Sea level changes from glacial to recent times

17 October 2014

Scientists have mapped changes in global sea level and ice volumes, through the last ice age into recent times, in the most comprehensive study of its kind.

These results provide key information for palaeo-climate modelling, for reconstructing coastal environments in pre-historical times, and the background signal for evaluating more recent anthropogenic contributions to sea level.

In a study reported in Proceedings of the National Academy of Sciences, an ANU-led team provides a high-resolution record of these changes from the onset about 35,000 years ago of the last peak glaciation into more recent time.

They found that sea levels have been stable for the last few thousand years and that for the past 6,000 years until about 100-200 years ago, there is no evidence for sea level oscillations greater than about plus or minus 25 centimetres over periods of 200 years or longer.

The implication is that during the past few thousand years the ice sheets have been stable at a time when climate also has been relatively stable.

"This record provides the benchmark for assessing the significance of recent change recorded instrumentally," said the leader of the study, Professor Kurt Lambeck, from the Research School of Earth Sciences.

The study has also identified changes in the Antarctica ice sheet as having been important enough to contribute some 25 metres to the total globally averaged rise of about 135 metres since the time of the peak glaciation, implying that at this time the ice approached the edge of the continental shelf around this continent.

"This is greater than generally accepted by glaciologists and a major challenge will be to reconcile the different views," said Professor Lambeck.

Over the past two decades, the team has collected many thousands of geological and archaeological measurements from across the world, from polar to equatorial latitudes, to build a record of the changes in volumes of the past ice sheets and in global sea level during glacial cycles.  As well as field observations they used numerical modelling to allow for land movements.

During the growth and decay of ice sheets, sea level does not fall and rise uniformly around the globe because of the deformation and gravitational changes of the planet during the redistribution of the ice and water loads. Hence the correction of the local field observations for these effects is essential and requires complex geophysically-based modelling of the combined earth-ocean-ice system, said Professor Lambeck.