Identifying Metocean Drivers of Turbidity Using 18 Years of MODIS Satellite Data: Implications for Marine Ecosystems under Climate Change

Abstract

Turbidity impacts the growth and productivity of marine benthic habitats due to light limitation. Daily/monthly synoptic and tidal influences often drive turbidity fluctuations, however, our understanding of what drives turbidity across seasonal/interannual timescales is often limited, thus impeding our ability to forecast climate change impacts to ecologically significant habitats. Here, we analysed long term (18-year) MODIS-aqua data to derive turbidity and the associated meteorological and oceanographic (metocean) processes in an arid tropical embayment (Exmouth Gulf in Western Australia) within the eastern Indian Ocean. We found turbidity was associated with El Niño Southern Oscillation (ENSO) cycles as well as Indian Ocean Dipole (IOD) events. Winds from the adjacent terrestrial region were also associated with turbidity and an upward trend in turbidity was evident in the body of the gulf over the 18 years. Our results identify hydrological processes that could be affected by global climate cycles undergoing change and reveal opportunities for managers to reduce impacts to ecologically important ecosystems.

Coastal dolphins and marine megafauna in Exmouth Gulf, Western Australia: informing conservation management actions in an area under increasing human pressure

“…1). The gulf is generally highly turbid (McKinnon and Ayukai 1996;Cartwright et al 2021), partially due to a strong tidal surge, with a 2.5 m tidal range flowing at 1-2/ms on a semidiurnal regime (Semeniuk 1993;Taylor and Pearce 1999). The gulf is hypersaline, with salinity ranging from ~36 to 38.5, with greater salinities occurring further south into the gulf (McKinnon and Ayukai 1996).…”

A Simple Procedure to Preprocess and Ingest High-Resolution Ocean Color Data into Google Earth Engine

“…This sensor measures spectral radiance at 36 bands with bands 8-16 dedicated to ocean color, phytoplankton, and biogeochemistry (https://modis.gsfc.nasa.gov/about/ specifications.php). It has contributed immensely to studies of marine ecosystems variability and change, to monitoring coastal eutrophication, and in assisting policy making for the protection of our environment [2,[17][18][19]. Although MODIS/Aqua continues to collect valuable data, with its aging, it may reach the end of life at any time.…”

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“…Long-term analyses utilising both MODIS satellite images and in situ recordings reveal an upward trend in turbidity in tropical coastal waters when management strategies are absent (Seers & Shears 2015;Cartwright et al 2021).…”

“…Acknowledged as an indicator of coastal water quality by the Australian and New Zealand Environmental and Conservation Council (ANZECC 2000), turbidity is rising in coastal ecosystems largely due to anthropogenic activities (Seers & Shears 2015). Owing to the intensification of meteorological and oceanographic processes (Cartwright et al 2021), dredging (Collin & Hart 2015), algal blooms (Seers & Shears 2015), and the exacerbation of soil erosion and estuarine sediment discharge through the replacement of coastal forests with farmland (Wolanski & Spagnol 2000), coral reefs are subject to an increasing frequency and intensity of turbidity plumes.Extreme plumes have escalated to an intensity so as to be visible from space (Figure 1). Long-term analyses utilising both MODIS satellite images and in situ recordings reveal an upward trend in turbidity in tropical coastal waters when management strategies are absent (Seers & Shears 2015; Cartwright et al 2021).…”

“…Owing to the intensification of meteorological and oceanographic processes (Cartwright et al 2021), dredging (Collin & Hart 2015), algal blooms (Seers & Shears 2015), and the exacerbation of soil erosion and estuarine sediment discharge through the replacement of coastal forests with farmland (Wolanski & Spagnol 2000), coral reefs are subject to an increasing frequency and intensity of turbidity plumes.Extreme plumes have escalated to an intensity so as to be visible from space (Figure 1). Long-term analyses utilising both MODIS satellite images and in situ recordings reveal an upward trend in turbidity in tropical coastal waters when management strategies are absent (Seers & Shears 2015; Cartwright et al 2021).…”