Glenn Johnstone

Benthic mats in Antarctica: biophysical coupling of sea-bed hypoxia and sediment communities

Transient white and grey mats were observed in depressions and enclosed basins in marine sediment in the Windmill Islands, East Antarctica. These patches have not been described in the Antarctic marine environment previously although a similar phenomenon has been described in the Arctic. Our aim was to describe the sediment geochemical and biological properties inside the patches and to determine their similarity to each other. We compared the benthic infaunal communities and the chemical properties of the sediment in the white patches to nearby sediment without white mats. We observed differences in sediment pH, Eh and elemental concentrations inside and outside patches. The benthic infaunal communities inside the patches were significantly different, lower in abundance and diversity, compared to outside the patches. The structure of the microbial communities within the mats was described by constructing clone libraries from four different patches. These clone libraries were dominated by bacteria from the bacteroidetes phylum. Clones closely related to sulphur-oxidising bacteria from the gammaproteobacteria and/or the epsilonproteobacteria were present in all libraries. This is the first detailed description of these patches in the Antarctic and demonstrates the link between physico-chemical factors and microbial and infaunal community structure. It appears that this phenomenon may be driven by the formation and persistence of sea-ice, and as both the spatial extent of sea-ice and its persistence in polar regions are likely to change under predicted climate change scenarios, we suggest this is a previously undocumented mechanism for climate change to impact polar ecosystems.

Submarine geomorphology and sea floor processes along the coast of Vestfold Hills, East Antarctica, from multibeam bathymetry and video data

Abstract A survey of nearshore areas in the Vestfold Hills, Antarctica, using high-resolution multibeam swath bathymetry provided both a detailed digital bathymetric model and information on sediment acoustic backscatter. Combined with underwater video transects and sediment sampling, these data were used to identify and map geomorphic units. Six geomorphic units identified in the survey region include: rocky outcrops, basins, pediments, valleys, scarps and embayments. In addition to geomorphic units, the data revealed sedimentary features that provide insights into post-glacial sediment transport and erosion in the area. Ice keel pits and scours are common, and sea floor channels, scour depressions and sand ribbons indicate transport and deposition by wind-driven currents and oceanographic circulation. Gullies and sediment lobes observed on steep slopes indicate mass movement of sediment. Some of these processes have not been directly observed to date, but their effectiveness in shaping the modern sea floor is clearly indicated by the sea floor mapping data. The embayments preserve a mantle of boulder sand probably deposited by cold-based glaciers which were flanked by faster-flowing ice in adjoining regions.

Seabed Character and Habitats of a Rocky Antarctic Coastline: Vestfold Hills, East Antarctica

Publisher Summary The Vestfold Hills is one of the largest ice-free areas on the East Antarctic coast. The coast is a complex of small islands, embayments, and fjords. Most of the coast is rocky, but a few sandy beaches are present. Water depths vary from 0 to 200 m in the survey area. High-resolution multibeam bathymetry, underwater video, and detailed diving surveys reveal a mosaic of rock outcrops, sediment-covered basins, and transition zones similar to pediments of desert landscapes. Iceberg scouring is common, but some areas are protected by peninsulas and islands. Biological communities are controlled by substrate and light level, with rocky substrates in shallow water, where ice-free conditions persist for most of the summer, dominated by macroalgae. Areas of sediment have invertebrate fauna and some macroalgae. Rocky areas in deep water or where sea ice persists through the summer are invertebrate dominated. Qualitative assessment of the data suggests that the benthic communities in the region can be broadly classified into three “end member” groupings governed by substrate type, water depth, and the persistence of sea ice at any site. Mobile invertebrates such as holothurians, echinoderms, and nemerteans are common in sediment areas. Preliminary analysis of data has shown no detectable differences between sediment communities in different geomorphic units with sedimentary seafloors, such as basins, channels, or pediments. Other factors, such as the frequency of ice-keel scouring and current activity, may yet emerge from the analysis.

A sediment mesocosm experiment to determine if the remediation of a shoreline waste disposal site in Antarctica caused further environmental impacts

A shoreline waste disposal site at Casey Station, Antarctica was removed because it was causing impacts in the adjacent marine environment (Brown Bay). We conducted a field experiment to determine whether the excavation created further impacts. Trays of clean, defaunated sediment were deployed at two locations within Brown Bay and two control locations, two years prior to remediation. Trays were sampled one year before, 1month before, 1month after and two years after the excavation. An increase in metals was found at Brown Bay two years after the remediation. However there was little evidence of impacts on sediment assemblages. Communities at each location were different, but differences from before to after the remediation were comparable, indicating there were unlikely to have been further impacts. We demonstrate that abandoned waste disposal sites in hydrologically active places in Antarctica can be removed without creating greater adverse impacts to ecosystems downstream.