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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Jan 2019

Research article | 09 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

Remote sensing of upwelling off Australia's north-east coast

Mochamad Furqon Azis Ismail1,4, Joachim Ribbe1, Johannes Karstensen2, and Vincent Rossi3 Mochamad Furqon Azis Ismail et al.
  • 1Faculty of Health Engineering and Sciences, School of Agricultural, Computational and Environmental Sciences, University of Southern Queensland, Toowoomba 4350, Queensland, Australia
  • 2GEOMAR, Helmholtz Centre for Ocean Research Kiel, 24105 Kiel, Germany
  • 3Mediterranean Institute of Oceanography (MIO, UM 110, UMR 7294), CNRS, Aix-Marseille University, University of Toulon, IRD, 13288 Marseille, France
  • 4Research Centre for Oceanography – Indonesian Institute of Sciences, Jakarta 14430, Indonesia

Abstract. Cross-shelf processes drive the exchange of water between the continental shelf and western boundary currents, leading to the import and export of heat, freshwater, sediments, nutrients, plankton, fish larvae, and other properties. Upwelling is an important process which modulates those exchanges. It regulates primary productivity, which in turn promotes higher trophic levels and fisheries. In this paper, we investigate upwelling events in the East Australian Current (EAC) intensification zone off Southeast Queensland through the analysis of remotely-sensed Chlorophyll-a (Chl-a) and Sea Surface Temperature (SST) as well as wind and ocean reanalysis products. A particular focus is on identifying the likely mechanisms that drive upwelling events during the austral autumn to winter which are evident from cold SST and enhanced Chl-a concentrations. Four complementary Upwelling Indices (UIs) are derived. Chl-a (UIChla) and SST (UISST) based indices characterize the oceanic response to upwelling, while indices based on wind (UIw) and current (UIc) data capture the forcing of upwelling. The spatial and temporal variability of all UIs is examined over the continental shelf. It reveals distinct seasonal patterns. For the northern region, UIs identify the well-known Southeast Fraser Island Upwelling System. It prevails during the austral spring to early summer and is driven by current- and upwelling favourable wind. In contrast, upwelling is enhanced over the southern shelf during austral autumn to winter. About 70 % of all UISST and UIChla identified upwelling events occur during this period. A case study is presented that provides observational evidence for the existence of a shelf-break upwelling. Simultaneous downwelling favourable wind stress and upwelling favourable current-driven bottom stress establish a flow convergence in the bottom boundary layer (BBL). These convergent BBL flows force upwelling of cold and nutrient-rich slope waters as evident from negative SST anomaly and enhanced Chl-a in austral autumn to winter. It is evident from these results that the shelf region is characterised by two distinct seasonally reoccurring upwelling regimes.

Mochamad Furqon Azis Ismail et al.
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Mochamad Furqon Azis Ismail et al.
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