The biogeography of red snow microbiomes and their role in melting arctic glaciers

The Arctic is melting at an unprecedented rate and key drivers are changes in snow and ice albedo. Here we show that red snow, a common algal habitat blooming after the onset of melting, plays a crucial role in decreasing albedo. Our data reveal that red pigmented snow algae are cosmopolitan as well as independent of location-specific geochemical and mineralogical factors. The patterns for snow algal diversity, pigmentation and, consequently albedo, are ubiquitous across the Arctic and the reduction in albedo accelerates snow melt and increases the time and area of exposed bare ice. We estimated that the overall decrease in snow albedo by red pigmented snow algal blooms over the course of one melt season can be 13%. This will invariably result in higher melt rates. We argue that such a ‘bio-albedo' effect has to be considered in climate models

Ice sheets as a significant source of highly reactive nanoparticulate iron to the oceans

The Greenland and Antarctic Ice Sheets cover ~\n10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40–2.54?Tg per year in Greenland and 0.06–0.17?Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting

Biolabile ferrous iron bearing nanoparticles in glacial sediments

Glaciers and ice sheets are a significant source of nanoparticulate Fe, which is potentially important in sustaining the high productivity observed in the near-coastal regions proximal to terrestrial ice cover. However, the bioavailability of particulate iron is poorly understood, despite its importance in the ocean Fe inventory. We combined high-resolution imaging and spectroscopy to investigate the abundance, morphology and valence state of particulate iron in glacial sediments. Our results document the widespread occurrence of amorphous and Fe(II)-rich and Fe(II)-bearing nanoparticles in Arctic glacial meltwaters and iceberg debris, compared to Fe(III)-rich dominated particulates in an aeolian dust sample. Fe(II) is thought to be highly biolabile in marine environments. Our work shows that glacially derived Fe is more labile than previously assumed, and consequently that glaciers and ice sheets are therefore able to export potentially bioavailable Fe(II)-containing nanoparticulate material to downstream ecosystems, including those in a marine setting. Our findings provide further evidence that Greenland Ice Sheet meltwaters may provide biolabile particulate Fe that may fuel the large summer phytoplankton bloom in the Labrador Sea, and that Fe(II)-rich particulates from a region of very high productivity downstream of a polar ice sheet may be glacial in origin

Bioavailable iron in the Southern Ocean: the significance of the iceberg conveyor belt

Productivity in the Southern Oceans is iron-limited, and the supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine reservoir. Glacial sediment sources of iron have rarely been considered, as the iron has been assumed to be inert and non-bioavailable. This study demonstrates the presence of potentially bioavailable Fe as ferrihydrite and goethite in nanoparticulate clusters, in sediments collected from icebergs in the Southern Ocean and glaciers on the Antarctic landmass. Nanoparticles in ice can be transported by icebergs away from coastal regions in the Southern Ocean, enabling melting to release bioavailable Fe to the open ocean. The abundance of nanoparticulate iron has been measured by an ascorbate extraction. This data indicates that the fluxes of bioavailable iron supplied to the Southern Ocean from aeolian dust (0.01–0.13 Tg yr-1) and icebergs (0.06–0.12 Tg yr-1) are comparable. Increases in iceberg production thus have the capacity to increase productivity and this newly identified negative feedback may help to mitigate fossil fuel emissions

The potential role of the Antarctic Ice Sheet in global biogeochemical cycles

ABSTRACTOnce thought to be devoid of life, the Antarctic Ice Sheet is now known to be a dynamic reservoir of organic carbon and metabolically active microbial cells. At the ice-bed interface, subglacial lake and sedimentary environments support low diversity microbial populations, adapted to perennial cold, anoxia and lack of light. The dynamic exchange of water between these shallow environments conveys meltwaters and associated sediments into the coastal ocean. This, together with the release of iceberg-rafted debris to more distal coastal environments, could be important for sustaining primary productivity in the iron-limited Southern Ocean, via the release of associated nutrients and bioavailable iron. We estimate the magnitude and review the wider impacts of the potential export of nutrients (N, P, C, Si and bioavailable Fe) dissolved and associated with suspended sediments in Antarctic runoff and entombed in iceberg rafted debris. Located beneath subglacial lakes and the subglacial till complex are deep sedimentary basins up to 14 km thick, located largely around the Antarctic periphery. These sedimentary basins are largely hydrologically decoupled from shallower lake and till environments by the presence of highly consolidated sediments which limit the penetration of glacial meltwaters to depth. They provide extensive habitats for sustained microbial activity over Ma timescales, and are likely to be a focal point for the anaerobic cycling of organic carbon and other elements in the deep sub-surface. Organic carbon buried in these basins during ice sheet formation is thought to be microbially cycled to methane gas, and the methane largely stored as hydrate within sediments, stabilised by the high pressure/low temperature conditions. We conclude that the export of nutrients and biogenic gases from deep and shallow subglacial Antarctic environments designates Antarctica as a potentially important component of the Earth's carbon cycle, and highlight the importance of evaluating these potential impacts further via global and regional-scale biogeochemical modelling.</jats:p