Greening of retreating glaciers: storage versus export of autochthonous organic matter

Lead Research Organisation: University of Bristol
Department Name: Geographical Sciences


Life exists whatever there is water and glaciers are no exception. Indeed glaciers are vast reservoirs of biological cells and debris. The debris can cover ca 1-10% of the surface of glaciers worldwide, and it is composed of inorganic and organic particles that are darker than the surrounding white icy surface and thus absorb the solar radiation better than the ice. The absorption of the solar radiation by the debris promotes melting of the ice which in turn promotes increased levels of microbial activity via the creation of unique and ideal life-habitats. The habitats are colonised by a diverse range of microorganisms, including viruses, bacteria and microscopic plants. In a recent NERC small grant, we measured the microbial activity associated with the debris at the surface of glaciers in Greenland, Svalbard and the Alps and we found that it was comparable to that found in very rich ecosystems from warmer regions. In fact, microbial activity in one gram of debris was roughly the same as in one gram of soil from the Mediterranean. The colonisation of the debris by microbes subsequently leads to further darkening of the ice surface. This is because we also found that the amount of photosynthesis (i.e., the process in which carbon dioxide is converted by plants to biomass, releasing oxygen) is much higher than the amount of respiration (i.e., the process in which oxygen is consumed and organic matter is biologically converted back to carbon dioxide). The consequence of higher photosynthesis than respiration is that the surface of glaciers is a self-sustained ecosystem in which organic matter can be accumulated. The result is even more enhanced absorption of solar radiation, promoting further melt and providing yet more water for microorganisms, which are then dispersed to other parts of the ice surface. This dispersal transfers the microbes, organic matter and debris to adjacent ecosystems, including those of the forefield and subglacial environments with the potential to sustaining life in other ecosystems. We hypothesise that glaciers become increasingly biological as they decay, and that glacier melting is, in part, a biologically-mediated process that initiates ecological succession long before the ice has disappeared. This project aims to quantify these biological effects on glacier mass balance, and to determine fluxes and quality of organic matter exported to downstream environments during deglaciation, by examining the surfaces of Arctic valley glaciers that are retreating markedly in response to summer melt. In doing so, we aim to produce the first quantification and characterisation of bio-physical effects on ice mass wastage during deglaciation.
Description One of the major outcomes of this proposal was the demonstration that microbial activity at the surface of glaciers and ice sheets are responsible for significant carbon and nitrogen fixation with implications for biogeochemical cycles at local and global scales. First, we presented data on microbial abundance and carbon budgets, collected along 3 small valley glaciers in Svalbard (summer 2009) and along a transect across the ablation zone of the Greenland ice sheet (summer 2010). We were able to analyse the relationships between the physical, chemical and biological variables determining the major controls of organic carbon production and utilisation. The results of C productivity suggest an overall net autotrophy on the Greenland Ice Sheet supporting the proposed role of ice sheet ecosystems in carbon cycling as regional sinks of CO2 and places of production of organic matter that can be a potential source of nutrients for downstream ecosystems. However, this role is less obvious in the small valley glaciers in Svalbard, particularly if only cryoconite holes are considered. We showed for the first time direct estimates of nitrogen fixation in Svalbard and Greenland ice to show that nitrogen fixation is likely of minor importance to the overall nitrogen budget of glaciers and ice sheets. However, we showed that nitrogen fixation is still potentially important as a source of nitrogen to microbial communities in the debris rich marginal zone close to the terminus of the glaciers, where nitrogen fixation may aid the colonization of subglacial and moraine-derived debris.

The results of these studies led further to the demonstration of strong links between microbial growth and albedo changes at the surface of glaciers and ice sheets, identifying microbial growth on ice as an important regulating factor of ice sheet wastage. First, an experiment recorded aeolian inputs, near-surface ice cores (throughputs) and meltwater stream outputs. In-stream cell fluxes compared to ice-derived fluxes and aeolian deposition indicated a storage of 90 million cells/m2/hr on the ice surface. The storage of cells clearly would result in 'biological darkening' of glacier surfaces. Such darkening would increase the amount of incident shortwave radiation available for ice ablation, and could be a contributing element to glacier thinning and wastage. Mostly important was the demonstration that algal communities (mostly desmids) growing directly on the bare ice, through their photophysiology, have an important role in changing albedo with their screening pigmentation, and subsequently may impact melt rates on the ice sheet. These data suggest that microbially colonised bare ice surfaces are likely to be locations of intense organic carbon accumulation. It is likely that cells are retained on the surface of the ice, while dissolved organic carbon may be transported downstream.

Finally, we could demonstrate that there is a high diversity of microbial communities on the surface of glaciers and the bioavailability of glacier-produced organic matter to heterotrophic bacteria is high. Microbially derived organic matter, as measured via microscopic, chromatographic, spectrophotometric and high temperature combustion techniques were clearly found all over the ice surface. Through an opportunity to combine a NERC PhD studentship within our NERC grant, we could demonstrate for the first time that viruses have an important role in controlling microbial activity on the surface of glaciers and ice sheets, impacting both the cycling of carbon and nutrients and microbial evolution.
Exploitation Route Research in polar regions is usually received with substantial excitement across different age groups. We produced a 45-min documentary (documentary entitled: Life on the Ice) together with BonneyFilms (, targeting A-level pupils about science in the Arctic. The documentary is currently under negotiation to make part of the library of GeoWeb (a new national resource for science and geography teachers) as well as the elibrary of National STEM Centre and it will also be distributed, at no cost, by Pumpkin Interactive which produces high quality educational resources for secondary schools and colleges.

The documentary has also been shown during Open Days, Science Alive and Nature Festival in Bristol as part of the University of Bristol public engagement. We believe that, at this stage, the main users of this research are NGOs and other academics. However, we also believe that the knowledge that glaciers and ice sheets harbour active microbial communities is also important for conservation bodies. We have advocated in our recent paper (Anesio and Laybourn-Parry 2012, Trends in Ecology and Evolution 27: 219-225) that the inclusion of glaciers and ice sheets as a biome with unique life adaptations has implications for the conservation of these climate-sensitive ecosystems. Understanding microbial life cycles in extreme cold conditions can inform understanding of the evolution and spread of life on Earth. As glaciers and ice sheets retreat and give way to the development of tundra, unique food web interactions will be compromised. Furthermore, of most concern will be the loss of biodiversity and potentially the loss from the biosphere of a pool of genes adapted to surviving and thriving in the cold.
Sectors Education,Environment

Description They are currently used for education purposes in secondary schools (Geography and Biology subjects) - see impact description.
First Year Of Impact 2011
Sector Education,Environment
Impact Types Societal

Description Life on the Ice 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience
Results and Impact A documentary that follows a team of scientists on a research project, starting in the labs of Bristol University and ending up in the world's most northerly community in Ny-Alesund, Norway. As the scientists carry out their research, we see what the experience of scientific research is like, how they live, what they do and what motivates these people to go to such extreme places.

The programme follows a team of scientists on a research project, starting in the labs of Bristol University to the world's most northerly community Ny-Alesund in Norway. As the scientists carry out their research, we see what the experience of scientific
Year(s) Of Engagement Activity 2012