Project 3:
Advances in ocean proxies
In order to gain insight into paleoceanographic conditions, it is necessary that we have a well-equipped toolbox, which we apply and interpret the results of appropriately. One component of our research therefore contributes to the development and application of a range of ocean proxies. The OACD group have advanced how we can use and interpret multi-species planktic foraminifera, revealing that the history of different water masses can be monitored in the same sediment samples by utilizing the specific habitat preferences of different species. We have undertaken trace metal analysis and worked with colleagues to calibrate and apply foraminiferal proxies (B/Ca and δ11B) that enable us to examine changes in the carbonate chemistry of the surface and deep ocean and thus examine the role of the North Atlantic in changes to atmospheric CO2. We have created a temperature calibration of benthic foraminifera Mg/Ca and are examining the fidelity of benthic foraminifera Mg/Ca by undertaking multi-species analysis of modern NW Atlantic cores. We have tested different methodological approaches for benthic foraminiferal clumped isotope paleothermometry and compared them to stable isotope and benthic foraminiferal Mg/Ca that I generated, alongside published ostracod Mg/Ca data; this approach led to robust reconstruction of past deep Arctic ocean temperature and a similar approach is being applied to the glacial North Atlantic.
The group have made significant methodological advances in the use of sediment grain size analysis (sortable silt mean grain size) to examine past changes in deep-sea currents. We have adopted the essential and highly informative approach of using multiple (and where possible, duplicated) core sites in depth transects to more fully constrain past changes in deep-sea currents. This approach allowed earlier apparently divergent records to be reconciled. Calibration of this grain size proxy has also enabled us to quantify the amplitude of past flow speed changes and by applying this to multiple depth transects, we are obtaining robust quantitative estimates on past changes in the Deep Western Boundary Current (DWBC) as a proxy for the Atlantic Meridional Overturning Circulation (AMOC).
Our research has also helped to develop chronostratigraphic tools and information. We have contributed to the development of North Atlantic tephra chronology during the deglaciation, provided important constraints on past changes in surface radiocarbon reservoir ages; assessed species-specific differences in benthic radiocarbon ages, examined and developed general chronostratigraphic frameworks in the North Atlantic. With UCL Geography colleagues, we pioneered the application of Spheroidal Carbonaceous Compounds in marine sediment cores as a stratigraphic marker for the Anthropocene. We are currently working on proxies to examine past ecological changes, including the development and application of fast methods for identifying coccospheres in sediment. As part of the EU iAtlantic project, we have been assessing the feasibility of undertaking a shot-gun sequencing approach to analyse ancient eukaryote DNA in North Atlantic sediment core.
- Thornalley, D.J.R., Bauch, H.A., Gebbie, G., Guo, W., Zielger, M., Bernasconi, S., Barker, S., Skinner, L. & Yu, J. (2015). A warm and poorly ventilated deep Arctic Mediterranean during the last glacial period. Science, 349, 706-710
- Thornalley, D.J.R., Elderfield H. & McCave, I.N., (2009). Holocene Oscillations in Temperature and Salinity of the Subpolar North Atlantic. Nature, 457, 711-714