Micromorphological features of mineral matter from cryoconite holes on Arctic (Svalbard) and alpine (the Alps, the Caucasus) glaciers

Journal Pre-proof Micromorphological features of mineral matter from cryoconite holes on Arctic (Svalbard) and alpine (the Alps, the Caucasus) glaciers Krzysztof Zawierucha, Giovanni Baccolo, Biagio Di Mauro, Adam Nawrot, Witold Szczuciński, Edyta Kalińska PII:

S1873-9652(19)30126-4

DOI:

https://doi.org/10.1016/j.polar.2019.100482

Reference:

POLAR 100482

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Polar Science

Received Date: 10 February 2019 Revised Date:

9 October 2019

Accepted Date: 10 October 2019

Please cite this article as: Zawierucha, K., Baccolo, G., Di Mauro, B., Nawrot, A., Szczuciński, W., Kalińska, E., Micromorphological features of mineral matter from cryoconite holes on Arctic (Svalbard) and alpine (the Alps, the Caucasus) glaciers, Polar Science, https://doi.org/10.1016/j.polar.2019.100482. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier B.V. and NIPR. All rights reserved.

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Micromorphological features of mineral matter from cryoconite holes on Arctic (Svalbard) and

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alpine (the Alps, the Caucasus) glaciers

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Krzysztof Zawierucha1, Giovanni Baccolo2, Biagio Di Mauro2, Adam Nawrot3,4, Witold

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Szczuciński5, Edyta Kalińska6,7*

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Department of Animal Taxonomy and Ecology, Adam Mickiewicz University, Poznań, Uniwersytetu Poznańskiego 6,

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61-614 Poznań, Poland 2

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Earth and Environmental Science Department, University of Milano-Bicocca, 20126, Milan, Italy

Institute of Geophysics, Polish Academy of Sciences, Księcia Janusza 64 street, 01-452 Warsaw, Poland 4

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Institute of Geology, Adam Mickiewicz University, Bogumiła Krygowskiego 12, 61-680 Poznań, Poland 6

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for Science Foundation, Leśna 11 street, 62-081 Przeźmierowo, Poland

Faculty of Earth Sciences, Nicolaus Copernicus University, Lwowska 1 street, 87-100 Toruń, Poland, [email protected]

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Faculty of Science, University of Tartu, Ravila 14A street, 50411 Tartu, Estonia

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Abstract: Mineral grain micromorphology is a useful proxy for reconstructing the history of mineral matter deposited

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on glaciers. In this study, we focus on the grain shape and micromorphology of mineral particles collected from

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cryoconite holes on glaciers in the Alps, the Caucasus and Svalbard. We use the scanning electron microscopy (SEM)

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to better understand the origin, transport regime, depositional processes, biofilm formations, degradation and grain

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transformation. Our results show that chemical and physical weathering are equally relevant in shaping mineral grains,

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although in polar and cold regions physical processes dominate. Grains with smooth edges owing to chemical

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weathering in some of the investigated samples, represent more than 60–70%. Comparison of main grain-type

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abundance helped to establish that climate is not the most important factor affecting grain micromorphology on glaciers,

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but local rock sources and supraglacial processes. We hypothesize that grain surface roughness plays an essential role

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with respect to biofilm formation, while at the same time bacteria-enhanced weathering enriches micromorphology (we

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observed polymeric substances on some of grains) and release critical compounds for nutrient-poor glacial systems.

1

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Thus, grain type and morphology might be an important factor influencing cryoconite granules formation and

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productivity of cryoconite holes.

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Keywords: sediment sources, grain morphology, quartz, polymeric substances, cryoconite

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1. Introduction

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Composition and characteristics of debris atop glaciers can aid in the better understanding of the

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processes occurring on glacier surfaces (e.g., Di Mauro et al., 2017; Karczewski et al., 1981; Serebryanny

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and Orlov, 1993). Supraglacial debris affects mass and energy exchange through changes in albedo and the

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control of the ablation rate, taking part in glacial sediment transport; in addition, it is one of the major

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components of specific supraglacial ecosystems (Di Mauro et al., 2017; Langford et al., 2014; Wientjes et

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al., 2011).

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In general, the major sources of supraglacial sediments may be divided into local (within the glacier

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catchment) and distant (mainly via long-distance wind transport). The dominating local sediment sources are

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slopes of mountains and nunataks adjacent to a glacier. The slopes are subjected to mass wasting, washing

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and aeolian processes, which transport the sediments on the glacier surface (e.g., Di Mauro et al., 2017;

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Karczewski et al., 1981; Kłysz, 1985). The local sources also include the material eroded underneath the

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glacier and transferred to the surface owing to the debris-rich basal ice layer deformation (e.g., folding,

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thrusting) and its emergence in the ablation zone (e.g., Hambrey et al., 1999; Rachlewicz and Szczuciński,

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2000; Swift et al., 2018). The following types of supraglacial sediment inputs are mostly based on long-

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distance transport of fine dust that can be suspended for thousands of kilometres (e.g., Grousset et al., 2003).

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They include various wind-blown minerals from widespread arid terrains, volcanic ash, marine and organic

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aerosols, extra-terrestrial material (e.g., micro-meteorites) and pollution (e.g., Gajda, 1958; Nagatsuka et al.,

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2014; Wientjes et al., 2011). Particulate matter transported to the glaciers from remote sources is deposited

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within accumulation and ablation zones. Therefore, their concentration and distribution on glacier surfaces

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are not only related to direct deposition but are also influenced by re-emergence processes based on the 2

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ablation of particulate matter-bearing ice that lead to the accumulation and concentration of impurities on the

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ablation surface (e.g., Wientjes et al., 2011)

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The combination of the processes acting in the supraglacial zone leads to mixing and interaction of

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mineral particulate matter of local and remote origin with organic compounds, bacteria and algae, and is

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responsible for the formation of a sediment called cryoconite (Cook et al., 2016). Its name means “cold-

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dust”, from ancient Greek ‘kryos’ and ‘konis’. The presence of cryoconite on glacier ice strongly changes the

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optical properties of ice, reducing its albedo, and thus facilitating enhanced input of energy to the glacier

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radiative balance (e.g., Di Mauro et al., 2017). Given cryoconite efficiency in absorbing solar radiation, it

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can easily induce the formation of cylindrical ice holes, called cryoconite holes, as a consequence of an

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increased ice melting rate (Brandt, 1931; Gribbon, 1979; Hodson et al., 2008; Wagner, 1938; Wharton et al.,

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1985). Owing to their morphology, cryoconite holes can be considered temporary sediment sinks, where

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mineral particles of remote and local origin are deposited because of atmospheric fallout, and due to both

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abiotic (flushing) and biotic (cyanobacteria movement as effect of phototaxis) processes on ice, as well as

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direct emergence from the glacial ice (Baccolo et al., 2017; Cook et al., 2016; Di Mauro et al., 2017; Gerdel

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and Drouet, 1960; Irvine-Fynn et al., 2011; Nagatsuka et al., 2016). Cryoconite holes also constitute complex

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ecosystems with high primary production and organism assemblages adapted to extreme supraglacial

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conditions (e.g., Cook et al., 2016; Kohshima, 1987; Takeuchi et al., 2000, 2010; Zawierucha et al., 2018).

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Mineral content that constitute cryoconite is complex, however, silt size fraction dominates, i.e.,

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particles with diameters ranging between 4 to 63 microns (e.g., Cook et al., 2016; Hodson et al., 2008;

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Nordenskiöld, 1875). Based on biophysical interactions with the mineral particulate matter and living

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organisms (mostly filamentous cyanobacteria which produce extracellular polymeric substances (EPS))

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constituting cryoconite, these sediment particles form granular - biologically active - structures, called

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cryoconite granules (Hodson et al., 2010; Takeuchi et al., 2010).

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Although, much attention has been paid during the last decades to the biological relevance of

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cryoconite and cryoconite granules (Cook et al., 2016; Stibal et al., 2012; Uetake et al., 2016), the knowledge

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of the mineral fraction sources and properties, e.g., mineral grain morphology, is still limited (Wientjes et al.,

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2011; Nagatsuka et al., 2010; Kalińska-Nartiša et al., 2017a). There is general agreement on the basic types 3

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of sediment sources for supraglacial material forming cryoconite, however a number of issues are still

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debated. They include the problem of relative contribution of local and distant sediment sources (e.g., Gajda,

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1958; Gerdel and Drouet, 1960; Kalińska-Nartiša et al., 2017a; Langford et al., 2014; Tedesco et al., 2013),

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the proportion of freshly delivered material and older particulate matter melted out from ice outcroppings in

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the ablation zone (Wientjes et al., 2011), the influence of multiple sediment sources (Nagatsuka et al., 2014).

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Another theme which was not investigated is the potential role played by alteration and weathering of

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mineral matter in the supraglacial environment (e.g., Karczewski et al., 2003; Skolasińska et al., 2016).

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Mineral grain shape and surface microtextures can be investigated through scanning electron

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microscopy (SEM) to reveal a variety of features resultant from grain history and sediment deposition

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(Mahaney, 2002). This method reflects grain source, weathering, mechanism of transport and sedimentary

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processes as a consequence of grain-to-grain or grain-to-bed interactions (Kalińska-Nartiša et al., 2017b;

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Mahaney, 1995; Woronko, 2016), as well as chemical alteration (Fischer et al., 2014; Gautier et al., 2001;

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Jonczak et al., 2016). Consequently, grain micromorphology has been applied, mainly for quartz grains, in

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various studies as a paleoclimatic (Mahaney, 2002) and paleoenvironmental proxy (e.g., Křížek et al., 2017;

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Kar et al., 2018).

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The genesis of the surface micromorphology may be the result of overprinting of a number of

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processes acting under various conditions and for variable time spans. Some of the features may be related to

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active aqueous transport lasting for few minutes (e.g. Costa et al., 2017; Kalińska-Nartiša et al., 2018), while

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other features may require much longer time to appear (e.g. Kalińska-Nartiša et al., 2017c). Successive

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processes may also erase or modify the primary grain morphology. Usually the microstructures developed in

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the dominating sedimentary environment (e.g. glacial, aeolian) are called primary, while the microstructures

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developed on minerals (e.g. due to postdepositional weathering) are called secondary (Woronko and

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Pisarska-Jamroży, 2016). Thus, the resulting micromorphology of grains forming the cryoconite is a

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combination of microrelief inherited from the host rocks (the sedimentary rocks formed in various climatic

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and depositional regimes), weathering of the host rocks, processes of erosion (e.g. glacial, aeolian), transport

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(avalanches, mass flows, meltwater transport, glacier flow) and processes taking place in cryoconite holes

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(biochemical and frost weathering). It should be also considered that the sediment sources for supraglacial 4

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environment could be different at different times and that supraglacial deposits may be easily subjected to

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reworking and secondary deposited (Karczewski et al., 2003; Skolasińska et al., 2016).

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In this study, we aim to present new data on mineral grains in cryoconite holes and on their shapes

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and micromorphology to better understand the origin, transport regime, depositional processes, biofilm

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formations, degradation and transformation of mineral grains found in such environments. In order to

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determine grain micromorphology controlling factors, samples were analysed from five glaciers from the

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European Alps, the Caucasus and the Svalbard archipelago. The glaciers represent different thermal regimes

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and are characterised by diverse climatic, geological, and geomorphological settings.

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2. Study areas

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The investigation was conducted for samples collected from glaciers representing different

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thermal types (polythermal, cold base and temperate), terminating on land and in fjords, with an ablation

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zone developed at altitudes that range from several tens of meters a.s.l. to over 2000 m a.s.l., and with a

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geological setting composed of various rock types (Table 1, Figure 1, 2). Two of the glaciers are alpine type

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glaciers: Adishi Glacier in the Caucasus and Morteratsch Glacier in the European Alps, while the remaining

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three glaciers are located in the Svalbard archipelago (European Arctic), namely Hansbreen, Longyearbrean

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and Ebbabreen and can be classified as tidewater (=Hansbreen) and valley glaciers (=two latter). The basic

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data, i.e., GPS coordinates of sampling points, geographic region, type of glacier, altitude above sea level

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and local geology for each of the sampled glaciers are listed in Table 1 and their general characteristics are

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found in the following.

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Adishi Glacier (Figure 1, S1 A-B) is located in Georgia, in the Svanetia region of the Central part

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of the Greater Caucasus mountain range. Due to the strong longitudinal gradients, the Caucasus Mountains

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climate is maritime in the west and a more continental in the east (multi-year mean air temperature for

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Mestia region calculated for period 1961 – 2013 was 5.9 ºC), with the warmest month – August (mean air

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temperature 7.6 ºC at the 2800 m a.s.l.) and coldest January with mean air temperature of -8 ºC at a height of

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2000 m a.s.l. (Tielidze, 2015). Tielidze (2015) mentioned that annual sum of precipitation for the southern 5

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slopes can be up to 3000-4000 mm. The Adishi Glacier is a valley glacier with a south-western exposition

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and surrounded by roughed mountains reaching 4858 m a.s.l. The glacier has been in retreat in recent

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decades: in 1960, the surface of Adishi Glacier was 10.5 km2 and it terminated at an altitude of 2330 m a.s.l.,

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while at present, it has shrunk to 9.5 km2 and ends at 2485 m a.s.l. (Gobejishvili et al., 2011; Tieledzie et al.,

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2015). The glacier is divided into three parts: the accumulation zone above 3800 m, which is surrounded by

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the highest peaks, an icefall (~1000 to 1300 meters high) and a terminal ice tongue with characteristic bands

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of lighter and darker ice called ogives that usually develop just below icefalls (Goodsell et al., 2002). The

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surface of the ablation zone is wavy, with numerous glacial wells, supraglacial channels and other ablation

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forms (Tieledzie, 2014). The comparison of aerial images taken after 1960 revealed that the amount of debris

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on the glacier surface is increasing (Tieledzie, 2014; Tielezie et al., 2015). Supraglacial cover constitutes

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various sediments, fine-grained debris, as well as gravels and boulders. The glacier catchment lithology is

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dominated by black shales, phthanite cherts, sandstones, mudstones, small amounts of marbles and volcanic

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rocks (Moores and Fairbridge, 1997).

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Morteratsch Glacier (Figure 1, S1 C-D) is located in the Bernina Range in the European Alps. It

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is a valley glacier that extends from an altitude of 2030 to 3976 m a.s.l. and is 15.81 km2 in area (Oerlemans

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and Klok, 2002). Since the Little Ice Age, Morteratsch Glacier has experienced a strong retreat and volume

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loss (Rossini et al., 2018; Zekollari and Huybrechts, 2018). Oerlemans et al (2009) reported a decreasing

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trend of surface albedo at the glacier. This was ascribed to the accumulation of debris from the lateral

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moraine. Furthermore, the relationship between inorganic and organic matter induces a further decrease of

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the albedo, promoting melting (Di Mauro et al., 2017). The Morteratsch valley belongs to the tectonic unit of

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the Bernina crystalline, which is composed mainly of granodiorite (Finger et al., 1997).

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Hansbreen (Hans Glacier, Figure 2, S1 E-F) is a tidewater, polythermal glacier located on the

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northern coast of Hornsund fjord, southern Spitsbergen (Jania et al., 1996). It is roughly 16 km long with an

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approximately 1.3 km-wide calving front and a surface area of 57 km2 (Błaszczyk et al., 2013). The altitude

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spans from the sea level to 490 m a.s.l. (Aas et al., 2016). The front of Hansbreen has been retreating since

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the end of the 19th century at an average contemporary rate of 40 m/year (Błaszczyk et al., 2013; Ćwiąkała et

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al., 2018). The oceanic influence makes the climate of western Spitsbergen relatively mild, with a mean 6

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annual air temperature approximately -4 ºC and mean annual precipitation of about 450 mm (Marsz and

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Styszyńska, 2013; Osuch and Wawrzyniak, 2016). The geology of the studied western part of the Hansbreen

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basin is dominated by gneisses, schists, amphibolites, phyllites, marbles, quartzites and conglomerates

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(Birkenmajer, 1990, 1992; Manecki et al., 1993). Supraglacial deposits are common along the margins of

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Hansbreen, resulting in the formation of various types of supraglacial deposits including cryoconite, dirt

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cones, ablation ridges, lateral and medial moraine and continuous covers (Szczuciński, 2000). The

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supraglacial sediments mostly originate from subglacial deposits transported towards the ice surface through

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deformation of basal ice layers (Rachlewicz and Szczuciński, 2000) and from the surrounding mountainous

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slopes. They are subjected to reworking mainly because of differential ablation, mass movement processes

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(e.g., debris flows) and meltwater action (Szczuciński, 2000; Karczewski et al., 2003).

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Longyearbreen (Longyear Glacier, Figure 2, S1 G-H) is a land-terminating, cold glacier (Sevestre

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et al., 2015), located nearby the town of Longyearbyen in the catchment of Adventfjorden, western

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Spitsbergen. The northeast-facing Longyearbreen has an area of ~2.5 km2, descending from over 1000 m to

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approximately 250 m a.s.l. It is located in the central part of the island and thus the climate is more

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continental (drier and with a lower mean annual air temperature) than in the Hornsund region (Przybylak et

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al., 2014). The catchment geology is composed of Palaeocene to Miocen rocks consisting of shales, siltstones

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and sandstones accompanied with coal seams, chert nodules, volcanic tuffs and clay-ironstones (Yde et al.,

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2008). Cryoconite holes were previously investigated on this glacier (Hodson et al., 2010; Langford et al.,

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2010, 2014; Zawierucha et al., 2019) and the results showed that the biological aggregation (formation of

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cryoconite granules) on the surface of the Longyearbreen is responsible for the development of an internal

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structure after the cementation of mineral grains (mostly quartz and dolomite) by filamentous

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microorganisms, and such granules might be eroded by flushing water.

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Ebbabreen (Ebba Glacier, Figure 2, S1 I-J) is a land-terminating polythermal glacier located in

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the central part of Spitsbergen, within the catchment of Billefjorden. This region is characterised by an inner-

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fjord climate type, similar to the climate of Longyearbreen, known for arid conditions and greater annual

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thermal contrasts than along the west coast of Spitsbergen (Rachlewicz and Styszyńska, 2007; Rachlewicz,

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2009, Małecki, 2015). Ebbabreen occupies Ebba valley and descends westward from approximately 1000 m 7

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to 100 m a.s.l. The glacier is 6.2 km long, covers an area of 20.4 km2 and is in recession since the termination

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of the Little Ice Age ca. 1900 AD (Rachlewicz et al., 2007). The catchment in the Ebba Valley is mostly

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built of Carboniferous–Permian sedimentary rocks (sandstones, mudstones, gypsum, limestones, anhydrites,

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dolomites, conglomerates) and pre-Devonian rocks (gneiss, schist, phyllite, amphibolite and syenite, granite,

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quartzite and marble; Dallmann et al., 1994). The material of supraglacial cover presents large grain size

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variability – from the clayey-silt fraction to boulder-size rocks (Gibas et al., 2005; Kłysz, 1985; Pleskot,

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2015; Rachlewicz, 2009).

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3. Methods

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3.1. Sampling

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Cryoconite samples were collected between 2014 and 2017. They were gathered by scooping the sediment

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from the bottom of single cryoconite holes and stored in clean plastic tubes. After sampling and transport,

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they were kept frozen (samples from Adishi) or treated with ethanol alcohol (remaining samples) in a room-

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temperature until further analyses. Samples were collected (Figures 1 and 2, S1, Table 1) from: (1) north-

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western part of Adishi Glacier (ca. 2500-2600 m a.s.l.) in July 2014; (2) the ablation zone of Morteratsch

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Glacier (ca. 2300-2500 m a.s.l.) during the summers of 2016 and 2017; (3) the western part of Hansbreen

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(23-101 m a.s.l.) in July 2014; (4) southern-east part of Longyearbreen (352-378 m a.s.l.) in August 2016;

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and (5) southern-east part of Ebbabreen (149-176 m a.s.l.) in August 2016. Altogether, 46 samples were

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collected (Hansbreen, Longyearbreen, Ebbabreen and Morterasch – 10 samples per glacier, and six samples

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from Adishi). The micromorphological analysis required ca. 1 cm3 of sediment.

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3.2. SEM analysis

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Sample preparation and analyses were performed at the laboratory of the Department of Geology,

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University of Tartu, Estonia. In order to homogenize the sediment, each sample was hand shaken and a tiny

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portion of sediment was taken by a small stainless spoon and placed - with a help of a stereomicroscope -

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onto a carbon double-sided sticky tape atop of SEM holder. Loose sediment rather than cryoconite granules 8

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was picked up. Once a sample room-dried, it was placed on an X-Y-Z tilt rotation stage in the vacuum

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chamber of a scanning electron microscope (SEM). The prepared sediment sample was examined by the

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Zeiss EVO MA 15 SEM in low vacuum mode, and with an energy dispersive spectrometer (EDS) providing

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semi-quantitative chemical composition of the randomly investigated grains and thus also their mineralogy.

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Coarse silt–very fined sand (ca. 0.031–0.125 mm) particles were considered for analysis.

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3.3. Morphology of grains The morphology of the mostly silt-size grains was classified into five classes (Woronko, 2007;

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Jonczak et al., 2016, see Table 2 for details):

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(1) A-type – fresh angular grains, presenting sharp edges and corners, likely associated to physical

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weathering;

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(2) B-type – grains transformed by chemical weathering with smooth edges, holes and caverns;

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(3) C-type – grains with scaly-grained precipitation;

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(4) D-type – grains with bulbous cover;

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(5) E-type – broken grains with a loss of at least 30% of original grain, representing B-type, C-type or D-type

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grains.

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In general, the classes A and E result from frost weathering and/or transport, and they are therefore

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interpreted as the consequence of physical actions; on the contrary, features of classes B, C and D are mainly

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linked to chemical processes. It should be taken into account that cryoconite is biogenic enriched sediment,

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and products of metabolism of bacteria (production of EPS) could weathered grains and form similar

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morphological characters to chemical weathering. Recent studies indicate that even 35% of mineral grains on

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ice are covered by biofilms (Smith et al., 2016), which can not be overlooked in the interpretation of grain

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micromorphology. Additionally, in certain cases, it was possible to recognize the microtextures atop the

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grain surface in accordance with the atlas of Mahaney (2002). Altogether, 4659 mineral grains (about 100 for

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each cryoconite sample) were analysed under SEM using a magnification of 500 to 4000 times.

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4. Results 9

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The observations under stereo-microscope revealed common occurrence of greyish minerals

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belonging to the silt-size fraction. They are mainly quartz and K-feldspar grains, as confirmed by the EDS. A

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summary of the results for each glacier is presented in Table 3. In general, B-type grains with smoothed

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edges dominate (up to 60%), while types E and A are also common, and types C and D are present only

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occasionally in the investigated cryoconite samples (Figure 3).

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The contribution of the most common B-type grains reaches on average between 49% and 60%

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for samples from Hansbreen and Adishi Glaciers, respectively (Figure 3). Among the B-type class grains, the

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degree of surface weathering and smoothing is highly variable. For example, on some of the grains holes and

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caverns are completely absent (Figure 4 A), whereas in other samples, B-type grains contain several of them

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(Figure 4 B–E). In addition, some B-type grains also show initially weathered microtextures similar to V-

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shape percussion marks (Figure 4 F). We estimate that ca. 50% of B-type grains is covered by numerous

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microtextures on their surface which may be the effect of both the presence of polymeric biofilm and the

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effect of weathering.

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The second most common group are E-type grains (Figure 4 G–H). They are the most abundant in

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cryoconite from the Hansbreen, where they contribute up to 58% in one analysed sample, and 47% on

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average. In contrast, in cryoconite sediments from Ebbabreen, the content of E-type grains is only 29% on

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average. A closer inspection of E-type grains reveals that both fresh (Figure 4 H) and older cracked surfaces

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occur (Figure 4 I). The latter are seen through a slight rounding of a crack edges likely due to chemical

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processes.

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The A-type grains (Figure 4 J-K) are the most abundant in samples from the Ebbabreen (Figure 3,

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Table 3), while they are the least common in the cryoconite material from the Longyearbreen. A-type grains

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are characterized by the occurrence of very fresh and plain breakage surfaces, numerous conchoidal features,

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straight and curved steps and parallel striations (Figure 4 L).

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Grains classified to the type C, with scaly-grained precipitations (most probably silt mixed with

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EPS) are in a minority (0.1 to 1.4% on average). They are characterised by various precipitations (compare

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Figure 4 M and N). The D-type grains with bulbous cover on the grain surface, are practically absent in the

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investigated samples, except of few grains in the samples from the Longyearbreen (Figure 4 O). However, 10

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since only few grains were found, their presence in the supraglacial environment of Longyearbreen should be

269

treated with caution.

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Apart from silt-size grains, also sand fraction grains were found and investigated in samples from

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Adishi Glacier. Transparent-light-grey quartz grains were recognized through stereo-microscope and SEM,

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they consist both in subrounded and angular grains, but well-rounded grains are not present. Surface of

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subrounded grains is covered by common precipitates with numerous solution pits and crevasses.

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Microtextures of mechanical origin are barely visible on these grains due to the precipitation. In contrast,

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angular grains contain abundant fracture faces and fresh surfaces with numerous conchoidal features with

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steps and gouges (Figure 5).

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The raw data on contribution of grains assigned to specific classes, were subjected to principal

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component analysis. The obtained major four principal components explain more than 99.9% of the total

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variance of the original data (Figure 6). However, it is not possible to identify any combination of

280

components in order to separate the samples in accordance to the glaciers where they were collected. This

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suggests that the local setting (Table 1) is not the single driving factor responsible for development of the

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grain type class.

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If the dominating grain types (classes: A, B and E – Figure 3) are considered and summed to

284

100%, then they may be displayed on a ternary diagram (Figure 7). Following this approach, a certain

285

grouping is revealed. The cryoconite sediments from the Ebbabreen are grouped closer to the A-type grain

286

endmember (interpreted as results of mainly physical weathering and deterioration), as also partly evidenced

287

by PCA analysis, since samples from Ebbabreen are found in correspondence of the original variable A-type

288

(Figure 6). The samples from the Longyearbreen and Adishi Glacier contain more grains of B-type

289

(interpreted as shaped by chemical weathering or biochemical weathering by microbial assemblages). In

290

turn, grains from Hansbreen are relatively enriched in E-types grains (interpreted as polygenetic - chemically

291

weathered and broken), as also revealed by PCA results (Figure 6, 7).

292 293

5. Discussion

11

294

5.1. Is grain morphology spatially variable?

295

Even though the climatic conditions (e.g. mean annual temperatures, length of ablation season), which may

296

influence physical and chemical weathering, in the Caucasus, the Alps and Svalbard are different, we found

297

that micromorphology of grain types are similar to some extent within the cryoconite holes of various

298

regions. Our results show that the most dominant type of grains in our study includes both chemically (B-

299

type) and physically-altered (A and E- types) ones. Considering that all the investigated areas have

300

experienced physical weathering conditions due to frequent temperature fluctuations around 0ºC and are

301

glaciated nowadays, our primary expectation was to find a strong signal related to glacial processes, i.e., a

302

dominant occurrence of A-type grains, related to mechanical weathering. Even though physically altered

303

grains constitute extensive part of mineral fraction, the B-type grains, associated with chemical alteration are

304

most abundant grain type in cryoconite. This indicates that not only physical weathering, but also chemical

305

weathering is dominate upon glaciers and both are important processes in shaping mineral grains. However,

306

there is nearly 3-times more A-type grains in the Ebbabreen’s cryoconite comparing with the Longyearbreen

307

that may suggest increased mechanical weathering atop of the Ebbabreen tongue, likely due to supply of

308

fresh grains from medial and lateral moraines. We can not exclude that cryoprotective features of many

309

substances produced by microorganisms (polysaccharides, lipids, antifreeze proteins) moderate physical

310

weathering in granules, which are consortia of grains and microbes (Langford et al., 2014; Hodson et al.,

311

2010; Smith et al., 2016; Vincent, 2007). However, further discussion on such topic require experimental

312

approach and detailed analysis of products of microbial metabolism, and their effects on grain morphology.

313

One of the driving factors in shaping mineral grain micromorphology observed in our samples might be

314

different grain mineralogy and dominating sediment transport that dependends on general landform features

315

such as mountain slope steepness and their proximity, as well as water availability and winds. For example,

316

minerals forming sandstones and siltstones of Longyearbreen are likely softer comparing with quartz diorites

317

of Morteratsch that may explain the higher percentage of A-type grains in this latter. However, this needs a

318

closer inspection and is undoubtedly a good avenue for further studies.

319 320 12

321

5.2. Origin of grain micromorphology

322

The grain micromorphology reflects grain history - origin, processes of transport, as well as process acting

323

already in cryoconite holes. The relative similarity of grain micromorphology in various settings suggest

324

some common overprint possibly related to common processes acting in supraglacial environment.

325

As was previously discussed in literature, the grains found in the supraglacial environment may have

326

followed various paths, being delivered from subglacial position, various subaerial settings surrounding the

327

glaciers or from distant areas (Gajda, 1958; Kłysz, 1985; Nagatsuka et al., 2014; Wientjes et al., 2011). In

328

case of material delivered from the subglacial environment, it is well known that the flowing glaciers

329

generally impose a large shear-stress at their bases, resulting in fresh conchoidal features of various sizes,

330

arcuate steps, linear fractures, high grain relief and angularity of subglacial grains (Hart, 2006, 2017;

331

Immonen, 2013). Such features are clearly seen within the investigated samples, as for example through the

332

A-type and E-type grains. However, according to Sweet and Soreghan (2010) and Sweet and Brannan

333

(2016), only straight and curve grooves, along with chattermarks, are produced by high-pressure fracturing

334

during glacial transport. In our study none of these microtextures have been found. Therefore, these grains

335

were unaffected by the stress, due to their smaller size, or these grains were not subjected to subglacial

336

conditions. The mechanism of grain shearing, along with frost weathering, is responsible for the production

337

of the E-type grains, and this happens when internal structure of grain is weakened and prone to damage

338

(Wright, 1995). The E-type cracked grains constitute vast part of all grains in investigated samples (Figure

339

3); this means that likely local freeze-thaw conditions influence grain shape and morphology.

340

Material taken from the Longyearbreen and the Adishi Glacier reveals relatively bigger contribution of the

341

weathered B-type and cracked E-type grains, whereas A-type grains are in minority. As stated before, these

342

B-type grains are interpreted as a product of chemical action. Cryoconite holes were previously investigated

343

on studied glaciers and the results showed that these glaciers are inhabited by diverse microbial communities

344

(Hodson et al., 2010; Langford et al., 2010, 2014; Makowska et al., 2016; Zawierucha et al., 2019) which

345

may influence, especially in cryoconite holes, biological weathering. Revealing of nutrients from primary

346

minerals through the biological weathering by microorganisms is well known phenomenon (Boyle and

347

Voight 1973; Etienne, 2002) and might take place in cryoconite holes. Alternatively, these grains may have 13

348

been delivered to the cryoconite system. Assuming that both glaciers have well-developed lateral moraines

349

surrounding the glaciers, these can act as potential sources for the supraglacial debris found on the glacier

350

surfaces. Since samples taken from the rest glaciers (the Hansbreen, Ebbabreen and Morterasch) reveal a

351

lower share of B type grains, the chemical or/and biochemical weathering may have been somehow limited,

352

for example with a lesser activity of microorganisms living in the holes or a lesser influence of meltwater.

353

It is widely acknowledged that cryoconite material might be isolated even decades from outer environment

354

(Fountain et al., 2004). This is possible when cryoconite holes are well isolated from the supraglacial

355

hydrological system, as in the case of Antarctic glacier, where cryoconite holes are usually isolated by a

356

well-developed ice lid. However, Arctic and Alpine European glaciers are completely different: they are

357

characterized by frequent melting events, and consequently cryoconite holes are less stable (Mueller et al.,

358

2001; Zawierucha et al., 2019). Sediments from Arctic cryoconite holes are often removed and redistributed

359

on the glaciers by flowing water within few days (Zawierucha et al., 2019). Significant meltwater amount

360

and open cryoconite holes in the Arctic may affect cryoconite grains by the inter-hole water-sediment mixing

361

(Mueller et al., 2001). In addition, some of the investigated cryoconite holes developed as a network of

362

channels, rather than single and isolated holes (Gajda, 1958). Such a morphology promotes meltwater flow,

363

thus affecting the grains. In summary, the large contribution of grain type B, point to a relevant role played

364

by chemical and/or biochemical weathering processes occurring within cryoconite holes.

365 366

5.3. Implications for glacial ecosystems

367

Grain surface roughness plays an important role in succession and biofilm formation (Dudley and

368

D’Antonio, 1991; Sekar et al., 2013). Microbes play an essential role in the environment by contributing to

369

the release of key nutrients from primary minerals (Boyle and Voigt, 1973; Uroz et al., 2009). Various grain

370

morphology of particular minerals, the presence of rough surfaces, often with caverns, better supports

371

colonisation than flat and smooth substrate (Baker, 1984; Dudley and D’Antonio, 1991). Therefore, the grain

372

morphology may be an important factor influencing bacteria colonisation of the supraglacial environment,

373

with important consequences on cryoconite granules formation and cryoconite biological productivity.

374

Microorganisms adapted to nutrient-limited ecosystems can promote the dissolution of minerals as was 14

375

suggested by Bennet et al., (2001), and directly benefit from the dissolved mineral nutrients. The supraglacial

376

environment is a good example of such harsh and nutrient-poor ecosystems, and for this reason similar

377

processes could be actually observed on the ice. Indeed, incorporating of nutrients and heavy metals by

378

microbes directly from mineral dust and dissolved matter in snow and ice was previously suggested

379

(Fjerdingstad, 1973; Nagatsuka et al., 2010). The cyanobacteria that commonly colonize glacier surfaces are

380

known as ecosystems engineers since they produce EPS which act as cryoprotection but also bind mineral

381

and organic particles, forming the so called cryoconite granules (Stibal et al., 2012; Takeuchi et al., 2010;

382

Uetake et al., 2016). Extracellular polymeric substance might also influence mineral grains chemical

383

weathering as one of the most abundant group of chemical components excreted by glacial primary

384

producers.

385

Our observation of grain micromorphology reveals that approximately half of the analyzed grains (mostly B-

386

type grains) are characterized by a relatively rough surface, sometimes with micro depressions and substrate

387

heterogeneity (various mineral grain shapes), hence providing potentially favorable conditions for organisms.

388

On the other hand, observations of precipitation and irregular surface micromorphology of grains most

389

probably constitute biofilms produced by microorganisms i.e. EPS (Langford et al., 2010, 2014; Smith et al.,

390

2016; Takeuchi et al., 2010). It is difficult to accurately determine the relative importance, for mineral

391

micromorphology, of bacterial direct colonization of grain surfaces versus adhesion of grains to extracellular

392

polymers within biofilms. Some cryoconite granules present a core built from quartz grains (Takeuchi et al.,

393

2010). Biological processes are involved in the formation of these spherical structures, and thus prolong the

394

residence time of mineral debris on the glacier (Hodson et al., 2010). The primary biological production of

395

supraglacial ecosystems does not concern only the surface of cryoconite granules but also their interior, due

396

to the translucence of quartz particles (Hodson et al., 2010). We suggest that the relations between glacial

397

ecosystem productivity and the mineral grain types, micromorphology, their transparency and chemical

398

composition, thus nutrient availability, may be a fruitful avenue of future ecological research on glaciers.

399

400

6. Conclusions

15

401

This study explores the micromorphology of mineral grains collected from cryoconite holes of glaciers from

402

Arctic, Alpine and Caucasus regions. We found that B-type grains with smooth edges, likely due to chemical

403

weathering, are frequent in the investigated cryoconite samples. This is in contrast with the general

404

assumption that polar and high mountain environments lead to the production of grains with angular forms

405

and irregular breakage pattern (A-type), as a consequence of mechanical processes, as freezing and the

406

effects due to glacier flow. The development of grain morphology has a complex and polygenetic history: it

407

can be partly inherited from source rocks, but it is also influenced by transport, deposition and weathering

408

processes. However, if we consider that cryoconite granules form in presence of liquid water, we may expect

409

that chemical weathering plays a dominant role on the surface of glaciers, and is responsible for the frequent

410

occurrence of B-type grains in cryoconite. Biological weathering may contribute to grain micromorphology,

411

since cryoconite holes are intended as biogeochemical reactors hosting various microbial assemblages. Grain

412

types differ more within cryoconite holes of the same climatic zone (Arctic) than between temperate and

413

polar latitudes, suggesting that regional climate is not the main factor that affects grain micromorphology.

414

Local glacier geomorphology and the geological setting seem more important in shaping the mineral grains.

415

Finally, grain micromorphology looks like an important factor influencing bacteria colonisation. However,

416

without laboratory experiments, it is hard to estimate whether bacteria colonise grains due to their variable

417

morphology, or metabolites produced by the bacteria, which have adhesive properties, capture fine particles

418

and enhance the weathering of grains. Nevertheless, future study will help in better understanding such

419

relation.

420 421

Acknowledgments

422

We would like to thanks two anonymous reviewers for their helpful and substantial comments on the

423

manuscript. Sampling on Arctic glaciers was supported via grant NCN 2013/11/N/NZ8/00597 to K.Z. K.Z

424

would like to thanks Maciej Wilk for logistical support during sampling in Caucasus and on Ebbabreen and

425

Longyearbreen as well as Jakub Małecki (Adam Mickiewicz University, Poznań) for remarks on Ebba

426

Valley. Contribution of W.S. was supported by National Science Centre (Poland) grant number

427

2013/10/E/ST10/00166. Studies on organic matter and productivity of glacial ecosystems is supported via 16

428

grant NCN 2018/31/B/NZ8/00198 to K.Z. A.N. was also partially supported within statutory activities No

429

3841/E-41/S/2018 of the Ministry of Science and Higher Education of Poland. The text was proofread by the

430

Cambridge

Proofreading

LLC.

17

431

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Nordenskiöld, A.E., 1875. Cryoconite found 1870, July 19th-25th, on the inland ice, east of Auleitsivik Fjord, Disco Bay, Greenland. Geol. Mag. 2, 157–162.

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Oerlemans, J., Klok, E.J., 2002. Energy balance of a glacier surface: analysis of automatic weather station

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623

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658

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661

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662

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663

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664

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665

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666

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667

150. https://doi.org/10.1007/s10201-017-0528-9

26

668

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669

from cryoconite holes on an Arctic valley glacier (Longyearbreen, Svalbard). Ecol. Res. 34(3), 370–

670

379.

671

Zekollari, H., Huybrechts, P., 2018. Statistical modelling of the surface mass balance variability of the

672

Morteratsch glacier (Switzerland): strong control of early melting season meteorological conditions,

673

J. Glaciol. 64, 275–288. doi: 10.1017/jog.2018.18. https://doi.org/10.1017/jog.2018.18

674 675

Figure Captions

676 677

Fig. 1. Map of the Adishi and Morteratsch glaciers and local geology. Squares indicate cryoconite sampling

678

area.

679

(https://www.openstreetmap.org/) and Geological Map of Georgia (Adamia and Gujabidze, 2004);

680

Morteratsch Glacier – GIS data from Swiss Federal Office of Topography.

681

Fig. 2. Map of Hansbreen, Longyearbreen and Ebbabreen and local geology. Squares indicate cryoconite

682

sampling

683

(https://svalbardkartet.npolar.no/).

684

Fig. 3. A) Total sum of the analyzed grains in all the samples from the particular glacier, B) Percentage

685

abundance of the different grain types (A to E see text for explanation) in cryoconite samples from the

686

studied glaciers.

687

Fig. 4. Examples of SEM images of the investigated grains. A–E) show B-type grains with different degree

688

of weathering (A – with smooth edges and with very little signs of weathering (arrow), D –most of the

689

surface is weathered and contains numerous holes); E) presents details on holes; F) V-shaped-like percussion

690

marks (arrow); G) examples of E-type (cracked) grains (arrows); H) freshly broken (arrow) E-type grain, the

691

remaining surface has characteristic of the class B grains; I) E-type grain with an older cracked surface

692

(arrow); J) A-type grain with fresh fracture surface (arrow); K) A -type grain with fresh conchoidal features

693

and arcuate steps (arrow); L) details on the arcuate steps; M) C-type grain with common precipitations; N)

694

C-type grain with moderately common precipitations; O) presumably D-type grain with bulbous cover.

695

Precipitation and not regular surface micromorphology on pictures C, M, N, and O could constitute biofilms

696

produced by microorganisms i.a. EPS (Smith et al., 2016). Many of fine particles on grains (B, M) are

697

attached to the surface due to adhesive properties of minerals as well as metabolites produced by bacteria

698

being part of cryoconite (Langford et al, 2010, 2014; Takeuchi et al., 2010).

699

Fig. 5. SEM micrographs of sandy quartz fraction from cryoconite on the Adishi Glacier. A and B)

700

subrounded grains with less excessive (A) and more excessive (B) precipitation on the surface; C) angular

Maps

were

area.

made

Maps

based

were

made

on:

Adishi

based

on

Glacier

GIS

–

data

GIS

from

data

from

Norwegian

OpenStreetMap

Polar

Institute

27

701

grain with fresh surfaces; D) details on precipitation with holes; E: fracture face (arrow); F: conchoidal

702

feature with steps and gouges (arrow).

703

Fig. 6. Principal component analysis. The first 4 principal components (from PC1 to PC4) explain more than

704

99.9 % of the total variance associated to the original data. In addition to data (see the legend to identify the

705

different glaciers, also the position of the original variables (Orig. Var., i.e. grain types, presented as black

706

crosses) in the multi-variate domain is shown.

707

Fig. 7. Ternary diagram of the relative contribution of grains type A (interpreted as effects of physical

708

deterioration due to physical weathering and crushing during transport), B (chemical weathering), and E

709

(polygenetic - grains shaped by chemical weathering and subjected to crushing) in the analyzed samples.

710

Letters A, M, H, E, and L refers to samples collected from Adishi Glacier, Morteratsch Glacier, Hansbereen,

711

Ebbabreen and Lyongearbreen respectively.

712

Fig. S1. General views of the particular glaciers and close-ups of the sampling areas on Adishi Glacier (A

713

and B), Morteratsch Glacier (C and D), Hansbreen (E and F), Lyongearbreen (G and H), and Ebbabreen (I

714

and J), respectively.

715 716 717 718 719 720 721 722

Table 1. Basic characteristics of the sampled glaciers and their catchments. Data sources are cited in the

723

description of study sites.

724 Glacier

Coordinates Region (WGS85)

Glacier type

Glacier thermal

Area 2

[m ]

regime

Sampling Mean

Mean

Dominating

sites

summer

annual

rock types in

altitude

temp. °C temp. °C the

m a.s.l. Adishi

Morteratsch

43°00′N,

the

42°59′E

Caucasus

46°24'34"N, the Alps 9°55'54"E

valley

temperate

9.5

2500-

catchments 10.6a

2.7a

2600 valley

temperate

15.8

23002500

shales, sandstones

8.0b

-5.0b

graniotids, gabbros

28

Hansbreen

77°1'27"N,

Arctic

tidewater polythermal

56.3

201-247

3.8c

-4c

gneisses,

15°36'15"E (Svalbard)

schists, amphibolites, phyllites, marbles, quartzites and conglomerates

Longyearbreen 78°10ʹ49ʺN, Arctic 15°30ʹ21ʺE Ebbabreen

valley

cold

2.5

352-378

6.2c

(Svalbard)

78°43ʹ36ʺN, Arctic 16°49ʹ16ʺE (Svalbard)

-4.4c

shales, siltstones and sandstones

valley

polythermal

20.4

149-176

6.4c

-5.3c

limestone, gypsum, sandstones, dolomites, gneiss, schist, amphibolite

725 726

a – https://en.climate-data.org/location/358389/, b - Oerlemans et al., (2009), c – Przybylak et al., (2014)

29

727

Table 2. Types of mineral grains and microtextures on their surface as observed in the investigated study. Type of grain/microtexture

Grain/microtexture characteristics

Due processes

A

All grains are sharp with fresh surfaces and, without traces of rounding.

Grain cracking due to glacial action

Reference pictures

10 µm

B

Rounded or partially-rounded grains with smooth edges sometimes accompanied with holes on their surface.

Grain smoothing due to chemical weathering

10 µm

30

Type of grain/microtexture

Grain/microtexture characteristics

Due processes

Reference pictures

C

Scaly-grained cover occurs entirely on a grain.

Silica precipitation on a grain surface.

10 µm

D

Bulbous, bubble-like cover occurs entirely on a grain, so that no fresh surfaces are invisible.

Etching by alkaline solution in warm and dry conditions

20 µm

E

Cracked grain, where part of a grain is characterised by a fresh surface due to cracking, whereas remaining surface is rounded and originates from the B-, Cor D-type grains thus carrying their characteristics.

Grain cracking due to frost action, being however a postsedimentary process.

10 µm

31

Type of grain/microtexture

Grain/microtexture characteristics

Due processes

holes

More less rounded or shapeless depressions and cavitions

Chemical activity and dwelling in the environment promoting mineral matter dissolution

Reference pictures

10 µm

V-shaped percussion marks

More or less triangular-shape depressions/pits

Impact due to high energetic subaqueous environments and grain-tograin colision

2 µm

32

Type of grain/microtexture

Grain/microtexture characteristics

Due processes

fresh surface

surface with no traces of precipitation, where all mechanical microtextures uncovered and well-expressed

Glacial crushing and fresh grain liberating from crystalline rocks

Reference pictures

10 µm

conchoidal features

shell-like fresh grain breakage

Impact or pressure on the grain surface

20 µm

arcuate steps

Step-like curved features strongly related with conchoidal features

Impact or pressure while the conchoidal planes intersect

1 µm

33

Type of grain/microtexture

Grain/microtexture characteristics

Due processes

Reference pictures

bulbous cover

Tuberous-like precipitation, often with small holes covering and entire surface of grain

Etching by alkaline solution in warm and dry conditions

1 µm

728 729 730 731 732 733 734 735 736 737 738 739 740 741 34

742 743 744

Table 3. Basic statistics for grain type counts for each glacier. Number of grains provided next to a glacier name is a total sum of the analyzed grains in all the

745

samples from the particular glacier. In the following are presented: the total number of the grains counted in particular class, average, minimum and maximum

746

grain number per sample and SE – standard deviation.

747 A

B

C

D

E

62 10.5 2 24 9.04

361 60.2 39 80 17.18

3 0.5 0 2 0.83

0 0 0 0 0

175 29.2 20 37 8.15

168 16.8 8 27 7.53

467 46.7 34 60 6.94

14 1.4 0 3 1.26

0 0 0 0 0

388 38.8 30 46 5.39

Number of counted grains 119 Average per sample 11.9 Min 5 Max 28 SE 6.93 Longyearbreen (1019 grains)

391 39.1 35 50 4.67

13 1.3 0 5 1.76

0 0 0 0 0

460 46 36 60 8.33

Adishi (601 grains) Number of counted grains Average per sample Min Max SE

Morteratsch (1037 grains) Number of counted grains Average per sample Min Max SE

Hansbreen (983 grains)

35

Number of counted grains Average per sample Min Max SE Ebbabreen (1019 grains) Number of counted grains Average per sample Min Max SE

65 6.5 2 18 5.94

544 54.4 28 68 12.36

1 0.1 0 1 0.31

4 0.4 0 1 0.51

405 40.5 24 58 11.83

254 25.4 9 40 8.64

459 45.9 34 56 6.75

11 1.1 0 3 0.87

0 0 0 0 0

295 29.5 18 47 8.72

748

36

Table 1. Basic characteristics of the sampled glaciers and their catchments. Data sources are cited in the description of study sites.

Glacier

Coordinates Region

Glacier

Glacier

Area

Sampling

Mean

Mean

Dominating

(WGS85)

type

thermal

[m2]

sites

summer

annual

rock types in the

altitude

temp.°C

temp. °C catchments

regime

m a.s.l. Adishi

43°00′N,

the

valley

temperate

9.5

2500-2600

10.6a

2.7a

Caucasus

shales, sandstones

42°59′E Morteratsch

46°24'34"N,

the Alps

valley

temperate

15.8

2300-2500

8.0b

-5.0b

graniotids, gabbros

9°55'54"E 77°1'27"N,

Hansbreen

Arctic

tidewater polythermal

56.3

201-247

3.8c

-4c

15°36'15"E (Svalbard)

gneisses, schists, amphibolites, phyllites, marbles, quartzites and conglomerates

Longyearbreen

Ebbabreen

78°10ʹ49ʺN, Arctic 15°30ʹ21ʺE (Svalbard) 78°43ʹ36ʺN, 16°49ʹ16ʺE

Arctic

valley

cold

2.5

352-378

6.2c

-4.4c

shales, siltstones and sandstones

valley

polythermal

20.4

149-176

6.4c

-5.3c

limestone, gypsum,

(Svalbard)

sandstones, dolomites, gneiss, schist, amphibolite

a – https://en.climate-data.org/location/358389/, b - Oerlemans et al., (2009), c – Przybylak et al., (2014)

Table 2. Types of mineral grains and microtextures on their surface as observed in the investigated study. Type of grain/microte xture

Grain/microtexture characteristics

Due processes

A

All grains are sharp with fresh surfaces and, without traces of rounding.

Grain cracking due to glacial action

Reference pictures

10 µm

B

Rounded or partially-rounded grains with smooth edges sometimes accompanied with holes on their surface.

Grain smoothing due to chemical weathering

10 µm

Type of grain/microte xture

Grain/microtexture characteristics

Due processes

C

Scaly-grained cover occurs entirely on a grain.

Silica precipitation on a grain surface.

Reference pictures

10 µm

D

Bulbous, bubble-like cover occurs entirely on a grain, so that no fresh surfaces are invisible.

Etching by alkaline solution in warm and dry conditions

20 µm

E

Cracked grain, where part of a grain is characterised by a fresh surface due to cracking, whereas remaining surface is rounded and originates from the B-, C- or D-type grains thus carrying their characteristics.

Grain cracking due to frost action, being however a postsedimentary process.

10 µm

Type of grain/microte xture

Grain/microtexture characteristics

Due processes

holes

More less rounded or shapeless depressions and cavitions

Chemical activity and dwelling in the environment promoting mineral matter dissolution

Reference pictures

10 µm

V-shaped percussion marks

More or less triangular-shape depressions/pits

Impact due to high energetic subaqueous environments and grain-to-grain colision

fresh surface

surface with no traces of precipitation, where all mechanical microtextures uncovered and well-expressed

Glacial crushing and fresh grain liberating from crystalline rocks

10 µm

Type of grain/microte xture

Grain/microtexture characteristics

Due processes

conchoidal features

shell-like fresh grain breakage

Impact or pressure on the grain surface

Reference pictures

20 µm

arcuate steps

Step-like curved features strongly related with conchoidal features

Impact or pressure while the conchoidal planes intersect

1 µm

bulbous cover

Tuberous-like precipitation, often with small holes covering and entire surface of grain

Etching by alkaline solution in warm and dry conditions

1 µm

1

Table 3. Basic statistics for grain type counts for each glacier. Number of grains provided next to a glacier

2

name is a total sum of the analyzed grains in all the samples from the particular glacier. In the following are

3

presented: the total number of the grains counted in particular class, average, minimum and maximum grain

4

number per sample and SE – standard deviation.

5 A

B

C

D

E

62 10.33 2 24 9.04

361 60.16 39 80 17.18

3 0.5 0 2 0.83

0 0 0 0 0

175 29.16 20 37 8.15

168 16.8 8 27 7.53

467 46.7 34 60 6.94

14 1.4 0 3 1.26

0 0 0 0 0

388 38.8 30 46 5.39

119 11.9 5 28 6.93

391 39.1 35 50 4.67

13 1.3 0 5 1.76

0 0 0 0 0

460 46 36 60 8.33

65 6.5 2 18 5.94

544 54.4 28 68 12.36

1 0.1 0 1 0.31

4 0.4 0 1 0.51

405 40.5 24 58 11.83

254 25.4 9 40 8.64

459 45.9 34 56 6.75

11 1.1 0 3 0.87

0 0 0 0 0

295 29.5 18 47 8.72

Adishi (601 grains) Number of counted grains Average per sample Min Max SE

Morteratsch (1037 grains) Number of counted grains Average per sample Min Max SE

Hansbreen (983 grains) Number of counted grains Average per sample Min Max SE Longyearbreen (1019 grains) Number of counted grains Average per sample Min Max SE Ebbabreen (1019 grains) Number of counted grains Average per sample Min Max SE

6 7

1

A

20 µm

D

B

C

10 µm

3 µm

E

20 µm

G

10 µm

J

2 µm

H

20 µm

F

10 µm

I

20 µm

K

L

10 µm

20 µm

10 µm

M

N

O

10 µm

10 µm

3 µm

A

100 µm

D

30 µm

B

C

30 µm

20 µm

E

F

30 µm

20 µm