Dissertations / Theses on the topic 'Leeuwin Current'
To see the other types of publications on this topic, follow the link: Leeuwin Current.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 27 dissertations / theses for your research on the topic 'Leeuwin Current.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Mohd, Akhir Mohd Fadzil. "Physical processes along the southern continental shelf and slope of Western Australia." University of Western Australia. School of Environmental Systems Engineering, 2010. http://theses.library.uwa.edu.au/adt-WU2010.0118.
Full textAbstract:
The circulation along the south coast of Western Australia was examined using field data and numerical modelling. Physical processes in this region, particularly along the continental shelf and slope regions, were poorly understood due to a paucity of field measurements. Data were collected during a research cruise on RV Southern Surveyor (04/2006) during April 2006 consisting of 18 CTD transects from Twilight Cove (126oE) to Cape Leeuwin (115oE) and was augmented by shipborne ADCP data. The field data set provided a detailed understanding of three major current systems: Leeuwin Current (LC), Leeuwin Undercurrent (LU) and Flinders Current (FC). The LC along the south coast exhibits different characteristics when compared to that along the west coast. The LC flows into the colder and lower salinity subantarctic environment of the south coast. This is evident in a strong geopotential gradient off the south-west corner of Australia (Cape Leeuwin) resulting in rapid acceleration of the LC as it reaches a maximum velocity in this region. Numerical modelling studies, using the Regional Ocean Modelling System (ROMS) indicated that wind stress is an important component of the dynamics in this region. This was identified when comparing summer and winter conditions when the winds act in opposite directions, from north-westerly to southeasterly respectively. Along the shelf break and slope, the Flinders Current (FC) interacts with LC. As the dominant current, the FC serves both as a surface and as an undercurrent, transporting sub Antarctic mode water (SAMW). This interconnection the FC and LU can be seen clearly from the salinity, temperature and velocities within the depth range 200-700m postulating a connection between subsurface waters off Tasmania (origin of the Flinders Current) and the tropical Indian Ocean through the Flinders and Leeuwin Undercurrents.
2
Domingues, Catia Motta, and Catia Domingues@csiro au. "Kinematics and Heat Budget of the Leeuwin Current." Flinders University. SOCPES, 2006. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20060612.211358.
Full textAbstract:
This study investigates the upper ocean circulation along the west Australian coast, based
on recent observations (WOCE ICM6, 1994/96) and numerical output from the 1/6 degree Parallel Ocean
Program model (POP11B 1993/97). Particularly, we identify the source regions of the Leeuwin
Current, quantify its mean and seasonal variability in terms of volume, heat and salt transports,
and examine its heat balance (cooling mechanism). This also leads to further understanding of the
regional circulation associated with the Leeuwin Undercurrent, the Eastern Gyral Current and the
southeast Indian Subtropical Gyre.
The tropical and subtropical sources of the Leeuwin Current are understood from an
online numerical particle tracking. Some of the new findings are the Tropical Indian Ocean source
of the Leeuwin Current (in addition to the Indonesian Throughflow/Pacific); the Eastern Gyral
Current as a recirculation of the South Equatorial Current; the subtropical source of the Leeuwin
Current fed by relatively narrow subsurface-intensified eastward jets in the Subtropical Gyre, which
are also a major source for the Subtropical Water (salinity maximum) as observed in the Leeuwin
Undercurrent along the ICM6 section at 22 degrees S.
The ICM6 current meter array reveals a rich vertical current structure near North West
Cape (22 degrees S). The coastal part of the Leeuwin Current has dominant synoptic variability and
occasionally contains large spikes in its transport time series arising from the passage of tropical
cyclones. On the mean, it is weaker and shallower compared to further downstream, and it only
transports Tropical Water, of a variable content. The Leeuwin Undercurrent carries Subtropical
Water, South Indian Central Water and Antarctic Intermediate Water equatorward between
150/250 to 500/750 m. There is a poleward flow just below the undercurrent which advects a
mixed Intermediate Water, partially associated with outflows from the Red Sea and Persian Gulf.
Narrow bottom-intensified currents are also observed.
The 5-year mean model Leeuwin Current is a year-round poleward flow between 22 degrees S and
34 degrees S. It progressively deepens, from 150 to 300 m depth. Latitudinal variations in its volume
transport are a response to lateral inflows/outflows. It has double the transport at 34 degrees S (-2.2 Sv)
compared to at 22 degrees S (-1.2 Sv). These model estimates, however, may underestimate the transport
of the Leeuwin Current by 50%. Along its path, the current becomes cooler (6 degrees C), saltier (0.6 psu)
and denser (2 kg m -3). At seasonal scales, a stronger poleward flow in May-June advects the
warmest and freshest waters along the west Australian coast. This advection is apparently spun up
by the arrival of a poleward Kelvin wave in April, and reinforced by a minimum in the equatorward
wind stress during July.
In the model heat balance, the Leeuwin Current is significantly cooled by the eddy heat
flux divergence (4 degrees C out of 6 degrees C), associated with mechanisms operating at submonthly time scales.
However, exactly which mechanisms it is not yet clear. Air-sea fluxes only account for ~30% of the
cooling and seasonal rectification is negligible. The eddy heat divergence, originating over a narrow
region along the outer edge of the Leeuwin Current, is responsible for a considerable warming of a
vast area of the adjacent ocean interior, which is then associated with strong heat losses to the
atmosphere. The model westward eddy heat flux estimates are considerably larger than those
associated with long lived warm core eddies detaching from the Leeuwin Current and moving
offshore. This suggests that these mesoscale features are not the main mechanism responsible for
the cooling of the Leeuwin Current. We suspect instead that short lived warm core eddies might
play an important role.
3
Boedeker, Scott. "A fine resolution model of the Leeuwin Current system." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA401599.
Full textAbstract:
Thesis (M.S. in Meteorology and Physical Oceanography) Naval Postgraduate School, December 2001.Thesis Advisor(s): Batteen, Mary L. "December 2001." Includes bibliographical references (p. 55-58). Also Available online.
4
Meuleners, Michael Joseph. "A numerical study of the mesoscale eddy dynamics of the Leeuwin Current system /." Connect to this title, 2005. http://theses.library.uwa.edu.au/adt-WU2007.0134.
Full text
5
Meuleners, Michael Joseph. "A numerical study of the mesoscale eddy dynamics of the Leeuwin Current system." University of Western Australia. School of Environmental Systems Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0134.
Full textAbstract:
[Truncated abstract] The study of eastern ocean boundary currents has been principally restricted to the Pacific and Atlantic ocean regions. The traditional view of the circulation near eastern ocean boundaries is that upwelling-favourable winds force surface waters offshore, leading to upwelling of cold, nutrient-rich subsurface water at the coast, the formation and offshore advection of a coastal front, and the generation of alongshore currents, generally having an equatorward surface flow and a poleward undercurrent. The eastern ocean boundary system of the southern Indian Ocean, off the west coast of Australia, is unique compared with these regions because a warm, poleward surface flow, known as the Leeuwin Current, dominates the dynamics over the continental shelf. Satellite imagery has shown the Leeuwin Current consists of a complex system of meanders, jet-like streams, and eddies, and has a seasonal and interannual variability. The oceanic circulation of the region between Carnarvon (latitude 25°S) and Jurien Bay (latitude 31°S) was examined using observational and remotely sensed data in conjunction with a detailed numerical modelling study. The model was validated using in situ ADCP and CTD data, and the horizontal eddy viscosity parameterization was tested against field observations. ... The resulting offshore meander grew laterally, shallowed, and closed to form an anticlockwise eddy to the original clockwise eddy’s south, forming a characteristic LC eddy pair (dipole). The model demonstrated the LC and Leeuwin Undercurrent (LUC) coupling played an important role in the onset of eddies at both sites. When an energy diagnostic scheme was used, the dominant instability process linked to the anticlockwise eddy’s development at site 1 was a mixed mode barotropic and baroclinic instability. The baroclinic instability’s source was the available potential energy stored within the mean lateral density gradient. The LC’s meandering southerly flow interacting with the LUC’s northerly subsurface flow generated the horizontal shear that sourced the barotropic instability. The dominant instability process at site 2 was baroclinic in origin. Possible links between the eddy field dynamics and the shelfslope region’s alongshore topographic variability were considered. The results of a suite of five model runs, differing only in the specification of bottom topography, were contrasted to investigate the effects. Except for the expected alongshore variability, delay in the onset of instabilities, varying growth rates, and some differences in the dominant wavebands’ mesoscale patterns, the overall impression was the response was similar.
6
Rennie, Susan Jane. "Oceanographic processes in the Perth Canyon and their impact on productivity." Thesis, Curtin University, 2005. http://hdl.handle.net/20.500.11937/1904.
Full textAbstract:
Submarine canyons are important to continental shelf ecosystems. They have a strong influence on shelf circulation and the distribution of biota. The Perth Canyon is a long, deep canyon on the Western Australian coastline that has attracted attention as a feeding area for pygmy blue whales (Balaenoptera musculus brevicauda). Despite existing on a highly oligotrophic coast, the Perth Canyon has the ability to support sufficient krill to feed these massive mammals. The aim of this study was to examine the physical processes within the Perth Canyon, and consider how these could affect productivity. Research areas included the interaction of the Leeuwin Current and Leeuwin Undercurrent with the canyon, the circulation within the canyon, the effect of wind forcing and the occurrence of upwelling. The oceanography of the Western Australian coast including seasonal productivity changes was also examined. This study utilised numerical modelling and collection of field data to develop a thorough understanding of the Perth Canyon. The numerical model ROMS (Regional Ocean Modelling System) was used to simulate a long stretch of coastline in which the Perth Canyon was centrally located. The model forced the Leeuwin Current and Undercurrent using density gradients, and the seasonal Capes Current was then generated by applying a surface wind stress. The simulations showed that primarily the Leeuwin Undercurrent interacted with the canyon. Eddies continually formed within the canyon, which enhanced vertical transport and could contribute to entrapment of passive drifters. The addition of wind had no discernible effect on canyon circulation although vertical velocities increased everywhere and shallow upwelling occurred along the shelf. The field data comprised moored temperature loggers, field cruises, and sundry data from satellite imagery, weather stations and whale observations.The temperature loggers, located on the canyon rim, indicated the range of processes that affect the canyon region. These processes included seasonal changes in the wind, the seasonal changes and meanders of the Leeuwin Current, storms, the near-diurnal sea breeze and inertial period changes, and other internal waves. The temperature loggers also indicated sporadic upwelling at the canyon rims, although this upwelling rarely extended into the Leeuwin Current. The field cruises gathered CTD, ADCP, nutrients and acoustic backscatter data. The water masses near the canyon were identified from their temperature, salinity and oxygen signatures. The deep chlorophyll maximum exhibited high spatial variability around the canyon. The circulation, in conjunction with the simulated circulation from ROMS, reiterated that eddies filled the canyon below its rims, and suggested that passive drifters would aggregate within the head. The acoustic backscatter reinforced this, showing that biota concentrated near the head of the canyon, which is where the whales were most often sighted feeding. The conclusions of this study were that the canyon is a region of enhanced productivity where upwelling is enhanced and aggregation of passive drifters is likely. Upwelling occurs more strongly when the Leeuwin Current is weakened or has meandered out of a region. Seasonal changes in productivity in the canyon conform to seasonal productivity arguments for the entire coastline, which accounts for the seasonal aggregation of blue whales. The physical processes in the Perth Canyon are variable and all are important to this marine ecosystem.
7
Huang, Ming-Jer. "The effect of salinity on density in the Leeuwin Current System." Thesis, Monterey, California. Naval Postgraduate School, 1996. http://hdl.handle.net/10945/26513.
Full textAbstract:
Approved for public release; distribution is unlimitedClimatological temperature and salinity fields are used to calculate the salinity contribution to density and dynamic height fields in the Leeuwin Current System (LCS). While the temperature gradient is primarily linear, with warmest water to the north, the salinity fields are spatially inhomogenous. A comparison of density fields, calculated with constant and variable salinity, shows that, off Western Australia, the density field is primarily determined by temperature. Off Southern Australia, the density field is dependent on warm and salty (subtropical) and fresh and cold (sub-Antarctic) water masses. While the dynamic height fields, calculated with constant and variable salinity, show similar flow patterns off Western Australia, different flow patterns are found off Southern Australia. In addition to the analysis of climatological fields, a primitive equation ocean model is used to investigate the role of salinity in the formation of currents and eddies in the LCS. Two identical ocean models, one with a climatological salinity field and the other with no horizontal salinity gradients, are run and compared with each other. Despite the model runs being initialized with similar temperature distributions, there are relatively large temperature and density differences in the Southern Australian region, due to the advection of water masses by the Leeuwin Current. Based on the climatological analyses and the results of the model experiments, it is concluded that, descriptively and dynamically, both temperature and salinity are essential to accurately characterize the large-scale circulation of the LCS
8
Butler, Christopher L. "Modeling studies of the Leeuwin Current off Western and Southern Australia." Thesis, Monterey, California. Naval Postgraduate School, 1994. http://hdl.handle.net/10945/30803.
Full textAbstract:
A high-resolution, multi-level, primitive equation ocean model is used to examine the response of an eastern boundary oceanic regime to thermal and wind forcing. The focus of this study is the anomalous Leeuwin Current System off Western and Southern Australia. Three types of experiments are conducted. The first type forces the model from rest with the Indian Ocean climatological temperature gradient as an initial condition only, while the second type repeats the first experiment with the added contribution of the North West Shelf water temperature profile. The role of irregular coastline geometry on the generation of currents and eddies is also examined by comparing these cases with and without an irregular (realistic) coastline. The third type, with an irregular coastline, forces the model from rest with constant thermal and wind forcing. A one-time application of the North West Shelf water is added during the model run. In all experiments, surface currents, undercurrents, meanders, and eddies are generated. The results from experiments with an irregular, rather than an idealized coastline, show preferred eddy generation locations. The results from the third type of experiment. which has the most realistic features, agrees well with available observations off Western and Southern Australia. These results support the hypothesis that both thermal and wind forcing are important mechanisms for the generation of many of the observed features in the Leeuwin Current System.
9
Tworek, Troy J. "The role of the planetary beta effect on currents and eddies in the Leeuwin Current System." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA383704.
Full textAbstract:
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, Sept. 2000.Thesis advisor(s): Batteen, Mary L. "September 2000." Includes bibliographical references (p. 159-161). Also available in print.
10
Kennedy, Richard A. "A numerical study of the forcing mechanisms of the Leeuwin current system /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FKennedy.pdf.
Full textAbstract:
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, September 2002.Thesis advisor(s): Mary L. Batteen, Curtis A. Collins. Includes bibliographical references (p. 93-96). Also available online.
11
Kennedy, Richard A. Jr. "A numerical study of the forcing mechanisms of the Leeuwin current system." Thesis, Monterey, California. Naval Postgraduate School, 2002. http://hdl.handle.net/10945/4998.
Full textAbstract:
Approved for public release, distribution is unlimitedTo investigate the role of wind forcing, bottom topography and thermohaline gradients in the Leeuwin Current System (LCS), several experiments are conducted with a sigma coordinate primitive equation model on a beta-plane. Results show that the LCS is an anomalous eastern boundary current (EBC) that generates a coastal poleward current, an equatorward undercurrent, and highly energetic mesoscale features such as meanders and eddies. Thermohaline gradient effects were shown to be the primary mechanism in the generation of a poleward (equatorward) current (undercurrent), eddies and meanders in the LCS. Inshore of the poleward surface flow, next to the coast, wind forcing plays an important role in generating an equatorward coastal current and upwelling. Bottom topography is shown to be an important mechanism for intensifying and trapping currents near the coast, weakening subsurface currents and intensifying eddies off capes. Overall, the results of the study compare well with available observations in the LCS.
12
com, barb muhling@gmail, and Barbara Muhling. "Larval fish assemblages in coastal, shelf and offshore waters of south-western Australia." Murdoch University, 2006. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061129.110448.
Full textAbstract:
Larval fish assemblages were investigated during a three-year multidisciplinary project conducted off the coast of south-western Australia. Larvae were sampled using replicated oblique bongo net tows along a five-station transect extending from inshore (18m depth) to offshore waters (1000m depth). A total of 148 taxa from 93 teleost families were identified. Larvae of Gobiidae, and Blenniidae were abundant inshore, while larvae of pelagic and reef-dwelling families, such as Clupeidae, Engraulidae, Carangidae and Labridae were common in continental shelf waters. Larvae of oceanic families, particularly Myctophidae, Phosichthydae and Gonostomatidae, dominated offshore assemblages. Inshore larval fish assemblages were the most seasonal, in terms of species composition and abundance, with offshore
assemblages the least so.
Multivariate statistical analyses revealed larval fish assemblages to have a strong temporal and spatial structure. Assemblages were closely correlated to water masses, with species distributions reflecting both cross shelf and along-shore oceanographic processes and events. The strength and position of the warm, southward flowing Leeuwin Current, and of the cool, seasonal, northward flowing Capes Current were shown to drive much of the variability in the marine environment, and thus larval fish assemblages.
Many of the distinctions between larval fish assemblages on the continental shelf were attributable to patterns of abundance in clupeiform larvae. While larvae of Engraulis australis and Spratelloides robustus showed clear seasonal and spatial distribution patterns, larvae of Sardinops sagax and Etrumeus teres were found throughout the year, with high interannual variability in abundance. Abundances of larvae from all pelagic clupeiform species were negatively correlated to microzooplankton concentrations. Peaks of abundance of S. sagax and E. teres, in particular, appeared to be better aligned with favourable transport and retention conditions.
A detailed comparison of the horizontal and vertical distribution of larval fishes highlighted the influence of contrasting oceanographic conditions between summer and winter on larval fish assemblages. Although most fish larvae were found above the thermocline, depth distributions differed between taxa, and were shown to influence their offshore transport. Neustonic fish larvae showed potential for significant dispersion during summer, as a result of offshore Ekman transport.
Mesoscale Leeuwin Current eddies were a feature of the oceanography of the region, and their influence on larval fish assemblages was examined in both an anti-cyclonic eddy (warm-core) and a cyclonic eddy (cold-core). The warm-core eddy contained larval fish assemblages that were distinct from those in the cold-core eddy, with lower larval fish concentrations, especially in the eddy centre. Although the eddies originated near the continental shelf, larval fish assemblages within both eddies were largely oceanic, probably a result of the age of the eddies when they were sampled (about 5 months).
Overall, larval fish assemblages showed strong temporal and spatial structure, and were well aligned to water masses in the region. The unique oceanography off south western Australia thus has considerable implications for both larval fish transport, and potential recruitment to regional fisheries.
13
Rutherford, Martin J. "Modeling studies of the Leeuwin Current using a high-resolution primitive equation model." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27139.
Full text
14
Phillips, Robyn L. "A fine resolution model of the Leeuwin Current System off western and southern Australia." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FPhillips.pdf.
Full textAbstract:
Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, September 2002.Thesis advisor(s): Mary L. Batteen, Curtis A. Collins. Includes bibliographical references (p. 85-88). Also available online.
15
Rennie, Susan Jane. "Oceanographic processes in the Perth Canyon and their impact on productivity." Curtin University of Technology, Centre for Marine Science and Technology, 2005. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16438.
Full textAbstract:
Submarine canyons are important to continental shelf ecosystems. They have a strong influence on shelf circulation and the distribution of biota. The Perth Canyon is a long, deep canyon on the Western Australian coastline that has attracted attention as a feeding area for pygmy blue whales (Balaenoptera musculus brevicauda). Despite existing on a highly oligotrophic coast, the Perth Canyon has the ability to support sufficient krill to feed these massive mammals. The aim of this study was to examine the physical processes within the Perth Canyon, and consider how these could affect productivity. Research areas included the interaction of the Leeuwin Current and Leeuwin Undercurrent with the canyon, the circulation within the canyon, the effect of wind forcing and the occurrence of upwelling. The oceanography of the Western Australian coast including seasonal productivity changes was also examined. This study utilised numerical modelling and collection of field data to develop a thorough understanding of the Perth Canyon. The numerical model ROMS (Regional Ocean Modelling System) was used to simulate a long stretch of coastline in which the Perth Canyon was centrally located. The model forced the Leeuwin Current and Undercurrent using density gradients, and the seasonal Capes Current was then generated by applying a surface wind stress. The simulations showed that primarily the Leeuwin Undercurrent interacted with the canyon. Eddies continually formed within the canyon, which enhanced vertical transport and could contribute to entrapment of passive drifters. The addition of wind had no discernible effect on canyon circulation although vertical velocities increased everywhere and shallow upwelling occurred along the shelf. The field data comprised moored temperature loggers, field cruises, and sundry data from satellite imagery, weather stations and whale observations.The temperature loggers, located on the canyon rim, indicated the range of processes that affect the canyon region. These processes included seasonal changes in the wind, the seasonal changes and meanders of the Leeuwin Current, storms, the near-diurnal sea breeze and inertial period changes, and other internal waves. The temperature loggers also indicated sporadic upwelling at the canyon rims, although this upwelling rarely extended into the Leeuwin Current. The field cruises gathered CTD, ADCP, nutrients and acoustic backscatter data. The water masses near the canyon were identified from their temperature, salinity and oxygen signatures. The deep chlorophyll maximum exhibited high spatial variability around the canyon. The circulation, in conjunction with the simulated circulation from ROMS, reiterated that eddies filled the canyon below its rims, and suggested that passive drifters would aggregate within the head. The acoustic backscatter reinforced this, showing that biota concentrated near the head of the canyon, which is where the whales were most often sighted feeding. The conclusions of this study were that the canyon is a region of enhanced productivity where upwelling is enhanced and aggregation of passive drifters is likely. Upwelling occurs more strongly when the Leeuwin Current is weakened or has meandered out of a region. Seasonal changes in productivity in the canyon conform to seasonal productivity arguments for the entire coastline, which accounts for the seasonal aggregation of blue whales. The physical processes in the Perth Canyon are variable and all are important to this marine ecosystem.
16
Sutton, Alicia. "Krill in the Leeuwin Current system: Influence of oceanography and contribution to Indian Ocean zoogeography." Thesis, Sutton, Alicia (2015) Krill in the Leeuwin Current system: Influence of oceanography and contribution to Indian Ocean zoogeography. PhD thesis, Murdoch University, 2015. https://researchrepository.murdoch.edu.au/id/eprint/31439/.
Full textAbstract:
Euphausiids (krill) are important in the food webs of pelagic ecosystems and constitute the prey of a range of species including fishes, whales and seabirds. However, knowledge about euphausiid diversity, distribution and abundance in the south-east Indian Ocean off Western Australia is limited. The influence of the Leeuwin Current system on horizontal and vertical structuring of euphausiid assemblages was investigated from a series of plankton surveys with concurrent oceanographic sampling along the west and north-west coasts of Australia. In total, 34 species of euphausiids were identified and assemblages were significantly structured across shelf, shelf break and oceanic waters, as well as alongshore. Further, vertical structuring of assemblages was evident from depth-stratified sampling across a thermohaline front between Leeuwin Current Water and Sub Tropical Surface Water. For all surveys, assemblages were related to a suite of environmental variables, and were significantly influenced by the physio-chemical properties of the prevailing water masses, as well as indicators of food availability, such as chlorophyll a. To ascertain the environmental variables driving euphausiid zoogeography in the Indian Ocean (20°N - 40°S and 20°E - 122°E), data on euphausiids from the Leeuwin Current system were combined with distribution records from the literature (spanning the past 50 years), to generate measures of species richness and taxonomic distinctness across the basin. Salinity and dissolved oxygen were found to be important drivers of euphausiid zoogeography, and were particularly significant with respect to the low numbers of species in the northern Indian Ocean. Finally, to understand the role of euphausiids in marine food webs off Western Australia, fatty acids and stable isotopes placed common euphausiid species from the Perth Canyon (32°S) as omnivorous but feeding primarily on dinfolagellates. Overall, this thesis expands on the knowledge of euphausiid diversity, distribution and abundance in the south-east Indian Ocean and confirms the influence of boundary currents on euphausiid distributions.
17
Cox, Anthony W. "Modeling studies of the effects of seasonal wind forcing and thermohaline gradients on the Leeuwin Current System." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA358830.
Full textAbstract:
Thesis (M.S. in Meteorology and Physical Oceanography) Naval Postgraduate School, December 1998."December 1998." Thesis advisor(s): Mary L. Batteen. Includes bibliographical references (p. 119-121). Also available online.
18
Bayler, Eric Judson. "Seasonal wind and ocean thermal forcing influences on the generation of the Leeuwin Current and its eddies." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28516.
Full text
19
Limbourn, Andrew John. "The condition at settlement of the western rock lobster, Panulirus cygnus George : spatial and temporal fluctuations." University of Western Australia. School of Animal Biology, 2010. http://theses.library.uwa.edu.au/adt-WU2010.0062.
Full textAbstract:
The condition at settlement of the western rock lobster pueruli presumably reflects both their energetic condition in reaching the near shore and subsequent recruitment into adult populations. In recruiting to the near shore the pueruli swim across the continental shelf where oceanographic conditions are complex and likely influence the success of recruitment. The results from the biochemical studies are interpreted in light of the oceanography off the coast of Western Australia. I investigated the nutritional condition of larval phyllosomata, post-larval puerulus and first instar post-pueruli juveniles of the spiny lobster, Panulirus cygnus, to determine energy use during the non-feeding transitional puerulus stage. Biochemical analyses of lipid, fatty acid (FA) and protein revealed that lipid, in particular phospholipids, is primarily used for energy during the nonfeeding puerulus stage. Monounsaturated FA showed the greatest decline with development, whereas the polyunsaturated FA showed a high degree of sparing, suggesting these FA are not used as a substrate for energy production. The knowledge gained on the biochemistry of energy use in P. cygnus was then used to investigate the spatial and temporal variability in the nutritional condition, in particular lipid condition, of puerulus collected at three near shore locations (Alkimos, Jurien Bay and Dongara) along the Western Australia coast, and one offshore location (Houtman Abrolhos Islands). The one offshore location was chosen as I hypothesised that arriving pueruli are likely to be in a better state of nutrition than those arriving at more coastal locations where the potential journey from offshore larval feeding grounds to the near shore is considerably greater. This element of my research showed lipid levels to be inversely related, generally, to shelf width but were variable, suggesting pueruli may travel complex trajectories to reach nearshore settlement. The lipid and FA composition of pueruli was also consistent with spatial and seasonal variation in Leeuwin Current and coastal productivity regimes.
20
Holliday, David. "Incorporation of larval fishes into a developing anti-cyclonic eddy of the Leeuwin Current: timing, sources and pathways." Thesis, Holliday, David (2009) Incorporation of larval fishes into a developing anti-cyclonic eddy of the Leeuwin Current: timing, sources and pathways. PhD thesis, Murdoch University, 2009. https://researchrepository.murdoch.edu.au/id/eprint/2345/.
Full textAbstract:
Meso-scale circulation and cross-shelf transport of planktonic biota associated with the formation of an anticyclonic (warm-core) eddy of the poleward-flowing Leeuwin Current (LC) were examined during a month-long, multidisciplinary voyage off south-western Australia. The study was based upon Lagrangian examination of upper ocean circulation and stations for depth-integrated (bongo nets) and depth-stratified (EZ nets) sampling of larval fishes were linked primarily with the locations of satellite-tracked oceanographic drifters.
The regional dominance of a modified LC water mass, particularly in the eddy field, indicated strong mixing between LC, shelf and oceanic subtropical surface water and the eddy had physical, chemical and biological signatures reflecting these source waters. High concentration of chlorophyll a (0.5 g L-1) in the eddy was derived, at least in part, from the shelf and was much greater than that in the surrounding ocean. In the study area, the horizontal distributions of larvae of fishes with both neritic and oceanic origins indicated strong onshore-offshore coupling. High concentrations of larval fishes in the eddy (1.0 – 3.0 larvae / m3) contrasted with those in the surrounding ocean. Assemblages were dominated by the larvae of oceanic mesopelagic taxa such as Myctophidae. Larvae of tropical neritic taxa (e.g. Bothidae, Pomacentridae) which were in much lower concentrations (<0.01 / m3) within the eddy, identified the LC as the major transport route for incorporation of neritic larvae. Incursions of the LC onto the shelf north (upstream) of the study area appear to be important for initial entrainment of neritic larvae into the current. In contrast, the occurrence of larvae of oceanic meso-pelagic fishes in the eddy appear to be the product of localised spawning in, or near, the eddy.
The night-time vertical distribution patterns of larval fishes showed highest concentrations between the surface and 80 m depth throughout the study region. These vertical distributions appear to be a function of size and developmental stage of larvae rather than a response to environmental conditions and the velocity field. A time of 8 days for transport around the eddy perimeter, as well as ejection of a drifter from the eddy, have important implications for the transport and fate of neritic larvae during eddy evolution. Opportunistic sampling across another eddy in 2007 allowed comparison of interannual variability in the LC eddy field. The seasonal regularity of warm-core LC eddies, which are characterised by enhanced productivity, may be important in the ecology of oceanic fish populations in the region. However, the low abundance of neritic larvae in the eddies suggests that the spring/summer spawning of many temperate coastal species allows avoidance of the potentially deleterious transport associated with the LC and eddy field in the austral autumn/winter.
21
Haller, Christian. "Application of Modern Foraminiferal Assemblages to Paleoenvironmental Reconstruction: Case Studies from Coastal and Shelf Environments." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7627.
Full textAbstract:
The aim of paleoenvironmental studies is to reconstruct characteristics of the past environment from fossil assemblages preserved in sedimentary strata. Thus, studies of modern surface assemblages, quantitatively correlated to the environmental parameters, are required before reliable interpretations can be made. For this dissertation, two different techniques were applied in two case studies: a reconstruction making use of a benthic foraminiferal transfer function from the intertidal marshes in the eastern Mississippi Sound, Alabama/Mississippi, and a qualitative reconstruction of ocean current activity on the Western Australian shelf.
Modern salt-marsh foraminifera were collected from Grand Bay, Pascagoula, Fowl River, and Dauphin Island across several elevation transects and different salinity regimes. Cluster analysis yielded nine dead biofacies and five live assemblages from Open Estuarine to Upland Transition. Canonical correspondence analysis indicated a strong relationship between distributions of dead biofacies and elevation. Both dissolution of calcareous species in the organic marsh sediment and the long-term accumulative nature of the dead assemblage favored the use of non-estuarine dead assemblages. A Weighted Average-Partial Least Squared transfer function was applied to the surface data and yielded a Root Mean Squared Error of Prediction (RMSEP) of 0.14 m, which represents 33% Mean Range of Tide at Grand Bay and 39% at Dauphin Island. The transfer function was applied to two sedimentary cores from Grand Bay and two from Dauphin Island, which revealed disparate developments between the regions during the last 1,900 years. While both Dauphin Island cores indicated relative sea-level trends aligned with other Gulf of Mexico studies, Grand Bay was likely impacted by a river avulsion event disconnecting Grand Bay from fluvial sediment influx, and by the erosion of a protective headland, Grand Batture Island. Sediments spanning the last ~100 years contained increased abundances of low marsh foraminifera likely associated with coastline erosion, which was most prominently displayed by a lithology shift towards grey silt in the Dauphin Island cores.
Surface carbonate sediments from Western Australia’s Northwestern Shelf and Carnarvon Ramp were collected from 127–264 m water depth. Foraminiferal assemblages changed between 127 m and 145–264 m due to rapidly decreasing water temperature in the thermocline, and loss of sufficient light for support of “larger” benthic foraminifera. Latitudinal differences were likely caused by three factors: (1) limited influence of the warm Leeuwin Current to support tropical taxa at the sampled depths, (2) reduced habitat diversity on the narrow Carnarvon Ramp compared to surrounding shelves, and (3) differing water-mass characteristics. The gathered information was used to interpret the assemblages from a Carnarvon Ramp core (total depth 300 m), providing insight into the activity of the warm, surficial Leeuwin Current for the last 3.54 My (Pliocene). Abundant infaunal taxa were inferred to indicate low oxygenation, increased supply of organic matter, and high sea-surface productivity during the absence of the Leeuwin Current above the coring site. Dominance of epifaunal species signified higher oxygenation at the sediment-water interface when upwelling of nutrient-rich waters was effectively suppressed by the Leeuwin Current. Around 1.14 Ma, waning of hypoxic conditions was initiated until a more substantial change was marked at 0.91 Ma. Suspension-feeding sponges became common sediment constituents during a Leeuwin Current flow optimum at ~0.6 Ma. The epifaunal taxa dominance persisted on the modern shelf, yet short episodes of infaunal peaks were likely caused by lateral shifts and fluctuating influence of the Leeuwin Current during more intense glacial cycles.
22
Hanson, Christine Elizabeth. "Oceanographic forcing of phytoplankton dynamics in the coastal eastern Indian Ocean." University of Western Australia. Centre for Water Research, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0033.
Full textAbstract:
[Truncated abstract] This work was the first large-scale biological oceanographic study to be undertaken in the coastal eastern Indian Ocean adjacent to Western Australia, and covered both northwest (Exmouth Peninsula to the Abrolhos Islands) and southwest (Cape Naturaliste to Cape Leeuwin) regions. The study area was dominated by the Leeuwin Current (LC), an anomalous eastern boundary current that transports tropical water poleward and prevents deep nutrients from reaching the surface by creating large-scale downwelling. Indeed, LC and offshore waters were consistently associated with low nitrate concentrations and low phytoplankton biomass and production (< 200 mg C m-2 d-1). However, the physical forcing of the LC was offset, during the summer months, by upwelling associated with wind-driven inshore countercurrents (Ningaloo and Capes Currents), which provided a mechanism to access high nutrient concentrations normally confined to the base of the LC. ... Limited seasonal investigations off the Capes region of southwestern Australia showed that the winter production scenario can be very different than summer conditions, with strong Leeuwin Current flow that meanders onto the continental shelf and entrains seasonally nutrient-enriched shelf waters. However, production in the LC was still low (≤450 mg C m-2 d-1) due to light limitation resulting from both increased light attenuation and reduced surface irradiance characteristic of the winter months. This investigation provides fundamental knowledge on physical-biological coupling off Western Australia, with implications for fisheries management in view of seasonal and inter-annual variability in the strength of both the Leeuwin Current and inshore countercurrents.
23
Paterson, Harriet. "Microzooplankton from oligotrophic waters off south west Western Australia : biomass, diversity and impact on phytoplankton." University of Western Australia. School of Animal Biology, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0031.
Full textAbstract:
[Truncated abstract] The role of marine microzooplankton in aquatic food webs has been studied in most regions of the world’s oceans, with the exception of the subtropical/temperate eastern Indian Ocean. This thesis addresses this gap in knowledge by investigating microzooplankton from five stations on a cross continental shelf transect and in two mesoscale features ∼300 km offshore of south west Western Australia. My primary focus was to measure and evaluate microzooplankton community change over space and time and their impact on phytoplankton on a cross shelf transect, sampling five stations from February 2002 December 2004 as part of a large multidisciplinary investigation into the pelagic ecosystem on the shelf (Chapter 2). This transect was named the Two Rocks transect. I also investigated an eddy pair (Chapter 5), which had originated from water in the vicinity of the Two Rocks transect, also undertaken as part of a larger study, investigating biophysical coupling within mesoscale eddies off south west Western Australia . . . The distribution of mixotrophic cells differed across the transect. Those mixotrophs that use photosynthesis as their primarily energy source exploited nutrient limited conditions inshore consuming particles, while mixotrophs that are primarily heterotrophic survived low prey conditions offshore by photosynthesizing. In the eddies, the grazing behaviour of microzooplankton was dependent on the specific phytoplankton assemblage in each eddy. The warm core eddy had a resident population of diatoms that were consumed by heterotrophic dinoflagellates present in high numbers. The cold core eddy had a warm cap which prevented upwelled water reaching the surface, resulting in stratification and a very active microbial food web, particularly in the surface.
24
Spooner, Michelle Ianthe. "The dynamics of the Leeuwin Current during the middle and late quaternary." Phd thesis, 2005. http://hdl.handle.net/1885/151678.
Full text
25
Moore, TS. "Physical oceanographic controls on phytoplankton distribution in the Banda Sea and Western Australian region." Thesis, 2007. https://eprints.utas.edu.au/20951/1/whole_MooreThomasSurman2007_thesis.pdf.
Full textAbstract:
Marine phytoplankton rely on nutrients and light to survive and grow. By controlling the supply of nutrients and by moving phytoplankton around the upper ocean, ocean physics play a critical role in influencing the distribution of phytoplankton. The physical processes that influence phytoplankton distribution act over a wide range of temporal and spatial scales. Using in-situ, and remotely-sensed measurements, this thesis investigates the relationship between ocean physics and phytoplankton distributions in the Banda Sea and off the coast of Western Australia, over a range of scales including synoptic mesoscale eddies, seasonal monsoons, climatological features and ENSO impacts.
In the Banda Sea, the distribution of chlorophyll-a is used as an indicator to describe the biophysical response of the Banda Sea to the seasonal winds of the southeast monsoon. The in-situ and remotely sensed data support the idea that phytoplankton respond to upwelling driven by the southeast monsoon (June - September). In-situ physical data from the BIOP98 cruise suggest an upwelling signal, and analysis of phytoplankton pigments indicates a community dominated by diatoms to the east and a more oligotrophic community to the west; further supporting the idea of an upwelling response. Satellite observations reveal a strong seasonal signal and an east-west gradient in chlorophyll-a, indicating monsoon driven upwelling on the eastern side of the basin. Remotely sensed observations of chlorophyll-a during the 1997-1998 El Nino suggest that the distribution of chlorophyll-a in the Banda Sea is modulated by ENSO, most likely through changes to the thermocline depth and wind regime.
South of the Indonesian Archipelago, the waters off central Western Australia (WA) are unique in terms of their biological and physical oceanographic character. Unusually for an eastern boundary current, the Leeuwin flows poleward and contributes to prevailing downwelling conditions along the WA coast. Significant spatial and temporal variability in phytoplankton distribution exists and a key regional feature of the phytoplankton variability is a seasonal peak in chlorophyll-a in the winter May-July period on the central WA shelf. To test the hypothesis that this seasonal cycle is related to nutrient inputs, this thesis attempts to address several potential sources: (1) upwelling from off-shelf; (2) rainfall and associated runoff; (3) Leeuwin Current transport; ( 4) shall owing and/or mixing of the nutricline; and (5) benthic supply. Nutrient inputs from Leeuwin Current transport and coastal runoff appear to be most important, although sparse data prevent a definite conclusion.
Phytoplankton distribution off central WA also displays persistent mesoscale features. Both satellite and in-situ estimates of surface chlorophyll-a suggest low phytoplankton concentrations in cyclonic ("upwelling") eddies and high concentrations in anti-cyclonic ("downwelling") eddies. The anti-cyclonic eddies entrain regionally high chlorophyll-a shelf waters and then export this material offshore as· these eddies propagate westward. The formation of these anti-cyclonic eddies occurs at two preferred zones along the central WA shelf, near 29°S and between 31° and 33°S, and their formation and movement offshore controls the mixed layer distribution of phytoplankton in the open ocean off the central WA coast during the May-October period.
26
GILLESPIE, LAURA. "Sedimentology of the Miocene Nullarbor Limestone; Southern Australia." Thesis, 2010. http://hdl.handle.net/1974/6257.
Full textAbstract:
The Miocene Nullarbor Limestone is the most recent formation in the Cenozoic Eucla Group and was deposited in the Eucla Basin, southern Australia, at ~38°S paleolatitude during the early to middle Miocene. The rocks form the modern surface of the vast, karsted Nullarbor Plain. Older Eucla Group marine carbonates (Eocene-earliest Miocene) are cool-water in nature and dominated by bryozoans and echinoderms. The Nullarbor Limestone is subtropical in composition and rich in coralline algae (rhodoliths and articulated types), large and small benthic foraminifera and molluscs. Diverse zooxanthellate corals are also present but not numerous. Deposition is interpreted to have taken place in three main paleoenvironments: rhodolith gravels, seagrass banks, and open seafloors.
The Southern Ocean extended inboard ~450 km from the shelf edge during Nullarbor Limestone deposition. Interpreted paleodepths ranged from the top to the base of the photic zone, implying a small slope over a wide shelf. The Miocene Eucla platform is therefore interpreted to have been epeiric in nature. Paleoenvironment distribution is explained using epeiric platform sedimentation patterns and comparisons with modern environments. Open seafloor environments, the deepest settings, are thought to have been below fair-weather wave base. Rhodolith gravels accumulated at intermediate depths, where waves frequently swept the seafloor. Seagrass banks developed in the shallowest waters farthest inboard, where wave energy had been largely dissipated.
Diverse corals, large benthic foraminifera and micrite envelopes inboard and in the western part of the basin support the notion of paleotemperatures generally above 20°C, the upper limit of subtropical carbonate accumulation. Although deposition occurred during the Miocene Climatic Optimum, a simple overall temperature increase cannot completely account for the subtropical nature of these sediments at mid-latitudes. Tropical components decrease from west to east, implying a temperature gradient, probably due to the warm proto-Leeuwin Current. Thus, these subtropical carbonates were deposited at mid-latitudes and their presence did not simply reflect a change in global climate.Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-12-23 16:05:47.981
27
Sanchez, Carla Maria 1978. "Controls on sedimentary processes and 3D stratigraphic architecture of a mid-Miocene to recent, mixed carbonate-siliciclastic continental margin : northwest shelf of Australia." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-05-2678.
Full textAbstract:
Determining the relative importance of processes that control the generation and preservation of continental margin stratigraphy is fundamental to deciphering the history of geologic, climatic and oceanographic forcing imprinted on their sedimentary record. The Northern Carnarvon Basin (NCB) of the North West Shelf of Australia has been a site of passive margin sedimentation throughout the Neogene. Cool-water carbonate sedimentation dominated during the early-middle Miocene, quartz-rich siliciclastics prograded over the shelf during the late-middle Miocene, and carbonate sedimentation resumed in the Pliocene. Middle Miocene to Pliocene siliciclastics were deposited as clinoform sets interpreted as delta lobes primarily based on their plan-view morphology and their relief of 40-100 m. Shelf-edge trajectory analysis suggests that part of this stratigraphic succession was built during a long-term, third order, regressive phase, producing shelf-edge deltas, followed by an aggradational episode. These trends appear to correlate with third-order global eustatic cycles. Slope incisions were already conspicuous on the slope before deltas reached the shelf-break. Nevertheless, slope gullies immediately downdip from the shelf-edge deltas are wider and deeper (>1 km wide, ~100 m deep) than coeval incisions that are laterally displaced from the deltaic depocenter (~0.7 km wide, ~25 m deep). This change in gully morphology is likely the result of greater erosion by sediment gravity flows sourced from shelf-edge deltas. Total late-middle to late Miocene margin progradation increased almost three times from 13 km in the southwest to 34 km in the northeast, where shelf-edge deltas were concentrated.
Flat-topped carbonate platforms seem to have initiated on subtle antecedent topographic highs resulting from these deltaic lobes. A reduction of siliciclastic supply to the outer paleo-shelf during the Pliocene combined with the onset of a southwestward-flowing, warm-water Leeuwin Current (LC) most likely controlled the initiation of these carbonate platforms. These platforms display marked asymmetry, likely caused by an ancestral LC, which created higher-angle, upcurrent platform margins, and lower-angle, downcurrent clinoforms. The along-strike long-term migration trend of the platforms could be the result of differential subsidence. These platforms constitute the first widespread accumulation of photozoan carbonates in the Northern Carnarvon Basin. They became extinct after the mid-Pleistocene when the LC weakened or became more seasonal.text