Phytoplankton and suspended sediment in the ocean absorb and scatter solar radiation, affecting the vertical distribution of heating and the stratification. These processes are especially important where a large gradient in water clarity is present.The GBR region is characterised by highly seasonal variable freshwater input from several rivers, which can lead to large sediment and nutrient discharge near the coast, strongly affecting the water optical properties. We use a coupled hydrodynamical-optical-biogeochemical ocean model (eReefs 4 km configuration) to investigate the feedback between phytoplankton heat absorption and the ocean dynamics in the GBR region. The optical model calculates heat absorption based on the absorption and scattering of 4 phytoplakton types, coloured-dissolved organic matter and 6 sediment fractions, and as a function of solar zenith angle.
Results show that heat absorption due to phytoplankton and sediment distribution is stronger near the coastal region, especially during the wet season and episodic rainfall events. Considering the spatial variability of heat absorption due to phytoplankton and suspended sediment concentrations can improve modelling the vertical distribution of heat. This study highlights the importance of considering water clarity and its spatial variability as an important process that drives hydrodynamic conditions, especially during extreme heating events.