About the Project
The fifth assessment report of the IPCC (AR5) states, “It is very unlikely that the AMOC will undergo an abrupt transition or collapse in the 21stcentury for the scenarios considered.” It also states, “However, a collapse beyond the 21st century for large sustained warming cannot be excluded.” Uncertainty as to whether such a change may or may not occur is compounded by our lack of understanding of the precise mechanisms (forcings and feedbacks) of the processes involved. This project will address this gap in understanding.
It is well known that the occurrence and magnitude of abrupt climate change is somehow linked to the size of continental ice sheets but the precise link is unknown. For example, the ~60m drop in global sea level (SL) between 70-80kyr ago witnessed several abrupt climate shifts that involved large changes in Atlantic Ocean circulation. However, it is not known whether the change in SL led to climate instability or vice versa, in part because of the poor constraints on the timing of ice sheet growth. This project will address this fundamental uncertainty in climate dynamics by placing critical constraints on the timing of SL fall during this major climate transition and during earlier times of ice growth.
Methodology: Benthic foraminiferal Mg/Ca ratios provide a well-established means of reconstructing calcification temperatures and, in combination with d18O measurements, provide an unparalleled approach for reconstructing changes in the oxygen isotope composition of seawater (d18Osw), a function of global ice volume. Here we will use this technique, possibly in combination with clumped isotope analyses, across major intervals of ice growth in multiple locations (necessary because the response at any individual site will be influenced by regional hydrographic changes as well as the effects of ocean mixing). We will also develop a detailed assessment of the component and combined errors in our sea level estimates. We will integrate our findings with alternative estimates of sea-level change (e.g. from ancient corals) and analyse state-of-the-art climate model results to investigate the possibility that the reconstructed history of d18Osw at any one site might simply be a function of internal ocean dynamics and regional variations in evaporation and precipitation.
Funding Notes
This studentship is very generously funded through NERC GW4+ Doctoral Training Partnership. It consists of full UK/EU tuition fees, as well as a Doctoral Stipend matching UK Research Council National Minimum (£14,296p.a. for 2016/17, updated each year) for 3.5 years.
Additional funding to the value £11,000 is available over the course of the programme for conference attendance, fieldwork allowance, travel allowance and other project costs. A further £4,000 is available in the form of as a training credits over the course of the programme for specialist training courses and/or opportunities.
References
1. K. B. Cutler, R. L. Edwards, F. W. Taylor, H. Cheng, J. Adkins, C. D. Gallup, P. M. Cutler, G. S. Burr, A. L. Bloom, Rapid sea-level fall and deep-ocean temperature change since the last interglacial period. Earth and Planetary Science Letters 206, 253-271 (2003).
2. H. Elderfield, M. Greaves, S. Barker, I. R. Hall, A. Tripati, P. Ferretti, S. Crowhurst, L. Booth, C. Daunt, A record of bottom water temperature and seawater delta O-18 for the Southern Ocean over the past 440 kyr based on Mg/Ca of benthic foraminiferal Uvigerina spp. Quaternary Science Reviews 29, 160-169 (2010).
3. S. Barker, G. Knorr, R. L. Edwards, F. Parrenin, A. E. Putnam, L. C. Skinner, E. Wolff, M. Ziegler, 800,000 years of abrupt climate variability. Science 334, 347-351 (2011).
4. M. F. Sanchez Goni, E. Bard, A. Landais, L. Rossignol, F. d'Errico, Air-sea temperature decoupling in western Europe during the last interglacial-glacial transition. Nature Geoscience 6, 837-841 (2013).
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