SMOOTH OR OSCILLATING LATE HOLOCENE SEA-LEVEL CURVE? EVIDENCE FROM THE PALAEO-ZOOLOGY OF FIXED BIOLOGICAL INDICATORS IN EAST AUSTRALIA AND BEYOND

Abstract The nature of late Holocene sea-level change has important palaeo-environmental implications for the understanding of past and present coastal, oceanic and climatic systems. This study develops a fixed biological indicator (FBI) method based on tubeworm–barnacle assemblages in order to construct a late Holocene sea-level curve for south east Australia. It also compares changes within and between mid-latitude regions of the Southern Hemisphere using the palaeo-biology of inter-tidal sub-fossils that have provided time–elevation data covering the past 5000 years. Five sites from around the mouth of the Port Hacking estuary, 29 km south of Sydney, are described in detail. The results suggest that, rather than relative sea-level describing a stable or smoothly falling pattern from a maximum of +1.0 m above present over the last ∼5000 years on the southeast Australian coast, there have been complex movements from a maximum of over 1.5 m, with at least one marked fall between 3500 and 3400 yr BP, and the possibility of a small positive oscillation around 1900 yr BP. Furthermore, changes in the inter-tidal species at our sites suggest that there was a period between 4300 and 2800 years where ocean temperatures were warmer than present. Our Port Hacking findings are compared with other studies from the east coast of Australia, as well as the Pacific Islands and Brazil. Evidence from each location suggests a broad similarity in the timing of environmental events and marine fluctuations across an expanse of the Southern Hemisphere. Are such similarities coincidental or part of mechanisms common to mid-latitude Southern Hemisphere regions?