Upper Part Of Continental Slope Research Articles

Upwellings and Downwellings Caused by Mesoscale Water Dynamics in the Coastal Zone of Northeastern Black Sea

The paper analyzes quasiperiodic upwellings and downwellings on the shelf and upper part of continental slope of the northeastern Black Sea. It is shown that these processes are related to changes in intensity and direction of alongshore current and the following geostrophic adjustment of the density field. The source of such changes is the meandering of the Black Sea Rim Current (RC). It leads to a quasiperiodic change in direction of the alongshore current, from northwestern (cyclonic RC meander) to southeastern (anticyclonic RC meander, or eddy). These cycles, or phases, have an average duration of about 10 days. During the northwestern phase, the permanent Black Sea pycnohalocline (hereafter pycnocline) and seasonal thermocline descend, their thickness increases, and so does the thickness of the upper mixed layer (UML). During the southeastern phase, both the pycnocline and seasonal thermocline ascend and become thinner, along with the UML, which also becomes thinner. In both phases, isopycnals in the pycnocline and isotherms in the thermocline demonstrate quasi-in-phase vertical oscillations, which have a good correlation with the speed and direction of the alongshore current. These correlations allow estimation of the magnitude of upwellings and downwellings in the shelf–slope area of the northeastern Black Sea using data series of current velocity profiles.

Characterization of Tsunami and Palaeo-tsunami deposits in the Neil Island, South Andaman, India

The nature of tsunamigenic and palaeo-tsunamigenic sediments in Neil Island, deposited by the great Indian Ocean in 2004 is documented herein. Pit, trench and core samples were collected from the four beaches, namely, Bharatpur, Ramnagar, Sitapur and Lakshmanpur; which exhibit distinguished anomalies in the sedimentological parameters, viz . skewness, kurtosis and standard deviation at various depths. The palaeontological study shows the simultaneous occurrence of characteristic benthic taxa of near-shore environment and upper part of continental slope along with the open ocean dweller planktic foraminifera- an intermixed foraminiferal assemblage is mainly due to the tsunami wave actions. The multiproxy approach reveals the occurrence of the tsunami and palaeo-tsunami deposits in Neil Island from 9 to 40 cm and below 60 cm depth, respectively.

ПРЕДВАРИТЕЛЬНЫЕ РЕЗУЛЬТАТЫ ЭКСПЕРИМЕНТАЛЬНОГО ИССЛЕДОВАНИЯ ДИНАМИКИ ПРИДОННОГО СЛОЯ НА ШЕЛЬФЕ–КОНТИНЕНТАЛЬНОМ СКЛОНЕ В ЧЕРНОМ МОРЕ

The preliminary results of an experimental study of a mechanism of the Black Sea anoxic layer ventilation related with the descent of oxygen-containing water down the bottom slope in Ekman boundary layer are presented. To study this mechanism, several automatic measuring stations were installed at the bottom of the shelf-continental slope zone in the depth range from 80 to 243 m, on the cross-section abeam of the Gelendzhik Bay. The observations that lasted for 1.5–2 months were fulfilled during two periods in the beginning and the end of 2018. The stations were registering hydrophysical (temperature, salinity, pressure and current velocity) and hydrochemical (dissolved oxygen concentration) parameters at a 0.5–2.5 m distance from the bottom. The acquired data are suitable for estimation of spatio-temporal parameters of water transfer in the bottom layer up and down the slope, depending on direction and intensity of alongshore current. Preliminary analysis of the first installation data confirmed the presence of bottom water transfer along the slope perpendicular to the shore. Also, in case of intense alongshore north-western current, a descent of the bottom layer water was observed. Such manner of water transfer conforms to both geostrophic adjustment and dynamics of the bottom Ekman boundary layer. However, variability of water density in the bottom layer, caused by vertical water transport, had about the same range as density fluctuations in the water column on the same depths. This fact disputes the effectiveness of Ekman transfer in the bottom layer as a water ventilation mechanism for the upper part of continental slope of the Black Sea (Zatsepin et al., 2007; Elkin, Zatsepin, 2017).

Feeding of soft sculpin Malacocottus zonurus (Psychrolutidae) in the western Bering Sea

The feeding of the soft sculpin Malacocottus zonurus dwelling on the shelf and in the upper part of continental slope of the western Bering Sea is studied from materials of trawl surveys in the years 1998–2000. Description of its food composition depending on the fish size is given. It is found that basically polychaetes, decapods, amphipods, mollusks, and fishes serve as its food. When the soft sculpin reaches a length of 15–20 cm, its feeding type changes.

中央日本南部の第四紀地殻運動 地殻運動の変化と場の移動

Various opinions on the Quaternary tectonism previously pointed out are discussed and summarized as follows:1) The tectonic culmination in the middle Quaternary is not at least an extensive phenomenon at this area.2) The uniform rate of deformation in the Quaternary seems to be accepted in the order of less than 105yrs, but not likely in the order of more than 106yrs.3) Although the accelerated rates towards the present are often suggested by many recent studies, these may be an apparent feature due to a fluctuation in a relatively short time span within a long-term displacement, or due to a change from a long-wave (or extensive) deformation to a short-wave (or limited) deformation. And also may result from a growing process, as typically expressed with formative advance of fault, even in a same stress condition.4) The SW Japan has been under the regional stress field of WNW-ESE compression through the Quaternary, being originated from the subduction of oceanic plates.5) The shallow depression along the median zone of SW Japan had come into existence simultaneously with the subduction along the Nankai Trough from the middle Pliocene. This may suggest the rejuvenation of the Philippine Sea Plate from that time.6) The leading edge of the underthrusting slab of the Philippine Sea Plate locates at the outer zone in the active segment of the Median Tectonic Line, whearas it extends to the inner zone in its inactive segment (Fig. 4A). These indicate that the outer zone underthrust at very low angle (ca 10°) by the plate behaves as a rigid bloack. As such belts as the outer zone, the longitudinal depression zone and the upwarping mountain of the inner zone have gradually shifted to the northwestward with the times (Fig. 4), these systematic migrations of tectonic province with miscellaneous changes of its process are likely caused by an advance of the underthrusting slab.7) The landward tilting terraces along the Pacific coast of SW Japan are considered to be caused by reverse faults which have emerged as accretionary prism on the upper part of continental slope from the middle to late Quaternary.