Raster grids detailing the benthic environment of South Georgia

This dataset contains raster grids in GeoTIFF format describing the benthic environment of South Georgia. The data include topographic layers that are directly calculated from a bathymetry grid (Slope, Aspect, Roughness, Slope, Terrain Ruggedness Index, Topographic Position Index). A benthic classification of the area is included, based on topographic layers. Also included are sea-bed environmental layers that are interpolated from global three dimensional grids (Alkalinity, Apparent Oxygen Utilisation, Omega Aragonite, Omega Calcite, Dissolved Oxygen, Nitrate, pH, Phosphate, Salinity, Silicate, Temperature, and Total CO2). These layers were used to construct a habitat suitability model for Octocorallia. The geographic extent is 43°57'56.65"W - 33°45'38.19"W and 52°47'29.50"S - 56° 9'11.03"S. The spatial resolution is 150m x 150m (except for benthic classification wihch is 450m x 450m). The map projection is EPSG:3762.

Seawater carbonate chemistry and proportion of different dissolution levels in live juvenile Limacina helicina antarctica from the natural environment and ship-board incubations

The carbonate chemistry of the surface ocean is rapidly changing with ocean acidification, a result of human activities. In the upper layers of the Southern Ocean, aragonite-a metastable form of calcium carbonate with rapid dissolution kinetics-may become undersaturated by 2050. Aragonite undersaturation is likely to affect aragonite-shelled organisms, which can dominate surface water communities in polar regions. Here we present analyses of specimens of the pteropod Limacina helicina antarctica that were extracted live from the Southern Ocean early in 2008. We sampled from the top 200 m of the water column, where aragonite saturation levels were around 1, as upwelled deep water is mixed with surface water containing anthropogenic CO2. Comparing the shell structure with samples from aragonite-supersaturated regions elsewhere under a scanning electron microscope, we found severe levels of shell dissolution in the undersaturated region alone. According to laboratory incubations of intact samples with a range of aragonite saturation levels, eight days of incubation in aragonite saturation levels of 0.94-1.12 produces equivalent levels of dissolution. As deep-water upwelling and CO2 absorption by surface waters is likely to increase as a result of human activities, we conclude that upper ocean regions where aragonite-shelled organisms are affected by dissolution are likely to expand.