Hydrology and Hydrochemistry of a High Arctic Glacier: Longyearbreen, Svalbard
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Hydrology and hydrochemistry of a High Arctic glacier: Longyearbreen, Svalbard Master Thesis, 2006 (Revised Edition) Mette Riger-Kusk Department of Earth Sciences, University of Aarhus Department of Geology, University Centre in Svalbard (UNIS) Acknowledgments I am extremely grateful to have had the opportunity to study geology in a place like Svalbard. This would not have been possible without financial support from the University Centre in Svalbard (UNIS) and the University of Aarhus. Water level measurements were kindly provided by Ole Humlum, Adjunct Professor at UNIS, while meteorological data were provided by the Norwegian Meteorological Institute. I wish to thank all the people who helped me during fieldwork. Karoline Bælum for great teamwork and many enjoyable hours during GPR data acquisition, Henrik Rasmussen and Rico Behlke for scooter assistance, Jannick Schültz for his help with digging snow pits and Helena Grev and Ken Martinussen for their help with water sampling. I also wish to thank all the people who decided to join me on my daily walks to Longyearbreen, and who paid me social calls during periods of camping. It was much appreciated. A special thank you also goes to Marie Kirkegaard Sørensen and Anne Camilla Stavnsgaard Nielsen for always offering a place to sleep during my stays in Aarhus. Furthermore, I would like to thank the staff at UNIS and Aarhus University, especially Berit Jakobsen, librarian at UNIS, for always finding the references I needed and those I did not know I needed. Fred Skancke Hansen, head of logistics and safety at UNIS, for help arranging the fieldwork and for not naming my fieldwork the most stupid fieldwork he had ever heard about. Bente Rasmussen, laboratory technician at the University Aarhus, for guiding me through the laboratory work and Ruth Nielsen, technical assistant at the University of Aarhus, for her map design and technical support. I wish to thank my supervisor Professor Niels Tvis Knudsen, University of Aarhus and associated Professor Hanne Hvidtfeldt Christiansen, University Centre in Svalbard for advice and encouragement during the fieldwork and writing process. In addition, I wish to thank Ph.D. Jacob Yde, University of Aarhus for his help and support during the entire making of this thesis. Finally, I wish to express my gratitude to my family, especially my mum, dad and brother, who have been there all the way, as always. And I wish to thank Mark, who made my time on Svalbard so amazing and who continues to inspire me every day. Front page photograph: Aerial photograph of the study area. The characteristic Sarkofagen mountain separates the two glaciers Larsbreen (furthest to the left) and Longyearbreen. Longyearbreen acts as a major transport routes for snow scooter traffic in the winter and spring and a scooter track is visible on the glacier (photograph: Rico Behlke, April 2004). I Abstract A detailed study of the hydrology and hydrochemistry of Longyearbreen, a small (2.9 km2) High Arctic valley glacier on Svalbard, is presented in this master thesis. Sedimentary rocks with a high content of organic matter are present in the study area and plant fossils and coal are abundant on the debris-covered frontal part of Longyearbreen. Fieldwork was carried out in the spring and summer of 2004 and comprised a GPR (Ground Penetrating Radar) survey with 100 MHz antennae and daily sampling of glacial meltwater for future oxygen isotope, solute and suspended sediment analyses. Water samples were collected manually twice a day during most of the ablation period. The GPR survey showed no indication of zones with temperate ice in the glacier, which was found to have a maximum ice thickness of 110 m. Longyearbreen is therefore thought to be entirely cold-based. However, evidence of a former zone of temperate ice was found in the uppermost parts of the glacier, where unclear ice/bed interfaces most likely reflect a layer of debris-rich basal ice. The glacier has probably undergone a change in thermal regime from polythermal to the present cold-based conditions since the end of the Little Ice Age. Ice- marginal thrust faults, which include the glacier bed, suggest that the marginal areas of the glacier have potentially been cold-based during the entire existence of the glacier. Ice depth differences between two GPR surveys show that during the last 11 years, average thinning of the glacier ice at different altitudes has been comparable to mass balance observations from other ice masses on Svalbard. The study of suspended sediment concentrations in the glacier meltwater revealed that due to the cold-based conditions, most of the transported sediment was acquired from ice- marginal and proglacial areas. No exhaustion of sediment supply was observed during the ablation period. Discharge measurements showed an early melt period where variations in snowmelt were dampened because of storage of meltwater in the snowpack and within the glacial drainage system. High solute concentrations in the meltwater arose from the preferential leaching of ions from the melting snowpack and the enrichment of the meltwater as it overflowed refrozen solute-rich water in a subglacial meltwater channel. A rapid transition occurred on 30 June from a snowmelt-dominated runoff to a runoff highly influenced by icemelt. Rapid and large discharge fluctuations were observed, reflecting the release of water from storage and a better correlation with air temperature and precipitation events. River meltwater was highly influenced by rapidly draining solute poor and 18O-rich icemelt. During the late ablation period, air temperature and discharge correlated well. Diurnal variations in δ18O value and solute content were related to diurnal variations in discharge. The variations in δ18O and Cl- reflected an increased proportion of snowmelt during low discharge, while a general raise in solute concentration during low ice ablation signified a larger influence of solute-rich pore water from the thawing active layer. Generally, the solute concentrations were high compared to previous studies of glacial 2- - meltwater, with SO4 as the dominant ion (41%) and HCO3 constituting only 5.8% of total solute content. The chemical evolution of the meltwater was from hydrolysis of feldspar and carbonates driven almost entirely by sulphide oxidation. The results suggest that chemical weathering of suspended sediments was of minor importance and that the majority of solutes in the glacial meltwater originated from seepage of solute-rich pore water from the active layer into the ice-marginal drainage channels. II Contents 1. Introduction 1 1.1 Outline of thesis 1 2. Study area description 2 2.1 Svalbard 2 2.2 Climate on Svalbard 2 2.3 Recent climatic variations on Svalbard 5 2.4 Glaciers on Svalbard 5 2.5 Geological setting of study area 6 2.6 Longyearbreen 7 3. Theoretical background 12 3.1 Glacial hydrology 12 3.1.1 Temperate glaciers 12 3.1.2 Polythermal glaciers 14 3.1.3 Cold glaciers 15 3.2 Ground Penetrating Radar (GPR) 17 3.2.1 GPR theory 17 3.2.2 GPR in glacial settings 18 3.3 Discharge variations 19 3.3.1 Seasonal evolution of the glacial drainage system 19 3.3.2 Glacial discharge studies on Svalbard 21 3.4 Suspended sediment transport 22 3.4.1 Sediment transport as an indicator of thermal regime 23 3.4.2 Suspended sediment studies on Svalbard 23 3.5 Glacier Hydrochemistry 24 3.5.1 Solute provenances 24 3.5.2 Drainage and acquisition of solutes by glacial meltwater 26 3.5.3 Seasonal changes in solute concentrations of bulk meltwater 29 3.5.4 Hydrochemistry studies of glacial meltwater 29 3.6 Oxygen isotope hydrology 30 3.6.1 Oxygen isotopes in precipitations 31 3.6.2 Oxygen isotopes in glacial meltwater 31 3.6.3 Oxygen isotope studies on Svalbard 33 4. Data collection and methods 34 4.1 GPR 34 4.1.1 Data processing 36 4.1.2 Source of error 41 4.2 Exploration of cave 41 4.3 Meteorological parameters 42 4.3.1 Source of error 42 4.4 Water level measurements 42 4.4.1 Source of error 43 4.5 Suspended sediment concentrations and meltwater chemistry 44 4.5.1 Source of error 47 5. Results 48 5.1 GPR 48 5.2 Weather data 54 III 5.3 Water level and discharge 56 5.4 Suspended sediment transport 62 5.5 Ions 68 5.6 Isotopes 84 6. Discussion 92 6.1 GPR 92 6.1.1 Uncertainties concerning the lengths of the survey lines 92 6.1.2 The thermal regime of Longyearbreen 92 6.1.3 Evidence of drainage structures 94 6.1.4 Comparison with previous GPR survey on Longyearbreen 95 6.2 Discharge 96 6.2.1 Variations in discharge during the ablation period 96 6.2.2 Annual variations in water flux 97 6.3 Suspended sediment transport 99 6.3.1 Sediment sources within the catchment of Longyearbreen 99 6.3.2 Comparison with previous studies of SSC in glacial meltwater 100 6.4 Ionic and isotopic composition of river water 102 6.4.1 Composition of the snowpack compared to previous studies 102 6.4.2 Ionic and isotopic composition of freshly precipitated snow and rain 103 6.4.3 Uncertainties concerning the applied methodology 104 6.4.4 Ionic and isotopic composition of meltwater during the ablation period 105 6.4.5 Solute provenances 109 6.4.6 Comparison with previous studies of meltwater composition 111 7. Conclusion 115 8. References 117 A APPENDIX 124 A.1 Map of Svalbard with location of glaciers 124 A.2 CMP surveys 125 A.3 GPR profiles 127 A.4 Cloud cover and air humidity 134 A.5 Photographs reporting the onset of ice ablation 135 A.6 Notes from fieldwork 136 A.7 SSC in western and eastern meltwater stream 140 A.8 Calculation of total sediment flux 141 A.9 Correlation coefficients 142 A.10 Solute content in western and eastern meltwater stream 144 A.11 Solute acquisition in the proglacial areas 145 A.12 Conductivity versus total solute content 146 A.13 GPR survey, 1993 147 A.14 Monthly air temperature and precipitation levels, 1995-1997 and 2004 149 A.15 Snow samples from Tellbreen 150 A.16 Comparison of solute in river meltwater in 1993 and 2004 151 A.17 Solute flux for Longyearbreen 153 IV 1.