Seasonal Snowpack Microbial Ecology and Biogeochemistry on a High Arctic Ice Cap Reveals Negligible Autotrophic Activity During Spring and Summer Melt

Snowpack ecosystem studies are primarily derived from research on snow-on-soil ecosystems. Greater research attention needs to be directed to the study of glacial snow covers as most snow cover lies on glaciers and ice sheets. With rising temperatures, snowpacks are getting wetter, which can potentially give rise to biologically productive snowpacks. The present study set out to determine the linkage between the thermal evolution of a snowpack and the seasonal microbial ecology of snow. We present the first comprehensive study of the seasonal microbial activity and biogeochemistry within a melting glacial snowpack on a High Arctic ice cap, Foxfonna, in Svalbard. Nutrients from winter atmospheric bulk deposition were supplemented by dust fertilization and weathering processes. NH4+ and PO43- resources in the snow therefore reached their highest values during late June and early July, at 22 and 13.9 mg m-2, respectively. However, primary production did not respond to this nutrient resource due to an absence of autotrophs in the snowpack. The average autotrophic abundance on the ice cap throughout the melt season was 0.5 & PLUSMN; 2.7 cells mL-1. Instead, the microbial cell abundance was dominated by bacterial cells that increased from an average of (39 & PLUSMN; 19 cells mL-1) in June to (363 & PLUSMN; 595 cells mL-1) in early July. Thus, the total seasonal biological production on Foxfonna was estimated at 153 mg C m-2, and the glacial snowpack microbial ecosystem was identified as net-heterotrophic. This work presents a seasonal album documenting the bacterial ecology of glacial snowpacks. Most research attention has been given to snow covers lying on top of soil ecosystems, and therefore we do not know enough about the ecology of glacial snowpack ecosystems. This is a major knowledge gap, given that most of the world's snow cover lies over glaciers, ice caps and ice sheets. This study shows that during the melt season on a High Arctic ice cap, Foxfonna in Svalbard, nutrients are most available during the peak of summer (June-early July transition period), but a shortage of photosynthesizing microbes can mean that they largely remain in situ until transported downstream by meltwater runoff. Processes with the capacity to generate high concentrations of essential nutrients such as N and P in snow and meltwater could therefore be described, because the primary producers did not sequester them. In contrast, an increase in bacterial cell numbers was observed during the same period. The glacial snowpack ecosystem was therefore net-heterotrophic due to the absence of autotrophs and proliferation of bacterial cells. Since the nutrient demand of the bacterial biomass is low, the ecosystem releases carbon, nitrogen, and phosphorus, rather than fixes it. Nutrients delivered by snow from marine and continental sources were supplemented by the dissolution of dust deposited from local sourcesAutotrophic communities were conspicuous by their absence within a High Arctic glacial snowpack during summerSecondary bacterial production therefore dominated the entire summer, with a superimposed ice layer of refrozen snowmelt providing temporary storage for low concentrations of nutrients and cells

Automated summary

Snowpack ecosystem studies have mainly focused on snow-on-soil ecosystems, leaving a knowledge gap in understanding glacial snowpack ecosystems. This study conducted a comprehensive investigation on the seasonal microbial ecology and biogeochemistry of a melting glacial snowpack on a High Arctic ice cap in Svalbard. It found that nutrient availability in the snowpack was highest during the peak of summer, but the absence of autotrophs resulted in the nutrients remaining in situ until transported downstream by meltwater runoff. Bacterial cells dominated the microbial abundance, making the glacial snowpack ecosystem net-heterotrophic.