H. P. Gunnlaugsson

H2O at the Phoenix Landing Site

Phoenix Ascending The Phoenix mission landed on Mars in March 2008 with the goal of studying the ice-rich soil of the planets northern arctic region. Phoenix included a robotic arm, with a camera attached to it, with the capacity to excavate through the soil to the ice layer beneath it, scoop up soil and water ice samples, and deliver them to a combination of other instruments—including a wet chemistry lab and a high-temperature oven combined with a mass spectrometer—for chemical and geological analysis. Using this setup, Smith et al. (p. 58) found a layer of ice at depths of 5 to 15 centimeters, Boynton et al. (p. 61) found evidence for the presence of calcium carbonate in the soil, and Hecht et al. (p. 64) found that most of the soluble chlorine at the surface is in the form of perchlorate. Together these results suggest that the soil at the Phoenix landing site must have suffered alteration through the action of liquid water in geologically the recent past. The analysis revealed an alkaline environment, in contrast to that found by the Mars Exploration Rovers, indicating that many different environments have existed on Mars. Phoenix also carried a lidar, an instrument that sends laser light upward into the atmosphere and detects the light scattered back by clouds and dust. An analysis of the data by Whiteway et al. (p. 68) showed that clouds of ice crystals that precipitated back to the surface formed on a daily basis, providing a mechanism to place ice at the surface. A water ice layer was found 5 to 15 centimeters beneath the soil of the north polar region of Mars. The Phoenix mission investigated patterned ground and weather in the northern arctic region of Mars for 5 months starting 25 May 2008 (solar longitude between 76.5° and 148°). A shallow ice table was uncovered by the robotic arm in the center and edge of a nearby polygon at depths of 5 to 18 centimeters. In late summer, snowfall and frost blanketed the surface at night; H2O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO3, aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.

Winds at the Phoenix landing site

[1] Wind speeds and directions were measured on the Phoenix Lander by a mechanical anemometer, the so-called Telltale wind indicator. Analysis of images of the instrument taken with the onboard imager allowed for evaluation of wind speeds and directions. Daily characteristics of the wind data are highly turbulent behavior during midday due to daytime turbulence with more stable conditions during nighttime. From L s ~77°-123° winds were generally ~4 m s -1 from the east, with 360° rotation during midday. From L s ~123°-148° daytime wind speeds increased to an average of 6-10 m s -1 and were generally from the west. The highest wind speed recorded was 16 m s -1 seen on L s ~147°. Estimates of the surface roughness height are calculated from the smearing of the Kapton part of the Telltale during image exposure due to a 3 Hz turbulence and nighttime wind variability. These estimates yield 6 ± 3 mm and 5 ± 3 mm, respectively. The Telltale wind data are used to suggest that Heimdal crater is a source of nighttime temperature fluctuations. Deviations between temperatures measured at various heights are explained as being due to winds passing over the Phoenix Lander. Events concerning sample delivery and frost formation are described and discussed. Two different mechanisms of dust lifting affecting the Phoenix site are proposed based on observations made with Mars Color Imager on Mars Reconnaissance Orbiter and the Telltale. The first is related to evaporation of the seasonal CO 2 ice and is observed up to L s ~95°. These events are not associated with increased wind speeds. The second mechanism is observed after L s ~111° and is related to the passing of weather systems characterized by condensate clouds in orbital images and higher wind speeds as measured with the Telltale.

A Comprehensive Investigation on Iron Cycling in a Freshwater Seep Including Microscopy, Cultivation and Molecular Community Analysis

Iron reduction and oxidation, as well as the microbial community involved in these processes, were investigated in a small pond that is continuously fed by slightly acidic, hypoxic, iron rich ground water. The seep area is located in a beech forest in central Jutland (Denmark), and beech litter is the dominant source of organic matter, carbon and energy for the microbial community. The pond is 30 to 50 cm deep with a water column depth ranging from 15 to 20 cm. Oxygen could only be detected down to 7 cm depth of the water column. Fe(II) concentrations increased with depth from about 30 μM close to the surface to ca. 100 μM at the bottom. The presence of Gallionella- and Sideroxidans-related strains was supported by clone library data, while Leptothrix-related 16S rDNA clones were not found. Samples amended with leaves, acetate, lactate and ethanol all showed stimulated iron reduction at the in situ temperature (about 10°C). In particular, dried beech leaves stimulated iron reduction without a lag phase while acetate was only degraded after a 22 day lag period at the in situ pH. The long lag phase is most probably due to the low pH that is responsible for high acetic acid concentrations (0.8–1.2 mM) at the start of the incubation. Light microscopy observations confirm the clone library data that Gallionella spp and other iron oxidizer related 16S rDNA sequences were relatively common. In addition, 16S rDNA sequences relatively similar to sequences of members of the iron reducer family Geobacteraceae were found. A clone library constructed with a primer set targeting specifically Geobacter-related strains revealed that strains most closely related to Geobacter thiogenes were predominant (19 out of 20 clones). By a combination of microscopy, cultivation and molecular investigations we have been able to provide several lines of evidence for a tight coupling of biological iron reduction and oxidation in this iron-rich fresh water seep.

Basal ice microbiology at the margin of the Greenland ice sheet

Abstract Basal ice at the margin of the Greenland ice sheet was studied with respect to its physical characteristics and microbiological community. The basal ice contained high concentrations of dissolved ferrous Fe and must therefore be anoxic. Oxygen consumption experiments indicate that 50% of the oxidation was due to biological activity while the rest could be attributed to chemical processes, most likely weathering reactions with ferrous Fe. At least six different Fe-containing mineral sources were detected in basal ice together with potential bioavailable Fe nanoparticles. An active denitrifier population was identified due to formation of 30N-dinitrogen gas after amendment of anoxic sediment slurries with 15N-NO3 −. Sulfate reduction could not be detected. The solid ice facies contained an abundant (∼108 cells cm−3) and complex microbial community that harbored representatives of at least eight major phyla within the domain Bacteria. The clone library was dominated by members of the β-subdivision of proteobacteria of which the largest proportion was affiliated to the genus Rhodoferax that comprises facultative aerobic iron reducers. The second most abundant phylum was Bacteroidetes. The solid ice facies had many physical similarities with the overlying debris-rich banded ice facies, indicating that they formed by similar subglacial processes and harbor similar microbial communities. This study extends our knowledge of life in subglacial environments such as beneath ice sheets. GenBank accession numbers: HM439882-HM439950; HQ144215-HQ144221.

Defect-related local magnetism at dilute Fe atoms in ion-implanted ZnO

Semiconductors, which are ferromagnetic at room temperature (RTFM), are strived after as potential multifunctional materials. For ZnO, RTFM has been achieved by heavy doping with 3d transition metals. However, neither the conditions for nor the origin of the magnetism is as yet understood. Here, by implanting ZnO at temperatures of 300–800K with dilute, radioactive Mn+57 ions, decaying to the Fe57m Mossbauer state, we show that, most likely, Fe atoms, located on Zn sites in a high-spin Fe3+ state at ⩽600K with large magnetic moments, are in a magnetically ordered atomic surrounding with ordering temperatures ⪢600K. The formation/annealing of the ordering is proposed to occur/disappear on an atomic scale upon the association/dissociation of complexes of Mn∕Fe probe atoms with the (mobile) Zn vacancies that are created in the implantation process. These results challenge present concepts to model (ferro)magnetic ordering in 3d-metal doped oxides and suggest this role of vacancies in the magnetism to be a ra...

Charge state dependence of the diffusivity of interstitial Fe in silicon detected by Mössbauer spectroscopy

Interstitial 57mFe atoms excited in the 14.4 keV Mossbauer state have been created in silicon at 400–800 K as a result of the recoil imparted on these daughter atoms in the β− decay of ion-implanted, substitutional 57Mn. Diffusional jumps of the interstitial 57mFe cause a line broadening in their Mossbauer spectra, which is directly proportional to their diffusivity. Thus, the charge-state-dependent diffusivity has been determined in differently doped material.

Paramagnetism in Mn/Fe implanted ZnO

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d-metal doped ZnO, we have undertaken on-line F57e Mossbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive M57n ions at room temperature. The Mossbauer spectra of the dilute Fe impurities are dominated by sextets whose angular dependence rules out an ordered magnetic state (which had been previously proposed) but are well accounted for on the basis of Fe3+ paramagnetic centers on substitutional Zn sites with unusually long relaxation times (>20 ns).

57Fe Mössbauer study of radiation damage in ion-implanted Si, SiGe and SiSn

Abstract The radiation damage created in silicon-based materials by ion implantation of radioactive 57 Mn ions at temperatures of 77–500 K has been studied by Mossbauer spectroscopy on the 14 keV γ-rays of the 57 Fe daughter atoms. At 77 K >60% of the probe atoms are located in a heavily distorted surrounding in all matrices, the remainder is found in tetrahedral interstitial sites. Two material dependent damage annealing stages have been found at 100–200 and 300–450 K. The first leads predominantly to an increase of the interstitial fraction, the second also to the occurrence of substitutional Mn in all matrices. A model is proposed to identify the annealing reactions, taking into account other Mossbauer and emission channeling data.

High temperature Mössbauer spectroscopy of titanomagnetite and maghemite in basalts

Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (Js-T) curves with Curie temperatures of about 840 K, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability of maghemite at temperatures above 620 K, this reversibility came as a surprise. For further studies of the magnetization-temperature relationship of these minerals, we have constructed an elliptical radiation-heated furnace in which Mössbauer spectra can be acquired at temperatures between 300 and 900 K. Measurements at different temperatures have been obtained for two types of basalts, one in which the magnetic minerals are nearly pure magnetite and the other where the room temperature spectrum indicates a mixture of maghemite and magnetite. The two series show different features of the collapse of the internal magnetic hyperfine field, and the composition of minerals in the samples changes during the treatment, showing maghemite.

Comparison of the mineralogical effects of an experimental forest fire on a goethite/ferrihydrite soil with a topsoil that contains hematite, maghemite and goethite

Abstract A long-standing unresolved puzzle related to the Danish temperate humid climate is the presence of extended areas with large Fe contents, where goethite and ferrihydrite are present in the topsoil along with hematite and maghemite. Hematite and, particularly, maghemite would normally be interpreted as the result of high temperature as found after forest fires. However, a body of evidence argues against these sites having been exposed to fire. In an attempt to get closer to an explanation of this Fe mineralogy, an experimental forest fire was produced. The results showed a clear mineralogical zonation down to 10 cm depth. This was not observed at the natural sites, which contained a mixture of goethite/ferrihydrite, hematite and maghemite down to 20 cm depth. The experimental forest fire left charcoal and ashes at the topsoil, produced high pH and decreased organic matter content, all of which is in contrast to the natural sites. The conclusion from this work is that the mineralogy of these sites is not consistent with exposure to forest fire, but may instead result from long-term transformation in a reducing environment, possibly involving microbiology.