Glacial Ecosystems Research Articles

Microbial primary production on an Arctic glacier is insignificant in comparison with allochthonous organic carbon input

Cryoconite holes are unique freshwater environments on glacier surfaces, formed when solar-heated dark debris melts down into the ice. Active photoautotrophic microorganisms are abundant within the holes and fix inorganic carbon due to the availability of liquid water and solar radiation. Cryoconite holes are potentially important sources of organic carbon to the glacial ecosystem, but the relative magnitudes of autochthonous microbial primary production and wind-borne allochthonous organic matter brought are unknown. Here, we compare an estimate of annual microbial primary production in 2006 on Werenskioldbreen, a Svalbard glacier, with the organic carbon content of cryoconite debris. There is a great disparity between annual primary production (4.3 mug C g(-1) year(-1)) and the high content of organic carbon within the debris (1.7-4.5%, equivalent to 8500-22 000 mug C g(-1) debris). Long-term accumulation of autochthonous organic matter is considered unlikely due to ablation dynamics and the surface hydrology of the glacier. Rather, it is more likely that the majority of the organic matter on Werenskioldbreen is allochthonous. Hence, although glacier surfaces can be a significant source of organic carbon for glacial environments on Svalbard, they may be reservoirs rather than oases of high productivity.

Bacteriophage in polar inland waters

Bacteriophages are found wherever microbial life is present and play a significant role in aquatic ecosystems. They mediate microbial abundance, production, respiration, diversity, genetic transfer, nutrient cycling and particle size distribution. Most studies of bacteriophage ecology have been undertaken at temperate latitudes. Data on bacteriophages in polar inland waters are scant but the indications are that they play an active and dynamic role in these microbially dominated polar ecosystems. This review summarises what is presently known about polar inland bacteriophages, ranging from subglacial Antarctic lakes to glacial ecosystems in the Arctic. The review examines interactions between bacteriophages and their hosts and the abiotic and biotic variables that influence these interactions in polar inland waters. In addition, we consider the proportion of the bacteria in Arctic and Antarctic lake and glacial waters that are lysogenic and visibly infected with viruses. We assess the relevance of bacteriophages in the microbial loop in the extreme environments of Antarctic and Arctic inland waters with an emphasis on carbon cycling.

Sediment–moss interactions on a temperate glacier: Falljökull, Iceland

AbstractWe present the results of preliminary investigations of globular moss growth on the surface of Falljökull, a temperate outlet glacier of the Vatnajökull ice cap, southern Iceland. Supraglacial debris has provided a basis for moss colonization, and several large (>500m2) patches of moss growth (Racomitrium spp.) are observed on the surface of the glacier. Each area of moss-colonized supraglacial debris shows a downslope increase in sphericity and moss cushion size and a decrease in percentage surface coverage of moss-colonized and bare clasts. It is suggested that moss growth on supraglacial debris allows preferential downslope movement of clasts through an associated increase in both overall mass and sphericity. Thermal insulation by moss cushions protects the underlying ice surface from melt, and the resulting ice pedestals assist in downslope sliding and toppling of moss cushions. The morphology and life cycle of supraglacial globular mosses is therefore not only closely linked to the presence and distribution of supraglacial debris, but also appears to assist in limited down-glacier transport of this debris. This research highlights both the dynamic nature of the interaction of mosses with supraglacial sedimentary systems and the need for a detailed consideration of their role within the wider glacial ecosystem.

Viral dynamics in cryoconite holes on a high Arctic glacier (Svalbard)

Viruses are an abundant and dynamic constituent of microbial communities in aquatic ecosystems. In this study we characterized the abundance of viruses associated first with the bottom sediment and overlying water of cryoconite holes and second with shallow ice cores of two different glaciers in Svalbard. Viral abundances were ca. 10–100 times lower than the average for marine and freshwater ecosystems in temperate regions. Virus to bacterium ratios (VBR) (average > 10, range between 0.7 and 74 in the water and ice samples) and a strong positive correlation between viral and bacterial abundance (r = 0.93, p < 0.01, N = 57) indicate that viruses most probably play an important role in controlling bacterial mortality and hence biogeochemical cycling on glaciers. Samples taken along a transect from the glacier ablation area to proglacial ponds in its forefield showed that viral abundance increased in response to a higher host availability, which in turn probably resulted from an increase in temperature and higher mineral levels in the ponds. In a transplantation experiment, viruses from cryoconite holes were incubated with a bacterial community from a proglacial lake. Results from the transplantation experiment showed that viruses from cryoconite holes were able to infect bacteria from proglacial lakes and thus influence biogeochemical cycles across different glacial ecosystems. Our data therefore suggest that viruses in cryoconite holes may be able to infect a broad range of bacterial species.

Heterotrophic bacterial and viral dynamics in Arctic freshwaters: results from a field study and nutrient-temperature manipulation experiments

Heterotrophic bacterial and viral concentrations (range, 0.7 × 104 to 206.2 × 104 ml−1 and 0.05 × 106 to 128.9 × 106 ml−1, respectively) were determined in several Arctic freshwater environments, including lakes and glacial ecosystems (78.55°N, 11.56°E). Our bacteria and virus results mirrored trends seen in temperate lakes, with an average virus-to-bacteria ratio (VBR) of 13 (range, 7.3–25.2) and viral concentrations and DOC positively correlated with bacterial concentrations (R = 0.964, P < 0.01 and R = 0.813, P < 0.05, respectively). Lysogenic bacteria, determined by induction with Mitomycin C, were not detected in any of the investigated Arctic freshwater environments. Nutrient-addition experiments at in situ and at elevated temperatures were performed to elucidate the factors which influenced the bacterial growth and the virus–bacteria interactions in Arctic freshwaters. Our results suggest that multiple limiting factors interacted and constrained bacterial growth. Bacterial concentrations and doubling times increased at elevated temperatures and appeared to be co-stimulated by phosphorus and carbon. However, viral concentrations showed a lack of response to nutrient addition thus indicating an uncoupling between bacteria and viruses in the experiment.

Biogeochemistry of snowmelt in an Antarctic glacial ecosystem

Solute mass balance, hydrochemical data, and hydrological process data are used to present the first detailed account of catchment biogeochemistry in an Antarctic melt season. The study was undertaken in a small glacial catchment in the maritime Antarctic (Signy Island, South Orkney Islands), where extreme ecosystem changes have been observed at the ice margin. Here melting caused a snowpack solute elution phase characterized by the production of extremely concentrated solutions just centimeters from the snow surface. These were equivalent to 2% marine water and dominated by sea‐salt aerosol. Nutrients were also present but were rapidly sequestered in snowpack and ice marginal environments. Thus the decoupling of nutrient dynamics from other snowpack solutes seems to occur almost immediately after melt and testifies to the presence of a glacial ecosystem. Although significant, the estimated rates of nutrient uptake were low (0.025 gNH4‐N/m2/yr and 0.0011 gPO4‐P/m2/yr, equivalent to 66 and 74% of total annual atmospheric inputs) and, in the case of NH4+, 2–3 orders of magnitude lower than those reported for temperate snowpacks. However, the data also demonstrated significant NO3− production (0.030 gNO3‐N/m2/yr or 3 times total atmospheric inputs) that appears to be associated with zones of high rock‐water contact at the ice margin. After the early snowpack elution phase, nutrient cycling was also greatly influenced by inputs from penguin and seal excreta. Thus local marine ecosystems enhance the nutrient content of meltwaters and fertilize the glacial, terrestrial, and aquatic ecosystems that are responding to climate change in the maritime Antarctic.

The High Arctic glacial ecosystem: new insights from nutrient budgets

This paper describes detailed budgets of water, Cl), dissolved Si and both inorganic and organic forms of nitrogen and phosphorus for two small glacier basins in Arctic Svalbard (Midre Love´nbreen and AustreBroggerbreen). Rates of nutrient deposition are modest, dominated by inorganic nitrogen and episodically enhanced by extreme events. Hence deposition rates are also variable, ranging from 20 to 72 kg NO3-N km)2 a)1 and 10–37 kg NH4-N km)2 a)1 over just two consecutive years. Deposition of dissolved organic and particulate forms of nitrogen (DONand PN respectively) also appears significant and therefore requires further investigation (3–8 kg DONN km)2 and 7–26 kg PN-N km)2 during winter – no summer data are available). Evidence for microbially mediated nutrient cycling within the glacial system is clear in the nutrient budgets, as is the release of large phosphorus, Si and organic/particulate nitrogen fluxes by subglacial erosion. The latter is entirely dependent upon the presence of subglacial drainage, promoting silicate mineral dissolution and the erosion of largely unweathered apatite. The large DON and PN fluxes are surprising and may relate to young organic nitrogen associated with microbial life within the glaciers. This is because wide spread assimilation of NH4 + and perhaps even nitrification occurs on the glacier surface, most likely within abundant cryoconite holes. Further microbial activity also occurs at the glacier bed, where denitrification and sulphate reduction is now known to take place. Thus a two component ‘glacial ecosystem’ is proposed that is highly sensitive to climate change.