Phytoplankton and zooplankton production in the Bonney Coast upwelling, Australia: A coupled physical-biological model investigation

The Bonney Coast Upwelling is a prominent seasonal coastal upwelling region that develops during November–April on Australia's southeastern continental shelf. This study couples a three-dimensional hydrodynamic model with a nitrogen-phytoplankton-zooplankton-detritus (NPZD) model to explore the plankton dynamics during the upwelling season. Findings suggest that, while the physical response to upwelling-favorable winds occurs rapidly on a timescale of 5–10 days, phytoplankton blooms develop only slowly on time scales of ∼30–60 days. To this end, the region of high zooplankton levels is predicted to form slowly on timescales of 2–3 months. As expected, the zooplankton maximum develops downstream from the upwelling center in the shallow waters of an adjacent bay (i.e., Long Bay) over an alongshore distance of 200–300 km. Unexpectedly, high zooplankton levels also develop on the inner shelf adjacent to the upwelling plume on spatial scales of 20–30 km, mainly due to the onshore transport of phytoplankton via lateral turbulent diffusion. Overall, remineralization by detritus contributes significantly (>50%) as nitrogen source to the photosynthetic phytoplankton production on the continental shelf.