Updated Mean Sea-Level Analysis: Australia

Watson, P.J., 2020. Updated mean sea-level analysis: Australia. Journal of Coastal Research, 36(5), 915–931. Coconut Creek (Florida), ISSN 0749-0208.As an island nation with 60,000 km of open coastline and extensive margins of increasingly urbanised intertidal estuarine foreshores, Australia is critically exposed to the global threat posed by rising sea levels into the future. This study provides a contemporary assessment of sea-level rise around Australia to the end of 2018, based on all available tide gauge records and satellite altimetry. The study provides the first national assessment of vertical land motion (VLM) around the coast, identifying margins more prevalent to subsidence, which in turn exacerbate the localised effects of a rising global mean sea level. These areas include coastlines between Townsville and Coffs Harbour, Burnie to Port Pirie, and Fremantle to Wyndham. State-of-the-art time-series analysis techniques applied to all high-quality tide gauge records exceeding 75 years in length (four sites) enabled improved insights into the temporal resolution of current rates of rise and accelerations in mean sea level around Australia than were previously available. Averaged across these four records in 2018, approximately 40% of the “relative” velocity observed (∼2.2 ± 1.8 mm/y, 95% confidence limit [CL]) is attributable to VLM. When corrected for VLM, only the Fort Denison site exhibits “geocentric” mean sea-level velocity in 2018 exceeding 2 mm/y. The average geocentric velocity across all four sites in 2018 equates to 1.3 ± 2.0 mm/y (95% CL). Interestingly, each long record exhibits similar temporal characteristics, whereby a low point in the velocity time series occurs sometime in the period from 1970 to 1990, after which velocity increases over time to a peak occurring sometime after ca. 2010, suggesting the presence of a small acceleration (albeit not statistically different to zero at the 95% CL) in the record.