Geologic, isostatic and anthropogenic signals affecting sea level records at tide gauge sites in southern Australia

Abstract

Sea level records from seven tide gauge sites in southern Australia include long-term records that have been used in global estimates of mean sea level trends. The influence of geologic, isostatic and anthropogenic impacts on these records, each with different rates of change, is demonstrated. First, comprehensive geological data of the last interglacial high sea level stand in southern Australia provide evidence of relative land movements over a 105 year time period demonstrating regional patterns of uplift. Second, well-defined geological data also exist for the Holocene postglacial sea level rise, primarily from the marine and intertidal sediments of the South Australian gulfs. Detailed studies, using vibrocoring and radiocarbon dating techniques, have been conducted to define the timing and relative height of the Holocene sea level highstand and its subsequent fall to present sea level. Reconstructed Holocene sea level curves demonstrate a consistent and predictable postglacial hydroisostatic warping of the continental margins over the last 6.5×103 year. Third, an anomalously low sea level curve from two metropolitan tide gauge sites is attributed to anthropogenically induced land subsidence occurring in the area over a 102 year time period. The revised mean sea level trends for this region illustrate the importance of extracting the geologic, isostatic and anthropogenic signals from the tide gauge data used in monitoring global mean sea level trends or calibrating satellite altimetry data.