Dune field pattern formation and recent transporting winds in the Olympia Undae Dune Field, north polar region of Mars

High-Resolution Imaging Science Experiment (HiRISE) imagery of the central Olympia Undae Dune Field in the north polar region of Mars shows a reticulate dune pattern consisting of two sets of nearly orthogonal dune crestlines, with apparent slipfaces on the primary crests, ubiquitous wind ripples, areas of coarse-grained wind ripples, and deflated interdune areas. Geomorphic evidence and dune field pattern analysis of dune crest length, spacing, defect density, and orientation indicates that the pattern is complex, representing two constructional generations of dunes. The oldest and best-organized generation forms the primary crestlines and is transverse to circumpolar easterly winds. Gross bed form-normal analysis of the younger pattern of crestlines indicates that it emerged with both circumpolar easterly winds and NE winds and is reworking the older pattern. Mapping of secondary flow fields over the dunes indicates that the most recent transporting winds were from the NE. The younger pattern appears to represent an influx of sediment to the dune field associated with the development of the Olympia Cavi reentrant, with NE katabatic winds channeling through the reentrant. A model of the pattern reformation based upon the reconstructed primary winds and resulting secondary flow fields shows that the development of the secondary pattern is controlled by the boundary condition of the older dune topography

The chronostratigraphy of Late Pleistocene glacial and periglacial aeolian activity in the Tuktoyaktuk Coastlands, NWT, Canada

Aeolian periglacial sand deposits are common in the Tuktoyaktuk Coastlands of Western Arctic Canada. Regionally extensive and thick aeolian sand-sheet deposits have been observed in two major stratigraphic settings: within a sand unit characterized by large aeolian dune deposits; and interbedded with glaciofluvial outwash from the Laurentide Ice Sheet (LIS). Small, localized sand sheets have also been observed along the tops of sandy bluffs, within sequences of drained thermokarst lakes deposits and as an involuted veneer above buried basal ice of the LIS. On the basis of radiocarbon and optically stimulated luminescence (OSL) dates from preserved periglacial aeolian sand sheets and dunes a regional chronostratigraphy is presented which indicates that both extensive dunes and sand sheets accumulated mainly between ca 30 and 13 ka. A switch to dominantly sand-sheet aggradation at ca 14–13 ka, with sand sheets forming widely until ca 8 ka, is attributed to (a) surface armouring by glacial deposits associated with the advance of the LIS; and (b) amelioration of the climate from cold aridity. An absence of OSL dates between ca 8 and 1 ka suggests that sand sheets stabilized during much of the Holocene. Local sand-sheet aggradation during recent centuries has occurred near sandy bluffs and on the floors of drained thermokarst lakes. The OSL dates constrain the maximum extent of the LIS in the Tuktoyaktuk Coastlands to Marine Isotope Stage 2

Barchan dune corridors: field characterization and investigation of control parameters

The structure of the barchan field located between Tarfaya and Laayoune (Atlantic Sahara, Morocco) is quantitatively investigated and compared to that in La Pampa de la Joya (Arequipa, Peru). On the basis of field measurements, we show how the volume, the velocity and the output sand flux of a dune can be computed from the value of its body and horn widths. The dune size distribution is obtained from the analysis of aerial photographs. It shows that these fields are in a statistically homogeneous state along the wind direction and present a `corridor' structure in the transverse direction, in which the dunes have a rather well selected size. Investigating the possible external parameters controlling these corridors, we demonstrate that none among topography, granulometry, wind and sand flux is relevant. We finally discuss the dynamical processes at work in these fields (collisions and wind fluctuations), and investigate the way they could regulate the size of the dunes. Furthermore we show that the overall sand flux transported by a dune field is smaller than the maximum transport that could be reached in the absence of dunes, i.e. in saltation over the solid ground.Comment: revised version for JGR-ES, 36 pages, 21 figure

Syngenetic sand veins and anti-syngenetic sand wedges, Tuktoyaktuk Coastlands, western Arctic Canada

Sand-sheet deposits of full-glacial age in the Tuktoyaktuk Coastlands, western Arctic Canada, contain syngenetic sand veins 1-21 cm wide and sometimes exceeding 9 m in height. Their tall and narrow, chimney-like morphology differs from that of known syngenetic ice wedges and indicates an unusually close balance between the rate of sand-sheet aggradation and the frequency of thermal-contraction cracking. The sand sheets also contain rejuvenated (syngenetic) sand wedges that have grown upward from an erosion surface. By contrast, sand sheets of postglacial age contain few or sometimes no intraformational sand veins and wedges, suggesting that the climatic conditions were unfavourable for thermal-contraction cracking. Beneath a postglacial sand sheet near Johnson Bay, sand wedges with unusually wide tops (3.9 m) extend down from a prominent erosion surface. The wedges grew vertically downward during deflation of the ground surface, and represent anti-syngenetic wedges. The distribution of sand veins and wedges within the sand sheets indicates that the existence of continuous permafrost during sand-sheet aggradation can be inferred confidently only during full-glacial conditions

Chronometry and formation pathways of gypsum using Electron Spin Resonance and Fourier Transform Infrared Spectroscopy

Gypsum is an authigenic precipitate that forms under periods of accentuated aridity and occurs widely in arid zones. However its use in quantitative paleoclimatology has been limited due to the absence of a method to determine the timing of its formation. We present here the results of a feasibility study that demonstrates that the timing of the formation event of gypsum can be estimated using Electron Spin Resonance (ESR) analysis. We used well documented samples from White Sands in New Mexico, USA, the Thar Desert, India and lakes in the Simpson Desert and Mallee Region, Australia and found that ESR ages could be obtained using radiation sensitive SO4-, SO3- radicals and a photobleachable signal O3-. ESR signals were consistent with control ages based on contextual information. These suggest that the dating signals (SO4-, SO3-) are stable over time scales >100 ka. We propose that this stability of the SO4- signals over geological time scales arises due to hydrogen bonding between the water proton and the SO4- radical and that the suitability of these radiation-induced radicals comes from their being a part of the host matrix. Further, ESR along with Fourier Transform Infrared (FT-IR) Spectroscopy methods additionally inform on the geochemical pathways for gypsum formation and help elucidate complex formation processes even in samples that appeared unambiguous gypsum precipitates. Thus, the presence of Hannebachite (CaSO3.1/2H2O) and Mn2+ in Thar and Australian samples suggested a reducing environment such that low valence sulfur reacted with CaCO3 to form hannebachite and eventually gypsum. The presence of sulfur, partially as sulfite in Thar gypsum samples suggested that redox cycles were mediated by microbial activity. Absence of these features in White Sands samples suggested oxic conditions during gypsum precipitation

Induction of aromatic ring: cleavage dioxygenases in Stenotrophomonas maltophilia strain KB2 in cometabolic systems

Stenotrophomonas maltophilia KB2 is known to produce different enzymes of dioxygenase family. The aim of our studies was to determine activity of these enzymes after induction by benzoic acids in cometabolic systems with nitrophenols. We have shown that under cometabolic conditions KB2 strain degraded 0.25–0.4 mM of nitrophenols after 14 days of incubation. Simultaneously degradation of 3 mM of growth substrate during 1–3 days was observed depending on substrate as well as cometabolite used. From cometabolic systems with nitrophenols as cometabolites and 3,4-dihydroxybenzoate as a growth substrate, dioxygenases with the highest activity of protocatechuate 3,4-dioxygenase were isolated. Activity of catechol 1,2- dioxygenase and protocatechuate 4,5-dioxygenase was not observed. Catechol 2,3-dioxygenase was active only in cultures with 4-nitrophenol. Ability of KB2 strain to induce and synthesize various dioxygenases depending on substrate present in medium makes this strain useful in bioremediation of sites contaminated with different aromatic compounds