Field investigation of dried lakes in western United States as an analogue to desiccation fractures on Mars

Potential Desiccation Polygons (PDPs), tens to hundreds of meters in size, have been observed in numerous regions on Mars, particularly in ancient (>3Gyr old) terrains of inferred paleolacustrine/playa geologic setting, and in association with hydrous minerals such as smectites. Therefore, a better understanding of the conditions in which large desiccation polygons form could yield unique insight into the ancient climate on Mars. Many dried lakebeds/playas in western United States display large (>50m wide) desiccation polygons, which we consider to be analogues for PDPs on Mars. Therefore, we have carried out fieldwork in seven of these dried lakes in San Bernardino and the Death Valley National Park regions complemented with laboratory and spectral analysis of collected samples. Our study shows that the investigated lacustrine/playa sediments have (a) a soil matrix containing 40-75% clays and fine silt (by volume) where the clay minerals are dominated by illite/muscovite followed by smectite, (b) carbonaceous mineralogy with variable amounts of chloride and sulfate salts, and significantly, (c) roughly similar spectral signatures in the visible-near-infrared (VIS-NIR) range. We conclude that the development of large desiccation fractures is consistent with water table retreat. In addition, the comparison of the mineralogical to the spectral observations further suggests that remote sensing VIS-NIR spectroscopy has its limitations for detailed characterization of lacustrine/playa deposits. Finally, our results imply that the widespread distribution of PDPs on Mars indicates global or regional climatic transitions from wet conditions to more arid ones making them important candidate sites for future in situ missions.

Calidad del 'sitio' en el oasis norte, Mendoza (Argentina)

La disminución del agua destinada al uso agrícola, la salinización de los acuíferos subterráneos y el advenimiento de la tecnología de Sistemas de Información Geográfica (SIG) han posibilitado conocer la calidad de los sitios, fundamentalmente los riesgos de salinización de los suelos del oasis del río Mendoza-Argentina. El presente trabajo se fundamenta en dos estudios anteriores: uno de relevantamiento de suelos y el otro de análisis de calidad de aguas subterráneas. En el primero se efectúo la actualización del relevantamiento de suelos del río Mendoza usando SIG. El muestreo de suelos y los análisis físicos (textura) y químicos (salinidad, conductividad eléctrica) se realizaron en 1974. Los lugares de muestreo y sus atributos, graficados como cobertura de puntos, se extrapolaron a sus zonas de influencia convirtiéndolos en polígonos y posteriormente se rasterizaron. El segundo trabajo fue la digitalización y georreferenciación, también al sistema de coordenadas Universal Transverse Mercator (UTM), de los mapas de las curvas de isosalinidad. La salinidad está medida por la conductividad eléctrica específica del agua subterránea de los tres niveles de explotación que existen en la cuenca norte de Mendoza. El monitoreo se realizó en el período 1990/1991. Las isolíneas, posteriormente, fueron rasterizadas. Con los procesos de superposición y tabulación cruzada de los SIG se integraron las diversas "capas" de datos de suelos y calidades de aguas subterráneas y se generaron mapas temáticos que expresan la clasificación y localización regional de calidades del sitio, basado fundamentalmente en los riesgos de salinización de los suelos.

Concentrations of suspended matter and heavy metals in melted ice- and snow water from the Barents Sea

In September-October 1998, during Cruise 14 of R/V Akademik Fedorov to the Barents Sea, in the region of 82° N between the Spitsbergen and Novaya Zemlya archipelagos samples of snow and ice were collected within four polygons. By means of atomic absorption with an electothermal atomizer (onboard the ship) in filtered (dissolved form) and unfiltered (sum of dissolved and particulate forms) samples of snow melt and ice melt concentrations of Fe, Mn, Cu, Cr, Ni, Co, Pb, and Cd were determined in order to estimate level of potential contamination of snow and ice with these metals. Excluding data on Ni, Cd (and probably Cu) in ice that were regarded to be unsatisfactory because of probable contamination of the ice samples during drilling concentrations of all the elements in snow and ice of the northern part of the Barents Sea appeared to be close to their background values or below. An attempt to identify the main sources of metal supply to snow from the atmosphere by comparison of ratios of metal particulate form to total content in snow of the Barents Sea and the same ratios in snow samples from clean regions of Finland and from contaminated areas of the Kola Peninsula showed that aerosols in the area of the expedition were supplied into the Barents Sea atmosphere from different sources, both natural and anthropogenic.

Seagrass and associated benthic community data derived from field surveys at Low Isles, Great Barrier Reef, conducted July-August, 1997

The distribution of seagrass and associated benthic communities on the reef and lagoon of Low Isles, Great Barrier Reef, was mapped between the 29 July and 29 August 1997. For this survey, observers walked or free-dived at survey points positioned approximately 50 m apart along a series of transects. Visual estimates of above-ground seagrass biomass and % cover of each benthos and substrate type were recorded at each survey point. A differential handheld global positioning system (GPS) was used to locate each survey point (accuracy ±3m). A total of 349 benthic survey points were examined. To assist with mapping meadow/habitat type boundaries, an additional 177 field points were assessed and a georeferenced 1:12,000 aerial photograph (26th August 1997) was used as a secondary source of information. Bathymetric data (elevation below Mean Sea Level) measured at each point assessed and from Ellison (1997) supplemented information used to determine boundaries, particularly in the subtidal lagoon. 127.8 ±29.6 hectares was mapped. Seagrass and associated benthic community data was derived by haphazardly placing 3 quadrats (0.25m**2) at each survey point. Seagrass above ground biomass (standing crop, grams dry weight (g DW m**-2)) was determined within each quadrat using a non-destructive visual estimates of biomass technique and the seagrass species present identified. In addition, the cover of all benthos was measured within each of the 3 quadrats using a systematic 5 point method. For each quadrat, frequency of occurrence for each benthic category was converted to a percentage of the total number of points (5 per quadrat). Data are presented as the average of the 3 quadrats at each point. Polygons of discrete seagrass meadow/habitat type boundaries were created using the on-screen digitising functions of ArcGIS (ESRI Inc.), differentiated on the basis of colour, texture, and the geomorphic and geographical context. The resulting seagrass and benthic cover data of each survey point and for each seagrass meadow/habitat type was linked to GPS coordinates, saved as an ArcMap point and polygon shapefile, respectively, and projected to Universal Transverse Mercator WGS84 Zone 55 South.

Documentation of manganese nodules form the northwest Indian Ocean

Microscopic and electron probe examination of some manganese nodules show that they consist of segregations of manganese-iron oxides in an interstitial material almost free of manganese but rich in iron and silicates. The segregations are widely spaced in the volcanic cores of the nodules but become more abundant towards their outer crusts where they form the centres of linked polygons of interstitial materials. Most of the minor elements are concentrated in the segregations compared to the interstitial materials. It is suggested that the structures observed result partly from solution and reprecipitation of elements in the original volcanic cores of the nodules and partly from the replacement and coating of these cores by manganese-iron oxides precipitated from sea water.

Age and chemical composition of volcanic rocks and minerals from the Vityaz Ridge

This paper reports results of geological studies carried out during two marine expeditions of R/VAkademik M.A. Lavrent'ev (Cruises 37 and 41) in 2005 and 2006 at the underwater Vityaz Ridge. Dredging has yielded various rocks from the basement and sedimentary cover of the ridge within three polygons. On the basis of radioisotope age determinations, petrochemical, and paleontological data all the rocks have been subdivided into the following complexes: volcanic rock of Paleocene, Eocene, Late Oligocene, Middle Miocene, and Pliocene-Pleistocene; volcanogenic-sedimentary rocks of Late Cretaceous - Early Paleocene, Paleogene (undifferentiated), Oligocene - Early Miocene, and Pliocene-Pleistocene. Determinations of age and chemical composition of the rocks have enabled to specify formation conditions of the complexes and to trace geological evolution of the Vityaz Ridge. Presence of young Pliocene-Pleistocene volcanites allows to conclude about the modern tectono-magmatic activity of the central part of the Pacific slope of the Kuril Islands.

Global Lithological Map Database v1.0 (gridded to 0.5° spatial resolution)

Lithology describes the geochemical, mineralogical, and physical properties of rocks. It plays a key role in many processes at the Earth surface, especially the fluxes of matter to soils, ecosystems, rivers, and oceans. Understanding these processes at the global scale requires a high resolution description of lithology. A new high resolution global lithological map (GLiM) was assembled from existing regional geological maps translated into lithological information with the help of regional literature. The GLiM represents the rock types of the Earth surface using 1,235,400 polygons. The lithological classification consists of three levels. The first level contains 16 lithological classes comparable to previously applied definitions in global lithological maps. The additional two levels contain 12 and 14 subclasses, respectively, which describe more specific rock attributes. According to the GLiM, the Earth is covered by 64 % sediments (a third of which is carbonates), 13 % metamorphics, 7 % plutonics, and 6 % volcanics, and 10% are covered by water or ice. The high resolution of the GLiM allows observation of regional lithological distributions which often vary from the global average. The GLiM enables regional analysis of Earth surface processes at global scales.

Composition of Fe-Mn nodules from the radiolarian belt of the Pacific Ocean

Typomorphic features of the main morphogenetic types of Fe-Mn nodules from the radiolarian belt have been considered on materials from polygons in the Clarion-Clipperton ore province and in the Central Basin of the Pacific Ocean. By character of surfaces, features of internal structure, mineral and chemical compositions, behavior of trace elements at selective leaching three genetic types of nodules have been divided: predominantly sedimentary, diagenetic, and sedimentary diagenetic. Their formation results from mechanism of growth.

Vegetation, soil and site characteristics of samples taken along the Yamal Transet in 2007-2008

The overarching goal of the Yamal portion of the Greening of the Arctic project is to examine how the terrain and anthropogenic factors of reindeer herding and resource development combined with the climate variations on the Yamal Peninsula affect the spatial and temporal patterns of vegetation change and how these changes are in turn affecting traditional herding of the indigenous people of the region. The purpose of the expeditions was to collect groundobservations in support of remote sensing studies at four locations along a transect that traverses all the major bioclimate subzones of the Yamal Peninsula. This data report is a summary of information collected during the 2007 and 2008 expeditions. It includes all the information from the 2008 data report (Walker et al. 2008) plus new information collected at Kharasavey in Aug 2008. The locations included in this report are Nadym (northern taiga subzone), Laborovaya (southern tundra = subzone E of the Circumpolar Arctic Vegetation Map (CAVM), Vaskiny Dachi (southern typical tundra = subzone D), and Kharasavey (northern typical tundra = subzone C). Another expedition is planned for summer 2009 to the northernmost site at Belyy Ostrov (Arctic tundra = subzone B). Data are reported from 10 study sites - 2 at Nadym, 2 at Laborovaya, and 3 at Vaskiny Dachi and 3 at Kharasavey. The sites are representative of the zonal soils and vegetation, but also include variation related to substrate (clayey vs. sandy soils). Most of the information was collected along 5 transects at each sample site, 5 permanent vegetation study plots, and 1-2 soil pits at each site. The expedition also established soil and permafrost monitoring sites at each location. This data report includes: (1) background for the project, (2) general descriptions and photographs of each locality and sample site, (3) maps of the sites, study plots, and transects at each location, (4) summary of sampling methods used, (5) tabular summaries of the vegetation data (species lists, estimates of cover abundance for each species within vegetation plots, measured percent ground cover of species along transects, site factors for each study plot), (6) summaries of the Normalized Difference Vegetation Index (NDVI) and leaf area index (LAI) along each transect, (7) soil descriptions and photos of the soil pits at each study site, (8) summaries of thaw measurements along each transect, and (9) contact information for each of the participants. One of the primary objectives was to provide the Russian partners with full documentation of the methods so that Russian observers in future years could repeat the observations independently.

Tab. 1: Approximate dimension of the pingos

A group of nine pingos occurs in the valley of a glacial meltwater river. The pingos rise from a plain of low-center polygons. Some pingos have a typical cone shape, but others are linear, apparently centered on ice wedges . The occurrence of most pingos at the junction of oversize ice wedge polygon ridges suggests that the injection of water and the segregation of ice occurred along pathways provided by the ice wedges.

Radiocarbon ages and diatom abundance in samples obtained from Qarlikturvik Valley, Bylot Island

The formation of many arctic wetlands is associated with the occurrence of polygon-patterned permafrost. Existing scenarios to describe and explain surface landforms in arctic wetlands (low-center and high-center polygons and polygon ponds) invoke competing hypotheses: a cyclic succession (the thaw-lake hypothesis) or a linear succession (terrestrialization). Both hypotheses infer the predictable development of polygon-patterned wetlands over millennia. However, very few studies have applied paleoecological techniques to reconstruct long-term succession in tundra wetlands and thereby test the validity of existing hypotheses. This paper uses the paleoecological record of diatoms to investigate long-term development of individual polygons in a High Arctic wetland. Two landform processes were examined: (1) the millennial-scale development of a polygon-pond, and (2) the transition from low-center to erosive high-center polygons. Diatom assemblages were quantified from habitats associated with contrasting landforms in the present-day landscape, and used as an analog to reconstruct past transitions between polygon types. On the basis of this evidence, the paleoecological record does not support either of the existing models describing the predictable succession of polygon landforms in an arctic wetland. Our results indicate a need for greater paleoecological understanding, in combination with in situ observations in present-day geomorphology, in order to identify patterns of polygon wetland development and elucidate the long-term drivers of these landform transitions.

Speciations of Mn and Fe in Fe-Mn nodules from the western part of the Clarion-Clipperton ore province

Hydrogenic forms of iron and manganese occurrence were studied in samples of ferromanganese nodules sampled within two polygons during Cruise 28 of R/V Dmitry Mendeleeev (1982) in the western part of the Clarion-Clipperton ore province. Contents of labile exchangeable Fe and Mn, amorphous hydroxides and poorly soluble compounds of Fe and Mn were analyzed. In nodules from DM28-2474 Polygon labile exchangeable Fe and Mn and amorphous hydroxides dominated; in nodules from DM28-2483 Polygon poorly soluble compounds dominated. Analysis of contents of labile forms of Fe and Mn occurrence in different morphological types of nodules distinguished predominantly hydrogenous botryoidal nodules, spheroidal and ellipsoidal intergrowth nodules, and hydrogenic-diagenetic discoid nodules.