Dynamics of the Ningaloo Current off Point Cloates, Western Australia

2006 ◽  
Vol 57 (3) ◽  
pp. 291 ◽  
Author(s):  
Mun Woo ◽  
Charitha Pattiaratchi ◽  
William Schroeder
Keyword(s):  
Numerical Model ◽  
Continental Shelf ◽  
Western Australia ◽  
Bottom Topography ◽  
Volume Transport ◽  
Relative Strength ◽  
Cross Sectional ◽  
Leeuwin Current ◽  
The North ◽  
Tropical Water

The Ningaloo Current (NC) is a wind-driven, northward-flowing current present during the summer months along the continental shelf between the latitudes of 22° and 24°S off the coastline of Western Australia. The southward flowing Leeuwin Current is located further offshore and flows along the continental shelf break and slope, transporting warm, relatively fresh, tropical water poleward. A recurrent feature, frequently observed in satellite images (both thermal and ocean colour), is an anti-clockwise circulation located offshore Point Cloates. Here, the seaward extension of the coastal promontory blocks off the broad, gradual southern shelf, leaving only a narrow, extremely steep shelf to the north. The reduction in the cross-sectional area, from the coast to the 50 m contour, between southward and northward of the promontory is ~80%. Here, a numerical model study is undertaken to simulate processes leading to the development of the recirculation feature offshore Point Cloates. The numerical model output reproduced the recirculation feature and indicated that a combination of southerly winds, and coastal and bottom topography, off Point Cloates is responsible for the recirculation. The results also demonstrated that stronger southerly winds generated a higher volume transport in the NC and that the recirculation feature was dependent on the wind speed, with stronger winds decreasing the relative strength of the recirculation.

Ring structure in the poleward boundary current off Western Australia in Summer

1983 ◽  
Vol 34 (4) ◽  
pp. 547 ◽  
Author(s):  
JC Andrews
Keyword(s):  
Structure Function ◽  
Western Australia ◽  
Large Scale ◽  
Function Analysis ◽  
Ring Structure ◽  
Boundary Current ◽  
Length Scales ◽  
Leeuwin Current ◽  
Tropical Water ◽  
Geopotential Anomaly

Data from five summer cruises off Western Australia are examined objectively using structure functions to establish principal length scales and amplitudes of mesoscale fields. Previous estimates of length scales using geopotential anomaly and geomagnetic electrokinetograph vectors as inputs to structure- function analyses gave length scales that differed by a factor of two. The present analysis shows that there are two length scales, which dominate in different parts of the flow, and this reconciles the two previous estimates. The shorter scale is λs = 157�25 km and the longer is λL = 309�28 km. Regions of strong large-scale currents have warm- and cold-core rings and mesoscale waves associated with them that assume the Rossby deformation scale. These are the λS structures. The longer, λL structures are found in regions of weak large-scale currents. Geopotential anomaly amplitudes and currents in the rings are, respectively, about 0.7 m2 s-2 (geopotential relief = 1 4 m2 s-1) and 70 cm s-1. Data from one summer cruise with a station density of approximately 12 per degree square are analysed in detail subjectively and the structure-function analysis is shown to be quantitatively meaningful. This cruise was near the shelf and shows the advection of low-salinity tropical water poleward over the slope in a narrow baroclinic current. Seaward cyclonic rings were associated with the current. The baroclinic structure of the current and of the rings is compatible with the winter behaviour of Lagrangian drifters released into the Leeuwin Current.

scholarly journals Study on the Spillover of Sediment during Typical Tidal Processes in the Yangtze Estuary Using a High-Resolution Numerical Model

2019 ◽  
Vol 7 (11) ◽  
pp. 390 ◽  
Author(s):  
Dechao Hu ◽  
Min Wang ◽  
Shiming Yao ◽  
Zhongwu Jin
Keyword(s):  
High Resolution ◽  
Numerical Model ◽  
Good Description ◽  
Sediment Concentration ◽  
Yangtze Estuary ◽  
Sediment Flux ◽  
The Yangtze Estuary ◽  
Cross Sectional ◽  
The North ◽  
The Difference

Because of special morphologies and complex runoff–tide interactions, the landward floodtide flows in Yangtze Estuary are observed to spill over from the North to the South Branches, carrying a lot of sediment. To quantitatively clarify the spillover problem, a two-dimensional numerical model using a high-resolution channel-refined unstructured grid is developed for the entire Yangtze Estuary from Datong to river mouths (620 km) and part of the East Sea. The developed model ensures a good description of the river-coast-ocean coupling, the irregular boundaries, and local river regimes in the Yangtze Estuary. In tests, the simulated histories of the tidal level, depth-averaged velocity, and sediment concentration agree well with field data. The spillover of sediment in the Yangtze Estuary is studied using the condition of a spring and a neap tide in dry seasons. For a representative cross-section in the upper reach of the North Branch (QLG), the difference of the cross-sectional sediment flux (CSSF) between floodtide and ebbtide durations is 43.85–11.26 × 104 t/day, accounting for 37.5–34.9% of the landward floodtide CSSF. The mechanics of sediment spillover in Yangtze Estuary are clarified in terms of a successive process comprising the source, transport, and drainage of the spillover sediment.

scholarly journals Water masses and nutrient sources to the Gulf of Maine

2015 ◽  
Vol 73 (3) ◽  
pp. 93-122 ◽  
Author(s):  
David W. Townsend ◽  
Neal R. Pettigrew ◽  
Maura A. Thomas ◽  
Mark G. Neary ◽  
Dennis J. McGillicuddy ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Deep Water ◽  
Gulf Of Maine ◽  
Volume Transport ◽  
Water Masses ◽  
Scotian Shelf ◽  
Nutrient Sources ◽  
The North ◽  
Freshwater Fluxes ◽  
The North Atlantic Oscillation

The Gulf of Maine, a semienclosed basin on the continental shelf of the northwest Atlantic Ocean, is fed by surface and deep water flows from outside the gulf: Scotian Shelf Water (SSW) from the Nova Scotian shelf that enters the gulf at the surface and slope water that enters at depth and along the bottom through the Northeast Channel. There are two distinct types of slope water, Labrador Slope Water (LSW) and Warm Slope Water (WSW); it is these deep water masses that are the major source of dissolved inorganic nutrients to the gulf. It has been known for some time that the volume inflow of slope waters of either type to the Gulf of Maine is variable, that it covaries with the magnitude of inflowing SSW, and that periods of greater inflows of SSW have become more frequent in recent years, accompanied by reduced slope water inflows. We present here analyses of a 10-year record of data collected by moored sensors in Jordan Basin in the interior Gulf of Maine, and in the Northeast Channel, along with recent and historical hydrographic and nutrient data that help reveal the nature of SSW and slope water inflows. We show that proportional inflows of nutrient-rich slope waters and nutrient-poor SSWs alternate episodically with one another on timescales of months to several years, creating a variable nutrient field on which the biological productivities of the Gulf of Maine and Georges Bank depend. Unlike decades past, more recent inflows of slope waters of either type do not appear to be correlated with the North Atlantic Oscillation (NAO), which had been shown earlier to influence the relative proportions of the two types of slope waters that enter the gulf, WSW and LSW. We suggest that of greater importance than the NAO in recent years are recent increases in freshwater fluxes to the Labrador Sea, which may intensify the volume transport of the inshore, continental shelf limb of the Labrador Current and its continuation as the Nova Scotia Current. The result is more frequent, episodic influxes of colder, fresher, less dense, and low-nutrient SSW into the Gulf of Maine and concomitant reductions in the inflow of deep, nutrient-rich slope waters. We also discuss evidence that modified Gulf Stream ring water may have penetrated to Jordan Basin in the summer of 2013.

scholarly journals Foraminiferal signatures of mass transport from the North-West Continental Shelf off Western Australia, IODP Expedition 356

2018 ◽  
Author(s):  
Briony Mamo ◽  
Willem Renema ◽  
Cecilia McHugh ◽  
Stephen Gallagher ◽  
Craig Fulthorpe ◽  
...  
Keyword(s):  
Mass Transport ◽  
Continental Shelf ◽  
Western Australia ◽  
North West ◽  
The North

scholarly journals Oceanographic influence on coastal zooplankton assemblages at three IMOS National Reference Stations in Western Australia

2020 ◽  
Vol 71 (12) ◽  
pp. 1672
Author(s):  
Erin McCosker ◽  
Claire H. Davies ◽  
Lynnath E. Beckley
Keyword(s):  
Western Australia ◽  
Detailed Comparison ◽  
Latitudinal Gradients ◽  
Zooplankton Abundance ◽  
Spatial And Temporal Patterns ◽  
North West ◽  
Leeuwin Current ◽  
National Reference ◽  
The North ◽  
E 32

Knowledge about the coastal zooplankton of the south-eastern Indian Ocean is limited, with few studies having compared assemblages across the latitudinal range of the western seaboard of Australia. The dominant oceanographic feature in this region is the Leeuwin Current, which transports warm, lower-salinity, tropical waters southward along the shelf-edge. This study examined data collected by Australia’s Integrated Marine Observing System at three coastal National Reference Stations located at 22°S 114°E, 32°S 115°E and 34°S 122°E. Spatial and temporal patterns in zooplankton abundance, composition and diversity were investigated, and differences in assemblage structure, particularly with respect to copepods, were related to oceanographic conditions. Clear dissimilarities among copepod assemblages were observed, becoming weaker in winter owing to enhanced connectivity of species driven by alongshore and cross-shelf transport in the Leeuwin Current. Both physical and biogeochemical factors were significant in structuring copepod assemblages, with seawater density, incorporating temperature and salinity, exerting the greatest influence. The results suggest that both broad-scale latitudinal gradients and mesoscale events contribute to variation in zooplankton assemblages in these waters. This study provides the first detailed comparison of zooplankton assemblages among the north-west, south-west and southern coastal waters of Western Australia, and enhances understanding of the processes influencing zooplankton distribution and structure.

scholarly journals The Leeuwin Current south of Western Australia

1993 ◽  
Vol 44 (2) ◽  
pp. 285 ◽  
Author(s):  
GR Cresswell ◽  
JL Peterson
Keyword(s):  
Wind Stress ◽  
Western Australia ◽  
Satellite Image ◽  
Subtropical Water ◽  
Tropical Waters ◽  
Leeuwin Current ◽  
Low Salinity ◽  
Tropical Water ◽  
Autumn And Winter

Satellite images as well as data collected in situ were used to follow the seasonal changes of the Leeuwin Current south of Western Australia (WA) in 1986-87. The current has two major sources: salty subtropical water from west of WA, and fresher tropical water from north of WA. In summer, the tropical waters are excluded by the strong equatorward wind stress. In autumn and winter, this wind stress is reduced and tropical waters flood southward to dominate the flow. Nevertheless, salty subtropical water is entrained en route, and so, whatever the season, the Leeuwin Current is more saline than the 'local' subantarctic waters off southern WA. From a research vessel, observations were made on the current and one of its offshoots in June 1987. The Leeuwin Current had a maximum surface speed of more than 1 m s-1 just beyond the shelf edge. Its warm, low-salinity surface core rode on a sheath of higher-salinity subtropical water that it had entrained upstream. The first survey of the offshoot showed it to be 50 km across and 130 m deep (for water warmer than 17�C), and it extended 200 km seaward (as deduced from a satellite image). Velocities in the offshoot ranged up to 1 m s-1 southward and 1 m s-1 north-eastward on the western and eastern sides, respectively. Richardson numbers were, in places, as low as 0.25. On a second survey two days later, the offshoot was found to have pinched off and the remnant bulge on the edge of the parent stream to have moved 30 km eastward. The flow around this bulge reached 1.6 m s-'. The offshoot/bulge was possibly first formed in April, and it kept its identity at least until August. During this time, it moved eastward at speeds between 2 and 15 km day-1. In June, the offshoot was estimated to contain water equivalent to five days' transport of the parent current.

Distribution and timing of spawning by the Australian pilchard (Sardinops sagax neopilchardus) off Albany, Western Australia

1992 ◽  
Vol 43 (6) ◽  
pp. 1437 ◽  
Author(s):  
WJ Fletcher ◽  
RJ Tregonning
Keyword(s):  
Continental Shelf ◽  
Western Australia ◽  
Outer Shelf ◽  
Spawning Activity ◽  
Leeuwin Current ◽  
Sardinops Sagax ◽  
Marine Embayment ◽  
Eggs And Larvae ◽  
Main Influence ◽  
Timing Of Spawning

The pattern of abundance of eggs and larvae of the Australian pilchard, Sardinops sagax neopilchardus, collected by plankton tows in the region off Albany, Western Australia, was investigated. In 1989, surface tows were undertaken at five localities extending from the marine embayment of Princess Royal Harbour to the continental shelf just outside King George Sound. In 1990, oblique tows were undertaken at six localities extending from just inside King George Sound to beyond the edge of the continental shelf. Eggs and larvae of pilchards were found in many months, but peaks in egg numbers were found in July and December of both 1989 and 1990. There was, however, only one peak in larva abundance, during December. Most eggs and larvae were found in the region 2-8 km offshore from the entrance to King George Sound. Few were found either well inside King George Sound and Princess Royal Harbour or in outer-shelf localities. Spawning in the Albany region therefore occurred inshore of the main influence of the eastward-flowing tropical waters of the Leeuwin Current. The implications of this spawning activity in relation to the fishery for this species and the potential for stock separation along this coast are discussed.

scholarly journals A Victorian emigrant: first observation and range extension of the nudibranch Tenellia catachroma (Burn, 1963) in Western Australia (Mollusca: Gastropoda)

2017 ◽  
Vol 129 (1) ◽  
pp. 37
Author(s):  
Matt J. Nimbs
Keyword(s):  
Western Australia ◽  
South Australia ◽  
Single Individual ◽  
Range Limit ◽  
The South ◽  
The West ◽  
Leeuwin Current ◽  
The North ◽  
Nearshore Environments ◽  
Shallow Subtidal

The southwest coast of Western Australia is heavily influenced by the south-flowing Leeuwin Current. In summer, the current shifts and the north-flowing Capes Current delivers water from the south to nearshore environments and with it a supply of larvae from cooler waters. The nudibranch Tenellia catachroma (Burn, 1963) was considered restricted to Victorian waters; however, its discovery in eastern South Australia in 2013 revealed its capacity to expand its range west. In March 2017 a single individual was observed in shallow subtidal waters at Cape Peron, Western Australia, some 2000 km to the west of its previous range limit. Moreover, its distribution has extended northwards, possibly aided by the Capes Current, into a location of warming. This observation significantly increases the range for this Victorian emigrant to encompass most of the southern Australian coast, and also represents an equatorward shift at a time when the reverse is expected.

scholarly journals A continental shelf scale examination of the Leeuwin Current off Western Australia during the austral autumn–winter

2011 ◽  
Vol 31 (17) ◽  
pp. 1858-1868 ◽  
Author(s):  
Evan Weller ◽  
David Holliday ◽  
Ming Feng ◽  
Lynnath Beckley ◽  
Peter Thompson
Keyword(s):  
Continental Shelf ◽  
Western Australia ◽  
Leeuwin Current ◽  
Austral Autumn
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