No description available.

The green porcelain crab, Petrolisthes armatus, has recently invaded oyster reefs of the South Atlantic Bight at mean densities of up to several thousand individuals m-². Despite the crab’s tremendous densities and wide-spread occurrence, its population dynamics, the reasons for its success, and its ecological impacts have remained unknown. We used field monitoring in two estuaries of coastal Georgia to assess spatial and temporal patterns of distribution, demographics, reproduction, and effects on native crabs. We used field and mesocosm experiments with constructed oyster reef communities of varying native species richness and adult porcelain crab additions to assess why the invader is successful and how it impacts native species and communities. We found P. armatus distributed throughout the estuaries, primarily in the lower regions and low intertidal. Sex ratios were 1:1 throughout the year. During warmer months mean densities ranged from 1,000-11,000 crabs m-², 20-90% of mature females were gravid, and numerous recruits were present. Despite decreases in density of 64->99% in the winter, populations rebounded in the spring. Maximum mean densities were 37 times the highest densities ever recorded and population fecundity exceeded that of the native range by an order of magnitude, but correlations did not show significant negative effects of P. armatus on native crabs. Field experiments suggested that invasion was successful due to tremendous recruitment overwhelming biotic resistance by native species richness or predation. The crab only needed structure to invade, but the presence of adult conspecifics significantly enhanced recruitment (i.e., intraspecific “invasional meltdown”). We documented several impacts on native biota, including the (1) suppression of oyster growth, benthic algal biomass, native crab recruitment, and native goby densities and the (2) enhancement of bivalve recruitment, macroalgal cover, and survivorship of oyster drills. We did not, though, see an effect on native taxonomic richness. The large direct and indirect effects of P. armatus on growth, survivorship, and recruitment of virtually all of the most common native species on oyster reefs in the short-term (4-12 weeks) and at relatively low experimental densities (750-1500 crabs m-²) imply considerable long-term consequences for a major hard-substrate habitat of the South Atlantic Bight.

A high-resolution astronomic tidal model has been developed that includes detailed inshore regions of the Atlantic Intracoastal Waterway and associated estuaries along the South Atlantic Bight. The unique nature of the model’s development ensures that the tidal hydrodynamic interaction between the shelf and estuaries is fully described. Harmonic analysis of the model output results in a database of tidal information that extends from a semi-circular arc (radius ~750 km) enclosing the South Atlantic Bight from the North Carolina coast to the Florida Keys, onto the continental shelf and into the full estuarine system. The need for tidal boundary conditions (elevation and velocity) for driving inland waterway models has motivated the development of a software application to extract results from the tidal database which is the basis of this thesis. In this tidal toolbox, the astronomic tidal constituents can be resynthesized for any open water point in the domain over any interval of time in the past, present, or future. The application extracts model results interpolated to a user’s exact geographical points of interest, desired time interval, and tidal constituents. Comparison plots of the model results versus historical data are published on the website at 89 tidal gauging stations. All of the aforementioned features work within a zoom-able geospatial interface for enhanced user interaction. In order to make tidal elevation and velocity data available, a web service serves the data to users over the internet. The tidal database of 497,847 nodes and 927,165 elements has been preprocessed and indexed to enable timely access from a typical modern web server. The iii preprocessing and web services required are detailed in this thesis, as well as the reproducibility of the Tidal Toolbox for new domains.

Addendum is inserted inside back cover. / Bibliography: leaves 240-246. / xii, 246 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied Mathematics, 1996?

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.

An accurate understanding of global patterns through geologic time depends upon multi-scale analyses of spatial variation within narrow temporal intervals. This work investigates geochemical and paleoecological patterns in modern brachiopod faunas which may serve as analogues for ancient brachiopod assemblages. The paleoclimatic utility of delta18O in the phosphatic phase of lingulid brachiopod shells requires valve secretion in equilibrium with seawater, an assumption tested (and rejected) when analyzed at scales ranging from millimeters to kilometers. By contrast, biological encrustation of the brachiopod fauna of the Southeast Brazilian Bight shows strong sensitivity to microenvironmental conditions such as host identity, shape, and size, and may prove useful for studies of ancient planktonic productivity. Comparison of encrustation patterns on naturally occurring brachiopods and bivalves collected from the same sites, and occupying the same size range, demonstrates that the results of encrustation studies on modern bivalves cannot be directly applied to ancient brachiopods. However, careful comparisons may reveal patterns of epibiont selectivity and the impact of changes in the relative abundance of host shells through geologic time. Finally, neither epibiont abundance nor diversity increase with host age as indicated by dated brachiopod shells from the past 1000 years. These results suggest that the temporal resolution of epibiont assemblages matches their spatial resolution, and strengthen evidence for competition among encrusting taxa. By documenting geochemical and paleoecological variation within shells and across a continental shelf, this work demonstrates the importance of understanding spatial variation across all scales before interpreting trends through time. / Ph. D.

The Great Australian Bight (GAB) was for many years thought to be an area of limited biological productivity due to a perceived lack of nutrient enrichment processes. These conclusions, however, were based on data from few studies in the western GAB which were assumed to reflect conditions throughout the entire GAB. More recent studies have reported the occurrence of coastal upwelling in the eastern GAB (EGAB) during summer/autumn (November-April), characterized by low sea surface temperatures and elevated concentrations of chlorophyll α, which suggests that certain areas of the GAB may be highly productive during certain times of the year. The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports the largest fishery in Australia (the South Australian Sardine fishery, annual catches since 2004 ~ 25,000 to 42,500 t), quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from < 100 mg C m⁻² day⁻¹ to > 500 mg C m⁻² day⁻¹. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. Shelf waters encompass an area of ~115,000 km², and the diverse coastal topography forms part of one of the longest stretches of southward facing coastline in the world. In summer-autumn, winds are upwelling favourable, and the Flinders current running along the continental slope causes the upwelling of the deep permanent thermocline from around 600 m depth (dynamic uplift), allowing nutrient rich cold water to entrain onto the shelf. In winterspring, the EGAB is dominated by westerly downwelling-favourable winds, and upwelling via the Flinders current is suppressed. Thus, the area is highly dynamic, with significant spatial and temporal variations in meteorology and oceanography which may drive variations in nutrient enrichment and productivity. This study represents the first intensive investigation of the primary and secondary productivity of the EGAB, and was designed to evaluate the general hypothesis that spatial and temporal variations in meteorology and oceanography in the EGAB will drive spatial and temporal variations in phytoplankton size structure, and primary and secondary productivity. It examines variations in primary and secondary productivity in the EGAB during the upwelling and downwelling seasons of 2004, and the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m⁻² day⁻¹) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m⁻² day⁻¹) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ~50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro nutrient concentrations could not be used to explain the difference in the low and high productivities (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humbolt currents. Temporal variation in mixing and primary productivity was examined in upwelling influenced nearshore waters off south western Eyre Peninsula (SWEP) in the EGAB. Mixing/stratification in the region was highly temporally variable due to the unique upwelling circulation in summer/autumn, and downwelling through winter/spring. Highest productivity was associated with pwelled/stratified water (up to 2958 mg C m⁻² d⁻¹), with low productivity during periods of downwelling and mixing (~300-550 mg C m⁻² d⁻¹), yet no major variations in macro-nutrient concentrations were detected between upwelling and downwelling events (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). We hypothesise that upwelling enriches the region with micro-nutrients. High productivity off SWEP appears to be driven by a shallowing of mixed layer depth due to the injection of upwelled waters above Z[subscript]cr. Low productivity follows the suppression of enrichment during downwelling/mixing events, and is exacerbated in winter/spring by low irradiances and short daylengths. Phytoplankton abundance and community composition was also examined in the shelf waters of the EGAB. Phytoplankton abundances were generally higher in near shore waters compared with offshore waters, and during the summer/autumn upwelling season compared with the winter/spring downwelling season. Three distinctly different phytoplankton communities were present in the region during the upwelling and downwelling seasons of 2004, and the upwelling season of 2005, with distinctions manifest in variations in the abundance of dominant types of phytoplankton, and differences in average cell sizes. In summer/autumn, waters influenced by upwelling were characterised by high phytoplankton abundances (particularly diatoms) and larger average cell sizes, while the warmer high-nutrientlow- chlorophyll (HNLC) waters in the region had lower phytoplankton abundances and smaller average cell sizes. The winter/spring community was made up of low abundances of relatively large cells. Diatoms always dominated, but evidence of Si limitation of further diatom growth suggests there may be an upper limit to diatom productivity in the region. The maximum observed diatom concentration of ~164,000 cells L⁻¹ occurred in February/March 2004, in an area influenced by the upwelled water mass. Variations in phytoplankton biodiversity in the shelf waters of southern Australia appear to be related to variations in the influence of upwelling in the region. Meso-zooplankton abundance and community composition was examined in the coastal upwelling system of the EGAB. Spatial and temporal variations were influenced by variations in primary productivity and phytoplankton abundance and community composition, which were driven by variations in the influence of upwelling in the region. Peak meso-zooplankton abundances and biomass occurred in the highly productive upwelling influenced nearshore waters of the EGAB. However, abundances were highly variable between regions and years, reflecting the high spatial and temporal variations in primary productivity and phytoplankton abundance that characterise the shelf waters of the region. Spatial and temporal variations in community composition were driven by changes in the abundance of classes of meso zooplankton common to all regions in both years of this study. Meroplanktonic larvae and opportunistic colonizers dominated the community through the upwelling season, in response to increased primary productivity and phytoplankton blooms. Differences in community composition between upwelling influenced waters and the more HNLC regions appear to be reflected in the relative abundances of cladocera and appendicularia, with cladocera more abundant in productive upwelling influenced areas, and appendicularia thriving in the more HNLC regions of the EGAB. Highest potential grazing rates in the EGAB occurred in nearshore regions with highest mesozooplankton biomass, most likely in response to the high phytoplankton biomass that occurs in the same regions. Peak meso-zooplankton grazing rates in the EGAB were ~80% less than those measured in south west Spencer Gulf in March 2007, and ~35% greater than grazing rates in the Huon Estuary in February 2005. Productivity in the EGAB shows significant spatial and temporal variation, with changes reflecting regional and seasonal variation in meteorology and oceanography, and the water masses present in the region. The overall productivity of a summer/autumn upwelling season was highly dependent on within-season variations in wind strength and direction, which dictate the number, intensity, and duration of upwelling events. Rates of primary productivity measured in the EGAB at a given time depended on the meteorological and oceanographic conditions in the region in the lead up to, and during, the sampling event. We hypothesise that during upwelling events, high productivity in the EGAB is driven by the enrichment of waters above Z[subscript]cr, but below the surface mixed layer, with micro-nutrients. Low productivity within summer/autumn upwelling seasons follows the suppression of this enrichment during downwelling/mixing events, and the overall productivity of the upwelling season will depend on the number, duration and intensity of these downwelling/mixing events. Low productivity during winter/spring is driven by the absence of upwelling, low irradiances and short daylengths. / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

The Great Australian Bight (GAB) was for many years thought to be an area of limited biological productivity due to a perceived lack of nutrient enrichment processes. These conclusions, however, were based on data from few studies in the western GAB which were assumed to reflect conditions throughout the entire GAB. More recent studies have reported the occurrence of coastal upwelling in the eastern GAB (EGAB) during summer/autumn (November-April), characterized by low sea surface temperatures and elevated concentrations of chlorophyll α, which suggests that certain areas of the GAB may be highly productive during certain times of the year. The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports the largest fishery in Australia (the South Australian Sardine fishery, annual catches since 2004 ~ 25,000 to 42,500 t), quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from < 100 mg C m⁻² day⁻¹ to > 500 mg C m⁻² day⁻¹. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. Shelf waters encompass an area of ~115,000 km², and the diverse coastal topography forms part of one of the longest stretches of southward facing coastline in the world. In summer-autumn, winds are upwelling favourable, and the Flinders current running along the continental slope causes the upwelling of the deep permanent thermocline from around 600 m depth (dynamic uplift), allowing nutrient rich cold water to entrain onto the shelf. In winterspring, the EGAB is dominated by westerly downwelling-favourable winds, and upwelling via the Flinders current is suppressed. Thus, the area is highly dynamic, with significant spatial and temporal variations in meteorology and oceanography which may drive variations in nutrient enrichment and productivity. This study represents the first intensive investigation of the primary and secondary productivity of the EGAB, and was designed to evaluate the general hypothesis that spatial and temporal variations in meteorology and oceanography in the EGAB will drive spatial and temporal variations in phytoplankton size structure, and primary and secondary productivity. It examines variations in primary and secondary productivity in the EGAB during the upwelling and downwelling seasons of 2004, and the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m⁻² day⁻¹) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m⁻² day⁻¹) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ~50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro nutrient concentrations could not be used to explain the difference in the low and high productivities (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humbolt currents. Temporal variation in mixing and primary productivity was examined in upwelling influenced nearshore waters off south western Eyre Peninsula (SWEP) in the EGAB. Mixing/stratification in the region was highly temporally variable due to the unique upwelling circulation in summer/autumn, and downwelling through winter/spring. Highest productivity was associated with pwelled/stratified water (up to 2958 mg C m⁻² d⁻¹), with low productivity during periods of downwelling and mixing (~300-550 mg C m⁻² d⁻¹), yet no major variations in macro-nutrient concentrations were detected between upwelling and downwelling events (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). We hypothesise that upwelling enriches the region with micro-nutrients. High productivity off SWEP appears to be driven by a shallowing of mixed layer depth due to the injection of upwelled waters above Z[subscript]cr. Low productivity follows the suppression of enrichment during downwelling/mixing events, and is exacerbated in winter/spring by low irradiances and short daylengths. Phytoplankton abundance and community composition was also examined in the shelf waters of the EGAB. Phytoplankton abundances were generally higher in near shore waters compared with offshore waters, and during the summer/autumn upwelling season compared with the winter/spring downwelling season. Three distinctly different phytoplankton communities were present in the region during the upwelling and downwelling seasons of 2004, and the upwelling season of 2005, with distinctions manifest in variations in the abundance of dominant types of phytoplankton, and differences in average cell sizes. In summer/autumn, waters influenced by upwelling were characterised by high phytoplankton abundances (particularly diatoms) and larger average cell sizes, while the warmer high-nutrientlow- chlorophyll (HNLC) waters in the region had lower phytoplankton abundances and smaller average cell sizes. The winter/spring community was made up of low abundances of relatively large cells. Diatoms always dominated, but evidence of Si limitation of further diatom growth suggests there may be an upper limit to diatom productivity in the region. The maximum observed diatom concentration of ~164,000 cells L⁻¹ occurred in February/March 2004, in an area influenced by the upwelled water mass. Variations in phytoplankton biodiversity in the shelf waters of southern Australia appear to be related to variations in the influence of upwelling in the region. Meso-zooplankton abundance and community composition was examined in the coastal upwelling system of the EGAB. Spatial and temporal variations were influenced by variations in primary productivity and phytoplankton abundance and community composition, which were driven by variations in the influence of upwelling in the region. Peak meso-zooplankton abundances and biomass occurred in the highly productive upwelling influenced nearshore waters of the EGAB. However, abundances were highly variable between regions and years, reflecting the high spatial and temporal variations in primary productivity and phytoplankton abundance that characterise the shelf waters of the region. Spatial and temporal variations in community composition were driven by changes in the abundance of classes of meso zooplankton common to all regions in both years of this study. Meroplanktonic larvae and opportunistic colonizers dominated the community through the upwelling season, in response to increased primary productivity and phytoplankton blooms. Differences in community composition between upwelling influenced waters and the more HNLC regions appear to be reflected in the relative abundances of cladocera and appendicularia, with cladocera more abundant in productive upwelling influenced areas, and appendicularia thriving in the more HNLC regions of the EGAB. Highest potential grazing rates in the EGAB occurred in nearshore regions with highest mesozooplankton biomass, most likely in response to the high phytoplankton biomass that occurs in the same regions. Peak meso-zooplankton grazing rates in the EGAB were ~80% less than those measured in south west Spencer Gulf in March 2007, and ~35% greater than grazing rates in the Huon Estuary in February 2005. Productivity in the EGAB shows significant spatial and temporal variation, with changes reflecting regional and seasonal variation in meteorology and oceanography, and the water masses present in the region. The overall productivity of a summer/autumn upwelling season was highly dependent on within-season variations in wind strength and direction, which dictate the number, intensity, and duration of upwelling events. Rates of primary productivity measured in the EGAB at a given time depended on the meteorological and oceanographic conditions in the region in the lead up to, and during, the sampling event. We hypothesise that during upwelling events, high productivity in the EGAB is driven by the enrichment of waters above Z[subscript]cr, but below the surface mixed layer, with micro-nutrients. Low productivity within summer/autumn upwelling seasons follows the suppression of this enrichment during downwelling/mixing events, and the overall productivity of the upwelling season will depend on the number, duration and intensity of these downwelling/mixing events. Low productivity during winter/spring is driven by the absence of upwelling, low irradiances and short daylengths. / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

The Great Australian Bight (GAB) was for many years thought to be an area of limited biological productivity due to a perceived lack of nutrient enrichment processes. These conclusions, however, were based on data from few studies in the western GAB which were assumed to reflect conditions throughout the entire GAB. More recent studies have reported the occurrence of coastal upwelling in the eastern GAB (EGAB) during summer/autumn (November-April), characterized by low sea surface temperatures and elevated concentrations of chlorophyll α, which suggests that certain areas of the GAB may be highly productive during certain times of the year. The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports the largest fishery in Australia (the South Australian Sardine fishery, annual catches since 2004 ~ 25,000 to 42,500 t), quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from < 100 mg C m⁻² day⁻¹ to > 500 mg C m⁻² day⁻¹. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. Shelf waters encompass an area of ~115,000 km², and the diverse coastal topography forms part of one of the longest stretches of southward facing coastline in the world. In summer-autumn, winds are upwelling favourable, and the Flinders current running along the continental slope causes the upwelling of the deep permanent thermocline from around 600 m depth (dynamic uplift), allowing nutrient rich cold water to entrain onto the shelf. In winterspring, the EGAB is dominated by westerly downwelling-favourable winds, and upwelling via the Flinders current is suppressed. Thus, the area is highly dynamic, with significant spatial and temporal variations in meteorology and oceanography which may drive variations in nutrient enrichment and productivity. This study represents the first intensive investigation of the primary and secondary productivity of the EGAB, and was designed to evaluate the general hypothesis that spatial and temporal variations in meteorology and oceanography in the EGAB will drive spatial and temporal variations in phytoplankton size structure, and primary and secondary productivity. It examines variations in primary and secondary productivity in the EGAB during the upwelling and downwelling seasons of 2004, and the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m⁻² day⁻¹) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m⁻² day⁻¹) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ~50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro nutrient concentrations could not be used to explain the difference in the low and high productivities (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humbolt currents. Temporal variation in mixing and primary productivity was examined in upwelling influenced nearshore waters off south western Eyre Peninsula (SWEP) in the EGAB. Mixing/stratification in the region was highly temporally variable due to the unique upwelling circulation in summer/autumn, and downwelling through winter/spring. Highest productivity was associated with pwelled/stratified water (up to 2958 mg C m⁻² d⁻¹), with low productivity during periods of downwelling and mixing (~300-550 mg C m⁻² d⁻¹), yet no major variations in macro-nutrient concentrations were detected between upwelling and downwelling events (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). We hypothesise that upwelling enriches the region with micro-nutrients. High productivity off SWEP appears to be driven by a shallowing of mixed layer depth due to the injection of upwelled waters above Z[subscript]cr. Low productivity follows the suppression of enrichment during downwelling/mixing events, and is exacerbated in winter/spring by low irradiances and short daylengths. Phytoplankton abundance and community composition was also examined in the shelf waters of the EGAB. Phytoplankton abundances were generally higher in near shore waters compared with offshore waters, and during the summer/autumn upwelling season compared with the winter/spring downwelling season. Three distinctly different phytoplankton communities were present in the region during the upwelling and downwelling seasons of 2004, and the upwelling season of 2005, with distinctions manifest in variations in the abundance of dominant types of phytoplankton, and differences in average cell sizes. In summer/autumn, waters influenced by upwelling were characterised by high phytoplankton abundances (particularly diatoms) and larger average cell sizes, while the warmer high-nutrientlow- chlorophyll (HNLC) waters in the region had lower phytoplankton abundances and smaller average cell sizes. The winter/spring community was made up of low abundances of relatively large cells. Diatoms always dominated, but evidence of Si limitation of further diatom growth suggests there may be an upper limit to diatom productivity in the region. The maximum observed diatom concentration of ~164,000 cells L⁻¹ occurred in February/March 2004, in an area influenced by the upwelled water mass. Variations in phytoplankton biodiversity in the shelf waters of southern Australia appear to be related to variations in the influence of upwelling in the region. Meso-zooplankton abundance and community composition was examined in the coastal upwelling system of the EGAB. Spatial and temporal variations were influenced by variations in primary productivity and phytoplankton abundance and community composition, which were driven by variations in the influence of upwelling in the region. Peak meso-zooplankton abundances and biomass occurred in the highly productive upwelling influenced nearshore waters of the EGAB. However, abundances were highly variable between regions and years, reflecting the high spatial and temporal variations in primary productivity and phytoplankton abundance that characterise the shelf waters of the region. Spatial and temporal variations in community composition were driven by changes in the abundance of classes of meso zooplankton common to all regions in both years of this study. Meroplanktonic larvae and opportunistic colonizers dominated the community through the upwelling season, in response to increased primary productivity and phytoplankton blooms. Differences in community composition between upwelling influenced waters and the more HNLC regions appear to be reflected in the relative abundances of cladocera and appendicularia, with cladocera more abundant in productive upwelling influenced areas, and appendicularia thriving in the more HNLC regions of the EGAB. Highest potential grazing rates in the EGAB occurred in nearshore regions with highest mesozooplankton biomass, most likely in response to the high phytoplankton biomass that occurs in the same regions. Peak meso-zooplankton grazing rates in the EGAB were ~80% less than those measured in south west Spencer Gulf in March 2007, and ~35% greater than grazing rates in the Huon Estuary in February 2005. Productivity in the EGAB shows significant spatial and temporal variation, with changes reflecting regional and seasonal variation in meteorology and oceanography, and the water masses present in the region. The overall productivity of a summer/autumn upwelling season was highly dependent on within-season variations in wind strength and direction, which dictate the number, intensity, and duration of upwelling events. Rates of primary productivity measured in the EGAB at a given time depended on the meteorological and oceanographic conditions in the region in the lead up to, and during, the sampling event. We hypothesise that during upwelling events, high productivity in the EGAB is driven by the enrichment of waters above Z[subscript]cr, but below the surface mixed layer, with micro-nutrients. Low productivity within summer/autumn upwelling seasons follows the suppression of this enrichment during downwelling/mixing events, and the overall productivity of the upwelling season will depend on the number, duration and intensity of these downwelling/mixing events. Low productivity during winter/spring is driven by the absence of upwelling, low irradiances and short daylengths. / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

The Great Australian Bight (GAB) is an extensive W-E striking continental margin basin that drifted northwards during the Cenozoic following rifting and separation from Antarctica in the mid/late Cretaceous. Seafloor spreading accelerated in the mid-Eocene and was associated with local volcanism. The mid-Eocene succession of the GAB is conspicuously mounded and separates a dominantly siliciclastic succession below from a fully marine carbonate succession above. The mounded succession was penecontemporaneous with major changes in global climate, oceanographic conditions and tectonic re-organization in the region, and thus may hold important clues as to the palaeo-environmental changes associated with these changes. The mid Eocene has so far only been described locally or in passing, usually by studies focused on either the siliciclastics below or the carbonates above. It was therefore chosen as a major focus point for the research project reported herein. Exploration activity in the GAB has been limited despite the presence of a working petroleum system and large target structures, but industry interest has increased over the past few years leading to 3D seismic surveys being acquired in the GAB. The focus for exploration is the Cretaceous succession beneath the relatively thin Cenozoic cover, which however, is still important in terms of shallow hazards and as overburden to the anticipated productive sections. As is often the case, the new 3D seismic data shows many overburden features in great detail and thus affords new insights to be gained that improve our understanding of the post-rift evolution of the marginThis thesis expands upon and reinterprets a pre-existing sequence framework in the Cenozoic GAB based from ODP Leg 182 results. A vast database of 2D and 3D seismic surveys has been integrated with exploration wells and borehole data and several surfaces have been calibrated to borehole and well constraints, then mapped to the maximum lateral extent across the available dataset. Surface mapping provided new insight into sequence deposition and palaeoenvironmental settings. Structure maps and thickness maps highlight key depocentre locations and trends over the Cenozoic GAB as well as stacked mass debris aprons. The newly discovered sequences raise new questions regarding trigger mechanisms in a-seismic areas and feed into industry geohazard perception models. The base surface of the Cenozoic framework hosts a plethora of mounded features across shelf and basinal section. All mounds within the dataset have been mapped. A set a bryozoan reef mounds have been interpreted lying parallel to the margin as linear complexes over 500 km. They coincide with the underlying siliciclastic delta clinoform breakpoints and provide insight into the changing palaeoenvironment at the 43 Ma mark, cessation of siliciclastics and regional marine transgression. Further mound mapping aided by 3D attribute extractions along the base Cenozoic unconformity led to the interpretation of a series of enigmatic igneous-based mounded features. The discoveries have been included in a comparative study, comparing all mounded features (igneous or carbonate) and contrasting their individual characteristics of geometry, seismic facies, dimension in order to understand mound origin and emplacement. A new grouping of mounds in the GAB has been established, the origin and emplacement mechanisms of which contribute to the global knowledge base.