Abstract
The interaction between the ocean and Antarctic ice shelves can form supercooled water. This water is colder than the freezing point temperature, but still liquid. Supercooled water increases sea-ice growth rates, and influences ice and ocean measurements.
The level of supercooling is calculated from measurements of conductivity, temperature and depth and requires high precision and accuracy. Frazil ice crystals can form in supercooled water and alter such measurements. As this effect is hard to measure and quantify with real frazil ice, experiments were carried out using microplastic particles. Supercooling is overestimated and is proportional to the volume concentration of the particles. The overestimate is smaller than the uncertainty in the calculations for low particle concentrations (1 × 10−4 m3 m−3), but can be resolved for high particle concentrations (up to 17 ± 1 mK for particle concentrations of 40 × 10−4 m3 m−3).
Fast ice is sea ice that does not drift with wind or ocean currents because it is attached to a stationary object e.g., the coastline. Supercooling influences fast-ice thickness. Vertical temperature profiles within the ice were used to calculate thickness changes with time. This thesis presents a unified processing technique for these data and an investigation of the accuracy and precision of different methods. Uncertainties of 1.0 ± 1.5 cm for data from McMurdo Sound (located in the western Ross Sea, Antarctica; experiences supercooling) and 2 ± 3 cm Utqia ̇gvik (located in the Chukchi Sea, Alaska; no supercooling) were obtained. These uncertainties are lower than the interannual variability in fast-ice thickness. The method described by Gough et al. (2012) was the best choice for calculating thickness from temperature.
The interannual variability in fast-ice thickness is influenced by various drivers, both oceanic and atmospheric. Analysis of ∼30 years of fast-ice thickness data collected in McMurdo Sound is presented and the contribution of different drivers to the temporal variability in thickness investigated. Freezing degree days and autumn–winter storminess had the strongest contribution to this variability. This work provides a baseline for studying extreme events, longterm trends and processes influencing fast-ice.
Overall, this thesis emphasises the value of repeatable and high-quality measurements over long time-scales to understand fast-ice processes.