SeaWiFS-derived Chl anomaly and related nutrient sources in the Queensland continental shelf waters

Abstract

Existing studies suggested that inshore parts of the Great Barrier Reef (GBR) lagoon are already or will soon become eutrophic as a result of anthropogenic nutrient enrichment. GBR phytoplankton dynamics generally displays a seasonal pattern, with algal standing stock (Chl) at an annual maximum during the summer wet season. Observations suggest that fluvial discharge is a primary source of nutrients for algal growth in this region, although upwelling, biological nitrogen fixation, and rainfall are also sources of new nutrients. Aeolian mineral dust deposition is thought to be a critical source of dissolved iron (dFe) for phytoplankton growth in some oceanic regions. However, research on aeolian dust delivery of nutrients to GBR waters has been very limited in comparison with fluvial nutrients. In this study, 8-day Chl anomalies in the Queensland continental shelf waters were computed from 8-day binned Chl and 8-day Chl climatology derived from SeaWiFS satellite data. Positive anomalies were initially examined in relation to fluvial discharge, upwelling, and dust storm events. Results indicated significant positive Chl anomalies in near-shore areas during the wet season may be due to fluvial nutrients and sediment. Significant positive Chl anomalies extended offshore in the southern area of the GBR lagoon during October and November of 2002 and 2009. This may reflect the impact of dustderived nutrients from dust storm events in eastern Australia. Unusual positive Chl anomalies in the continental shelf waters from Fraser Island to the Gold Coast may be the result of seasonal upwelling.