Comparison of near seabed currents at two locations in the Porcupine Sea Bight—implications for benthic fauna

2003 ◽  
Vol 83 (4) ◽  
pp. 683-686 ◽  
Author(s):  
Martin White
Keyword(s):  
Historical Data ◽  
Benthic Fauna ◽  
Tidal Currents ◽  
Depth Range ◽  
Bottom Currents ◽  
Hexactinellid Sponge

Recent measurements of benthic currents, within the depth range where the highest abundance of the hexactinellid sponge Pheronema carpenteri are found, have been made and compared to historical data for the northern Porcupine Sea Bight region where no Pheronema have been recorded. Bottom currents at a location where Pheronema have not been recorded are much higher than a location where the sponges have previously been sampled. The measurements provide some evidence to support the hypothesis that the sponges favour a location adjacent to regions where enhanced bottom tidal currents are found, but currents experienced by the sponges themselves are much reduced.

scholarly journals On the possible presence of oxygen in the upper sediment layer of the hydrogen sulfide zone in the Black Sea

2019 ◽  
Vol 59 (1) ◽  
pp. 166-169
Author(s):  
P. A. Stunzhas ◽  
M. B. Gulin ◽  
A. G. Zatsepin ◽  
E. A. Ivanova
Keyword(s):  
Black Sea ◽  
Benthic Fauna ◽  
Water Layer ◽  
Bottom Layer ◽  
The Black Sea ◽  
Depth Range ◽  
Sediment Layer ◽  
Bottom Water Layer ◽  
Long Time ◽  
Eukaryotic Organisms

In the northeastern Black Sea the search was performed for living eukaryotic organisms (micro- and meiobenthos) in hypoxic and anoxic conditions as well as measurement of O2 in the bottom water layer and in the upper layer of sediments. The results have shown the presence of a deep maximum abundance of zoobenthos in a depth range of 215–244 m. This aggregation of benthic fauna occupies a layer of 30 m along the vertical. In general, the proportion of active meiobenthos was no greater than 1.5% of the total number of organisms recorded from the sample.The presence of aerobic benthos near the upper boundary of the H2S zone can be explained by: sliding down of sediments from a higher depth; quasi-periodic O2 supply due to fluctuations in the position of the isopycna and/or sinking of waters downslope in the bottom Ekman layer. Also, in the case of physical entry of oxygen into the bottom layer, it can remain for a relatively long time in the upper part of the H2S zone due to the lack of deep Mn+2 flux and reaction with it.

scholarly journals CURRENT VIEWS ON THE DIVERSITY AND DISTRIBUTION OF DEEP-WATER MEIOBENTHOS AT THE TURKISH SHELF (BLACK SEA)

2017 ◽  
Vol 14 ◽  
pp. 60-73
Author(s):  
Nelli G. Sergeeva ◽  
Derya Ürkmez
Keyword(s):  
Black Sea ◽  
Deep Water ◽  
Benthic Fauna ◽  
Taxonomic Diversity ◽  
The Black Sea ◽  
Depth Range ◽  
Free Living ◽  
Higher Taxa ◽  
Strong Current ◽  
High Level

Deep-water meiobenthos of Turkish shelf has been evaluated at the Black Sea exit of İstanbul Strait (Bosphorus) and off Sinop peninsula as a result of three scientific cruises. Taxonomic diversity of meiobenthos communities was studied at the Black Sea exit of Bosphorus on a transect with a depth range of 75-300 m. The bottom sediments were collected at the area during two cruises, on board RV "Arar'' (of Turkey) and ''Maria S. Merian" (of Germany) in November 2009 and April 2010, respectively. Data on meiobenthos inhabiting both normoxic and extreme conditions was collected in the studied area and meiobenthos composition included 26 high level taxa. In addition, 2-3 morphotypes of benthic fauna were recorded as incertae sedis, which require further study. The number of higher taxa decreased from 22 to 14-8 when switching from oxygenic conditions (50-125 m) to the anoxic hydrogen sulphide environment (226-300 m). The constant components of meiobenthos included protists (Ciliophora, Gromiidea and soft-shelled Foraminifera), and metazoans were constantly represented by Nematoda and Harpacticoida. In 2011, a quantitative study on meiobenthic composition of the oxic/anoxic interface at the western part off Sinop Peninsula (Southern Black Sea) has also been investigated. The material was collected by ROVs during the expedition (Black Sea Leg) of the exploration vessel (E/V) Nautilus. Results showed that the taxa composition of meiobenthos ranged from 4 to 10 major groups. Free-living marine nematodes were numerically the dominant taxon at each station. Total abundances decreased in parallel to increasing water depth, hence decreasing oxygen levels.

New insights into sedimentary processes and related morphologies in tidal straits: the case of the Rio-Antirio Sill (Greece)

2021 ◽  
Author(s):  
Romain Rubi ◽  
Aurélia Hubert-Ferrari ◽  
Elias Fakiris ◽  
Dimitris Christodoulou ◽  
Xenophon Dimas ◽  
...  
Keyword(s):  
High Resolution ◽  
Tidal Currents ◽  
Internal Tides ◽  
Tectonic Activity ◽  
Depositional Model ◽  
Carbonate Production ◽  
Sea Floor ◽  
Bottom Currents ◽  
Gulf Of Corinth ◽  
Underwater Camera

<p>Straits are crossed by marine currents that are amplified due to the water constriction. These nearshore high-velocity flows are problematic for offshore infrastructures (bridge pillars, cables, pipelines etc), but constitute an under-estimated carbon-free kinematic energy source. Most of the straits are dominated by tidal currents which flow axially to the seaway, with reversal directions and phase difference between the two interlinked basins. These tidal currents interplay with: (i) sediment sources that also includes in situ carbonate production and deltas, (ii) tectonic activity, and (iii) inherited lowstand features, all shaping the sea floor into complex geomorphologies. Previous studies have highlighted a common tidal-strait depositional model with a strait-center zone in erosion and on each side a dune-bedded strait zone with 3D and 2D tidal dunes and tidal ripples.</p><p>Here, we present an alternative tidal-strait model based on an interdisciplinary approach using high-resolution geophysical and oceanographical data to better constrain the processes acting at the sea floor. We focus on the Rion-Antirion strait in Greece which controls the connection between the Gulf of Corinth and the Mediterranean Sea. Based on high-resolution multibeam bathymetry (MBES) over an area of 211km<sup>2</sup>, we identify and quantify the morphologies by extracting bathymetric swath profiles. These results are integrated with currents data (ADCP) and CTD profiles. In addition,  we use high-resolution Chirp subbottom profiles and high-resolution sparker seismic reflection profiles to document the stratigraphy and morphology of the sedimentary beds and erosional features. To complete this dataset, we use a towed underwater camera to image the sea-floor.</p><p>We define three zones, each characterized by common hydrodynamics, bedforms and morpho-bathymetric features which reveal an asymmetric strait. (1) The western zone is dominated by tectonics with salt diapirism and faults which interact with bottom currents to form erosional pools and ridge systems. (2) The strait center zone displays abrasion surfaces which consists on a rough rock-paved plateau surface encrusted by living red corals and sponges. Moreover, a moat cuts this plateau that localizes the sill at its eastern tip. This strait center area is dominated by inherited hard-ground fluviatile deposits which are abraded by bidirectional tidal-currents. (3) The eastern zone shows a deeper bathymetry with smoother features. The sediments are veneered on slopes forming plastered drifts and spits while the basin axis presents large chutes and pools. The bottom-currents in this zone, are related to internal tides from the Gulf of Corinth that are delayed with respect to the tidal currents. These internal-tide currents (3m/s) are three times faster than the oceanic tidal-currents in the strait (1m/s).</p><p>In conclusion, we document a tidal-strait system, which is interacting with active tectonics, and internal-tides along its axis. In results, Rion strait displays complex bathymetric features without any 3D or 2D tidal dunes. Thus, it provides a new end member to the tidal-strait depositional model. This end member is characterized by a re-localization of the erosion, bypass and deposition. It illustrates the key role of internal tides for straits located at the boundary between a confined deep-basin and the open-sea.</p>

scholarly journals Fish landings and Oman shelf area

2016 ◽  
Vol 21 ◽  
pp. 25
Author(s):  
Sergey A. Piontkovski ◽  
H.E. Hamed S. Al-Oufi ◽  
Nadir M. Al-Abri
Keyword(s):  
Historical Data ◽  
Demersal Fish ◽  
Fish Biomass ◽  
Depth Range ◽  
Shelf Area ◽  
Artisanal Fishery ◽  
Field Surveys ◽  
Positive Linear Relationship ◽  
Minimum Zone ◽  
Oxygen Minimum

Data from five field surveys carried out along the shelf in the 20-250m depth range and historical data on artisanal fishery were analyzed. A positive linear relationship between the demersal fish biomass and the shelf area was pronounced for a certain (intermediate) stratum only: 50-100m. No statistical link was found for the strata above it (25-50m) and beneath it (100-150m and 150-250m). The pronounced one was associated with the low boundary of the oxygen minimum zone impinging on the shelf. Annual landings of demersal fishes in the region with the largest shelf area exceeded landings in the region with the smallest area by as much as 1.6 times. The ratio of small pelagic to demersal fish landings decreased as a factor of 10, from small to large shelf areas.

Vertical distribution of Benthic Invertebrates in the Bed of the Thomson River, Victoria

1988 ◽  
Vol 39 (6) ◽  
pp. 775 ◽  
Author(s):  
R Marchant
Keyword(s):  
Vertical Distribution ◽  
Benthic Invertebrates ◽  
Benthic Fauna ◽  
Late Summer ◽  
Sample Surface ◽  
Depth Range ◽  
The Vertical Distribution ◽  
Surber Sampler

The vertical distribution of the benthic fauna was studied at three sites on the Thomson River using a freeze-corer. Samples were taken over two years in early and late summer. At each site an average of 72 to 84% of the fauna was found in the 0-10 cm zone of the riverbed, 10-20% in the 10-20 cm zone and 6-8% in the 20-30 cm zone; flooding at one site was followed by an increase in the depth to which the fauna penetrated. Surface percentage abundances were probably underestimated because of the inability of the corer to sample surface rocks and their fauna consistently and because the coring operation disturbs the surface fauna to some extent before it can be frozen. Nevertheless, the results indicate that in the Thomson River the majority of the fauna is within the depth range (0-10 cm) of a Surber sampler.

Near-bottom Currents in the Mid-Atlantic Ridge Rift Valley

1975 ◽  
Vol 12 (4) ◽  
pp. 703-710 ◽  
Author(s):  
George H. Keller ◽  
Susan H. Anderson ◽  
J. William Lavelle
Keyword(s):  
Rift Valley ◽  
Tidal Currents ◽  
Bottom Current ◽  
Mean Flow ◽  
Bottom Currents ◽  
Unidirectional Flow ◽  
Local Topography ◽  
Mid Atlantic Ridge

Near-bottom current measurements during a 46 day period (October to December 1973) in the rift valley of the Mid-Atlantic Ridge just south of the Azores reveal a mean flow at two stations of 2.6 and 8.2 cm/s, predominantly trending parallel to the northeast orientation of the valley. Maximum velocities recorded at the sites were 14.4 and 24.2 cm/s. Semi-diurnal tidal currents appear to strongly influence the flow within the valley causing current reversals, except in areas where local topography and constrictions in the valley apparently result in a unidirectional flow to the northeast.

Fiscal rules: Excessive limitation or indispensable instrument of fiscal sustainability?

2016 ◽  
pp. 5-29 ◽  
Author(s):  
E. Gurvich ◽  
I. Sokolov
Keyword(s):  
Historical Data ◽  
Federal Budget ◽  
Fiscal Sustainability ◽  
Fiscal Rules ◽  
External Shocks ◽  
Base Price ◽  
Depth Analysis ◽  
Fiscal Balance ◽  
Lower Size ◽  
Budget Expenditure

In-depth analysis of international and Russia’s experiences with implementing fiscal rules is presented. Theoretical and empirical evidences are suggested in favor of retaining the present fiscal rules with some modifications aimed at ensuring: a) a relatively stable level of federal budget expenditure with guaranteed full execution of all commitments; b) countercyclical fiscal policy, based on flexibleand proper reaction to revenue changes; and c) robustness of fiscal rules to internal and external shocks. The main new features suggested include modified calculation of the oil base price, different measurement of cyclical fiscal revenues, lower size of structural fiscal balance, and thorough specification of sources for each item of the balance. The modified rules envisage increased flexibility by relaxing to a pre-set extent and for a pre-set time spending limits in response to extreme shocks. The suggested version of fiscal rules has been tested by application to historical data for 2005-2015, and macro projections for 2015-2025.

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