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Wintertime circulation off southeast Australia: Strong forcing by the East Australian Current

Sat, 01 Jan 2005 00:00:00 GMT

Título: Wintertime circulation off southeast Australia: Strong forcing by the East Australian Current Autor(es): Cirano, Mauro; Middleton, John F. Abstract: Numerical results and observations are used to examine the sub–weather band wintertime circulation off the eastern shelf slope region between Tasmania and Cape Howe. The numerical model is forced using wintertime-averaged atmospheric fluxes of momentum, heat, and freshwater and using transports along open boundaries that are obtained from a global ocean model. The boundary to the north of Cape Howe has a prescribed transport of 17 Sv, which from available observations represents strong forcing by the East Australian Current (EAC). Nonetheless, the model results are in qualitative (and quantitative) agreement with several observational studies. In accord with observations, water within Bass Strait is found to be driven to the east and north with speeds of up to 30 cm s−1 off the southeast Victorian coast. The water is colder and denser than that found farther offshore, which is associated with the southward flowing (warm) EAC. In agreement with observations the density difference between the two water masses is about 0.6 kg m−3 and leads to a cascade of dense Bass Strait water to depths of 300 m and as a plume that extends 5–10 km in the cross-shelf direction. Typical vertical velocities of the model cascade are 20 m d−1. Along-isobath currents become bottom intensified with speeds of 20 cm s−1 or so at depths of 200 m. The EAC is found to flow along isobaths and to the south and then west past Tasmania with speeds of up to 20 cm s−1. Mesoscale eddies grow to diameters of 100 km (speeds <40 cm s−1), and in accord with observations a semipermanent anticyclonic eddy is found to the east of Cape Howe. Tipo: Artigo de Periódico

Evidence of a Mid-Holocene Sea Level Highstand from the Sedimentary Record of a Macrotidal Barrier and Paleoestuary System in Northwestern Australia

Sun, 01 Jan 2006 00:00:00 GMT

Título: Evidence of a Mid-Holocene Sea Level Highstand from the Sedimentary Record of a Macrotidal Barrier and Paleoestuary System in Northwestern Australia Autor(es): Lessa, Guilherme; Masselink, Gerhard Abstract: This study addresses the mid- to late Holocene stratigraphy and sea level history of a macrotidal barrier and paleoestuary system located along the relatively unstudied northwest coast of Australia. Thirty-nine shallow cores were obtained from three transects perpendicular to the barrier and paleoestuary axis. Seven sedimentary facies were identified on the basis of sediment texture, carbonate content, and foraminifera assemblages: slope, upper intertidal mud, upper intertidal sand flat, lower intertidal sand flat, barrier, estuarine beach, and flood tide delta. The sedimentary infill reveals a fining upward succession of marine sediments up to 6 m thick, mostly along a regressive sequence. All facies are of Holocene age and started to be laid down when sea level was approximately 3 m below present elevation. A radiocarbon date from the topmost sedimentary facies (upper intertidal mud) indicates that relative sea level was at least 1 m higher than today by 2720 years BP. At this time, the estuary was at the final stages of sedimentary infill, with tidal inundation reduced to a minimum. Further evidence of a higher relative sea level during the Holocene is in the form of estuarine beach deposits found at the back of the paleoestuary at an elevation above the present day beach/dune interface. Net nearshore transport in the area, driven by tidal current asymmetry, is northward, and it is proposed that this has significantly influenced the alongshore component of the barrier progradation and evolution of the barrier estuary. Tipo: Artigo de Periódico