Professor Eelco Rohling
Australian Laureate Fellowship description and results
Coral sea-level benchmark database
(1) High-resolution investigation of ocean/climate changes during the Neogene, and in particular the Quaternary, to determine the nature, timing and magnitude of natural climate variability. This interest spans the globe, but is generally focussed on marginal seas and anoxic deposits. Because of their small volume and restricted communication with the open ocean, marginal seas show virtually immediate responses to climatic perturbations, in an amplified fashion, and they therefore represent excellent monitoring sites for even the smallest climate perturbations. Anoxic sediments are of interest because of the lack of bioturbation, which allows very high sampling resolutions, and because they represent an extreme response to (climatic) changes in buoyancy forcing. Studies of the Mediterranean and Red Sea basins have provided many insights that transcend regional boundaries, such as: timing, phasing and intensity of variability in the monsoons and the westerlies; sensitivity of thermohaline systems to climatic variability; nutrient storage and recycling in stratified systems; ecological responses to adverse conditions; and quantitative assessments of the applicability of stable oxygen isotopes for palaeosalinity reconstructions. The immediate global impact of marginal-seas research is especially evident from our new, independent, high-resolution (~200 years) method for global sea-level reconstruction, based on Red Sea and Mediterranean d18O records. Recent attention has shifted strongly toward studies of palaeo-climate sensitivity, quantification of the relationship between past greenhouse gas forcing and sea level, assessment of past rates of change in major climate parameters (e.g., ice volume, temperature, monsoon strength, etc.) and their timing relationships.
(2) Theoretical and applied (integrated with proxy records) modelling of present-day and past states of circulation and property distribution. This aspect focusses especially on the potential for quantification of natural processes from (palaeo-) oceanographic proxies, including realistic confidence intervals. The work ranges across purely theoretical (“what if”) considerations, targeted simulation of observed changes, and aspects concerned with quantitative interpretation of proxy data. A strong component in this modelling concerns the robustness of simulated results, since a solution that depends too much on small changes/uncertainties in the essential assumptions may not be very significant. Hence, sensitivity testing and expression of confidence limits play a key role in the modelling efforts.
(3) Theoretical and practical/analytical research on the use of conservative properties and d18O to trace deep-water formation, advection and mixing processes in the modern ocean. This mainly concerns theoretical arguments and new interpretations of existing data sets. Collaborative examples include: an evaluation of the nature of salinity changes in the Mediterranean Sea during the last 50 years; a study of deep-water formation processes in the Japan Sea based on using a combination of noble gas and stable isotope analyses; and assessments of the potential for use of oxygen isotope ratios to track temporal changes in salinity. Part of the latter included the compilation of a global stable oxygen isotope distribution database that was used in validation of a present-day to last glacial maximum global modelling study, and which now forms part of a database held for public access at http://www.giss.nasa.gov/data/o18data/.
(4) Assessment of changes in deep-sea ventilation states and nutrient distribution mechanisms, the interactions with the organic and inorganic carbon cycle, and the impact of ecological responses on proxy records. This work concerns fundamental aspects that underlie the reconstructions and modelling projects listed above. It specifically focusses on climate-driven changes in the mechanisms and timing of nutrient loading and availability for production (by nutricline shoaling). This includes the development of non-steady state arguments between nutrient recharge and nutrient utilisation, and the development of a deeper understanding of carbon burial fluxes and their ecological impacts at the sea floor.
(5) Integration of Holocene palaeoclimate research with archaeological records. There now exist sufficient high-resolution palaeoceanographic/climatic records from the eastern Mediterranean to Arabian Sea region to allow accurate comparisons of the signals with those in the archaeological record of the Near and Middle East. Correlations between the different types of records are established by using a combination of radiocarbon dating, ash-layer correlations, pollen records, and (climatic) event stratigraphy, involving experts from all relevant disciplines. This line of work offers interesting feedback from an entirely different line of science, which improves communication and interaction across disciplinary boundaries and helps to fuel new ideas and re-evaluation of traditional interpretations.
- Principal investigator, Rohling - Australian Laureate Fellowship “Sea level change and climate sensitivity”