Atmospheric ice nucleating particles - is there a fingerprint of past changes in polar snow and ice?

BACKGROUND. Cloud droplets freeze homogeneously at temperatures below -37ºC, but the presence of ice nucleating particles (INP) can induce freezing at much higher temperatures. Even small numbers of INP have a large impact on cloud optical properties and lifetime, precipitation and therefore climate. However, INP sources and their temporal and spatial variability are only poorly understood causing significant uncertainty in the representation of clouds in climate models in the Arctic and above the Southern Ocean, including coastal Antarctica. A quantitative understanding of the origin and temporal variability of INP is needed to reduce uncertainties in regional and global climate predictions, especially in the high latitudes, which currently experience the strongest warming. Recent observations suggest that some INP are preserved in polar snow and ice. Thus, polar ice cores may be a potential tool to extend the instrumental record and to infer changes of INP abundance in polar regions over past centuries and millennia.

PROJECT AIMS AND METHODS. The project objectives are (a) to establish the relationship of ice nucleating particle (INP) concentrations in polar air and snow and (b) to evaluate the century-scale atmospheric INP variability at a polar location, based on measurements of available ice core samples. In a first step the student will adapt and validate an existing droplet assay method to measure INP concentrations in polar snow and ice core samples. Then the student will quantify the modern air-snow relationship of INP, measuring INP spectra from air filter and snow samples. Samples will be available from the year-round sea ice drift expedition (MOSAiC) in the Arctic during 2019-20 as well as from Halley station in coastal Antarctica. And finally, the student will estimate the historic variability and trends of INP abundance over the past few centuries, from the pre-industrial to present day, by measuring INP concentrations in polar ice core samples held in the BAS archive. The atmospheric relevance and climate impacts of the inferred regional atmospheric INP record will be assessed based on a sensitivity study in close collaboration with chemistry and climate modellers at BAS.

CANDIDATE REQUIREMENTS. Degree in physics, chemistry or related Earth/Environmental Science, with experience in experimental work in the laboratory and good numerical skills (e.g. basic knowledge of Matlab, Python or equivalent).

TRAINING. You will be part of a dynamic research team (AIC) at BAS, which is working on a wide range of environmental topics in the polar regions, and one that is studying fundamental aspects of ice nucleation in the School of Physics (Univ. of Bristol). You will have outstanding opportunities to develop practical and data analysis competences and gain a deep understanding of both climate science and ice physics. Full training in the instrument, laboratory and modelling techniques will be provided, together with broader transferrable skills training. You will have a potential field work opportunity at a site in the Arctic or Alps. You will attend an atmospheric sciences summer school and receive support to publish results in peer-reviewed journals and at (inter)national conferences.