Abstract
Abstract. A cryoconite granule is a near-spherical aggregation of biota and abiotic particles found upon glacier surfaces. Recently, microstructural studies have revealed that photosynthetic microorganisms and extracellular polymeric substances (EPS) are omnipresent within cryoconite granules and have suggested their importance as biological "forming factors". To assess these forming factors, and their biological control over aggregate size and stability, across a typical Arctic valley glacier surface, a suite of rapid, spectrophotometric, microplate methods were utilised. Subsequent spatial mapping of these data revealed distinct patterns. Labile carbohydrates were found to increase up-glacier, suggestive of EPS production for cryoprotection and nutrient assimilation. Conversely, pigment concentrations were found to increase towards the glacier terminus and valley sides, suggestive of allochthonous input, a general reduction in physical disturbance and of the build-up of photosynthetic pigments and less labile cyanobacterial sheath material. Aggregate size was found to increase towards the glacier edges, linked to the input of particulate matter from the valley sides, and to broadly increase down-glacier, in the same way as pigment concentrations. Statistical analyses of transect data revealed that the photoautotrophic count and carbohydrate–chlorophyll ratio of the cryoconite sampled could explain 83% of the measured variation in aggregate size and stability. Considering solely aggregate size, the number and length of photoautotrophic filaments could explain 92% of the variation in this parameter. These findings demonstrate the two-dimensional distribution of key biological controls upon cryoconite aggregation for the first time, and highlight the importance of filamentous cyanobacteria and EPS production to the development of stable cryoconite granules.
Highlights
Cryoconite granules are biologically active aggregations of microorganisms, mineral particles and organic matter
Considering solely aggregate size, the number and length of photoautotrophic filaments could explain 92 % of the variation in this parameter. These findings demonstrate the twodimensional distribution of key biological controls upon cryoconite aggregation for the first time, and highlight the importance of filamentous cyanobacteria and extracellular polymeric substances (EPS) production to the development of stable cryoconite granules
Mean concentration data, mean aggregate size data and Incident radiation (IR) receipt were plotted as contour maps (Fig. 2)
Summary
Cryoconite granules are biologically active aggregations of microorganisms, mineral particles and organic matter. Located on the surface of glaciers and ice sheets, cryoconite material harbours a complex and variable microbial community (Hodson et al, 2008; Edwards et al, 2011; Cameron et al, 2012), sourced largely from aeolian input (Pearce et al, 2009) This material is important as it acts as a biogeochemical reactor (Hodson et al, 2008; Stibal et al, 2012), feeding proglacial environments, and acts to darken the surface of the glacier (Takeuchi et al, 2001; Yallop et al, 2012), driving ice melt. Radionuclide analysis (Tieber et al, 2009) and timelapse imagery (Irvine-Fynn et al, 2011) both suggest that, despite seasonal meltwater flow, cryoconite can reside on the ice surface for extended time periods, up to decades, thereby
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