Drivers of upwelling events and biological responses in the far Northern Great Barrier Reef region.

Upwelling events along the northern shelf edge of the Great Barrier Reef (GBR) are key drivers of ecosystem health and resilience. Understanding the timing, frequency, and drivers of these upwelling events are critical for predicting ecosystem responses to climate change and improving marine management best practices. This study utilises a 12 year dataset from a coupled hydrodynamical-optical-biogeochemical ocean model (eReefs, 4 km resolution) to examine the spatial and temporal variability of upwelling events along the far northern GBR. We focus on the seasonal and interannual variability of upwelling, its relationship to surface chlorophyll concentrations, and the physical processes driving these events. We find that upwelling events are most likely to reach the surface during the Australian summer when the mixed layer is shallower and conditions are conducive to vertical mixing. Significant interannual variability appears to be linked to broader atmospheric-oceanic drivers, such as the El Niño Southern Oscillation. At the shorter time scale, we show that monsoonal wind bursts strongly influence the strength and frequency of upwelling events, with an additional modulation by the spring-neap tidal cycle.