, including three depositional paleo-geomorphological elements: (1) broad or U-shaped, unconfined erosional-depositional channels; (2) frontal splays-lobes; and (3) non-channelized sheets. CS2 (Quaternary) consists mainly of a set of high-angle clinoforms, shelf-margin deltas and lower slope unidirectionally migrating channels.The relative sea level changes reflected in the sequence architecture of the study area are basically consistent with Haq's global sea level curve, but the development of regional unconformities were apparently enhanced by tectonic uplift. The development of high-angle (thick) clinoforms in the Quaternary may be attributed to a high sediment supply rate and rapid tectonic subsidence. The formation of the unidirectionally migrating channels appears to have resulted from the combined effects of the northeastward South China Sea Warm Current (SCSWC) and downslope gravity flow. The formation of the slope channels in the outer-shelf to shelf-break zone may be predominately controlled by bottom current, whereas those developed along the middle to lower slope zone may be dominated by gravity flow.

Evaluation of ecosystem status in the shelf-slope zone of the northeastern Black Sea based on the trophic index (TRIX)

The water conditions and trophic status in the shelf-slope zone and bays of the northeastern Black Sea were evaluated on the basis of monitoring data from 2007–2014. It has been shown that the concentrations of nutrients and chlorophyll “a” in the studied area are at the level of the pristine period (of the late 1970s). The concentration of mineral nitrogen in the surface water layer varied from 0.19 to 5.64 μM. The concentration of phosphates differed from analytical zero to 0.56 μM. The concentration of chlorophyll “a” in different seasons ranged from 0.24 to 0.89 μg/L. The trophic index characterizes the status of the marine shelf ecosystem near Gelendzhik city as “excellent” even in the bays. Significant year-to-year differences in the index were not detected. The range between the values of the trophic index in the bays and open sea was low (3.7 and 3.2, respectively).

Subsatellite polygon for studying hydrophysical processes in the Black Sea shelf-slope zone

The first data on the creation of the subsatellite polygon on the Black Sea shelf and continental slope in the Gelendzhik area (designed in order to permanently monitor the state of the aquatic environment and biota) and the plans for maintaining and developing this polygon are presented. The autonomous measuring systems of the polygon in the composition of bottom stations with acoustic Doppler current profilers (ADCP), Aqualog robotic profilers, and thermo-chains on moored buoy stations should make it possible to regularly obtain hydrophysical, hydrochemical, and bio-optical data with a high spatial-time resolution and transmit these data to the coastal center on a real-time basis. These field data should be used to study the characteristics and formation mechanisms of the marine environment and biota variability, as well as the water-exchange processes in the shelf-deep basin system, ocean-atmosphere coupling, and many other processes. These data are used to calibrate the satellite measurements and verify the water circulation numerical simulation. It is assumed to use these data in order to warn about the hazardous natural phenomena and control the marine environment state and its variation under the action of anthropogenic and natural factors, including climatic trends. It is planned to use the polygon subsatellite monitoring methods and equipment in other coastal areas, including other Black Sea sectors, in order to create a unified system for monitoring the Black Sea shelf-slope zone.