Use MODIS data to investigate the spatial and temporal variability of the Bonney Coast Upwelling

The Bonney Coast upwelling is a large seasonal upwelling system along Australian southern shelves, from Cape Jaffa (SA) to Cape Nelson (VIC), during favourable coastal winds. The Bonney Coast upwelling, with nutrient enriched water, has been recognised as a key ecological feature. During the upwelling season (Austral Summer), swarms of krill and aggregation of blue whales are frequently found in this part of continental shelf. The upwelling is also important in the life cycle of juvenile southern Bluefin tuna and benefits other marine life. The oceanographic characteristics of the Bonney Coast upwelling are well understood through marine surveys and mooring data, as well as satellite images. However, the systematic and accurate mapping and understanding of the dynamic of the upwelling system has not been conducted. This study aims to map and investigate the spatial and temporal variability of the Bonney Coast upwelling using time-series of MODIS data. The data include more than 170 SST and Chlorophyll-a images (from July 2002 to Dec 2016), with a spatial resolution of ~1km. A combination of Topographic Position Index (TPI) and image segmentation techniques was used to map the spatial extent of the Bonney Coast upwelling. The Chlorophyll-a and SST signatures of the upwelling areas have also been extracted. The results confirmed that the Bonney Coast upwelling is indeed a seasonal system occurred between November and April. The upwelling is often most intensive in February and March. There is strong inter-annual variation. For example, in the summer of 2008-09, upwelling was only identified in February 2009; while, in the summers of 2013-14 and 2015-16, the upwelling was identified in all of the six months. Whether this inter-annual variation is influenced by the ENSO events is under further investigation. During intensive upwelling events (e.g., in Feb and Mar), the upwelling influences more than 10,000 km2 surface area, with the SST anomaly more than 1oC lower than that of its surrounding areas. The upwelling areas often have mean Chlorophyll-a concentrations over 0.8 mg/m3 which is nearly double of the mean summer Chlorophyll-a concentration in Australian continental shelf. This abstract was submitted/presented to the 2017 Australian Marine Science Association Conference - AMSA (https://www.amsa.asn.au/2017-darwin)