Dr David Thornalley
Lecturer (2013 – present)
Department of Geography
University College London
Tel.: +44 (0)20 7679 0506
I am interested in understanding the causes and mechanisms of climate change on decadal to millennial timescales. I use a range of sedimentary and geochemical proxies in marine sediment cores, with a particular emphasis on reconstructing past changes in the circulation of the North Atlantic.
Lecturer, University College London (2013-present)
Postdoctoral Research Scholar, Woods Hole Oceanographic Institution (2011-2013)
Postdoctoral Research Associate, Cardiff University (2008-2011)
PhD University of Cambridge (2008)
MSci, MA University of Cambridge (2004)
Moffa Sánchez, P., Born, A., Hall, I.R., Thornalley, D.J.R., Barker, S. 2014. Solar forcing of North Atlantic surface temperature and salinity over the past millennium. Nature Geoscience 7, 275-278
Moffa Sánchez, P., Hall, I., Barker, S., Thornalley, D.J.R., Yashayaev I. 2014. Surface ocean changes in the Eastern Labrador Sea during the last millennium. Paleoceanography, doi: 10.1002/2013PA002523.
Griffiths, J., Barker, S., Hendry, K., Thornalley, D.J.R., van de Flierdt, T., Anderson, R. & Hall, I. 2013. Evidence of silicic acid leakage to the tropical Atlantic via Antarctic intermediate water during Marine Isotope Stage 4. Paleoceanography, doi:10.1002/palo.20030.
Thornalley, D.J.R., Blaschek, M., Davies, F.J., Praetorius, S., Oppo, D.W., McManus, J.F., Hall, I.R., Kleiven, H., Renssen., H. & McCave, I.N. 2013 Long-term variations in Iceland-Scotland overflow strength during the Holocene. Climate of the Past, 9, 1627-1656.
Yu, J., Thornalley, D.J.R., Rae, J., McCave, I.N., 2013. Calibration and application of B/Ca, Cd/Ca and d11B in Neogloboquadrina pachyderma (sinistral) to constrain CO2 uptake in the subpolar North Atlantic during the last deglaciation. Paleoceanography, 28, doi:10.1002/palo.20024.
Thornalley, D.J.R., Barker, S., Becker, J., Knorr, G. & Hall, I.R., 2013. Abrupt changes in ocean circulation during the onset of full glacial conditions. Paleoceanography, 28, doi: 10.1002/palo.20025.
Thornalley, D.J.R., Barker, S., Broecker, W.S., Elderfield, H. & McCave, I.N., 2011. The deglacial evolution of North Atlantic deep convection. Science, 331, 202-205.
Hall, I.R., Evans, H.K. and Thornalley, D.J.R., 2011. Deep water flow speed and surface ocean changes in the subtropical North Atlantic during the last deglaciation. Global & Planetary Change doi:10.1016/j.gloplacha.2010.12.001
Thornalley, D.J.R., McCave, I.N. & Elderfield, H., 2011. Tephra in deglacial ocean sediments south of Iceland: Stratigraphy, geochemistry and oceanic reservoir ages. Journal of Quaternary Science, doi: 10.1002/jqs.1442
Thornalley, D.J.R., Elderfield, H. & McCave, I.N., 2010. Reconstructing deglacial North Atlantic surface hydrography and its link to the Atlantic overturning circulation. Global & Planetary Change, doi:10.1016/j.gloplacha.2010.06.003
Thornalley, D.J.R., Elderfield, H. & McCave, I.N., 2010. Intermediate and Deep Water Paleoceanography of the northern North Atlantic over the last 21,000 years. Paleoceanography, 25, PA1211, doi:10.1029/2009PA001833.
Thornalley, D.J.R., McCave, I.N. & Elderfield, H., 2010. Freshwater Input and Abrupt Deglacial Climate Change in the North Atlantic: Paleoceanography, 25, PA1201, doi:10.1029/2009PA001772.
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.
McCave, I.N., Kiefer, T., Thornalley, D.J.R. & Elderfield, H., 2005. Deep Flow in the Madagascar-Mascarene Basin Over the Last 150,000 Years: Philosophical Transactions of the Royal Society of London A, 363, 81-99.
During the late Quaternary, the Earth’s climate system has undergone climate oscillations on a range of timescales, from multi-decadal processes to glacial-interglacial cycles occurring every ~100,000 years. Changes in ocean circulation played a significant role in these climate events by altering the global redistribution of heat, dissolved nutrients and carbon. My research focuses on constraining how the circulation of the ocean changed in the past and the mechanisms by which these changes affected the global climate system.
I use a wide range of tools including: faunal and elemental ratio (e.g., Mg/Ca, B/Ca, Cd/Ca) analysis of foraminifera to reconstruct water mass properties; geochemical proxies of circulation such as measurement of Pa/Th ratios, Nd isotopes and radiocarbon concentrations; examination of the detrital components of sediment such as ice-rafted detritus and geochemical analysis of tephra for improving stratigraphy; and sediment grain size analysis (e.g. sortable silt analysis) to reconstruct relative changes in paleo-current strength.
Ongoing projects include:
The response of the Western Boundary Undercurrent to past abrupt climate change
Deep water produced in the high latitude North Atlantic forms a deep western boundary current (locally termed the Western Boundary Undercurrent, WBUC) that flows southward, at depth, along the eastern margin of North America. The WBUC plays an important role in rapidly transmitting climate signals into the ocean interior and helping ventilate the world’s ocean. I am using grain size analysis to examine how the flow speed structure of the WBUC altered between warm and cold climate intervals during the last glacial period and the Holocene (Figure 1).
Figure 1. By measuring variations in the grain size of sediment in cores taken from the Northwest Atlantic, I am investigating how the flow speed structure of the Western Boundary Undercurrent (WBUC) altered under different climate states
Holocene changes in the strength of the Nordic Seas Overflows
The overflow of cold, dense water from the Nordic Seas into the North Atlantic plays a critical role in the global thermohaline circulation, and the compensating inflow of Atlantic surface waters helps warm NW Europe. Using grain size data from cores taken south of Iceland, I am investigating the strength of the eastern Nordic Seas overflow throughout the Holocene (~0-11,000 years ago), examining likely controls and effects. With collaborators from WHOI, I will be collecting new cores on a cruise in May 2014. These cores will be used to examine changes in the overflows over the past 2000 years, focussing on whether or not there have been any changes between the Little Ice Age and the present day.
Deglacial changes in the circulation of the Northeast Atlantic and Arctic Mediterranean
The termination of the last Ice Age was accompanied by abrupt changes in ocean circulation. The Northeast Atlantic in particularly was subject to dramatic reorganisations that are thought to have had an impact on global climate evolution through this period. I am calibrating and using elemental ratios in benthic foraminifera to constrain changes in the physical and chemical properties of the Northeast Atlantic and Nordic Seas. I am also using benthic radiocarbon dating to help constrain the ventilation of this oceanographic region since the last glacial.
Figure 2. A sediment core from south of Iceland. Ongoing work involves correlating volcanic ash layers (black layers) in the cores to similar ash layers found in Greenland ice cores to help determine lead-lag relationships between different climate archives. Measuring the elemental ratios in foraminifera (microscopic, single-celled organisms), found within the core, can also be used to reconstruct the past physical and chemical properties of the ocean and determine its role during past climate change.
Subpolar gyre dynamics during the Holocene
The strength of the North Atlantic’s subpolar gyre varies on annual to millennial timescales and it is likely involved in feedback mechanisms that impact atmospheric circulation and the overturning circulation of the ocean. In collaboration with scientists from Cardiff University, we are investigating how the circulation of subpolar gyre changed on decadal timescales throughout the last 2,000 years, as well as investigating millennial scale changes throughout the Holocene.
My work over the last 5 years has been focussed on understanding the role of the North Atlantic in abrupt climate change. This work has revealed unexpected variability in the properties of both the surface and deep ocean, resulting in publications in Nature and Science, which have been reported on by NERC Planet Earth as well as the wider public media.
- GEOGG130: Climate Dynamics (MSc Climate Change)
- GEOGG135: Biological Indicators of Environmental Change
- GEOGG136: Non-biological Indicators of Environmental Change
- Forthcoming MSc module - Oceans and Climate Change
- Forthcoming - GEOG3007: Palaeoclimate
2013-present: Rehemat Bhatia, Geochemical signals in greenhouse and icehouse planktonic foraminifera (Co-supervisor).