Testing the interactions between chemical weathering and glacial cycles using novel isotope tracers.

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Throughout geological time, feedback processes have prevented runaway greenhouse and icehouse states, keeping Earth's climate within habitable limits. The continental weathering of silicate rocks has been proposed to play an important role in such climate stability but is surprisingly poorly quantified. This project seeks to provide new constraints on the operation of weathering as a climate feedback. Laboratory experiments will be used to investigate element release and lead (Pb) isotope systematics during the chemical weathering of silicate rocks over a range of lithologies and grain sizes. These results will then be applied to examine variability in silicate weathering through Quaternary glacial-interglacial cycles. Because the ocean is the ultimate repository for the particulate and dissolved products of continental denudation, ocean sediment cores represent unique archives of past weathering changes.A novel combination of isotope tracers extracted from different fractions of marine sediments will quantify weathering changes in response to past climate perturbations. There is also scope to explore Li isotope records in speleothems as proxies for terrestrial weathering linked to terrestrial ice sheet retreat. This research will be carried out in state-of-the-art geochemistry labs within the LOGIC group at UCL. Expertise will be developed in marine sediment extractions, chemical separations, and analysis of both radiogenic and non-traditional stable isotopes by multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS).