Smithers, Scott, Hopley, David, and Mclean, Roger (2018) Holocene sea level on the Great Barrier Reef: reflections on four decades of debate and the legacy of the 1973 expedition to the northern great barrier reef. Atoll Research Bulletin, 2018 (619). pp. 79-103.

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Abstract

The main aim of the Royal Society and Universities of Queensland expedition to the northern Great Barrier Reef in 1973 was to elucidate the recent history of the reefs, especially in response to Holocene sea-level change. The expedition comprised three separate phases, lasted four months and was led by David Stoddart. At the time there was strong debate about the pattern of mid-late Holocene sea level both globally and in Australia and especially over whether the last phase of the post-glacial transgression showed a decelerating trend, or stable pattern, or whether there had been a highstand above present sea level. Members of the 1973 expedition included protagonists who supported a Holocene high as well as those who held the view that sea level had not reached above its present position in the past few millennia. Here we reflect on the advances in understanding Holocene sea-level changes on the northern Great Barrier Reef as a result of the expedition and its report published in a series of papers in 1978. First, we identify four key contributions of the expedition: (1) a detailed assessment of several geomorphological and biological sea-level indicators and the water-levels to which they refer; (2) recognition that the upper surface of coral microatolls can provide a reliable and precise record of contemporary and palaeo-sea levels; (3) that surveys of microatoll elevation and 14C determinations on several reefs in the northern GBR provided unequivocal evidence that present sea level was first achieved about 6000 years ago then shortly thereafter rose 1.0 to 1.3m to a highstand that was possibly maintained to about 3000 yr BP before falling to its modern level; and, (4) although the concept of hydro-isostacy was still in its infancy the geographic pattern of age/sea level results from the expedition demonstrated that apparent sea-level differences across the GBR could be explained by the isostatic contribution. Second, we review the many sea level studies on the Great Barrier Reef since publication of the expedition's report in 1978 distinguishing those that focus on the northern sector and then the central and southern sectors of the GBR. This assessment reveals that the general pattern of mid-late Holocene sea-level history established during the expedition has not changed significantly, although improved calibration of 14 Cages has modified the time-frame. It is also clear that there are substantial differences in the abundance and quality of Holocene sea-level data, indicator types and interpretations through out the length and breadth of the GBR. Third, from this analysis we identify two contentious issues, one relating to the elevation, timing, duration and geographic extent of the Holocene highstand, and the other on whether the fall of sea-level from that high to its present position has been smooth or oscillating. Finally, we conclude by noting that these contentious issues were also present over four decades ago at the time of the 1973 expedition but are still to be resolved.

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