Groundwater seepage landscapes from distant and local sources in experiments and on Mars

© 2014 Author(s). Valleys with theater-shaped heads can form due to the seepage of groundwater and as a result of knickpoint (waterfall) erosion generated by overland flow. This ambiguity in the mechanism of formation hampers the interpretation of such valleys on Mars, particularly since there is limited knowledge of material properties. Moreover, the hydrological implications of a groundwater or surface water origin are important for our understanding of the evolution of surface features on Mars, and a quantification of valley morphologies at the landscape scale may provide diagnostic insights on the formative hydrological conditions. However, flow patterns and the resulting landscapes produced by different sources of groundwater are poorly understood. We aim to improve the understanding of the formation of entire valley landscapes through seepage processes from different groundwater sources that will provide a framework of landscape metrics for the interpretation of such systems. We study groundwater seepage from a distant source of groundwater and from infiltration of local precipitation in a series of sandbox experiments and combine our results with previous experiments and observations of the Martian surface. Key results are that groundwater flow piracy acts on valleys fed by a distant groundwater source and results in a sparsely dissected landscape of many small and a few large valleys. In contrast, valleys fed by a local groundwater source, i.e., nearby infiltration, result in a densely dissected landscape. In addition, valleys fed by a distant groundwater source grow towards that source, while valleys with a local source grow in a broad range of directions and have a strong tendency to bifurcate, particularly on flatter surfaces. We consider these results with respect to two Martian cases: Louros Valles shows properties of seepage by a local source of groundwater and Nirgal Vallis shows evidence of a distant source, which we interpret as groundwater flow from Tharsis

Morphology of the recently re-classified Tasman masked booby (Sula dactylatra tasmani) breeding on the Kermadec Islands

Once thought to be extinct, the Tasman Booby Sula tasmani has recently been re-classified as a subspecies of the Masked Booby S. dactylatra on the basis of genetic data. This re-classification raises the issue of whether this novel clade has a distinct morphology. Morphological differences in size, as well as coloration of integuments, bill and iris have been found in other subspecies of the Masked Booby but have not yet been reported for live Kermadec Islands breeding individuals. Museum specimens from this breeding location have been separated from other Pacific breeding subspecies by their longer wings. We sampled a total of 21 individuals from North Meyer Islet, Kermadec Group, New Zealand, and applied molecular sexing to obtain sex-specific morphometric measurements. We matched dimorphism in vocalization with genetic sexing results and photographic documentation of human-assessed bill, foot and eye coloration. While culmen measurements were consistent with reports from museum specimens, wing chords from living specimens of Tasman Masked Boobies were 3% and 4% larger in males and females, respectively. Females had larger culmens and wings than males, consistent with the low extent of sexual dimorphism reported from museum skins. Adult Tasman Masked Boobies had yellow to buff-yellow feet, while fledglings, as in most sulids, had grey to greyish-yellow feet. Our findings confirm the distinctively long wing and particular iris coloration previously reported for the taxon and provide the first description of integument coloration of live specimens. This study highlights the importance of including in situ assessment in taxon descriptions

Estimating precipitation on early Mars using a radiative-convective model of the atmosphere and comparison with inferred runoff from geomorphology

We compare estimates of atmospheric precipitation during the Martian Noachian-Hesperian boundary 3.8 Gyr ago as calculated in a radiative-convective column model of the atmosphere with runoff values estimated from a geomorphological analysis of dendritic valley network discharge rates. In the atmospheric model, we assume CO2-H2O-N2 atmospheres with surface pressures varying from 20 mb to 3 bar with input solar luminosity reduced to 75% the modern value. Results from the valley network analysis are of the order of a few mm d-1 liquid water precipitation (1.5-10.6 mm d-1, with a median of 3.1 mm d-1). Atmospheric model results are much lower, from about 0.001-1 mm d-1 of snowfall (depending on CO2 partial pressure). Hence, the atmospheric model predicts a significantly lower amount of precipitated water than estimated from the geomorphological analysis. Furthermore, global mean surface temperatures are below freezing, i.e. runoff is most likely not directly linked to precipitation. Therefore, our results strongly favor a cold early Mars with episodic snowmelt as a source for runoff. Our approach is challenged by mostly unconstrained parameters, e.g. greenhouse gas abundance, global meteorology (for example, clouds) and planetary parameters such as obliquity- which affect the atmospheric result - as as well as by inherent problems in estimating discharge and runoff on ancient Mars, such as a lack of knowledge on infiltration and evaporation rates and on flooding timescales, which affect the geomorphological data. Nevertheless, our work represents a first step in combining and interpreting quantitative tools applied in early Mars atmospheric and geomorphological studies.Comment: accepted in Planetary and Space Science, 37 pages, 14 figures, 2 table

a comparison of morphological and petrological methods

In planetary sciences, the emplacement of lava flows is commonly modelled using a single rheological parameter (apparent viscosity or apparent yield strength) calculated from morphological dimensions using Jeffreysʼ and Hulmeʼs equations. The rheological parameter is then typically further interpreted in terms of the nature and chemical composition of the lava (e.g., mafic or felsic). Without the possibility of direct sampling of the erupted material, the validity of this approach has remained largely untested. In modern volcanology, the complex rheological behaviour of lavas is measured and modelled as a function of chemical composition of the liquid phase, fractions of crystals and bubbles, temperature and strain rate. Here, we test the planetary approach using a terrestrial basaltic lava flow from the Western Volcanic Zone in Iceland. The geometric parameters required to employ Jeffreysʼ and Hulmeʼs equations are accurately estimated from high-resolution HRSC-AX Digital Elevation Models. Samples collected along the lava flow are used to constrain a detailed model of the transient rheology as a function of cooling, crystallisation, and compositional evolution of the residual melt during emplacement. We observe that the viscosity derived from the morphology corresponds to the value estimated when significant crystallisation inhibits viscous deformation, causing the flow to halt. As a consequence, the inferred viscosity is highly dependent on the details of the crystallisation sequence and crystal shapes, and as such, is neither uniquely nor simply related to the bulk chemical composition of the erupted material. This conclusion, drawn for a mafic lava flow where crystallisation is the primary process responsible for the increase of the viscosity during emplacement, should apply to most of martian, lunar, or mercurian volcanic landforms, which are dominated by basaltic compositions. However, it may not apply to felsic lavas where vitrification resulting from degassing and cooling may ultimately cause lava flows to halt

Variation in plasma oxidative status and testosterone level in relation to egg-eviction effort and age of brood-parasitic common cuckoo nestlings

To avoid competition for parental care, brood-parasitic Common Cuckoo (Cuculus canorus) nestlings evict all of the host's eggs and nestlings within a few days after hatching. Little is known about the physiological effects of eviction behavior on the cuckoo nestling's oxidative balance or about age-related variation in plasma oxidative status and testosterone level of developing birds. We examined whether the cuckoo nestling's plasma oxidative status was related to prior effort in eviction and quantified variation in the level of reactive oxygen metabolites, of nonenzymatic antioxidant capacity, and of testosterone concentration in plasma at various phases of the cuckoo's development. Levels of both reactive oxygen metabolites and antioxidant capacity were greater in older than in younger nestlings, suggesting that younger nestlings effectively counterbalance their increased production of free radicals, whereas, near fledging, levels of reactive oxygen metabolites increase despite improved antioxidant capacity. Possibly, overall energy expenditure increases with age and elevates the production of reactive oxygen species to a rate higher than what the antioxidant system could eliminate. Plasma testosterone level was the highest at nestlings' intermediate phase of growth. High levels of testosterone may be required during the period of fastest growth, and when the growth rate levels off near fledging, testosterone levels may also decline. Cuckoo chicks that evicted more host eggs from steeper nests had higher plasma levels of reactive oxygen metabolites shortly after the eviction period, suggesting that eviction is costly in terms of an increased level of oxidative stress. Para evitar la competencia por el cuidado parental, los polluelos parásitos de nidada de Cuculus canorus desalojan todos los huevos y los polluelos del hospedador a los pocos días después de la eclosión. Se sabe poco sobre los efectos fisiológicos del comportamiento de desalojo en el balance oxidativo de los polluelos de C. canorus o sobre la variación en el estatus oxidativo del plasma y el nivel de testosterona relacionado con la edad de las aves en desarrollo. Examinamos si el estatus oxidativo del plasma de los polluelos de C. canorus se relacionaba con un esfuerzo previo de desalojo y cuantificamos la variación en el nivel de metabolitos reactivos de oxígeno, la capacidad antioxidante no enzimática y la concentración de testosterona en el plasma en varias fases del desarrollo de C. canorus. Tanto los niveles de metabolitos reactivos de oxígeno como la capacidad antioxidante fueron superiores en los polluelos de mayor edad que en los más jóvenes, lo que sugiere que los polluelos de menor edad contrarrestan eficazmente el aumento de la producción de radicales libres, mientras que, cuando se apróximan al abandono del nido, los niveles de metabolitos reactivos de oxígeno aumentan a pesar de una mejora en la capacidad antioxidante. Posiblemente, el gasto total de energía se incrementa con la edad, elevándose la producción de formas reactivas de oxígeno a una tasa mayor de la que el sistema antioxidante puede eliminar. El nivel de testosterona en el plasma fue máximo en la fase intermedia del crecimiento de los polluelos. Pueden requerirse altos niveles de testosterona durante el período de mayor crecimiento y, cuando la tasa de crecimiento se estabiliza cerca del abandono del nido, los niveles de testosterona también podrián disminuir. Los polluelos de C. canorus que desalojaron más huevos del hospedador en nidos con una estructura más empinada tuvieron niveles de plasma de metabolitos reactivos de oxígeno en plasma más altos poco después del período de desalojo, sugiriendo que el desalojo es costoso en términos de un incremento en el nivel de estrés oxidativo

The PanCam instrument on the 2018 Exomars rover: Scientific objectives

Geophysical Research Abstract

Spatial and Alignment Analyses for a field of Small Volcanic Vents South of Pavonis Mons Mars

The Tharsis province of Mars displays a variety of small volcanic vent (10s krn in diameter) morphologies. These features were identified in Mariner and Viking images [1-4], and Mars Orbiter Laser Altimeter (MOLA) data show them to be more abundant than originally observed [5,6]. Recent studies are classifying their diverse morphologies [7-9]. Building on this work, we are mapping the location of small volcanic vents (small-vents) in the Tharsis province using MOLA, Thermal Emission Imaging System, and High Resolution Stereo Camera data [10]. Here we report on a preliminary study of the spatial and alignment relationships between small-vents south of Pavonis Mons, as determined by nearest neighbor and two-point azimuth statistical analyses. Terrestrial monogenetic volcanic fields display four fundamental characteristics: 1) recurrence rates of eruptions,2 ) vent abundance, 3) vent distribution, and 4) tectonic relationships [11]. While understanding recurrence rates typically requires field measurements, insight into vent abundance, distribution, and tectonic relationships can be established by mapping of remotely sensed data, and subsequent application of spatial statistical studies [11,12], the goal of which is to link the distribution of vents to causal processes