Exploring the origin of snow water isotopic signals in the Arctic

Lead supervisor: Dr Xin Yang

Location: Atmosphere, Ice and Climate (AIC), British Antarctic Survey (BAS)

Duration: 8 weeks

Suitable undergraduate degrees: Chemistry, Physics, Earth Science, Meteorology

Project background

Snowpacks on sea ice and coastal areas play a key role in the air-sea interactions. For example, remote sensing (both ground-based and satellite-based) data show that sea ice has the largest reactive bromine loading on Earth. It has been proposed that snowpack and/or blowing snow dominate the release of reactive bromine. It has been found that reactive bromine plays a key role in polar atmospheric chemistry, as it not only rapidly destroys ozone, but also oxidises elemental mercury and other key organic compounds. Surface snow (the top few cm) is at the centre of the exchange of gases or particulates, as the thin layer is directly influenced by both physical and chemical processes such as dry and wet depositions, precipitation, evaporation or sublimation and post-deposition photochemical modifications. The origin of surface snow is critical in terms of understanding the observations and interpreting the variation of the data. Water isotopic signal (δD) is one of the proxies that can be used to diagnose the source or origin of water vapour or precipitated snowfall.

We have more than a thousand snow samples collected from Eureka, a high Arctic site in Canada (80N, 86W) during February-March 2018 and 2019. Snow samples were mainly from three sampling locations: off-shore and on-shore sites at sea level and at the top of a hill ~600 m above the sea level. Surface snow was collected on a daily basis from three sub-layers (0-0.2 cm, 0.2-0.5 cm and 0.5-1.5 cm). The reason why we focus on the top few cm of snow is because of the relatively low precipitation in winter-early spring, and snowpack depth in Eureka has not changed much since last December. In addition, we have column snow samples collected at an irregular interval. Most of the snow samples underwent ionic analysis with a small portion selected for water isotopic δD analysis. The ionic data have been analysed carefully in a recent study with a scientific paper in preparation. The aim of this proposal is to look into the water δD dataset to diagnose the origin of the snow samples. The focus will be on a few selected cases during which enhanced snow bromide or nitrate were measured. You are also expected to run the online NOAA HYSPLIT back-trajectory models and check meteorology datasets to explore the history of air masses approaching Eureka. The outcome of this work will be used to evaluate a proposed mechanism of sea salt aerosol production (and consequent bromine release) from sublimating windblown saline snow particles.