The Airlink Environmental Impact Monitoring Program commenced in 2008 to monitor the environmental impact of operating Wilkins runway located in the Windmill Islands, East Antarctica. Initially the intent for the thesis was to examine snow and air samples taken as part of the monitoring program for atmospheric particulate matter (APM) and to determine the difference between APM in the snow and air samples. The difference between APM in snow has not been previously determined, and any significant differentiation in APM between snow and air could have consequences for ice core APM identification and interpretation. Due to contamination concerns and low particle numbers, a comparison between APM in air and snow was not possible. Instead a full identification of APM in snow and air was made, and from this, a large marine diatom assemblage was found in snow from one of the sampling campaigns, which led the thesis to explore the source and variability of diatoms within snow in Antarctica.
Diatoms have been found in many ice cores from around Antarctica, including many remote inland sites. Diatoms are commonly used in sediments for palaeoclimatic reconstructions as individual species are specific to certain environmental conditions such as sea ice cover, salinity, and water temperature. Thus it could be possible that diatoms found preserved within ice cores may provide similar palaeoclimatic information on their source area. A large marine diatom assemblage was found at Wilkins runway after an anomalous weather event that also caused a strong sea salt influence in the snow and a pseudomorph of the sea ice mineral ikaite (CaCO3.6H2O). The assemblage consisted of 16 diatom species that were sourced from an Antarctic local summer coastal community with limited sea ice coverage. These conditions were noted close to Wilkins runway on a satellite image taken at the time of the anomalous weather event. Coinciding with increases in sea salt in snow, increases in heavy metals and in particular Cr and V, which correlated well with sea salt, were noted. The anomalous weather event at Wilkins highlighted the possibility that diatoms may be used for palaeoclimatic reconstructions if the predominant weather conditions favoured diatom deposition.
Mill Island, located near Bunger Hills, East Antarctica, was chosen for an in-depth, seasonal study into diatom deposition due to the coastal influences at the island, high accumulation rate, and availability of samples. A total of 22 diatom species were found and other biological particles including chrysophyte species and cysts, dinoflagellate species and faecal pellets. Seasonally, more diatoms were found in the core during the summer months, which reduced rapidly in winter. The species assemblage changes over summer, with a sea-ice related assemblage in early summer, which is followed by an open-water assemblage in late summer/autumn. The diatom abundance and species assemblage appears to reflect the diatom assemblage and abundance in the ocean surrounding Mill Island. Diatoms preserved at times appear to be highly fragmented, sometimes showing dissolution features. The fragmentation of diatom frustules have previously been attributed to the glacial reworking of sediments, however in this case, the high amount of faecal material present that contains fragments of partially dissolved diatom frustules, provides evidence that the fragments may be from the digestion of diatoms by zooplankton.
Diatom abundance correlates very well with the sea ice extent at a radius of 100-150 km from Mill Island, which suggests that the diatoms are largely transported over these distances. The only exception is in spring 2006, when sea ice in the zone around Mill Island had not broken up. From the presence of methanesulphonic acid, indicating biological activity, and back-trajectory modelling indicating an increased wind speed, it is theorised that these diatoms were transported from further distances than the 100-150 km previously indicated. No increases in sea salt were noted with high diatom abundance at Mill Island, due to the diatoms being representative of the available particles in the Southern Ocean and sea salt, more indicative of wind strength, which showed large increases during winter storms. The preservation of diatom frustules in the Mill Island core potentially allows for the determination of annual changes in species assemblage due to various forcings such as climate change and whaling.