Publisher Correction: Ice sheets matter for the global carbon cycle.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Ice sheets matter for the global carbon cycle.

The cycling of carbon on Earth exerts a fundamental influence upon the greenhouse gas content of the atmosphere, and hence global climate over millennia. Until recently, ice sheets were viewed as inert components of this cycle and largely disregarded in global models. Research in the past decade has transformed this view, demonstrating the existence of uniquely adapted microbial communities, high rates of biogeochemical/physical weathering in ice sheets and storage and cycling of organic carbon (>104 Pg C) and nutrients. Here we assess the active role of ice sheets in the global carbon cycle and potential ramifications of enhanced melt and ice discharge in a warming world.

Aeolian abrasion of rocks as a mechanism to produce methane in the Martian atmosphere.

Seasonal changes in methane background levels and methane spikes have been detected in situ a metre above the Martian surface, and larger methane plumes detected via ground-based remote sensing, however their origin have not yet been adequately explained. Proposed methane sources include the UV irradiation of meteoritic-derived organic matter, hydrothermal reactions with olivine, organic breakdown via meteoroid impact, release from gas hydrates, biological production, or the release of methane from fluid inclusions in basalt during aeolian erosion. Here we quantify for the first time the potential importance of aeolian abrasion as a mechanism for releasing trapped methane from within rocks, by coupling estimates of present day surface wind abrasion with the methane contents of a variety of Martian meteorites, analogue terrestrial basalts and analogue terrestrial sedimentary rocks. We demonstrate that the abrasion of basalt under present day Martian rates of aeolian erosion is highly unlikely to produce detectable changes in methane concentrations in the atmosphere. We further show that, although there is a greater potential for methane production from the aeolian abrasion of certain sedimentary rocks, to produce the magnitude of methane concentrations analysed by the Curiosity rover they would have to contain methane in similar concentrations as economic reserved of biogenic/thermogenic deposits on Earth. Therefore we suggest that aeolian abrasion is an unlikely origin of the methane detected in the Martian atmosphere, and that other methane sources are required.

Potential methane reservoirs beneath Antarctica.

Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 10(15) g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.

Determination of dissolved oxygen in the cryosphere: a comprehensive laboratory and field evaluation of fiber optic sensors.

Recent advances in the Cryospheric Sciences have shown that icy environments are host to consortia of microbial communities, whose function and dynamics are often controlled by the concentrations of dissolved oxygen (DO) in solution. To date, only limited spot determinations of DO have been possible in these environments. They reveal the potential for rates of change that exceed realistic manual sampling rates, highlighting the need to explore methods for the continuous measurement of DO concentrations. We report the first comprehensive field and laboratory performance tests of fiber-optic sensors (PreSens, Regensburg, Germany) for measuring DO in icy ecosystems. A series of laboratory tests performed at low and standard temperatures (-5 to 20 °C) demonstrates high precision (0.3% at 50 µmol/kg and 1.3% at 300 µmol/kg), rapid response times (<20 s), and minimal drift (<0.4%). Survival of freeze thaw was problematic, unless the sensor film was mechanically fixed to the fiber and protected by a stainless steel sheath. Results of two field deployments of sensors to the Swiss Alps and Antarctica largely demonstrate a performance consistent with laboratory tests and superior to traditional methods.