sill depth

Three piston cores from Bedford Basin, a silled coastal inlet, provide the basis for a micropaleontological study of postglacial to recent sediments. Five faunal units (four foraminiferal, one arcellacean) are found in core 79-11: a surface assemblage, followed by deep estuarine, marginal marine, transition, and freshwater (arcellacean) assemblages. The other cores contain only expanded marine sequences. The top of the transition zone in core 79-11 has a C-14 age of 5830 ± 230 years BP, indicating a rise in sea level of at least 20 m (the sill depth) during the Holocene.Four dinoflagellate assemblage zones are found in core 79-11. The first (O. centrocarpum – B. tepikiense) is typical of a silled basin with marine water of near-normal salinity; the second (P. conicoides – Cyst C) indicates a temperate marine environment with strong fluvial influence (marginal marine); the third (P. limbatum) is dominated by freshwater cysts, and the fourth (Dinocyst sp. A) is dominated by subarctic brackish water cysts.Four pollen assemblage zones are found in core 79-11. Zones C1–C3 indicate mixed boreal–deciduous forest vegetation. Zone B indicates early Holocene park–woodland vegetation, the base of which has a C-14 age of 7705 ± 550 BP. The palynozones in the marine sediment core are correlatable with C-14 dated stratigraphies from Nova Scotian lakes.Foraminifera and dinoflagellate assemblages in core 79-11 reflect the response of the microfauna and microflora to changes in water depth, salinity, and temperature, which have accompanied changes in sea level and climate during the past 8000 years. Major changes in the marine biota during the recent period of urban development may be due to increased sediment influx and effluent discharge. The effects of anthropogenic changes are small, however, compared to those accompanying the Holocene marine transgression.

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Pollution of the Outer Oslofjord

Water Science & Technology ◽

10.2166/wst.1991.0317 ◽

1991 ◽

Vol 24 (10) ◽

pp. 321-322

Author(s):

Kjell Baalsrud

Keyword(s):

North Sea ◽

General Circulation ◽

Sea Water ◽

Sewage Treatment ◽

Circulation Pattern ◽

Polluted Water ◽

The North ◽

Recreation Area ◽

The North Sea ◽

Sill Depth

The Outer Oslofjord has recently been subject to concern. 1. The Inner Oslofjord. Covers an area of 193 km2, is 160 m deep and is separated from the Outer Oslofjord by the narrow Drøbak sound with a sill depth of less than 20 metres. This part of the Oslofjord constitutes an enclosed body of sea water, sensitive to pollution, receiving sewage from approximately 650,000 inhabitants. In spite of modern sewage treatment, the fjord still suffers torn eutrophication problems resulting in reduced oxygen in the deep water, and areas of anoxic bottom water. The fjord is an important recreation area. 2. The Outer Oslofjord. Recent findings indicate that eutrophication is slowly increasing. An increasing eutrophication of the Outer Oslofjord wil also increase the need (and cost) of better sewage treatment in the Inner Oslofjord. 3. The North Sea. The quality of the water in the Oslofjord area is also dependent on the water it receives from the Skagerrak. The Skagerrak water will periodically receive polluted water from the southern North Sea and Kattegat. When these episodes coincide with water renewals between the Oslofjord and the Skagerrak, the fjord will receive polluted water from other countries. The Oslofjord water will in turn discharge into the Skagerrak, but due to the general circulation pattern, this will mainly influence the Norwegian south-east coast.

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South Adriatic Recipes: Estimating the Vertical Mixing in the Deep Pit

Frontiers in Marine Science ◽

10.3389/fmars.2020.565982 ◽

2020 ◽

Vol 7 ◽

Author(s):

Vanessa Cardin ◽

Achim Wirth ◽

Maziar Khosravi ◽

Miroslav Gačić

Keyword(s):

Time Series ◽

Heat Equation ◽

Gravity Current ◽

Vertical Mixing ◽

Temperature Structure ◽

Temperature Profiles ◽

Eof Analysis ◽

Vertical Temperature ◽

Current Events ◽

Sill Depth

The available historical oxygen data show that the deepest part of the South Adriatic Pit remains well-ventilated despite the winter convection reaching only the upper 700 m depth. Here, we show that the evolution of the vertical temperature structure in the deep South Adriatic Pit (dSAP) below the Otranto Strait sill depth (780 m) is described well by continuous diffusion, a continuous forcing by heat fluxes at the upper boundary (Otranto Strait sill depth) and an intermittent forcing by rare (several per decade) deep convective and gravity-current events. The analysis is based on two types of data: (i) 13-year observational data time series (2006–2019) at 750, 900, 1,000, and 1,200 m depths of the temperature from the E2M3A Observatory and (ii) 55 vertical profiles (1985–2019) in the dSAP. The analytical solution of the gravest mode of the heat equation compares well to the temperature profiles, and the numerical integration of the resulting forced heat equation compares favorably to the temporal evolution of the time-series data. The vertical mixing coefficient is obtained with three independent methods. The first is based on a best fit of the long-term evolution by the numerical diffusion-injection model to the 13-year temperature time series in the dSAP. The second is obtained by short-time (daily) turbulent fluctuations and a Prandtl mixing length approximation. The third is based on the zero and first modes of an Empirical Orthogonal Function (EOF) analysis of the time series between 2014 and 2019. All three methods are compared, and a diffusivity of approximately κ = 5 · 10−4m2s−1 is obtained. The eigenmodes of the homogeneous heat equation subject to the present boundary conditions are sine functions. It is shown that the gravest mode typically explains 99.5% of the vertical temperature variability (the first three modes typically explain 99.85%) of the vertical temperature profiles at 1 m resolution. The longest time scale of the dissipative dynamics in the dSAP, associated with the gravest mode, is found to be approximately 5 years. The first mode of the EOF analysis (85%) represents constant heating over the entire depth, and the zero mode is close to the parabolic profile predicted by the heat equation for such forcing. It is shown that the temperature structure is governed by continuous warming at the sill depth and deep convection and gravity current events play less important roles. The simple model presented here allows evaluation of the response of the temperature in the dSAP to different forcings derived from climate change scenarios, as well as feedback on the dynamics in the Adriatic and the Mediterranean Sea.

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Bathymetry and oceanic flow structure at two deep passages crossing the Lomonosov Ridge

10.5194/os-2017-14 ◽

2017 ◽

Author(s):

Göran Björk ◽

Martin Jakobsson ◽

Karen Assmann ◽

Leif Andersson ◽

Johan Nilsson ◽

...

Keyword(s):

Water Exchange ◽

The Arctic ◽

Morphological Evidence ◽

Lomonosov Ridge ◽

Hydrographic Data ◽

Bathymetric Survey ◽

Water Properties ◽

Makarov Basin ◽

Topographical Feature ◽

Sill Depth

Abstract. The Lomonosov Ridge represents a major topographical feature in the Arctic Ocean which has a large effect on the water circulation and the distribution of water properties. This study presents detailed bathymetric survey data along with hydrographic data at two deep passages across the ridge: A southern passage (80–81° N) where the ridge crest meets the Siberian continental slope and a northern passage around 84.5° N. The southern channel is characterized by smooth and flat bathymetry around 1600–1700 m with a sill depth slightly shallower than 1700 m. A hydrographic section across the channel reveals an eastward flow with Amundsen Basin properties in the southern part and a westward flow of Makarov Basin properties in the northern part. The northern passage includes an approximately 72 km long and 33 km wide trough which forms an intra basin in the Lomonosov Ridge morphology (the Oden Trough). The eastern side of Oden Trough is enclosed by a narrow and steep ridge rising 500–600 m above a generally 1600 m deep trough bottom. The deepest passage (the sill) is 1470 m deep and located on this ridge. Hydrographic data show irregular temperature and salinity profiles indicating that water exchange occurs as midwater intrusions bringing water properties from each side of the ridge in well-defined but irregular layers. There is also morphological evidence that some rather energetic flows may occur in the vicinity of the sill. A well expressed deepening near the sill may be the result of seabed erosion by bottom currents.

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Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution ocean model

Climate of the Past ◽

10.5194/cp-11-233-2015 ◽

2015 ◽

Vol 11 (2) ◽

pp. 233-251 ◽

Cited By ~ 6

Author(s):

R. P. M. Topper ◽

P. Th. Meijer

Keyword(s):

Deep Water ◽

Ocean Model ◽

Messinian Salinity Crisis ◽

Deep Water Formation ◽

Western Basin ◽

Eastern Basin ◽

Water Characteristics ◽

Water Formation ◽

Sill Depth ◽

The Mediterranean

Abstract. A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations of the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation). A series of experiments with different sill depths in the Atlantic–Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is shallower and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin, a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic–Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth &leq;10 m, is a plausible scenario for the second stage of the Messinian Salinity Crisis during which halite was rapidly accumulated in the Mediterranean. With the model setup and experiments, a basis has been established for future work on the sensitivity of Mediterranean circulation to changes in (palaeo-)bathymetry and external forcings.

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Deep water Exchanges in Bute Inlet, British Columbia

Journal of the Fisheries Research Board of Canada ◽

10.1139/f75-246 ◽

1975 ◽

Vol 32 (11) ◽

pp. 2075-2089 ◽

Cited By ~ 4

Author(s):

C. A. Lafond ◽

G. L. Pickard

Keyword(s):

British Columbia ◽

Time Series ◽

Dissolved Oxygen ◽

Deep Water ◽

Annual Cycle ◽

Water Exchange ◽

Renewal Processes ◽

Strait Of Georgia ◽

Circulation Patterns ◽

Sill Depth

Bute Inlet is a fjord of the British Columbia mainland coast connected to the Strait of Georgia through Sutil Channel. The properties of the waters in the inlet were observed during a series of cruises from June 1972 to June 1974 with the main objective of determining the water exchange below the top 100 m.Vertical longitudinal sections and time-series plots of salinity, temperature, and dissolved oxygen distributions measured during the 2-yr survey were used to analyze the circulation patterns and renewal processes of the water below 100 m.Inflows of deep water from the Strait of Georgia into Bute occurred frequently during the study period, and took place when the water from the Strait of Georgia above the inlet sill depth was denser than the water in the basin of the inlet. Volumes of some inflows into Bute were estimated, and calculations indicate that inflow speeds could be large enough to be recorded by existing current meters. The renewal of the deep water in Bute Inlet basin appears to be basically consistent with the annual cycle of deepwater replacement in the Strait of Georgia with its year-to-year variations.

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The Oceanography of Hebron Fjord, Labrador

Journal of the Fisheries Research Board of Canada ◽

10.1139/f56-043 ◽

1956 ◽

Vol 13 (5) ◽

pp. 709-758 ◽

Cited By ~ 10

Author(s):

David C. Nutt ◽

Lawrence K. Coachman

Keyword(s):

Inorganic Phosphate ◽

Eddy Diffusivity ◽

High Arctic ◽

Ice Formation ◽

Vertical Movements ◽

Flushing Time ◽

Thermohaline Convection ◽

Run Off ◽

Rate Of Oxygen Consumption ◽

Sill Depth

Hebron Fjord, extending some 28 miles into the northeast coast of Labrador at about latitude 58° 10′ N., and having a sill at depth of 59 m. across its mouth, was visited at various periods during 1949, 1952 and 1954. The present paper deals with the oceanographic regime and physical environment in the fjord and adjacent coastal waters. Data on tides and currents, and on contributions of fresh water from precipitation run-off and ice melting are given. Oceanographic factors discussed include temperature, salinity, dissolved oxygen, inorganic phosphate, temperature–salinity relationships, and long-term trends. Ice formation as an oceanographic phenomenon is considered. Computations of thermohaline convection are made, and the effects of ice formation and exchange in determining the winter oceanographic structure are discussed. Above sill depth exchange occurs principally by horizontal movements and a flushing time of about 68 days is computed. Below sill depth exchange must involve vertical movements and occurs principally by convection in winter. Calculations of the A factors of eddy conductivity and eddy diffusivity are made. Dynamic computations of water transport are given. During winter a water temperature of −1.75 °C. exists at all levels in the fjord, rising in summer only to −1.68° at 250 m. and −1.00° at 100 m., causing the bottom waters to remain an isolated pocket of high Arctic environment during the summer and fall seasons as contrasted with the disappearance of negative temperatures down to 120 m. by mid-October outside the fjord. Inorganic phosphate increases with depth; photosynthesis maintains oxygen at super-saturation above 30 m. during summer, and the rate of oxygen consumption and renewal by vertical transport below 80 m. is calculated.

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The evolution of mode-2 nonlinear internal waves over the northern Heng-Chun Ridge south of Taiwan

Nonlinear Processes in Geophysics ◽

10.5194/npg-22-413-2015 ◽

2015 ◽

Vol 22 (4) ◽

pp. 413-431 ◽

Cited By ~ 7

Author(s):

S. R. Ramp ◽

Y. J. Yang ◽

D. B. Reeder ◽

M. C. Buijsman ◽

F. L. Bahr

Keyword(s):

Internal Waves ◽

High Frequency ◽

Velocity Structure ◽

Primary Study ◽

Turbulent Dissipation ◽

Nonlinear Internal Waves ◽

Mode 2 ◽

Sill Depth ◽

The Waves ◽

Very High

Abstract. Two research cruises were conducted from the R/V OCEAN RESEARCHER 3 during 05–16 August 2011 to study the generation and propagation of high-frequency nonlinear internal waves (NLIWs) over the northern Heng-Chun Ridge south of Taiwan. The primary study site was on top of a smaller ridge about 15 km wide by 400 m high atop the primary ridge, with a sill depth of approximately 600 m. A single mooring was used in conjunction with shipboard observations to sample the temperature, salinity and velocity structure over the ridge. All the sensors observed a profusion of mode-2 NLIWs. Some of the waves were solitary, while others had as many as seven evenly spaced waves per packet. The waves all exhibited classic mode-2 velocity structure with a core near 150–200 m and opposing velocities in the layers above and below. At least two and possibly three most common propagation directions emerged from the analysis, suggesting multiple generation sites near the eastern side of the ridge. The turbulent dissipation due to overturns in the wave cores was very high at order 10−4–10−3 W kg−1. The energy budget suggests that the waves cannot persist very far from the ridge and likely do not contribute to the South China Sea transbasin wave phenomenon.

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Oceanography of Saanich Inlet in Vancouver Island, British Columbia

Journal of the Fisheries Research Board of Canada ◽

10.1139/f62-001 ◽

1962 ◽

Vol 19 (1) ◽

pp. 1-37 ◽

Cited By ~ 94

Author(s):

R. H. Herlinveaux

Keyword(s):

Dissolved Oxygen ◽

Sound Velocity ◽

Fresh Water ◽

Hydrogen Sulphide ◽

Sound Channel ◽

Strait Of Georgia ◽

Saanich Inlet ◽

Sill Depth ◽

Anomalous Transmission ◽

High Concentrations

Saanich Inlet is a fjord (24 km long) having a submerged (75-m) sill at the entrance, behind which there is a deep (234-m) basin. The properties of the water have been observed from time to time from 1927 through 1960. The resulting data are reviewed to provide representative values and structures of temperature, salinity, density (σt), dissolved oxygen content and sound velocity for each month throughout the year. Above the sill depth the properties of the water are normal and continuous with those in the approaches which connect with the Strait of Georgia. The waters below the sill depth are isolated, oxygen-deficient, and usually contain hydrogen sulphide. There is considerable ambient variation in the structures because the currents are too weak to disperse or mix the locally generated concentrations.The runoff into the head of the inlet is negligible. The major source of fresh water is in the approaches. It intrudes the inlet and provides a weak estuarine flushing mechanism above the sill depth. The waters below the sill are flushed only when the water in the approaches becomes sufficiently dense to cascade over the sill into the deep basin.The sound-ranging conditions are far from ideal. From March through July there is a major sound channel at mid-depths above the sill. This vanishes in August and a sound divergence zone develops and persists until December. In addition, the ambient variations provide anomalous transmission conditions.During the autumn (September through November) high concentrations of fish have been observed at the sill depth, associated with the oxycline. Probably the fish are attracted to the area by very large concentrations of zooplankton (Euphausids) that have been observed there at the same time.

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Researching on the Single Lock Chamber Automatic Layout Algorithm

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.678.39 ◽

2014 ◽

Vol 678 ◽

pp. 39-42

Author(s):

Xu Chen ◽

Jing Zhu ◽

Zhao Zhang

Keyword(s):

Utilization Rate ◽

Layout Algorithm ◽

Single Chamber ◽

Safety Distance ◽

Lock Chamber ◽

Automatic Layout ◽

Sill Depth

Arrange the ships reasonable as much as possible in the lock chamber, can help improving the traffic ability and the utilization rate of the lock. At present, it is not enough for the factors that considered in the automatic layout algorithm, such as: the safety distance between the ships, ship bottom sill depth. The algorithm can be further optimized. This paper will present a new automatic layout algorithm for single chamber which is able to enhance the efficiency of the chamber space and improve the traffic ability.

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