Drying colloidal systems: laboratory models for a wide range of applications

The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art

3D time-lapse imaging of polygonal patterned ground in the McMurdo dry valleys of Antarctica

We surveyed four sets of polygons at 0.5 m line spacing using 100 and 200 MHz antennas for 3D GPR imaging at two field locations in the McMurdo Dry Valleys of Antarctica, one in Victoria Valley and the other in Beacon Valley. The aim was to use 3D GPR and time-lapse 3D GPR to resolve subsurface structure and PPG process activity over the thaw season of polygonal patterned ground (PPG) in Antarctica. We applied migration and topographic corrections to the data sets before collating the data into 3D cubes. The subsurface structure can be analyzed using the processed profiles and resulting 3D data cubes. Signal was received down to 12 m (200 MHz) and 20 m (100 MHz) depth. Variations in salt concentrations, soil horizons and crack penetration may be interpreted using these data sets. The time-lapse images from Victoria Valley show reductions in signal through the season provisionally identified with changing quantities of free water and salts associated with PPG activity. The results show that 3D GPR allows the collection of valuable information about the subsurface structure and processes of PPG and provides a way to monitor changes in these processes as climatic conditions evolve

The thermal springs of bockfjord, svalbard: occurrence and major ion hydrochemistry

The Troll and Jotun thermal springs of northern Svalbard, with temperatures of up to 25.6°C, are derived from a major fault forming the junction between Devonian sandstones and Proterozoic marbles, mica schists and gneisses. The Troll waters are dominated by Na–HCO3 compositions and the Jotun waters by Na–Cl compositions. The pristine thermal water source has a sub-neutral pH and is highly reducing. Taken at face value, common geothermometers suggest temperatures at depth of 130–180°C for the Troll springs (corresponding to a depth of 1.6–2.3 km), with 10–30% thermal water diluted by 70–90% cold water. Such geothermometers may, however, be inappropriate to the cool, high CO2 waters of Bockfjord, and real temperatures at depth and dilution factors are probably considerably lower. The salinity of the thermal water appears to be only partially derived from water–rock interaction; Br\Cl ratios suggest that seawater or possibly evaporites may be a source of chloride salinity

The thermal springs of Bockfjorden, Svalbard: II: selected aspects of trace element hydrochemistry

Waters from the Trollkjeldene (Troll springs) and Jotunkjeldene (Jotun springs) thermal springs on northern Svalbard have been analysed by ICP-AES, ICP-MS and IC techniques for a wide range of major and trace elements. Although it is plausible that the thermal waters originate from a deep reservoir in siliceous rocks, it appears that a significant component of their hydrochemical signature is derived from dissolution of higher-level Hecla Hoek marbles. Rare earth elements (REEs) show some degree of enrichment of heavy REEs in the water phase, relative to the marbles and to the travertines that precipitate from the waters. A strong positive Eu anomaly is also observed in the waters, suggesting preferential mobilisation of Eu under reducing conditions. The ratio Nb/Ta is rather well-preserved between the marbles, the waters and the travertines

Geomicrobiology of Meltwater From the Western Margin of the Greenland Ice Sheet

Subglacial environments are cold, dark, and possess a range of redox conditions. These environments are gaining attention in global biogeochemical cycles as to their role in releasing bioavailable micronutrients such as Fe and the production of greenhouse gases. However, there is uncertainty about how the microbial communities interact with lithology and mediate geochemical reactions under glacial conditions. We examined the microbial communities and their influence on elemental cycling in two glacial environments along the western Greenland Ice Sheet margin: Thule in the north (76ºN, 68ºW) and Kangerlussuaq in the south (67ºN, 51ºW). The north is dominated by supraglacial melting with considerable contribution from the periglacial environment; the south has a well-developed subglacial drainage system. The lithology is sedimentary rocks in the north and crystalline rocks in the south and this difference was reflected in the geochemistry of the drainages. Runoff in the north was oxygen saturated throughout the season. A change from Na and Cl dominance in spring to Ca and SO4 and overall increase in solute concentration marked a stronger contribution from active layer thawing. In the south, waters were undersaturated in oxygen at times, presumably due to biological and chemical sinks of subglacial origin. The meltwater here was dominated by HCO3, SO4 and Ca. In subglacial outflows Fe (oxyhydr)oxide concentrations increased with decreasing oxygen concentration suggesting their formation under oxygen limiting conditions. The high abundance of sulfate implies oxidation of iron sulfides which is consistent with inverse modeling of subglacial weathering processes under anoxic conditions. Meltwater in both locations transported reactive particulate iron which in the north consisted mainly of Fe oxides while Fe(oxyhydr)oxides dominated in the south. DNA and RNA signatures indicate microbial phylotypes that are active in iron reduction, sulfidic mineral weathering, sulfur oxidation, and sulfide reduction supporting the assumption that FeS2 oxidation and formation of particulate reactive Fe(oxyhydr)oxide is microbial mediated. Our data suggest the presence of active microbially iron and sulfur cycling in ice-covered and ice-free zones near the margin of the Greenland Ice Sheet

Seasonal Changes of Chemical, Isotopic and Microbiological Signatures in Meltwater Outflows of the West Greenland Ice Sheet

The faster rate of melting of the Greenland Ice Sheet and its implications for global hydrological and biogeochemical cycles has led to detailed studies of hydrological pathways and biogeochemical processes on top, within, and underneath the Ice Sheet. A challenge up to now is the identification of water sources and pathways and their seasonal development that can provide important information about glacier dynamics. Most studies are based on bulk glacier outflow and attempts that separate hydrographs in different water sources are often based on a combination of isotopic, geochemical, and hydrological information. These parameters can be indicative for meltwater sources as well as being indicative for fast and delayed flow. In this paper we present stable isotopes of water and strontium together with detailed chemical analysis and microbial counts. The data are used to evaluate the potential and limits of these parameters to delineate sources of water and solutes throughout a season and its implication for identifying and quantifying major biogeochemical processes. The study is performed at two terrestrial outflows of the West Greenland Ice Sheet: i) Thule on the Pituffik Peninsula (76°N, 68°W) and ii) Kangerlussuaq (Sondre Stromfjord, 67°N, 50°W). To identify primary meltwater sources fresh snow was collected along transects and depth profiles on the Ice Sheet catchment area and basal ice was collected from the border of the Ice Sheet. Supraglacial and bulk meltwater samples were collected throughout the season together with precipitation such as rain and snow. All samples were analyzed for isotopes, major and trace elements, organic and inorganic carbon and microbial counts. Stable isotope of waters collected on the surface of the Ice Sheet display an elevation and depth trend; however, there is overlap in the stable isotope ratios suggesting that isotopes alone may not be sufficient to identify meltwater source areas. Contrary, rain has unique isotope characteristics of rain each event allowing quantification of its contribution to bulk meltwater. Meltwater chemistry can be used to identify meltwater routing in and below the ice sheet and changes from sodium and chlorite dominated snowmelt water to calcium, magnesium and sulfate dominated water which is related to mineral weathering processes are seen throughout the season. In addition, strontium isotope ratios and stable isotopes of sulfate can be used to identify solute provenance areas and the contribution of microbial activity in solute sequestration, respectively

Geomicrobiology of Subglacial Meltwater Samples From Store Landgletscher and Russell Glacier, West Greenland

The melting of the Greenland Ice Sheet provides direct connections between atmospheric, supraglacial and subglacial environments. The intraglacial hydrological pathways that result are believed to accommodate the microbial colonization of subglacial environments; however, little is known about the abundance, diversity and activity of microorganisms within these niches. The Greenland Ice Sheet (1.7 million square kilometers) and its associated surpaglacial and subglacial ecosystems may contribute significantly to biogeochemical cycling processes. We analyzed subglacial microbial assemblages in subglacial outflows, near Thule and Kangerlussuaq, West Greenland. The investigative approach included correlating microbial diversity, inferred function, abundance, melt water chemistry, O-18 water isotope ratios, alkalinity and sediment load. Using Illumina sequencing, bacterial small subunit ribosomal RNA hypervariable regions have been targeted and amplified from both extracted DNA and reverse transcribed rRNA. Over 3 billion sequence reads have been generated to create a comprehensive diversity profile. Total abundances ranged from 2.24E+04 to 1.58E+06 cells mL-1. In comparison, the total abundance of supraglacial early season snow samples ranged from 3.35E+02 to 2.8E+04 cells mL-1. 65 % of samples incubated with cyano ditoyl tetrazolium chloride (CTC), used to identify actively respiring cells, contained CTC-positive cells. On average, these cells represented 1.9 % of the estimated total abundance (1.86E+02 to 2.19E+03 CTC positive cells mL-1; 1.39E+03 cells mL-1 standard deviation); comparative to those measured in temperate freshwater lakes. The overarching objective of our research is to provide data that indicates the role of microbial communities, associated with ice sheets, in elemental cycling and in the release of biomass and nutrients to the surrounding marine biome

Seasonal and Regional Variability in Dissolved and Particulate Iron Fluxes via Glacial Runoff Along the West Greenland Coast

Subglacial weathering, due to biogeochemical and physical weathering processes, can affect the chemical evolution of subglacial waters and release dissolved and particulate iron via glacial runoff. Iron is a growth limiting nutrient and plays a critical role in the biogeochemical cycles of coastal and marine waters. More recently, dissolved and colloidal iron derived from subglacial sources have been considered an important contributor of Fe fluxes to the ocean; however, their dependency on lithology, grain size, and microbial activity is not well understood. This study characterizes the solute chemistry, in particular iron mineralogy and dissolved iron concentrations, released from beneath the Greenland Ice Sheet (GrIS), from two locations along the West Greenland coast, Thule (76°N, 68°W) and Kangerlussuaq (67°N, 50°W). We hypothesize that the subglacial lithology has a control on Fe fluxes from the GrIS to coastal and marine systems. The underlying bedrock in Thule is the Precambrian Dundas and Narssarssuk sedimentary formations which include sandstone, siltstone, and shale. The bedrock in Kangerlussuaq is dominated by Archean granodioritic gneiss and amphibolite within the Nagssugtoqidian Orogen. Supra and subglacial meltwater samples were collected directly in front of the Ice Sheet over an entire melt season in 2011 (North River, Thule) and 2012 (Akuliarusiarsuup Kuua River, Kangerlussuaq). In situ parameters such as temperature, pH, dissolved oxygen, and electrical conductivity were recorded in order to interpret meltwater chemistry. Dissolved Fe(II) and Fe(III) species were fixed immediately and analyzed within 24 hours after sampling in the field laboratory using a spectrophotometer and 10 cm cell. Total dissolved iron (FeT) of different size fractions (<0.22 and <0.05 μm) of iron were determined back in the home laboratory using reaction cell ICP MS. Preliminary results demonstrate that subglacial meltwater of North River has average FeT concentrations of 200 nM and 10 nM in the <0.22 and <0.05 μm size fraction, respectively, indicating that FeT in the <0.22 μm fraction is mostly (95%) in form of colloidal iron. In comparison, data from Kangerlussuaq show an average FeT of 580 nM in the <0.22 μm size fraction and 150 nM in the <0.05 μm fraction. Suspended load in North River increased throughout the ablation period in concurrence with variation in discharge, from an average of 0.08 g/L in the early melt stages (June), 0.21 g/L during the high melt (July-August), and 0.15 g/L during the late melt (end of August-September). Initial estimates for the suspended load for subglacial flow in Kangerlussuaq are 0.30 g/L on average. The suspended load will be analyzed for iron by sequential extraction in order to characterize how iron partitions between oxide and (oxyhydr)oxide minerals in the sediment. This comprehensive study will allow us to identify biogeochemical processes involved in the mobilization of iron and to evaluate how increased melting of GrIS will affect Fe fluxes to coastal and marine environments

Understanding of Silicate Weathering in Subglacial Environment by Inverse Modeling of West Greenland Glacial Meltwater

The acceleration of chemical weathering due to physical processes in glaciers has been studied in various systems. In our study we consider the potential role of microbes in addition to physical weathering to enhance weathering in runoff from the Greenland Ice sheet (GrIS). Sub- and supra- glacial weathering products in bulk meltwater are used to determine reaction processes and assess solute provenance. Most current models estimate that 80-100% of the dominant ion Ca2+ is derived from weathering of trace carbonates. The potential for significant silicate-derived Ca2+ is not generally considered. We hypothesize that seasonal changes in subglacial water routing and water residence times have a large impact on the weathering of lithologies with differing geochemical reactivity. This study deconvolutes the solute chemistry in runoff from the GrIS using PHREEQCi, a computer-based speciation mass-balance model. The model utilizes a mass balance approach and allows multiple alternative weathering scenarios under different hydrological conditions to be tested simultaneously. It is parameterized using seasonal chemical and mineralogical field data from Thule (76°N, 68°W), West Greenland. Hypothetical geochemical weathering scenarios suggest Ca-feldspar dissolution is an important solute source and silicate weathering is likely to be dominated by Ca-feldspar weathering in GrIS, due to their relatively high dissolution rates. The proportion of silicate dissolution decreases with increasing discharge on the seasonal timescale, and this reflects the seasonal expansion of the channelized system. At places where the development of channelized system is limited and most waters are routed through a distributed system, silicate minerals, which are more abundant but less reactive than carbonates, have sufficient time to dissolve and may have a greater contribution, approximately equal amounts of Ca2+ as carbonates, to the major solutes