Ice types from the Greenland ice 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 glacier 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 glaciers 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 water 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 icebergs: 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. G E U S - draft, to be finalized 3 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. G E U S - draft, to be finalized 4 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). G E U S - draft, to be finalized 5 Ice types from the Greenland ice sheet 5 2. Scientific background The processes leading from the precipitation of snow 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. G E U S - draft, to be finalized 6 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.