Upwelling and bleaching on the Great Barrier Reef (MTSRF Project 2.5i.2)

As part of MTSRF Task 2.5i.2, a range of indices were investigated to quantify upwelling on the central Great Barrier Reef (GBR), Australia. These indices are necessary for exploring environmental and biological relationships in areas where upwelling may be sporadic and less intense, especially along western boundary currents such as the East Australian Current. 'Upwelling days' (the number of days of upwelling, inferred from erratic downward temperature spikes) and diurnal variation in subsurface temperature (max-min, 20m depth) were found to be the best metrics to describe the duration and intensity of upwelling events, respectively. These were used to examine key characteristics of shelf-break upwelling in the central GBR. Temperature logger data (20m) were used to derive 'upwelling days' and the local mean summer temperatures (Dec - Feb) and NOAA AVHRR Pathfinder data were used to derive regional SSTs. To investigate the best metrics to quantify upwelling and to explore relationships between these metrics, SST and coral bleaching. Exploration of upwelling indices was done using hierarchical classification trees. Linear regression analysis was used to explore relationships between upwelling and SST and coral bleaching events, especially 1998 and 2002.Coordinates of the temperature logger sites are:Magnetic Island (Florence Bay): LATITUDE -19.12248, LONGITUDE 146.88155Kelso Reef: LATITUDE -18.44701, LONGITUDE 146.98907Myrmidon Reef: LATITUDE -18.25673, LONGITUDE 147.38104