Atmospheric CO2 concentrations are close to 400 ppmv today. Before the industrial revolution, the most recent time with such high levels was during the warm middle Pliocene, about 3-3.5 million years ago. At that time, mean sea level stood 12-32 m above the present level. Ice ages did occur during the Pliocene, but they were not severe, with sea-level lowerings of only about 50 m (due to phases of continental ice build-up). As CO2 levels dropped and Earth’s climate cooled from the warm middle Pliocene to the Present, sea-level during ‘interglacials’ (warm periods in between ice ages) dropped to values close to those of today. In addition, ice ages became strongly intensified, with sea-level lowerings during the past five ice ages reaching up to 130 m below the present level. For scale, this means that these ice ages contained almost three times the volume of the modern Greenland and Antarctic ice sheets combined.
This general picture is well supported, but until recently there have not been enough independent methods to measure sea-level changes in ancient times. We need several independent methods, because each individual method of sea-level reconstruction has its own limitations, and it is only by comparing estimates from several independent methods that we can hope to see the systematic patterns that portray true sea-level change. Early in 2014, we presented a new method (Rohling, E.J., Foster, G.L., Grant, K.M., Marino, G., Roberts, A.P., Tamisiea, M.E., and Williams, F., Sea-level and deep-sea-temperature variability over the past 5.3 million years. Nature, 508, 477–482, 2014). We are currently in a major effort to improve the results from that method, using sediment cores from the eastern Mediterranean. This material spans the most recent 3.3 million years. We are looking for enthusiastic candidates to investigate critical intervals of time in the development of the sea-level change patterns.
The work will help develop an understanding of the stages through which ice-age cycles increased, and will be coupled with parallel efforts on characterizing CO2 changes. This understanding provides important context to the debate about the potential implications of future climate change.
If you are excited about understanding the nature of ice-age cycles, then contact us (Prof. Eelco J Rohling, or Dr. Katharine Grant)!
We can support projects on this topic at Honours, MSc, and PhD level.