7. Tidal mixing

2019 ◽  
pp. 98-115
Author(s):  
David George Bowers ◽  
Emyr Martyn Roberts
Keyword(s):  
Water Depth ◽  
Deep Ocean ◽  
Tidal Currents ◽  
The Other ◽  
Tidal Mixing ◽  
Shelf Seas ◽  
Tidal Mixing Front ◽  
Tidal Streams

‘Tidal mixing’ describes tidal mixing in shelf seas, where the water is shallow and tidal currents can be much faster than in the deep ocean. Most of the energy lost from the tide through friction is first converted into turbulence, which then makes a very effective mixing mechanism, stirring the Sun’s heat downwards. Shelf seas at temperate latitudes in summer are divided into stratified regions and vertically mixed regions, depending on the tidal streams’ strength and the water depth. The transition from one to the other happens rapidly and creates a tidal mixing front. Tidal mixing in estuaries is also discussed along with the harnessing of tides to generate electricity.

6. Tides and the Earth

2019 ◽  
pp. 84-97
Author(s):  
David George Bowers ◽  
Emyr Martyn Roberts
Keyword(s):  
Deep Ocean ◽  
The Body ◽  
Internal Tides ◽  
Earth’S Rotation ◽  
Tidal Friction ◽  
The Earth ◽  
Shelf Seas ◽  
The Creation ◽  
Tidal Streams ◽  
Additional Loss

‘Tides and the Earth’ explains that the energy in tides comes, ultimately, from the Earth’s spin. Tidal streams, rubbing against the seabed, lose energy through friction and, to make up for this loss, energy is transferred into the tide from the Earth’s spin. As a result, Earth’s rotation is gradually slowing and the day is lengthening. Most tidal friction happens in shelf seas, where the currents are strongest and the water is shallow, but there is an additional loss of energy in the body of the deep ocean, through the creation of waves called internal tides, which mix the interior of the deep ocean.

Behavioural observations on the scavenging fauna of the Patagonian slope

1999 ◽  
Vol 79 (6) ◽  
pp. 963-970 ◽  
Author(s):  
Martin A. Collins ◽  
Cynthia Yau ◽  
Conor P. Nolan ◽  
Phil M. Bagley ◽  
Imants G. Priede
Keyword(s):  
Soft Tissues ◽  
Deep Ocean ◽  
Rapid Response ◽  
The Other ◽  
Falkland Islands ◽  
Antimora Rostrata ◽  
Consumption Rates ◽  
Patagonian Toothfish ◽  
Primary Consumers ◽  
Dissostichus Eleginoides

The scavenging fauna of the Patagonian slope (900–1750 m), east of the Falkland Islands was investigated using the Aberdeen University Deep Ocean Submersible (AUDOS), an autonomous baited camera vehicle designed to photograph scavenging fish and invertebrates. The AUDOS was deployed on ten occasions in Falkland waters. Nine experiments were of 10–14 h duration and baited with 800 g of squid and one experiment lasted six days, baited with a 10 kg toothfish (Dissostichus eleginoides). Analysis of photographs revealed considerable patchiness in the composition of the scavenging fauna. Hagfish (Myxine cf. fernholmi) dominated three of the shallower experiments including the 6-d experiment, arriving quickly from down-current, holding station at the bait and consuming the soft tissues first, with consumption rates of up to 200 g h−1. In the other experiments, stone crabs (Lithodidae), the blue-hake (Antimora rostrata) and amphipods were the primary consumers, but the rate of bait consumption was lower. Patagonian toothfish (D. eleginoides) were attracted to the bait at each experiment, but did not attempt to consume the bait. The patchiness in the fauna may be a result of depth, substratum and topography, but in general the rapid response of the scavenging fauna indicates that carrion is rapidly dispersed, with little impact on the local sediment community.

scholarly journals An improved parameterization of tidal mixing for ocean models

2014 ◽  
Vol 7 (1) ◽  
pp. 211-224 ◽  
Author(s):  
A. Schmittner ◽  
G. D. Egbert
Keyword(s):  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Tidal Mixing ◽  
Overturning Circulation ◽  
Microstructure Measurements ◽  
High Resolution Bathymetry ◽  
Diurnal Tides

Abstract. Two modifications to an existing scheme of tidal mixing are implemented in the coarse resolution ocean component of a global climate model. First, the vertical distribution of energy flux out of the barotropic tide is determined using high resolution bathymetry. This shifts the levels of mixing higher up in the water column and leads to a stronger mid-depth meridional overturning circulation in the model. Second, the local dissipation efficiency for diurnal tides is assumed to be larger than that for the semi-diurnal tides poleward of 30°. Both modifications are shown to improve agreement with observational estimates of diapycnal diffusivities based on microstructure measurements and circulation indices. We also assess impacts of different spatial distributions of the barotropic energy loss. Estimates based on satellite altimetry lead to larger diffusivities in the deep ocean and hence a stronger deep overturning circulation in our climate model that is in better agreement with observation based estimates compared to those based on a tidal model.

Development of Method/Apparatus for Close-Visual Inspection of Underwater Structures (Especially Pipelines) in Muddy and Unclear Water Condition

2011 ◽  
Author(s):  
Jasper A. Agbakwuru ◽  
Ove T. Gudmestad ◽  
John G. Groenli ◽  
Helge Skjaveland
Keyword(s):  
Laminar Flow ◽  
Water Depth ◽  
Visual Inspection ◽  
The Other ◽  
The Novel ◽  
Clear Water ◽  
Water Condition ◽  
Initial Stage ◽  
Time Required ◽  
Underwater Structures

Ordinarily, the Remotely Operated Vehicles and underwater divers, even with modern illuminating lamps, would be unable to observe objects clearly in muddy or unclear underwater condition. Efforts have therefore been made to demonstrate that in such underwater condition, it is possible to perform visual inspections and observations adequately and reliably for underwater leaking structures using novel equipment. The novel equipment works by simply supplying a clear laminar flow of water which flows over the surface of the structure to be observed. A camera eye is then placed to observe through the steady flowing clear water. Different configurations of the equipment were checked and it was found that the equipment with fitted valves installed in the flooding box in-line with flowing clear water produced the best result. The volume of water required for the observations appears constant and independent of the depth of water except during the first initial stage of flooding. On the other hand, the period of time required for clear observations increases with increase in water depth. The performance of the equipment was found independent of the nature of underwater visibility. The benefits of this work ranges from leaking structures’ close-visual inspection including leaking pipelines, to subsea pipeline field joint wrap damage inspection for beach pulls in cofferdams. This technique is considered cheap, robust and flexible.

scholarly journals The Mediterranean Sea Overturning Circulation

2019 ◽  
Vol 49 (7) ◽  
pp. 1699-1721 ◽  
Author(s):  
Nadia Pinardi ◽  
Paola Cessi ◽  
Federica Borile ◽  
Christopher L. P. Wolfe
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Eastern Mediterranean ◽  
Deep Ocean ◽  
Western Mediterranean ◽  
The Other ◽  
Strait Of Gibraltar ◽  
Water Formation ◽  
Dense Water Formation ◽  
Meridional Overturning

AbstractThe time-mean zonal and meridional overturning circulations of the entire Mediterranean Sea are studied in both the Eulerian and residual frameworks. The overturning is characterized by cells in the vertical and either zonal or meridional planes with clockwise circulations in the upper water column and counterclockwise circulations in the deep and abyssal regions. The zonal overturning is composed of an upper clockwise cell in the top 600 m of the water column related to the classical Wüst cell and two additional deep clockwise cells, one corresponding to the outflow of the dense Aegean water during the Eastern Mediterranean Transient (EMT) and the other associated with dense water formation in the Rhodes Gyre. The variability of the zonal overturning before, during, and after the EMT is discussed. The meridional basinwide overturning is composed of clockwise, multicentered cells connected with the four northern deep ocean formation areas, located in the Eastern and Western Mediterranean basins. The connection between the Wüst cell and the meridional overturning is visualized through the horizontal velocities vertically integrated across two layers above 600 m. The component of the horizontal velocity associated with the overturning is isolated by computing the divergent components of the vertically integrated velocities forced by the inflow/outflow at the Strait of Gibraltar.

scholarly journals S2P3-R (v1.0): a framework for efficient regional modelling of physical and biological structures and processes in shelf seas

2015 ◽  
Vol 8 (10) ◽  
pp. 3163-3178 ◽  
Author(s):  
R. Marsh ◽  
A. E. Hickman ◽  
J. Sharples
Keyword(s):  
Internal Tides ◽  
Tidal Mixing ◽  
Regional Modelling ◽  
Biological Phenomena ◽  
Horizontal Variation ◽  
Shelf Seas ◽  
Shelf Sea ◽  
Practical Tool ◽  
Regional Adaptation ◽  
Eddy Fluxes

Abstract. An established one-dimensional (1-D) model of Shelf Sea Physics and Primary Production (S2P3) is adapted for flexible use in selected regional settings over selected periods of time. This Regional adaptation of S2P3, the S2P3-R framework (v1.0), can be efficiently used to investigate physical and biological phenomena in shelf seas that are strongly controlled by vertical processes. These include spring blooms that follow the onset of stratification, tidal mixing fronts that seasonally develop at boundaries between mixed and stratified water, and sub-surface chlorophyll maxima that persist throughout summer. While not representing 3-D processes, S2P3-R reveals the horizontal variation of the key 1-D (vertical) processes. S2P3-R should therefore only be used in regions where horizontal processes – including mean flows, eddy fluxes and internal tides – are known to exert a weak influence in comparison with vertical processes. In such cases, S2P3-R may be used as a highly versatile research tool, alongside more complex and computationally expensive models. In undergraduate oceanography modules and research projects, the model serves as an effective practical tool for linking theory and field observations. Three different regional configurations of S2P3-R are described, illustrating a range of diagnostics, evaluated where practical with observations. The model can be forced with daily meteorological variables for any selected year in the reanalysis era (1948 onwards). Example simulations illustrate the considerable extent of synoptic-to-interannual variability in the physics and biology of shelf seas. In discussion, the present limitations of S2P3-R are emphasised, and future developments are outlined.

Biological studies in the vicinity of a shallow-sea tidal mixing front. I. Physical and chemical background

1985 ◽  
Vol 310 (1146) ◽  
pp. 407-433 ◽  
Keyword(s):  
Ammonium Nitrogen ◽  
Tidal Mixing ◽  
Irish Sea ◽  
Total Biomass ◽  
Shallow Sea ◽  
High Biological Activity ◽  
Biological Studies ◽  
Chemical Background ◽  
Tidal Mixing Front ◽  
Physical And Chemical

A study has been made of the distribution and activities of bacteria and zooplankton as they varied seasonally in 1980 and 1981 in the vicinity of a shallow-sea tidal mixing front in the western Irish Sea (approximate position 53° 20' N, 5° 45' W to 53° 50' N, 5° 0' W ). This paper presents the physical and chemical background to these studies as shown by the variations in temperature and salinity and concentrations of chlorophyll a , phaeopigments, cellular adenosine triphosphate (ATP), nitrate, nitrite and ammonium nitrogen, in sections normal to the front. Observations at drogue stations were made to establish the extent of diurnal variations in these properties but these appeared to be small relative to other variations. As the front developed, higher chlorophyll a concentrations appeared in the surface stratified water, in contrast to the bottom stratified water and mixed water, with highest concentrations at the surface at the stratified side of the front and in subsurface patches in the vicinity of the pycnocline. As the phytoplankton populations increased nitrate became depleted in the surface stratified water but nitrite and ammonium nitrogen concentrations remained at about the same levels. Cellular ATP concentration did not appear to be a useful measure of total biomass but indicated high biological activity in the surface stratified water.

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