Geir Vatne

Contemporary rates of chemical denudation and atmospheric CO2 sequestration in glacier basins: an Arctic perspective.

This paper presents new estimates of solute fluxes from five high Arctic glacier basins in Svalbard. These estimates are combined with data from two other glacier basins to assess the effectiveness of chemical denudation on Svalbard and to estimate rates of temporary (or transient) CO2 drawdown. We use a solute provenance model to partition solutes into marine, aerosol, atmospheric and crustal components and to estimate their annual fluxes. Crustally derived solute fluxes are equivalent to a mean chemical denudation rate of 350 Σmeq+ m−2 a−1 for Svalbard (range: 160–560 Σmeq+ m−2 a−1), which lies within the global range of 94–4200 Σmeq+ m−2 a−1 for 21 glacier basins in the northern hemisphere, and is close to the continental average of 390 Σmeq+ m−2 a−1. Specific annual discharge is the most significant control upon chemical denudation in the glacierized basins, and basin lithology is an important secondary control, with carbonate-rich and basaltic lithologies currently showing the greatest chemical denudation rates. Estimates of transient CO2 drawdown are also directly associated with specific annual discharge and rock type. On Svalbard transient CO2 drawdown lies in the range 110–3000 kg C km−2 a−1, whilst the range is 110–13000 kg C km−2 a−1 for the northern hemisphere glacial data set. Transient CO2 drawdown is therefore usually low in the Svalbard basins unless carbonate or basalt rocks are abundant. The analysis shows that a large area of uncertainty in the transient CO2 drawdown estimates exists due to the non-stoichiometric release of solute during silicate hydrolysis. Silicate hydrolysis is particularly non-stoichiometric in basins where the extent of glacierization is high, which is most probably an artefact of high flushing rates through ice-marginal and subglacial environments where K-feldspars are undergoing mechanical comminution. Copyright

Glacier characteristics and sediment transfer system of Longyearbreen and Larsbreen, western Spitsbergen

Two small high-Arctic glaciers (Longyearbreen and Larsbreen) on Svalbard (78°N 15°E) were studied with respect to glaciological and hydrological characteristics. Fieldwork during the melting season of 1993 and 1994 was coupled with digital map analysis based on high-resolution digital elevation models (DEM) to reveal the dynamics and temperature regime of small glaciers in a high-Arctic environment, and its relationship to the material transport and sedimentation of these glaciers. The study showed Longyearbreen and Larsbreen to be low activity glaciers, cold-based with temperate patches, and thus having a low potential of basal erosion. The transport of ions and suspended solids in the glacial meltwater implies storage of material in and around the glacier which comes into contact with the meltwater. The study suggests that small Arctic glaciers couple the slope system with the fluvial system and therefore build a highly effective denudation system. Small polythermal glaciers are therefore important in understanding Pleistocene and Holocene landform development in cold regions.

Geometry of englacial water conduits, Austre Brøggerbreen, Svalbard

The internal geometry of three englacial conduits located on Austre Brøggerbreen, Svalbard, was investigated by tracer experiments and by direct exploration. The tracer tests produced short-lived and highly peaked tracer return curves with high through-flow velocities. The direct inspections revealed the entrances to be of two types. Type I consisted of a moulin with an initial 39 m vertical shaft drained by a semicircular and near-horizontal englacial channel trending diagonally across the direction of ice flow, parallel to tectonic structures observed on the ice surface. The type II entrances sloped gently into the ice in the direction of the ice flow, and became englacial by gradual down-cutting of supraglacial meltwater channels into the glacier surface. No traces of tectonic structures were observed in the ice surface that could have initiated the type II entrances. Englacial conduits with gentle slopes were meandering. With increasing slope, a winding waterfall?plunge-pool geometry was developed, the channels being high (>3 m) compared to their width (30?150 cm).

Integrated vulnerability mapping for wards in Mid-Norway

The future climate of Norway is expected to become “warmer, wetter, and wilder”, and it is anticipated that this will cause more extreme weather events. Local authorities therefore need to increase their ability to assess weather-related hazards such as flooding and landslide, as well as peoples’ capacities to cope with such events. Any evaluation of future vulnerability towards natural hazards should use todays situation as the baseline. In this article, we present this baseline: a vulnerability assessment for the present. Our vulnerability assessment incorporates both physical and social dimensions of vulnerability and screens Mid-Norway at the lowest administrative level. The results reveal a considerable geographic variation regarding vulnerability. The assessment identifies the most vulnerable localities within a municipality and could thus be relevant for the local authorities. By incorporating knowledge held by the local authorities, the vulnerability mapping could be made even more relevant.

Ice-marginal sediment delivery to the surface of a high-arctic glacier: Austre Broggerbreen, Svalbard

Abstract. Enhanced delivery of water‐saturated, ice‐marginal sediments to the glacier surface is a response to glacier thinning that has the potential to increase both levels of sediment transfer through the glacier hydrological system and total basin sediment yields. Preliminary observations made during summer 2007 at Austre Brøggerbreen, Svalbard, confirm that ice‐marginal debris flows in the upper reaches of the glacier are actively delivering sediments to the glacier surface, which may then be flushed into the glaciers hydrological system. During a four‐day observation period, several stochastic pulses in water turbidity were observed at a single portal where solely supra‐ and englacial drainage emerge at the glacier margin. The erratic suspended sediment fluxes were hypothesized to originate from ice‐marginal sources. Quantitative analysis of continuous turbidity and discharge data confirm that discharge is not driving these turbidity pulses and, combined with observational data, that the most likely origin is the delivery of water‐saturated sediments to the glacier surface from ice‐marginal, debris flows with subsequent transfer to the portal via the glacial drainage system. These observations illustrate the potential importance of the paraglacial component to the overall sediment cascade of deglaciating basins and highlight the need for careful interpretation of turbidity records, where stochastic pulses in turbidity may be attributed to sources and processes other than ice‐marginal sediment inputs.

Meltwater routing in a high arctic glacier, Hannabreen, northern Spitsbergen

Electrical conductivity and chemistry of meltwaters draining glaciers have been used to study spatial differences and seasonal variations in melwater routing (e.g. Collins 1977, 1979 Tranter et al. 1993, Hodgkins et al. 1995). Collins (1977,1979) suggested a model to separate bulk runoff into a rapid englacial flow component and a delayd subglacial flow component. The model is based on the higher electrical conductivity of the subglacial component than the englacial component, assuming the conductivity of each component to be relatively constant throughout the ablation season. Tranter et al. (1993) argues that althrough such a model describes many features of the subglacial drainage system, it is unlikely that the chemical composition of each component is constant over the ablation season. The anionic composition of meltwater seems to provide a diagnostic basis for determining the flow routing of meltwater. SO4 2- is particularly useful, because sulphide oxidation is a rapid reaction which commonly goes t...

Subrecent sediment dynamics and sediment budget of the braided sandur system at Sandane, Erdalen (Nordfjord, Western Norway)

A study was carried out of the subrecent sediment budget of a braided sandur system in a U-shaped valley linked to the Jostedalsbreen ice field in Nordfjord, in Western Norway. Special focus was on (i) the detection of different zones with negative, positive or balanced subrecent (following the Little Ice Age advance) sediment budget within the braided sandur system, (ii) the identification of sediment sources upstream of Sandane and from the slope systems to both sides of the braided sandur system, and (iii) the analysis of the subrecent sediment budget of the entire Sandane system. A combination of methods was applied in the analysis. The upstream part of Sandane was found to be characterised by a negative subrecent sediment balance, with erosion of coarse sediments from the Little Ice Age advance. In comparison, the downstream parts of Sandane have a balanced to slightly positive subrecent sediment budget, with formation of younger flood sediments and more stable channels. Thus, the subrecent sediment budget of Sandane appears to be slightly negative. Present-day coupling of slope and fluvial systems is limited and only a rather small amount of sediments is directly transported from the slopes into the braided sandur. In sum, fluvial sediment transport following the Little Ice Age period appears to be supply-limited.

Bed load transport in a steep snowmelt-dominated mountain stream as inferred from impact sensors

The article reports results from bed load transport investigations using impact sensors in Vinstra, a steep snowmelt-dominated mountain stream in Central Norway. The impact sensors proved able to detect thresholds for bed load entrainment. With increasing discharges surpassing the threshold for entrainment, both the magnitude and variance in impact force increases, but also showing differing rating relationships on rising and falling flows. Substantial bed load transport was only observed during the snowmelt-dominated spring flood period and impact magnitude was observed on average to follow diurnal variations in discharge during the spring flood event, but with a clockwise hysteresis relationship.

Morphological dynamics of an englacial channel

Despite an interest in the hydraulic functioning of supraglacial and englacial channels over the last 4 decades, the processes and forms of such ice-bounded streams have remained poorly documented. Recent glaciological research has demonstrated the potential significance of so-called “cutand-closure” streams, where englacial or subglacial flow paths are created from the long-term incision of supraglacial channels. These flow paths are reported to exhibit step-pool morphology, comprising knickpoints and/or knickzones, exaggerated in dimensions in comparison to supraglacial channels. However, little is known of the development of such channels’ morphology. Here, we examine the spatial organisation of step pools and the upstream migration of steps, many of which form knickzones, with repeated surveys over a 10-year period in an englacial conduit in cold-based Austre Brøggerbreen, Svalbard. The observations show upstream step recession to be the dominant process for channel evolution. This is paralleled by an increase in average step height and conduit gradient over time. Characteristic channel-reach types and step-riser forms are consistently observed in each of the morphological surveys reported. We suggest that the formation of steps has a hydrodynamic origin, where steppool geometry is more efficient for energy dissipation than meanders. The englacial channel system is one in rapid transition towards a quasi-equilibrium form within a decadal timescale. The evolution and recession of knickzones reported here result in the formation of a 37 m deep moulin shaft, suggesting that over time an incising supraglacial channel may evolve towards an englacial channel form exhibiting a stable end-point characterised by a singular vertical descent, which potentially can reach the glacier bed. This challenges the prevailing notions that crevasses or hydrofractures are needed to form deep moulins. Our observations highlight the need to further examine the adjustment processes in cutand-closure channels to better understand their coupling to supraglacial meltwater sources and potential significance in cold-based glacier hydrology and ice dynamics.