Historically, ocean transparency has been most often measured using Secchi disk as a useful index of water quality. Doron et al. (2011) adapted Lee’s algorithm to estimate Secchi depth from satellite ocean color data using an extensive set of coincident satellite

and in situ measurements (>400 matchups) from both coastal and oceanic waters. A recent study evaluated KdPAR, Z1% and Kd490, derived with three bio-optical algorithms applied to Moderate Imaging Spectroradiometer (MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) observations, using optical data from the coastal waters off South Florida and the Caribbean Sea ( Zhao et al., 2013). The algorithm by Lee Buparlisib in vitro et al. (2007) showed the overall best performance, while empirical algorithms performed well for clear offshore waters but underestimated KdPAR and Kd490 in coastal waters. Zhao et al. (2013) suggested

their findings lay the basis for synoptic time-series studies of water quality in coastal ecosystems, although more work is required to minimize bottom interference in optically shallow waters. This study uses a new approach to assess check details the relationships between the terrestrial runoff of freshwater and its associated fine sediments and nutrients to the daily to inter-annual variation in water clarity, using the central section of the shallow GBR continental shelf as a model system. The study was based on 10 years of remote sensing and environmental data (2002–2012), a new GBR-validated photic depth algorithm for MODIS-Aqua data (Weeks et al., 2012) and statistical models. The study shows that annual mean water clarity in the central GBR is strongly related to discharges by the large

Burdekin River. The study then assessed the spatial extent (inshore to ∼120 km offshore) and the duration of reduction in water clarity beyond the duration of the flood plumes. The results suggest that reductions in the sediment and nutrient loads of the Burdekin River will likely result in significantly improved water clarity downstream of the river mouth and across much of the central GBR, both during PAK5 the wet season and throughout the following dry season. Water clarity was calculated by applying a GBR-validated ‘photic depth’ algorithm to MODIS-Aqua, i.e., determining the depth where 10% of the surface light level is still available (GBR Z10%). The method is fully described in Weeks et al. (2012). In brief: GBR Z10% was calculated with the algorithm of Lee et al., 2002 and Lee et al., 2007 based on the regression coefficients of satellite data against GBR Secchi depth data. Many of the >5000 records of Secchi depth (collected by the Australian Institute of Marine Science and the Queensland Department of Primary Industries and Fisheries between 1994–1999 and 1992–2012) pre-dated the MODIS-Aqua satellite data (2002–2012), hence both MODIS-Aqua and SeaWiFS data (1997–2010) were used.