Snowmelt on the Antarctic Peninsula has been increasing for decades because of rising temperatures, and it shows no signs of stopping. As the snow melts, it can release nutrients that eventually make their way into downstream marine ecosystems. However, along the way, snow-dwelling microbes may use and transform these nutrients, influencing their downstream effects.
Despite the potential importance of microbes residing in Antarctic snow, few studies have investigated their role in melting. New research by Hodson et al. addresses this gap in knowledge by illuminating the activity and influence of microbes inhabiting wet snow on Livingston Island, located off the tip of the Antarctic Peninsula.
During austral summer in 2013 and 2014, the research team collected snow samples at five different sites in the island’s Hurd Peninsula region. Three sites were less than 100 meters from the shoreline, one site was 500 meters inland, and the fifth site was 750 meters inland. The scientists investigated the chemical, physical, and biological characteristics of the snowpack at each site.
To assess the snow algal population, they used microscopy and laser counting techniques (flow cytometry), finding that red-pigmented algae were dominant at the snow surface, whereas green algae were present below. Bacterial cells are too small for detailed characterization in this way, so the team focused on the cells’ ribosomal RNA (16S rRNA). Although microbes have evolved over millions of years, rRNA genes have changed very little. Measuring slight changes in this easily sequenced gene therefore gives clues to how closely microbes in a given population are related and allows researchers to establish the bacterial community structure.
Genetic sequencing of 16S rRNA genes in the snow samples revealed that microbial communities closer to the coast consisted of a greater diversity of bacterial species than those in the inland glacial snowpacks. Inland communities consisted mostly of typical snow bacteria, whereas coastal communities also had species associated with soil and the ocean.
The scientists also found evidence that algae growing on the surface of the snowpacks can accelerate melting. This is because some algae produce pigments that darken the snow and increase absorption of solar radiation. Such algae were much more plentiful near the coast than inland, likely thanks to fertilization with calcium from rock debris and with ammonium from the droppings of penguins and seals.
At both inland and coastal sites, microbial activity increased concentrations of dissolved organic and inorganic carbon in the snow. It also increased the amount of carbon dioxide in interstitial air pockets within the snow. These concentrations were higher for snowpacks closer to the shoreline.
Dissolved organic carbon can serve as a food source for other microbes and for marine life, so these findings indicate that Antarctic snow-dwelling microbes can indeed influence nutrients in meltwater. The authors propose that the effects of microbial activity on downstream nutrients be taken into account when considering the full impact of warming on the Antarctic Peninsula. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1002/2016JG003694, 2017)
—Sarah Stanley, Freelance Writer