Small Particles Have Big Impact on Glacial Health

A recent study by Heidi Smith et al. in the desolate McMurdo Dry Valleys of Antarctica has shown that microbial life in biofilms is present across a large part of the region’s ice, suggesting that the stability of polar ice can be influenced by even the smallest of organisms.

Biofilms—thin, slimy bacterial layers that can adhere to a surface—were discovered in conjunction with the windblown dust that accumulates on snow and ice called cryoconite. The research found that a combination of biofilms and cryoconite is capable of enhancing the rate of glacial melting, meaning that the planet may be more vulnerable to sea level rise than previously imagined.

As an important component in the planet’s hydrological and carbon cycles, glacial melting affects sea levels and the chemistry of our oceans. This meltwater enhances the movement of fluids from terrestrial environments to oceans, as well as the transport of nutrients to aquatic ecosystems. In the McMurdo Dry Valleys, the activity of microorganisms on the glacier surface enables the accumulation of organic matter on minerals found in the ice’s dusty cryoconite layers. This relationship results in the darkening of ice over time, making it less efficient at reflecting incoming sunlight than it would be normally. As most of Antarctica’s ice lies atop the continental landmass,  increased melting at the Earth’s southern pole may lead to an appreciable rise in global sea levels.

A view of the Canada Glacier involved in the field study. (Source:Joe Mastroianni, National Science Foundation)
A view of the Canada Glacier involved in the field study (Source: Joe Mastroianni/National Science Foundation).

Prior research in alpine glacial environments and on the Greenland Ice Sheet (Langford et al. 2010) established a correlation between biofilm development and the darkening of cryoconite particles, pointing towards the synergistic possibility of biologically enhanced rates of melting. Until the recent publication of key research by Heidi Smith et al., the role of biofilms in Antarctica was largely unknown.

In conversation with GlacierHub, Smith stated that “the role of biofilms in different glacial locations has not been explored.” She added “due to differences in environmental pressures (temperature extremes, nutrient availability, levels of UV radiation, and rates of flushing), it is possible that the role of biofilms in glacial surface processes varies by location.” Smith’s team was able to establish the precedence of biofilms at extreme southern latitudes in their research and also contributed to the larger body of scientific evidence supporting the role of microbes in influencing reflectivity, otherwise known as albedo, of glaciers.

Smith and her research colleagues employed a variety of methods to investigate the interactions between the biological and mineralogical components of Antarctic ice. Microbial species were identified in the lab via pyrosequencing (which determines the order of nucleotides in DNA by detecting the release of the pyrophosphate ion) as well as epifluorescent microscopy (which utilizes a compound microscope equipped with a high-intensity light source). The team’s research yielded four unique bacterial components in biofilms found in cryoconite holes. Interestingly, Smith told GlacierHub that “while some organisms identified in this study have also been found in cryoconite holes from the Greenland Ice sheet, the relative abundance of individual organisms in each of these locations appears to be geographically distinct.”

transantarctic_mountain_hg
The Trans-Antarctic Mountains, a prominent feature in Northern Victoria Land (Source: Hannes Grobe/Alfred Wegener Institute).

The primary region for fieldwork and sampling for the study was an ice-lidded cryoconite hole on the Canada Glacier, located near Victoria Land, Antarctica. When asked about why the team chose to work in this isolated region, Smith replied: “There are previous studies from this region that have focused on cryoconite hole geochemistry, rates of microbial activity and microbial assemblage composition; therefore, we could place samples from this study into a larger framework.”

Following fieldwork on the glacier, subsequent laboratory analysis showed that enriched levels of nitrogen and carbon isotopes were present when Bacteroidetes (one of the four main bacterial phyla) was incubated in the presence of compounds such as sodium bicarbonate and ammonia. These findings point to the conclusion that the spatial organization within a microbially rich biofilm can promote the transfer of chemical compounds and nutrients. Such a result serves to validate the hypothesis that the formation of biofilms may enhance the accumulation of organic material on cryoconite minerals, thus affecting the color and reflectivity of glacial surfaces.

The study concluded that not only are biofilms present in nearly thirty-five percent of cryoconite holes in Antarctica, but that due to regional differences in the distribution of black carbon between the study region and the Arctic, biofilm may play a heightened role (relative to the northern hemisphere) in promoting biological activity on glaciers. Smith added, “In addition to influencing levels of glacial melt, biofilms have the potential to alter marine ecosystems through glacial runoff.” Additionally, she said, “There is also the potential for increases in CO2 release, which contributes to the rising temperatures globally.”

The research by Smith and her team points to important feedback loops with future increases in temperature, as longer melt seasons will stimulate biofilm communities, which alone have the capacity to increase rates of glacial melt. If temperatures continue to rise, the positive feedback between a warmer climate and lower reflectivity on ice surfaces may lead to exponentially faster rates of glacial melt and sea level rise. Overall, these findings illustrate the environment’s sensitivity to the emissions that human populations generate, suggesting that given enough pressure, Antarctic ice may enter a runaway downward spiral of rapid melting. 

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