P. Nørnberg

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.

Comparison of methods for analysis of organic and inorganic phosphorus in river sediment

During a study of the dynamics of sediment nitrogen, phosphorus (P) and organic matter in rivers, a common method for analysis of soil P differentiating between total phosphorus (TP), inorganic phosphorus (Pi) and organic phosphorus (Po = TP - Pi) revealed serious errors. Negative values of Po were calculated in approx. 40% of 420 river sediment samples and the reproducibility was low. The method involved a mild extraction from 2 mm wet-sieved samples, respectively ignited (550°C for 2 h) and unignited, by shaking for 2 h at room temperature with 0.1 M H2SO4. The poor reproducibility of the initial method was greatly improved by grinding the dried sediment to <250 μm. Even better results were obtained by also changing to stronger extractants (1 M HCl and 7.7 M HCl) and by boiling for 20 min. The combined effect of grinding and changing extractant yielded approx. 30% more Pi and up to 44% more TP, and good reproducibility was achieved. Further, the number of negative Po values has reduced to 8%. Analysing sediment P in 1094 sub-samples, in 282 iron-poor samples only 5% of the Po values were negative, and in 812 iron-rich samples 10% of the Po values became negative. About 75% of the negative Po-values were associated with very low organic contents (<0.6% loss on ignition). We conclude, that extraction involving 1 M HCl can be recommended for routine determinations of TP and Pi in river sediments, and to determine Po when TP - Pi > 10 mg P kg−1 dw. For very iron-rich sediment, however, some reservation still must be made due to some interference, possibly arising during the ignition phase.

Coastal and near-shore changes correlated with die-back in eel-grass (Zostera Marina, L.)

Abstract The die-back of eel-grass ( Zostera marina, L.) is found to have played an important role with regard to near-shore sedimentation and coastal changes. In a natural harbour at Kyholm, Denmark a hiatus is found between silty sediments that date from about 4000 BC and overlying modern sandy sediments. It is suggested that this is a consequence of the die-back of eel-grass in the nineteen-thirties, resulting in mobilisation and disturbance of nearshore sediments and the shoreward movement of mobilised sandy material into the harbour. The coastal morphology of Kyholm was relatively stable from 1802 to 1933, but between 1933 and 1978 there have been two periods of drastic progradation correlated with die-back of eel-grass.

Effects on soils of an oak invasion of a Calluna heath, Denmark. I: Morphology and Chemistry

Abstract Where oak has been invading Hjerl Hede for the last century, four profiles were described and sampled for analyses in a trench extending into a Calluna stand from a pioneer oak about 70 years old. Three additional profiles were studied, one opposite to the oak, a second in another stand of Calluna and a third in an oak forest. Comparisons were then made of the morphology and chemistry of the profiles to identify early changes associated with the invasion. Principal differences attributed to the oak invasion were a marked reduction in the surface layer of organic matter and its conversion from mor to moder, a slight increase in pH of the uppermost horizons under the oak, slight changes in colours from black to brown in deeper horizons and the blurring of their boundaries. Amounts of iron extractable by pyrophosphate and tetraborate from the B horizons in the trench were smaller under the oak than under the Calluna .

Characters of three Udults and their relevance to the composition and structure of virgin rain forest of Amazonian Ecuador

Abstract Three well-drained soil profiles from Anangu, Amazonian Ecuador, are described and their characteristics are discussed in relation to vegetation composition and structure within a small area of undisturbed terra firme rain forest. The soils are clayey, kaolinitic, udic, isohyperthermic, and rich in aluminium and are classified as Typic Hapludult and Typic Paleudults, with affinities to Inceptisols and Oxisols. The clay material of one profile includes expansible minerals which increase the CEC compared to that of the other profiles. The nutrient status is low and the clay content and aluminium saturation are high compared to other soils in tropical America. The properties most restrictive to plant growth are likely to be low soil pH, low concentrations of exchangeable calcium and extractable phosphorus, high aluminium saturation, high content of clay and high concentration of extractable manganese. However, these properties differ among the profiles. The three plots differ with regard to species composition and basal area of trunks. These differences correlate with soil concentration of aluminium, calcium, manganese, phosphorus, and clay. Many rare species occur on soils with a low concentration of calcium and high concentration of aluminium. A low basal area of trunks occurs on soil with high clay content and low phosphorus concentration. The conclusions about tree-soil relationships from Anangu are only tentative, but suggest that a high local species diversity in western Amazonia may be caused in part by local variations in soil characteristics.

Effects on soils of an oak invasion of a Calluna heath, Denmark, II. Changes in organic matter and cellulose decomposition

Abstract The investigation had two parts. In the first, organic matter was extracted from samples of the O through Bh horizons of seven profiles and then split into humic and fulvic acids. Part of the fulvic acid was treated with polyvinyl-pyrrolidone. In the other part, strips of cotton cloth were placed into the soils for two months, removed and tested for tensile strength to measure their decomposition. The amounts of humic and fulvic acids were both greater under Calluna than under the oaks. Profile distribution was also sharply contrasted under Calluna , being very low in the O horizons and high in the B horizons. Distribution was virtually uniform under the oak. The adsorption of fulvic acids by polyvinyl-pyrrolidone and the decomposition of the cotton strips indicated greater biological activity under the oaks than in the heath. These several differences are attributed to the replacement of one type of vegetation by another.

Simulation of the Martian dust aerosol at low wind speeds

[1] Performing realistic simulations is crucial for developing, testing, and subsequently analyzing results of experiments sent to the surface of Mars. A wind tunnel has been constructed, in which the atmospheric conditions of pressure and wind speed are controlled to match those observed by the Pathfinder mission to Mars. Injection into the wind tunnel of an analogue dust from Salten Skov in Denmark allows simulation of the Martian aerosol. Here experiments can be tested in preparation for a planned mission to the planet (Mars Exploration Rovers to be launched in 2003). Observations of adhesion and cohesion effects have been made in the wind tunnel, which are relevant to particle transport and of significance for validating the performance of specific experiments on Mars. Preliminary studies have been made, at Mars atmospheric pressure, of dust capture on magnet arrays similar to those flown on the Mars Pathfinder mission.

A Facility for Long-Term Mars Simulation Experiments: The Mars Environmental Simulation Chamber (MESCH)

We describe the design, construction, and pilot operation of a Mars simulation facility comprised of a cryogenic environmental chamber, an atmospheric gas analyzer, and a xenon/mercury discharge source for UV generation. The Mars Environmental Simulation Chamber (MESCH) consists of a double-walled cylindrical chamber. The double wall provides a cooling mantle through which liquid N(2) can be circulated. A load-lock system that consists of a small pressure-exchange chamber, which can be evacuated, allows for the exchange of samples without changing the chamber environment. Fitted within the MESCH is a carousel, which holds up to 10 steel sample tubes. Rotation of the carousel is controlled by an external motor. Each sample in the carousel can be placed at any desired position. Environmental data, such as temperature, pressure, and UV exposure time, are computer logged and used in automated feedback mechanisms, enabling a wide variety of experiments that include time series. Tests of the simulation facility have successfully demonstrated its ability to produce temperature cycles and maintain low temperature (down to -140 degrees C), low atmospheric pressure (5-10 mbar), and a gas composition like that of Mars during long-term experiments.

Imogolite related to podzolization processes in Danish podzols

The possible presence of imogolite was investigated in three Danish podzols underneath heather, spruce, and in a glade in a coniferous forest with ferns and grasses. Only a small quantity of proto-imogolite allophane material was detected in the lower B horizons underneath heather and in the glade. No well-crystallized imogolite was detected in any of the ecosystems. The relation to present-day soil-forming processes was studied in parallel under heather and spruce. Soil water was collected monthly from December 1997 to May 1999. The soil water sampling depths correspond to levels below the A, E, Bh, and Bs horizons. Identification of imogolite was done by chemical extractions, infrared spectrometry (IR), and transmission electron microscopy (TEM). Soil water analysis showed high Al concentrations underneath the spruce system compared to the heather system and compared to what was found elsewhere in Scandinavia. The elevated concentration was not due to weathering of Al-containing primary material. Instead, the source was degradation of formerly deposited organically complexed metals and up-concentration due to a high interception loss. C/Al and C/Fe ratios have been used as indicators of immobilization of metal-organic complexes by saturation in the B horizon. Former investigations from northern Scandinavia showed that the saturation ratios achieved from laboratory investigations were never reached in the field. Contrary to this, ratios, clearly indicating saturation were found in this study. Therefore, immobilization of organo-metal complexes by saturation is possible in the investigated acid systems.

Effects of N-deposition on ion trapping by B-horizons of Danish heathlands.

Coastal and inland heaths constitute a dominating fraction of the relatively few semi-natural ecosystems in Denmark. At the inland heath, the soil forming factors have been active with the same vegetation type during the last 2000 years, whereas at the coastal heath, these soil forming factors have only been active over a couple of hundred years, due to the activity of windblown sand. Effects on ion-balance and soil processes of nitrogen deposition on a young dune heath and an old inland heath have been investigated. Different levels of NH4NO3have been applied to the two heathlands, and rain, throughfall water and soil water chemistry below the experimental plots have been analysed. Results show that the ability to retain added, as well as deposited, nitrogen requires the presence and the integrity of a humifyed H-subhorizon. When the mor-layer for some reason breaks down, the nutrients will be retained by the B-horizons as a kind of back-up, and most probably be reused by the new vegetation. One year after destructive heather beetles attack on the inland heath, the mor-layer started to decompose. A large translocation of organic compounds, complexed associated cations and nitrogen-species, started from the mor-layer to the top of the B-horizon where they precipitate. The podzolic B-horizons can be seen as nutrient trap to the mor-layer.