Shelf-Break Exchange in the Bering, Chukchi and Beaufort Seas

2014 ◽  
pp. 133-165 ◽  
Author(s):  
William J. Williams ◽  
Emily Shroyer ◽  
Jaclyn Clement Kinney ◽  
Motoyo Itoh ◽  
Wieslaw Maslowski
Keyword(s):  
Shelf Break

scholarly journals Infragravity Wave Radiation Across the Shelf Break

2018 ◽  
Vol 123 (7) ◽  
pp. 4483-4490 ◽  
Author(s):  
P. B. Smit ◽  
T. T. Janssen ◽  
T. H. C. Herbers ◽  
T. Taira ◽  
B. A. Romanowicz
Keyword(s):  
Shelf Break ◽  
Wave Radiation ◽  
Infragravity Wave

Numerical simulations of the interaction of internal waves with a shelf break

2006 ◽  
Vol 18 (7) ◽  
pp. 076603 ◽  
Author(s):  
S. K. Venayagamoorthy ◽  
O. B. Fringer
Keyword(s):  
Numerical Simulations ◽  
Internal Waves ◽  
Shelf Break

scholarly journals Stability of a buoyancy-driven coastal current at the shelf break

2002 ◽  
Vol 452 ◽  
pp. 97-121 ◽  
Author(s):  
C. CENEDESE ◽  
P. F. LINDEN
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Unstable Mode ◽  
Shelf Break ◽  
Coastal Current ◽  
Surface Currents ◽  
Flat Bottom ◽  
Vertical Boundary ◽  
Axisymmetric Disturbances ◽  
A Current

Buoyancy-driven surface currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. Different bottom topographies that simulate both a continental slope and a continental ridge were introduced in the container. The topography modified the flow in comparison with the at bottom case where the current grew in width and depth until it became unstable once to non-axisymmetric disturbances. However, when topography was introduced a second instability of the buoyancy-driven current was observed. The most important parameter describing the flow is the ratio of continental shelf width W to the width L* of the current at the onset of the instability. The values of L* for the first instability, and L*−W for the second instability were not influenced by the topography and were 2–6 times the Rossby radius. Thus, the parameter describing the flow can be expressed as the ratio of the width of the continental shelf to the Rossby radius. When this ratio is larger than 2–6 the second instability was observed on the current front. A continental ridge allowed the disturbance to grow to larger amplitude with formation of eddies and fronts, while a gentle continental slope reduced the growth rate and amplitude of the most unstable mode, when compared to the continental ridge topography. When present, eddies did not separate from the main current, and remained near the shelf break. On the other hand, for the largest values of the Rossby radius the first instability was suppressed and the flow was observed to remain stable. A small but significant variation was found in the wavelength of the first instability, which was smaller for a current over topography than over a flat bottom.

Temporal and spatial patterns of spawning in jack mackerel, Trachurus declivis (Pisces:Carangidae), during 1988-91 in eastern Tasmanian waters

1995 ◽  
Vol 46 (5) ◽  
pp. 831 ◽  
Author(s):  
A Jordan ◽  
G Pullen ◽  
J Marshall ◽  
H Williams
Keyword(s):  
Thermal Structure ◽  
Shelf Break ◽  
Eastern Coast ◽  
Jack Mackerel ◽  
Spatial And Temporal Patterns ◽  
Cold Event ◽  
Temporal And Spatial ◽  
High Concentrations ◽  
Break Region ◽  
Eggs And Larvae

Ichthyoplankton surveys conducted during the summer and autumn of 1988-89, 1989-90 and 1990-91 along the eastern coast of Tasmania were used to examine the spatial and temporal patterns of eggs and larvae of jack mackerel, Trachurus declivis. Results indicate that the species spawns along the entire eastern coast during summer. Trachurus declivis eggs were most abundant at shelf-break stations, indicating that spawning is concentrated in this region, although high concentrations of eggs were present on the inner shelf in 1988-89, which can be attributed to rapid onshore transport in that year. Larvae were evenly dispersed over the shelf, with the distribution of larval ages showing no indication of inshore recruitment. Considerable interannual differences in sea surface temperatures and vertical thermal structure were apparent, with the warmer waters and strong thermal stratification in the summer of 1988-89 resulting from the influx of subtropical East Australian Current (EAC) water onto the shelf, which corresponded with a major La Nina 'cold event' at that time. It is suggested that the distribution of spawning is unaffected by the interannual variations in oceanography as the mature population spawns in deeper water in the shelf-break region that is unaffected by the warming in surface waters.

scholarly journals Application of seismo-stratigraphic interpretation techniques to offshore West Greenland

1988 ◽  
Vol 140 ◽  
pp. 64-66
Author(s):  
J.A Chalmers
Keyword(s):  
Pilot Study ◽  
Seismic Data ◽  
Seismic Interpretation ◽  
Shelf Break ◽  
The West ◽  
Regional Geology ◽  
West Greenland ◽  
Oil Companies ◽  
Greenland Basin ◽  
Basement Ridge

A pilot study is being conducted to determine if the use of seismo-stratigraphic interpretation techniques can increase the understanding af the geology of offshore West Greenland in order to reassess the prospectivity of the area. During the period 1975 to 1979, a number of concessions offshore West Greenland were licensed to various consortia of oil companies to search for petroleum. Some 40 000 km of seismic data were acquired, all of which is now released. Five wells were drilled, all of them dry, and all concessions were relinquished by the industry by 1979. The regional geology of offshore West Greenland has been summarised by Manderscheid (1980) and Henderson et al. (1981). They show the West Greenland Basin to consist of fairly uniformly westward dipping sediments bordered near the shelf break by a basement ridge. These authors used what may be termed 'conventional' techniques of seismic interpretation. However, since that time the techniques of seismo-stratigraphy (Vail et al., 1977; Hubbard et al., 1985) have become established. They are now being applied to study seismic data acquired during the mid-1970s.

scholarly journals Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

Ocean Science ◽  
2011 ◽  
Vol 7 (2) ◽  
pp. 185-202 ◽  
Author(s):  
G. D. Williams ◽  
M. Hindell ◽  
M.-N. Houssais ◽  
T. Tamura ◽  
I. C. Field
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Mixed Layer ◽  
Growth Rates ◽  
Shelf Break ◽  
Upper Ocean ◽  
Ocean Stratification ◽  
Glacier Tongue ◽  
Ice Growth ◽  
Continental Shelf Break

Abstract. Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140–148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine rejection in the local coastal polynyas. In 2005, two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for several weeks from the end of February. One of the seals migrated west to the Dibble Ice Tongue, apparently utilising the Antarctic Slope Front current near the continental shelf break. In 2010, immediately after that year's calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and sampled the Commonwealth Bay polynya from March through April. Here we present observations of the regional oceanography during the summer-fall transition, in particular (i) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (ii) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (iii) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth. Heat and freshwater budgets to 200–300 m are used to estimate the ocean heat content (400→50 MJ m−2), flux (50–200 W m−2 loss) and sea ice growth rates (maximum of 7.5–12.5 cm day−1). Mean seal-derived sea ice growth rates were within the range of satellite-derived estimates from 1992–2007 using ERA-Interim data. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer/fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

scholarly journals Diagnosing transit times on the northwestern North Atlantic continental shelf

2018 ◽  
Author(s):  
Krysten Rutherford ◽  
Katja Fennel
Keyword(s):  
North Atlantic ◽  
Gulf Of Maine ◽  
Circulation Model ◽  
Shelf Break ◽  
Genetic Connectivity ◽  
Western Boundary ◽  
Coastal Current ◽  
Scotian Shelf ◽  
Grand Banks ◽  
Transit Times

Abstract. The circulation in the northwestern North Atlantic Ocean is highly complex, characterized by the confluence of two major western boundary current systems and several shelf currents. Here we present the first comprehensive analysis of transport paths and timescales for the northwestern North Atlantic shelf, which is useful for estimating ventilation rates, describing circulation and mixing, characterizing the composition of water masses with respect to different source regions, and elucidating rates and patterns of biogeochemical processing, species dispersal and genetic connectivity. Our analysis uses dye and age tracers within a high-resolution circulation model of the region, divided into 9 sub-regions, to diagnose retention times, transport pathways, and transit times. Retention times are shortest on the Scotian Shelf (~ 3 months) where the inshore and shelf-break branches of the coastal current system result in high along-shelf transport to the southwest. Larger retention times are simulated on the Grand Banks (~ 4 months), in the Gulf of St. Lawrence (~ 12 months) and the Gulf of Maine (~ 6 months). Source water analysis shows that Scotian Shelf water is primarily comprised of waters from the Grand Banks and Gulf of St. Lawrence, with varying composition across the shelf. Contributions from the Gulf of St. Lawrence are larger at near-shore locations, whereas locations near the shelf break have larger contributions from the Grand Banks and slope waters. Waters from the deep slope have little connectivity with the shelf, because the shelf-break current inhibits transport across the shelf break. Grand Banks and Gulf of St. Lawrence waters are therefore dominant controls on biogeochemical properties, and on setting and sustaining planktonic communities on the Scotian Shelf.

scholarly journals Rapid Generation of Upwelling at a Shelf Break Caused by Buoyancy Shutdown

2015 ◽  
Vol 45 (1) ◽  
pp. 294-312 ◽  
Author(s):  
Jessica Benthuysen ◽  
Leif N. Thomas ◽  
Steven J. Lentz
Keyword(s):  
Boundary Layer ◽  
Vertical Mixing ◽  
Shelf Break ◽  
Bottom Boundary Layer ◽  
Ekman Transport ◽  
Bottom Boundary ◽  
Middle Atlantic ◽  
Time Period ◽  
Rapid Generation ◽  
Offshore Transport

AbstractModel analyses of an alongshelf flow over a continental shelf and slope reveal upwelling near the shelf break. A stratified, initially uniform, alongshelf flow undergoes a rapid adjustment with notable differences onshore and offshore of the shelf break. Over the shelf, a bottom boundary layer and an offshore bottom Ekman transport develop within an inertial period. Over the slope, the bottom offshore transport is reduced from the shelf’s bottom transport by two processes. First, advection of buoyancy downslope induces vertical mixing, destratifying, and thickening the bottom boundary layer. The downward-tilting isopycnals reduce the geostrophic speed near the bottom. The reduced bottom stress weakens the offshore Ekman transport, a process known as buoyancy shutdown of the Ekman transport. Second, the thickening bottom boundary layer and weakening near-bottom speeds are balanced by an upslope ageostrophic transport. The convergence in the bottom transport induces adiabatic upwelling offshore of the shelf break. For a time period after the initial adjustment, scalings are identified for the upwelling speed and the length scale over which it occurs. Numerical experiments are used to test the scalings for a range of initial speeds and stratifications. Upwelling occurs within an inertial period, reaching values of up to 10 m day−1 within 2 to 7 km offshore of the shelf break. Upwelling drives an interior secondary circulation that accelerates the alongshelf flow over the slope, forming a shelfbreak jet. The model results are compared with upwelling estimates from other models and observations near the Middle Atlantic Bight shelf break.

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