The Hillarys Transect (3): Optical and chlorophyll relationships across the continental shelf off Perth

An interdisciplinary study of the waters across the continental shelf off Perth, Western Australia, has provided the first detailed climatology of the physical, chemical, optical, and biological processes across the shelf. In support of this work, remote-sensing data were utilised to provide a broad view of the spatial and temporal chlorophyll concentration dynamics, to support in situ observations, and to help “fill the gaps” inherent in in situ point sampling.In situ validation of remote-sensing products was carried out monthly off Perth over a 27-month period. Biological and physical measurements were made along a 40 km east–west transect, 20 km north of Perth. Results of the study have shown that in water deeper than 30–35 m, and where viewing conditions were suitable, the in situ measurements of chlorophyll concentration were within the 35% uncertainty of the SeaWiFS product.An increase in the in situ measurements of near-coastal chlorophyll concentration was evident during the 1998 winter period (May–July), but the apparent seasonal increase was not evident in the in situ data for 1997. The SeaWiFS chlorophyll concentration estimates have been used to show the seasonal fluctuation of chlorophyll concentration in Perth coastal waters from November 1997 to the end of 2004. The remotely sensed data show a clear seasonal cycle, with maximum chlorophyll concentration occurring during May, June and July for waters off Perth. Also evident from the remotely sensed data was an increase in water column light attenuation during winter, coincident with the increase in chlorophyll concentration. The potential now exists to further develop remote-sensing techniques and to integrate remotely sensed products into routine water-quality monitoring programmes for WA waters.