Seasonal production regimes off south-western Australia: influence of the capes and Leeuwin Currents on phytoplankton dynamics

Document Type

Journal Article


CSIRO Publishing


Faculty of Computing, Health and Science


Computing, Health and Science Faculty Office




Hanson, C. E., Pattiaratchi, C. B., & Waite, A. M. (2005). Seasonal production regimes off south-western Australia: influence of the Capes and Leeuwin Currents on phytoplankton dynamics. Marine and Freshwater Research, 56(7), 1011-1026. Available here


Temporal primary production dynamics were investigated off south-western Australia, where the summer upwelling regime of the Capes Current was compared with early winter conditions characterised by strengthened near-shore Leeuwin Current flow. Seasonal upwelling in this region sourced nitrate levels of ≥ 1 μM from the nutricline at the base of the Leeuwin Current's mixed layer, with total water column production reaching a maximum of ∼950 mg C m -2 day-1 in the Capes Current. Stable isotope signatures of particulate matter indicated that productivity off south-western Australia was heavily reliant on nitrate as a nitrogen source, with mean δ15N ranging from ∼4 to 5‰ under both upwelling and non-upwelling (winter) conditions. Unexpectedly, significant nutrient enrichment within the Leeuwin Current (up to 3.1 μM nitrate) occurred during winter, likely as a result of the meandering Leeuwin Current flooding the inner shelf north of the study area and entraining relatively high-nutrient shelf waters in its southwards flow. However, early winter production under these nutrient-replete conditions (mean ± s.d. 310 ± 105 mg C m -2 day-1) was significantly lower than in summer (695 ± 140 mg C m-2 day-1) due to light limitation, both as a result of reduced surface irradiance characteristic of the winter months and significantly higher light attenuation within the water column as compared with summer conditions.





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