Kurt Lambeck

Australia/Paesi Bassi

Premio Balzan 2012 per le scienze della Terra solida con particolare attenzione ai contributi interdisciplinari

Progetto di ricerca

Sea-level Change during Glacial Cycles

Kurt Lambeck is Emeritus Professor at Australian National University. The research component of the second part of his Balzan Prize addresses three important elements of the broad subject of sea-level change.
The first involves geophysical modelling of interactions between ice sheets, the solid earth and sea level. One of the goals of the project is to develop a version of the numerical models suitable for use by ‘non-experts’ so as to make the methodology available to geologists and archaeologists. Another goal is to develop the next iteration of ice sheet models with a particular focus on the Antarctic ice sheet, which up to now has played a rather passive role in the discussion of past sea levels, despite its being important in assessing the future of this ice sheet in a framework of a warming planet. Other targets include an improved ice sheet model for southern Greenland and improvements in the North American ice sheet model. These models provide improved reference points for testing climate models under conditions very different from today as well as the basis for palaeogeographic reconstructions during recent glacial cycles to explore possible constraints on human migrations.
The second deals with past interglacials as analogs of the present interglacial, which is particularly important because its traces are best preserved in the geological record. Its climate was similar to today, but possibly a few degrees warmer, and sea levels were 4-6 meters higher than today. But the precise timing of this occurrence and any variability within the interglacial interval remains poorly constrained. Yet this information is important in the context of current climate change debate for understanding the sensitivity of ice sheets to changes in temperature. Field sites for which the team has preliminary information include: Western and Northern Australia, the Seychelles, and the Mediterranean. Earlier interglacials will also be examined including the Pliocene (~ 3 million years ago), when the global glacial-interglacial cycles were markedly different from those of the past 800,000 years.
The third theme is the present interglacial (the Holocene). Ocean volumes have remained approximately constant during the past 6,000 years, but periodically the argument arises that large amplitude (1-2 m) changes have occurred within relatively short time periods (a few hundred years). If correct, this has major implications for the instability of the climate system when the planet is not in an ice age. There are many reasons why this question remains debated. One is of the nature of the observational evidence. Another is land movement caused by tectonic and global dynamic processes. A third is the ongoing interaction between the past ice sheets and the solid earth and oceans. These issues will be addressed in order to arrive at what should be a definitive answer to the question of sea-level (and hence climate) stability or instability during interglacial periods.
Balzan funding has enabled a research associate to be appointed for two years at the Australian National University (ANU) to work on the modelling aspects of the various components of the earth-ocean-ice system. The appointee, Dr. Anthony Purcell, has experience in this research area, so as to build on past work. A second appointment of a Postdoctoral Fellow, Dr Hélène Rouby, has been made together with the École Normale Supérieure (ENS) in Paris to work on the analysis of sea-level data to develop high-resolution models for sea-level change in low- and mid-latitude regions. This is part of a longer-term proposal to transfer the ANU software and experience to ENS for use by French researchers and to introduce a more complex mantle rheology into the models.
Support was also provided to Ye-Ying Sun from the University of Hong Kong (UHK) to work as a Balzan Student at the Australian National University (ANU) during 2013 compiling and analyzing sea-level data from South East Asia, from Malaysia to Japan, and learning the elements of geophysical modelling. This work is significant for both the global studies and for examining the past subsidence rates of the large east and southeast Asian river deltas. Contributions to two field projects have been made to permit students to extend their PhD work. One is a project with Brigid Morrison from the University of Tasmania to collect further core samples from sites in Tasmania, and to provide radiocarbon dating to examine the rise of sea level during the past 7,000 years. The significance of this study is that it may answer questions about the role of Antarctica to the global sea-level change since the last glacial maximum. The other project has provided support for PhD student Brenda Dechnik from Sydney University to participate in fieldwork in the Seychelles that examines earlier interglacial reefs that are now above sea level. These projects focus on specific scientific targets that bring together young and experienced researchers in selected field environments, in the requisite laboratory methods and in computational methods. Further field projects involving young researchers in Australia are being examined and will be gradually introduced.
Sea level is an important component of the four-yearly Intergovernmental Panel on Climate Change assessment of the science of climate change. In May 2013, the Final Draft of the Working Group 1 report was delivered. It highlighted many important questions in need of better answers, which the research inspired by Lambeck’s Balzan Prize project may contribute significantly to providing.

Excerpt from the: The Balzan Prizewinners’ Research Projects: An Overview 2016