The East Australian Current (EAC) is a strong, low nutrient, western boundary current that dominates the East Coast of Australia. However, the nutrient variability and resulting productivity in the EAC is poorly understood. In this study we relate canonical patterns in the position of the EAC offshore Brisbane with changes to the nutrient dynamics.
We used hydro-chemical data collected on the R/V Investigator offshore south-eastern Queensland during repeat EAC mooring voyages over an 8-year period from 2015-2022. The nutrient peak in the water column occurs below the subsurface (deeper than 50m) on the western flank of the southward flowing EAC. Previous work has suggested that the EAC varies between two positions - inshore and offshore. The nutrient data suggests that during the periods of the inshore position of the EAC, nutrient concentrations are lower, and deeper in the water column, compared to the offshore position of the EAC. Based on nitrate/phosphate ratios, the supply of high nutrient waters was determined to arise from intermediate depth ocean waters. Additionally, nutrient relationships were altered with variations in the position of the EAC. In this region, nutrients drive productivity, with evidence that interannual variability may be driven by the El Niño Southern Oscillation.