New paper shows sea levels around Australia have declined over the past 7000 years

A new paper published in Quaternary Science Reviews is the "First synthesis of post-glacial sea level data around Australia in over 25 years," and shows that sea levels around Australia were from about 1 to 2.5 meters higher than the present 7000 years ago during the Holocene Thermal Maximum [which lasted 4000 years between 9000 to 5000 years ago]. The authors note that Australia is relatively stable tectonically and thus sea level data is not complicated by post-glacial isostatic and other adjustments, which would add considerable uncertainty to sea level reconstructions.   

According to the authors,

"Many of the issues, which challenged sea-level researchers in the latter part of the twentieth century, remain contentious today. Divergent opinions remain about: (1) exactly when sea level attained present levels following the most recent post-glacial marine transgression (PMT); (2) the elevation that sea-level reached during the Holocene sea-level highstand; (3) whether sea-level fell smoothly from a metre or more above its present level following the PMT; (4) whether sea level remained at these highstand levels for a considerable period before falling to its present position; or (5) whether it underwent a series of moderate oscillations during the Holocene highstand."

Fig. 7. Summary of the key sea-level data from Western Australia including barnacles, tubeworms (Baker et al., 2005), swash zone deposits ( [172] and [173]) and coral pavements (Collins et al., 2006).

Fig. 5. Summary of key sea-level data from New South Wales (compiled in Sloss et al., 2007). 

Fig. 4. Summary of sea-level data for the Queensland region (a). Indicators include barnacles ( [8] and [98]), beachrock (Hopley, 1980), foraminiferal transfer function (Woodroffe, 2009), mangroves (Larcombe et al., 1995), coral microatolls (Chappell et al., 1983) and oyster beds ( [8], [98] and [132]). Note the clear offset between the microatolls, barnacles and oysters compared with the beachrock and foraminifera data. The data fit within a tighter envelope when only the most reliable indicators are considered where the elevations can be directly measured to the modern counterparts (b; barnacles, microatolls and oyster beds).

Sea levels rose at a much faster rate from the peak of the last ice age around 20,000 years until about 8,000 years ago, and have been relatively stable over the past 8000 years.
Fig. 2. Summary of data showing the post-glacial sea-level rise for the Australasian region. The envelope is drawn to capture intertidal indicators and the zone between the terrestrial and marine directional indicators. Sites include New Zealand (NZ: e.g. Gibb, 1986), north-west shelf (NW shelf: e.g. [235], [236] and [116]), Huon Peninsula (Huon: e.g. [41],[65], [152] and [47]), Queensland (QLD: e.g. Larcombe et al., 1995), Sunda Shelf (Sunda: [88] and [89]), Western Australia (WA: e.g. [66], [178] and [179]), Northern Territory (NT: Woodroffe et al., 1987), South Australia (SA: Belperio et al., 2002) and New South Wales (NSW: Sloss et al., 2007). The following vertical errors have been assigned to the data: ±3 m for the intertidal (Inter.) indicators, +10, −1 for the marine indicators and +1, −10 for the terrestrial (Terr.) indicators. Note that meltwater pulse 1A (1A) is well represented in the Sunda Shelf data set.

Post-glacial sea-level changes around the Australian margin: a review

• Stephen E. Lewis^a, , , 
• Craig R. Sloss^b, 
• Colin V. Murray-Wallace^c, 
• Colin D. Woodroffe^c, 
• Scott G. Smithers^d

• ^a Catchment to Reef Research Group, TropWATER, James Cook University, Townsville, Queensland 4811, Australia
• ^b Earth, Environmental and Biological Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia
• ^c School of Earth & Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia
• ^d School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia

• http://dx.doi.org/10.1016/j.quascirev.2012.09.006, How to Cite or Link Using DOI

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Abstract

It has been known since Rhodes Fairbridge’s first attempt to establish a global pattern of Holocene sea-level change by combining evidence from Western Australia and from sites in the northern hemisphere that the details of sea-level history since the Last Glacial Maximum vary considerably across the globe. The Australian region is relatively stable tectonically and is situated in the ‘far-field’ of former ice sheets. It therefore preserves important records of post-glacial sea levels that are less complicated by neotectonics or glacio-isostatic adjustments. Accordingly, the relative sea-level record of this region is dominantly one of glacio-eustatic (ice equivalent) sea-level changes. The broader Australasian region has provided critical information on the nature of post-glacial sea level, including the termination of the Last Glacial Maximum when sea level was approximately 125 m lower than present around 21,000–19,000 years BP, and insights into meltwater pulse 1A between 14,600 and 14,300 cal. yr BP. Although most parts of the Australian continent reveals a high degree of tectonic stability, research conducted since the 1970s has shown that the timing and elevation of a Holocene highstand varies systematically around its margin. This is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice-melt, including a process known as ocean siphoning (i.e. glacio-hydro-isostatic adjustment processes).

Several seminal studies in the early 1980s produced important data sets from the Australasian region that have provided a solid foundation for more recent palaeo-sea-level research. This review revisits these key studies emphasising their continuing influence on Quaternary research and incorporates relatively recent investigations to interpret the nature of post-glacial sea-level change around Australia. These include a synthesis of research from the Northern Territory, Queensland, New South Wales, South Australia and Western Australia. A focus of these more recent studies has been the re-examination of: (1) the accuracy and reliability of different proxy sea-level indicators; (2) the rate and nature of post-glacial sea-level rise; (3) the evidence for timing, elevation, and duration of mid-Holocene highstands; and, (4) the notion of mid- to late Holocene sea-level oscillations, and their basis.

Based on this synthesis of previous research, it is clear that estimates of past sea-surface elevation are a function of eustatic factors as well as morphodynamics of individual sites, the wide variety of proxy sea-level indicators used, their wide geographical range, and their indicative meaning. Some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level, the inter-comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years. These issues need to be thoroughly understood before proxy sea-level indicators can be incorporated into credible reconstructions of relative sea-level change at individual locations. Many of the issues, which challenged sea-level researchers in the latter part of the twentieth century, remain contentious today. Divergent opinions remain about: (1) exactly when sea level attained present levels following the most recent post-glacial marine transgression (PMT); (2) the elevation that sea-level reached during the Holocene sea-level highstand; (3) whether sea-level fell smoothly from a metre or more above its present level following the PMT; (4) whether sea level remained at these highstand levels for a considerable period before falling to its present position; or (5) whether it underwent a series of moderate oscillations during the Holocene highstand.

Highlights

► First synthesis of post-glacial sea level data around Australia in over 25 years. ► Critical review of sea-level indicators used to reconstruct past sea-level change. ► Calibrated radiocarbon ages determine when sea level attained modern elevations. ► Examines the magnitude and length of the mid-Holocene highstand around Australia. ► Assesses the mechanisms responsible for mid–late Holocene sea-level changes