Ice types from the Greenland sheet Contents

EXECUTIVE SUMMARY ...... 3

1. INTRODUCTION ...... 4

2. SCIENTIFIC BACKGROUND ...... 6 2 .1 Supraglacial, englacial and subglacial meltwater drainage ...... 7

3. ICE TYPES ...... 9 3 .1 The ice type ...... 10 3 .2 The basal ice type ...... 12 3 .3 Bubble-free “blue ice” type ...... 12

4. LOCAL USE OF ICE MELTWATER ...... 14

5. GUIDE TO ICE TYPES IDENTIFICATION ...... 15 5 .1 Glacier ice type ...... 15 5 .2 Basal ice type ...... 18 5 .3 Clotted ice type ...... 20 5 .4 Bubble-free “blue ice” type ...... 21

REFERENCES ...... 24 Executive Summary

This report provides information on the characteristics and appearance of the different ice types occurring in the calved ice from outlet of the Greenland ice sheet. The focus is on the implications in terms of age, origin and purity of the ice, and on the related issues of quality consistency, sustainability of the production, and availability of the ice. Building on results from previous reports and investigations, and on the available scientific literature, useful indications and practical recommedations in the selection of the type of ice will be discussed for all of the above key characteristics.

Ice ”types” are technically described in the scientific literature using the term “ice facies”, which refer to the appearance of the ice in such terms as layering, crystal size, shape and orientation, bubbles content, and colour. The differences between the glacier ice type composing the bulk of the ice sheet and other ice types resulting from localized refreezing connected with supraglacial, englacial and subglacial hydrology are discussed, since ice produced by these processes is sig- nificantly different in the key characteristics of relevance to the production of bottled products, primarily as an ingredient in beverages, admixture in cosmetics, etc.

The first section provides an introduction to the subject stating the aims and scope of the pres- ent report, and references relevant previous work carried out by GEUS.

The second section of the report provides required scientific and technical background in a con- cise form, at the same time shielding the reader from unnecessary terminological complexities existing in the scientific literature, e.g. in connection with the basal ice layer. The main prelimi- nary conclusion from this section is that the calved glacier ice types offer the most consistent and abundant source material in terms of purity and protection from natural or anthropic chemi- cal, biological and physical contributions. Reliable estimation of the age of the ice appears to be important both from water quality and from marketing considerations (NIRAS Greenland a/s, 2008), and the glacier ice type is the material of choice, when ice that is thousands of years old is desired. The third section briefly gives some information on relevant local uses of water obtained by melting the ice.

The fourth section provides an illustrated guide to the identification of the most significant ice types to be found in : glacier ice, bubble-free ice (or so-called “blue ice”), basal ice and clotted ice, a subtype of basal ice deserving particular mention. Several photographs and sche- matic text are intended to enable personnel in the field to confidently identify the different types of ice encountered.

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Ice types from the Greenland ice sheet 3 1. Introduction

This report was produced after the Greenlandic Ministry of Industry, Labour and Mineral Re- courses expressed interest in a document discussing the various types of ice that may be found in the icebergs calved from tidewater glacier outlets of the ice sheet, with particular focus on their suitability for the production of high-quality water for the production of bottled water, beverages and cosmetics.

During the last ten years GEUS has produced several reports (Fig. 1) in relation to a potential export of ice as a high-quality product on the world market. The results have been presented in a umber of reports: Bøggild, Weidick & Olesen (2000), Mayer et al. (2003), Ahlstrøhm et al. (2006), Alstrøm et al. (2007) and Binderup et al. (2007).

This report aims at providing an overview of the characteristics and appearance of the different ice types occurring in the calved ice from outlet glaciers of the Greenland ice sheet, with a spe- cial emphasis on the glaciological processes responsible for their origin and their implications for the procurement of ice suitable for production of high-quality water.

The main concept underlying the entire document is that process-related considerations provide a convenient scientific frame of reference for deriving practical recommendations of general validity within the context of the present lack of sufficient empirical experience from similar production and commercialization projects.

In particular, we will focus on the processes responsible for the formation of the ice, and on their characteristic features preserved in the appearance of the ice.

It must be stressed that the scope of this report does not allow for a summary of all the findings from the previous reports produced by GEUS on this subject and cited in this text, and it cer- tainly does not make it possible to provide complete coverage of today's knowledge of the to- pic based on current scientific literature. Interested readers are therefore encouraged to see the cited literature for a more complete overview.

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Ice types from the Greenland ice sheet 4

Fig. 1 – Division of Greenland into major glacier hydrology districts (after Weidick et al., 1992). The areas investigated by previous GEUS reports are shown in green (Bøggild, Weidick & Ole- sen, 2000), red (Mayer et al., 2003), blue (Binderup et al., 2007) and magenta (Ahlstrøhm et al., 2006; Alstrøm et al., 2007).

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Ice types from the Greenland ice sheet 5 2. Scientific background

The processes leading from the of in the accumulation area of the ice sheet to its transformation into ice, and the subsequent transport along a flow line have been summarized in the previous reports mentioned above in section 1. Several interrelated factors contribute to the ultimate value of ice from a natural ice mass as a suitable source material of high-quality meltwater, including: ice purity, age, origin and availability in the required quantity, the protec- tion of the ice from possible recent and contemporary natural and anthropic pollutants, the con- sistency of ice properties with time (over the projected life span of the production), and with space (over the area where the ‘fishing’ of icebergs is planned).

Snow accumulating in the interior of the ice sheet and turning into ice is transported by glacier flow toward the margin of the ice sheet (Fig. 2). In the context of searching for pure ice suitable for meltwater production and export, the fundamental idea is that glacier ice derived from snow fallen before the appearance of anthropic pollution will only contain a very small natural content of solutes, ash, soot and terrestrial dust particulate, plus an exceedingly small amount of extra- terrestrial meteoric particles. Field investigations and modelling work (Mayer et al., 2003) have shown that ice with an estimated age of about 5000 years can be procured from several glaciers.

Fig. 2 – Possible paths (in an idealized east-west cross section of the Greenland Ice Sheet) fol- lowed by a unit volume of ice formed from snow accumulated in the interior of the ice sheet.

Since ice as a material is impermeable and ice sheet dynamics in the investigated sectors of the ice sheet can be modelled in sufficient detail to meet the requirements of the intended purpose, it is possible to estimate the purity and age of the ice that reaches the margin of the ice sheet. However, a degree of complexity is introduced by the hydrological system of the ice sheet, com- posed of interconnected supraglacial, englacial and subglacial drainage networks. The implica- tions of relevance to the present report are outlined in the following section 2.1.Ice from the ice sheet can be obtained from icebergs naturally produced by calving at the terminus of tidewater outlet glaciers. No penetration of chloride from sea water into ice growlers was found during a sampling programme in 2008 (Mai 2008a). Such ‘fishing’ of suitable icebergs is the method of choice for procuring ice (Mai, 2008). ICompanies using this approach will encounter ice formed through a number of processes and under diverse environmental conditions.

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Ice types from the Greenland ice sheet 6

In sections 2.2 below, most of the complexities and terminological inconsistencies existing in the scientific literature have been simplified and summarized as much as possible. This provides a concise and consistent treatment of how to recognize ice types in the field and understand their significance.

2.1 Supraglacial, englacial and subglacial meltwater drainage

As pointed out above, the bulk of the ice mass is impermeable and this prevents meltwater and present-day precipitation from seeping through it and possibly contaminating the ice.

In the ablation area of the ice sheet, most of the meltwater produced by surface ablation is routed through the supraglacial network of meltwater channels, and either enters the englacial drainage system through moulins and crevasses or feeds supraglacial lakes (Fig. 3).

These lakes can ultimately drain through moulins or crevasses (e.g., Das et al. 2008).

While the details of the englacial and subglacial drainage systems are not known and various hypotheses exist, in general the conduits can be expected to follow the steepest hydraulic gradi- ent, which is normal to the local equipotential lines (dashed lines in Fig. 4).

3 km

lake

moulin

Fig. 3 - Map of surface drainage near the margin of the Greenland ice sheet near Ilulissat. The dots represent moulins and the black patches represent supraglacial lakes (after Thomson et al., 1988)

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Ice types from the Greenland ice sheet 7 The englacial channels are connected to the subglacial drainage network, and convincing evidence has accumulated showing that these channels are directly connected with the subglacial drainage so that increased meltwater availability at the surface quickly prompts an acceleration of ice sheet flow (Zwally et al., 2002). The englacial conduit therefore provide pathways for chan- nelized water drainage through the ice mass, while the bulk of the ice as a material is effectively impermeable.

The formation and closure of moulins, crevasses and englacial drainage channels is caused by the interplay of several physical processes, which are controlled by water availability, by the me- chanical stresses within the ice, and by the rheology of the ice (i.e., the quantitative relation link- ing stress and deformation). It is important to note that the cross section of any englacial con- duits adapts to the amount of water flowing through it. When water flow increases, energy is made available to further melt the ice walls and enlarge the conduit; on the other hand, when the conduit drains or the hydraulic pressure decreases, the ice walls will shrink and ultimately close due to ice deformation. The higher density of liquid water in comparison to ice can enhance the propagation of crevasses, which form where the tensile strength of the ice is exceeded, if the crevasses become filled with meltwater. Close to the margin of the ice sheet, crevasses form in response to the topography underlying the ice, or due to the local pattern of ice flow. Crevasses may close again at a later time as a result of the stress conditions becoming compressive, or refreezing. In such cases, the newly formed ice can easily be distinguished from the surrounding glacier ice due to its peculiar appearance (bubble-free ice).

Fig. 4 – Equipotential surfaces (dashed lines) and drainage paths across an ice mass (after- Knight, 1999)

A treatment of ice sheet hydrology beyond these few notes would exceed the limits and scope of this report, but the points mentioned above are important in our context because fast, deep movements of surface meltwater have the potential to adversely impact the purity of the water produced by melting the ice, if care is not observed in excluding nonglacier ice material.

The following section of this report will focus on the idea of classifying the various types of ice according to their appearance by introducing the concept of “ice types”.

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Ice types from the Greenland ice sheet 8 3. Ice types

Classifying natural materials based on their appearance is a convenient method because it is often possible to interpret a set of characteristics as typical of a given origin or process. 3.This Ice approach types is widely used in and geology in connection with the technical term “facies”, where a facies is described as ‘‘a rock or sediment unit that exhibits lithological, struc- Classifying natural materials based on their appearance is a convenient method because it is tural or faunal characteristics which enable it to be distinguished from other rock or sediment often possible to interpret a set of characteristics as typical of a given origin or process. units. Although the term refers to all characteristics of a particular material, in practice the re- Thiscognition approach of facies is widely is based used on in the glaciology visible composition and geology and in connectionstructure of with materials the technical that are term de- “facies”,tectable wherein the field’’a facies (Sleewaegen is described et al.,as 2003;‘‘a rock p. or 257). sediment unit that exhibits lithological, struc- tural or faunal characteristics which enable it to be distinguished from other rock or sediment In the following we will describe ice types based on their visual appearance, and link them to units. Although the term refers to all characteristics of a particular material, in practice the re- their origins. Unfortunately, not all ice types can be easily identified or unequivocally inter- cognition of facies is based on the visible composition and structure of materials that are de- preted, but the most important ones are described in the following sections. The occurrence of tectable in the field’’ (Sleewaegen et al., 2003; p. 257). the most important ice types is depicted in Fig. 5, where an idealized cross section along a flow Inline the is schematized. following we will describe ice types based on their visual appearance, and link them to their origins. Unfortunately, not all ice types can be easily identified or unequivocally inter- preted, but the most important ones are described in the following sections. The occurrence of the most important ice types is depicted in Fig. 5, where an idealized cross section along a flow line is schematized. GREENLAND ICE SHEET most mountain glaciers

equilibrium line accumulationaccumulation area area ablationablation area area dry snow zonepercolationpercolation zone superimposedsuperimposed ice wet snow zone zone zone wet snow zone ice zonezone

maximum height of surface at the end of last winter

surface in summer

nono runoff runoff runoffrunoff possible possible runoffrunoff occurs occurs REGELATION GLACIER ICE ICE

DEBRIS CLOTTED ICE ICE

BEDROCK Fig. 5 – Schematic representation of the relative position of the most important ice types with depth from the surface of the ice sheet and with distance from the margin (from Menzies, 2002). It must be noted that the diagram is not to scale, and that in reality the glacier ice type is by far the most abundant. Fig. 5 – Schematic representation of the relative position of the most important ice types with depth from the surface of the ice sheet and with distance from the margin (from Menzies, 2002). It must be noted that the diagram is not to scale, and that in reality the glacier ice type is by far the most abundant.

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G E U S - draft, to be finalized 9 3.1 The glacier ice type

The bulk of the ice sheet is composed of ice formed by compaction and recrystallization of snow that has accumulated at the surface. The colour of this bubbly ice typically ranges between white and light blue, depending upon illumination and the thickness of the observed object (Fig. 6 and 8 to 12). The air bubbles are widespread and represent interstitial air trapped during the firnification process (transformation of snow into ice). Its chemical content is tightly linked to the atmospheric composition at the time of the original snow accumulation, and in the case of the ice sheet, the particulate content is very low, especially for ice formed during the Holocene (the post-glacial period, beginning about ten thousand years ago.

The scientific literature dealing with the Greenland ice sheet abounds in detailed investigations of glacier ice properties in terms of ice composition, ice texture (crystal size and shape, bubble content, seasonal layering and so on) and ice fabric (the orientation of crystallographic axes and planes). Most of this information derives from studies and provides a fairly detailed knowledge of the ice sheet stratigraphy at the drilling sites in terms of climate history and ice deformation. Of relevance to the present discussion, especially with regard to the appearance of glacier ice, is the evolution of crystal size with depth, which is known to steadily increase in the upper few hundred metres of the ice sheet from about one to a few millimetres and then to re- main fairly constant or even decrease due to deformation and recrystallization as the ice de- forms and flows (see Thorsteinsson, 1996 for a detailed treatment and further references). It must be noted that deep ice cores are typically drilled in the dry snow zone (Fig. 5) while, gener- ally speaking, the ice that is discharged at the margin may also have formed below the dry snow zone. In such a case some more or less extensive melting would have occurred during the summer following its deposition as snow. The refreezing within the snowpack of the resulting meltwater would have produced a texture including a fraction of larger crystals, but again deformation and recrystallization processes may later have affected the crystal size. In the field, it is often pos- sible to recognize the crystal boundaries because they tend to melt or sublimate and may there- fore appear as tiny grooves upon careful inspection.

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Fig. 6 – Glacier ice floating in the area of Eqi Sermia, north of Ilulissat (photo: Dorthe Pedersen, GEUS)

Another important piece of information obtained from deep ice cores concerns the fate of the air bubbles trapped in the glacier ice. As a given volume of ice becomes buried at increasing depths and pressures within the ice sheet, bubbles shrink and their internal pressure increases. When pressure increases even further, the gaseous molecules contained in the bubbles may enter the crystal lattice of a new solid phase and convert into clathrate hydrates (see e.g. Kipfstuhl et al., 2001). When the ice is brought back to atmospheric pressure at the margin of the ice sheet (or by drilling an ice core), the high pressure bubbles can expand somewhat due to ice deformability, and the clathrate hydrates will also tend to revert to bubbles after some time, as has been ob- served in deep ice cores (Svensson et al., 2005). It can therefore be expected that air bubbles have re-appeared by the time this ice is collected from calved icebergs.

The existence of high-pressure bubbles in glacier ice from the ice sheet is well known from the peculiar “popping” sound it produces when it melts, which resembles miniature “explosions” as the air escapes (Svensson et al., 2005).

Since glacier ice can derive from old (e.g., pre-industrial era) snow, it provides the best assuran- ces in terms of purity and protection from contaminants, and is best suited for determining age and offering consistent properties.

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Ice types from the Greenland ice sheet 11 3.2 The basal ice type

“Basal ice may be defined as ice that has acquired a distinctive suite of physical and/or chemical characteristics as a result of processes operating at or near to the bed of an ice mass” (Hubbard, Cook and Coulsen, in press). Typically, ice from the basal ice layer is formed either by the freez- ing of water at the bed of a glacier or by transformation (recrystallization) of glacier ice by thermal, strain and hydraulic conditions close to the bed. This results in a chemical composition and physical structure that differs from that of glacier ice above. Over the past 30 years numer- ous basal ice types have been identified, named and classified. However, the resulting descrip- tions and names are inconsistent and no single scheme encompasses all of the different ice types that exist at different ice masses (Hubbard, Cook and Coulsen, in press).

In spite of it making up only a tiny fraction of the bulk volume of the ice sheet, the basal ice type is nonetheless of critical relevance in our context for three different reasons:

1. It is known to be affected by the chemical composition of the geological materials at the glacier bed, and by subglacial hydrology, voiding any guarantee of determining the age of the ice and of isolation from contaminants

2. It can be bubble-free, and the cleanest subtypes almost devoid of solid particulate may at times be mistaken for the so-called “blue ice” (discussed in the following section)

3. Some icebergs “fished” at the calving front of tidewater glacier will also contain ice from the basal ice layer (Fig. 13 to 16)

Another important subtype belonging to the basal ice type is the clotted type (Fig. 16), which is typically several metres thick, but can less commonly reach thicknesses of tens of metres. It is characterized by clear ice with dispersed lenticular aggregates of mud-sized debris (clots) at concentrations of 0.1 g/l (less common) to 80 g/l (more common), occasionally defining very crude layers. The type is essentially clear with crystals of 2–5 cm. It typically contains no in- corporated bubbles but the crystal boundaries may be sometimes marked by pockets of gas (Hubbard, Cook and Coulsen, in press; Sugden et al., 1987).

It is important to note that the basal ice type can be more appropriately viewed as an assem- blage, or sequence, of basal ice subtypes with a decreasing amount of subglacially-derived con- tent as we proceed from the ice bed to the overlying “clean” glacier ice. This further complicates the task of positively identifying the various subtypes.

We will limit our discussion here of the implications by noting that ice from the basal ice layer should be regarded as unsuitable for the production of pure meltwater.

3.3 Bubble-free “blue ice” type

Given the widespread use of the term “blue ice” it is important first to clarify what the meaning of this term may be, if any. As a matter of fact, ice of sufficient thickness is always blue, in the very

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Ice types from the Greenland ice sheet 12 same way as liquid water in the sea also appears bluish. Bubbly ice tends to appear lighter or even whitish because bubbles scatter the light at all wavelengths before it has travelled deep enough through the ice for the blue colour to become noticeable. This is why the bubble-rich glacier ice generally appears “less blue” than bubble-free ice, all the rest being the same (i.e. am- bient light, size of the ice mass, viewing direction and so on). It is clear that the colour is a rather poor parameter to assess the origin of a given mass of ice. It is therefore no surprise that the term “blue ice” does not exist in the scientific literature. It must be stressed that the term “blue ice areas” is used in Antarctic glaciology (see e.g. Bintania 1999) and “blue ice” is occasionally used in science, but they have no relation to anything of interest within our present dis- cussion. The only appropriate existing term is “blue bands” (Fig. 7 and 17 to 20), and this refers to veins that range in thickness from a few centimetres to up to a metre, and can be observed on the ice sheet, in icebergs and elsewhere (e.g. Reeh, Oerter & Thomsen, 2002; Diemand, 2001; Stenborg, 1968).

Fig. 7 – glacier ice at Eqi Sermia, north of Ilulissat: notice the blue bands pointed to by the arrow markers (photo: Dorthe Pedersen, GEUS)

Ice devoid of air bubbles is most commonly formed through refreezing of water. Blue bands, characterized by bubble-free and coarsely crystallized ice with a significantly different compo- sition from the surrounding glacier ice have commonly been regarded as resulting from the freez- ing of water-filled crevasses.

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Ice types from the Greenland ice sheet 13 A variety of bubble-free ice has also been found to occur within the basal ice layer, expecially higher up in the types sequences of the basal ice layer where the reduced particulate content could make it resemble “clean” ice (see the previous section on basal ice).

Since it is normally impossible to reliably assess the age of the “blue ice” type, and it may contain an unknown fraction of recent surface , it is considered unsuitable for the production of high-quality water.

4. Local use of ice meltwater

It has been found that ice from calved icebergs is locally procured and used, specifically for small-scale beer brewing. Preliminary accounts point to the possibility of recognizing the best “varieties” of ice allowing brewing beer with success, and also to rate the procured ice from the best to the poorest quality.

Given the sensitivity of the brewing process to the quality of the water and to the presence of contaminants, and the ensuing economic value locally accorded to this “high-quality” ice, this information has been deemed relevant for the present report. Evaluating this potentially useful existing local knowledge while at the same time warning against possible “myths” unsupported by the current scientific understanding of the glaciological processes involved would be particu- larly valuable.

It should be noted that these local experiences pertain to the procurement of ice from floating icebergs calved from outlet glaciers, and concur therefore with what has been found to be the preferred source of ice when consideration is given to the sustainability and impact of the pro- duction, namely the fishing of suitable icebergs (Mai, 2008). Among other considerations, it is reported that fishing of suitable icebergs can only be carried out far from any settlement since even the tiniest trace of sea water pollution from fuel and other chemicals would spoil the ice for the intended use. However, since this very small-scale procurement of suitable ice is only carried out sporadically and by a very restricted number of people, properly documenting it requires a significant amount of time and no detailed information is yet available that could be included in this report. Should such information become available, several points will need to be discussed:

• Is there a scientifically viable explanation for the claimed quality characteristics of the various ice types?

• Are the criteria used for rating the ice “quality” clear, objective, sound and reproducible?

• What is the evidence in support or against the use of bubbly vs. bubble-free (or so- called “blue ice”)?

• Is there any observation of solid particulate, even in minute amounts, at the bottom of the vessels where the “high-quality” ice is melted?

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Ice types from the Greenland ice sheet 14 5. Guide to ice types identification

In this section we provide a schematic description aimed at the identification of the ice types which may occur within the icebergs calved from outlet glaciers of the Greenland ice sheet. It must be noted that in this section, in line with the stated purpose of being a practical aid in the field, the clotted ice subtype will be illustrated separately from the basal ice type even though it properly belongs to it. This is to focus the reader on a possibly easily mistaken type of ice. A number of pictures are also provided for visual reference.

As is unavoidable with any schematic description of natural materials, some simplifications have been necessary and the properties listed below reflect those typical for each specific ice type. This is particularly true for parameters such as the crystal size. The reader is referred to the relevant sections 3.1 – 3.3 for more detailed information and scientific background. Fur- thermore, the observation conditions may strongly affect other properties such as the colour.

5.1 Glacier ice type

Genesis: compaction and recrystallization of snow at high elevations on the ice sheet

Age: variable but on the order of thousands of years and assessable through modelling

Potential for contamination: low

Appearance (bulk): white or light blue masses of ice of all sizes up to the largest icebergs.

Appearance (close-up): clear with abundant bubbles and almost no solid particulate

Bubble content: high, with abundant small bubbles, sometimes containing pressurised gases producing typical “microexplosions” when the ice is melted

Particulate content: extremely low and very fine grained

Crystal size: typically several millimetres, occasionally larger

Abundance: very high

Association with other types: glacier ice can be associated to any other type with:

• Sharp contacts with bubble-free “blue ice”

• Sharp or transitional contacts with basal ice

• Transitional contacts with clotted ice

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Fig. 8 – Glacier ice. from the area of Eqi Sermia, north of Ilulissat (photo: Dorthe Pedersen, GEUS).

Fig. 9 – Glacier ice. from the Narsarsuaq area. Note the light blue colour being more intense in the shadowed area to the right, where the light emerges from the ice after having travelled through a significant thickness (photo: Dorthe Pedersen, GEUS).

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Fig. 10 – Glacier ice. from the Narsarsuaq area (photo: Dorthe Pedersen, GEUS).

Fig. 11 – Glacier ice. from the area of Eqi Sermia, north of Ilulissat (photo: Dorthe Pedersen, GEUS).

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Fig. 12 - Glacier ice. from Disko Bay. Notice that a few centimetre-thick veins of clear ice can be seen in transparency (photo: Dorthe Pedersen, GEUS).

5.2 Basal ice type

Genesis: extensive deformation close to the glacier bed, including adfreezing processes

Age: variable and impossible to estimate

Potential for contamination: high

Appearance (bulk): very variable, generally containing some dirt.

Appearance (close-up): very variable, generally containing some dirt.

Bubbles content: generally low or bubble-free

Particulate content: from low to extremely high, all grain sizes are possible

Crystal size: very variable, up to several centimetres.

Abundance: low or medium

Association with other types: glacier ice can be associated to any other type with:

• Sharp or transitional contacts with bubbly glacier ice

• Sharp contacts with “blue ice”

• Transitional contacts with clotted ice

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Fig. 13 – Debris-laden basal ice floating in the area of Eqi Sermia, north of Ilulissat. Since stones and finer particles tend to be more concentrated on the melting surfaces, the may appear darker than the ice it contains really is (photo: Dorthe Pedersen, GEUS)

Fig. 14 – Dirty basal ice floating in the area of Eqi Sermia, north of Ilulissat (photo: Dorthe Pedersen, GEUS)

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Fig. 15 – Basal ice in glaciotectonic contact with glacier ice in an iceberg floating in the area of Eqi Sermia, north of Ilulissat. Note the high content of debris and the brecciated texture of the basal ice. Note also the fracture planes affecting the glacier ice close to the contact, and their dark injected fillings (photo: Dorthe Pedersen, GEUS)

5.3 Clotted ice type

Genesis: basal entrainment by regelation-related processes in the interior of the ice sheet

Age: variable and impossible to estimate

Potential for contamination: high

Appearance (bulk): light blue-grey or light amber masses of ice

Appearance (close-in): the distinctive feature is the content of small lenses of very fine grained solid particulate

Bubbles content: high, with abundant small bubbles, sometimes containing pressurised gases producing typical “microexplosions” when the ice melts

Particulate content: extremely low and very fine grained

Crystal size: 2 to 5 centimetres

Abundance: low

Association with other types: glacier ice can be associated to any other type with:

• Sharp or transitional contacts with bubbly glacier ice

• Transitional contacts with basal ice

• Sharp contacts with “blue ice”

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Fig. 16 – A small block of clotted ice floating in the area of Eqi Sermia, north of Ilulissat. Note the small lenticular aggregates in an otherwise clear ice matrix (photo: Dorthe Pedersen, GEUS)

5.4 Bubble-free “Blue ice” type

Genesis: refreezing of water filling crevasses or other voids

Age: recent but extremely variable and impossible to estimate

Potential for contamination: very high

Appearance (bulk): blue bands within larger glacier ice icebergs, or small blue icebergs

Appearance (close-in): clear ice crystals without bubbles or with very few bubbles, little or no particulate

Bubbles content: bubble-free, or occasionally with a few tubular bubbles or bubble trails

Particulate content: little or no particulate content

Crystal size: typically several centimetres to tens of centimetres

Abundance: generally low, locally may be more abundant

Association with other types: glacier ice can be associated to any other type with:

• Sharp contacts with bubbly glacier ice

• Sharp contacts with basal ice

• Sharp contacts with clotted ice

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Fig. 17 – Bubble-free “blue ice” (lower right part of the iceberg) in sharp contrast with whitish glacier ice from the Nuuk Fiord (photo: Dorthe Pedersen, GEUS).

Fig. 18 - Bubble-free “blue ice” from Narsarsuaq area (photo: Dorthe Pedersen, GEUS).

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Fig. 19 – Glacier ice containing several blue bands in the area of Eqi Sermia, north of Ilulissat (photo: Dorthe Pedersen, GEUS).

Fig. 20 - Glacier ice containing deformed blue bands in Disko Bay (photo: Dorthe Pedersen, GEUS).

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Ice types from the Greenland ice sheet 23 References

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