A fluctuating southern hemisphere Holocene relative sea-level model: new sites, possible errors, sources and mechanisms?

Abstract

There is an on-going debate on the mechanisms and sources that could underpin the extensive relic mid- to late-Holocene higher shoreline evidence found around Australia, SE Asia and southern Brazil. Is the evidence regionally specific and variable from hydro-isostatic rebound or is there a relative climate-induced coincidence in the time elevation measurements suggestive of common response mechanisms? This research reports on a number of advances looking at these alternative hypotheses. Firstly, dating and relative height measurements of relic and present fixed inter-tidal biological indicators of the same species at new sites in South Australia, Western Australia and Tasmania ('Galeolaria') and in Queensland ('Saccostrea') seem to support an oscillating-type model in the context of height measurement of variations in the current inter-tidal zones at these localities and tidal regimes. Secondly, a same species comparison between Tasmania, King Island and the Australian mainland suggest a rate of hydro-isostatic readjustment in Bass Strait. Similar work is being undertaken for The Great Barrier Reef. Thirdly, the rates of change in the +/-1m statistical oscillating model is broadly coincident with the timing of glacial advances and retreats of southern hemisphere glaciers during the mid-late Holocene and such events could occur as multiples of ~1400yr Bond Cycles. The exception could be an event 2600 to 2800 yrs BP, where apparently anomalous higher sea levels of ~1.5 to ~2.5m above present occurred for a short period of time (significantly above the millennial average of +1.0m above present). The possible origin could be a sudden melt of the Antarctic Ice Sheet at that time, from a warming of over 1.0°C for a ~120 yr period from 2850 to 2730, rather than from any fluctuation produced from glacial melting.