Water induced sediment levitation enhances downslope transport on Mars

On Mars, locally warm surface temperatures (~293 K) occur, leading to the possibility of (transient) liquid water on the surface. However, water exposed to the martian atmosphere will boil, and the sediment transport capacity of such unstable water is not well understood. Here, we present laboratory studies of a newly recognized transport mechanism: “levitation” of saturated sediment bodies on a cushion of vapor released by boiling. Sediment transport where this mechanism is active is about nine times greater than without this effect, reducing the amount of water required to transport comparable sediment volumes by nearly an order of magnitude. Our calculations show that the effect of levitation could persist up to ~48 times longer under reduced martian gravity. Sediment levitation must therefore be considered when evaluating the formation of recent and present-day martian mass wasting features, as much less water may be required to form such features than previously thought

Amazonian chemical weathering rate derived from stony meteorite finds at Meridiani Planum on Mars

© The Author(s) 2016.Spacecraft exploring Mars such as the Mars Exploration Rovers Spirit and Opportunity, as well as the Mars Science Laboratory or Curiosity rover, have accumulated evidence for wet and habitable conditions on early Mars more than 3 billion years ago. Current conditions, by contrast, are cold, extremely arid and seemingly inhospitable. To evaluate exactly how dry today's environment is, it is important to understand the ongoing current weathering processes. Here we present chemical weathering rates determined for Mars. We use the oxidation of iron in stony meteorites investigated by the Mars Exploration Rover Opportunity at Meridiani Planum. Their maximum exposure age is constrained by the formation of Victoria crater and their minimum age by erosion of the meteorites. The chemical weathering rates thus derived are ~1 to 4 orders of magnitude slower than that of similar meteorites found in Antarctica where the slowest rates are observed on Earth

Stable carbon isotopes in dissolved inorganic carbon: Extraction and implications for quantifying the contributions from silicate and carbonate weathering in the Krishna River system during peak discharge

Stable carbon isotope ratios of dissolved inorganic (DIC) and organic carbon (DOC) are of particular interest in aquatic geochemistry. The precision for this type of analysis is typically reported in the range of 0.1‰ to 0.5‰. However, there is no published attempt that compares δ13C measurements of DIC and DOC among different laboratories for natural water samples

Zonal variability in primary production and nitrogen uptake rates in the southwestern Indian Ocean and the Southern Ocean

Hydrographic parameters along with the primary and new production measurements were carried out during the austral summer, 2009, in the southwestern Indian Ocean and Indian sector of the Southern Ocean (SO). The production varies from 185 to >900mgCm -2d -1 in different zones of SO. The zonal variations in production accompany variations in SST, salinity and nutrients. Further, the new production (0.3 to 4.1mmolNm -2d -1) covaries with the overall production, while the uptake of reduced forms of nitrogen (both NH 4 and urea) show opposite trends. In the NO 3 limiting environment (north of subtropical convergence), NH 4 uptake dominates the total regenerated production, whereas, urea uptake dominates the regenerated production under Si, light and micronutrient (e.g., Fe) limiting conditions (found between the subtropical convergence and Antarctica). On the basis of the C and N uptake data, the studied region can be divided into five zones (from the south to the north) viz., located between (i) the Antarctic continent and the polar front (Antarctic zone; ANZ), (ii) the polar and subantarctic fronts (SAF) (Polar frontal zone; PFZ), (iii) SAF and Agulhas Retroflection fronts (ARF) (South Subtropical front; SSTF), (iv) subtropical frontal zone (STFZ), and (v) ARF and the north subtropical front (Subtropical zone; STZ). Except at SSTF, regenerated production dominates in all the zones. From the south to the north, this could be due to different reasons e.g., light, grazing by zooplankton, supply of key micronutrients (probably Fe), Si-limitation, or NO 3-limitation. In the absence of such limitations, the maximum possible f-ratio in SO could be as high as 0.78±0.12 and under such conditions the region could export most of the total production to the deep. Supply of micronutrients through the Agulhas return current and from the Crozet Island supports the higher chl a, C uptake and new production at the 48°E transect relative to the 57.5°E transect. The C:N assimilation ratio is found to be 5.64, marginally lower than the canonical Redfield ratio. This slight difference is likely due to the variation in the composition of phytoplankton and NO 3-limitation in some zones. A comparison with earlier results shows that seasonal and spatial variations in f-ratios in these zones are much higher than its inter-annual variability

Eccentricity and obliquity paced carbon cycling in the Early Triassic and implications for post-extinction ecosystem recovery

The timing of marine ecosystem recovery following the End Permian Mass Extinction (EPME) remains poorly constrained given the lack of radiometric ages. Here we develop a high-resolution carbonate carbon isotope (delta C-13(carb)) record for 3.20 million years of the Olenekian in South China that defines the astronomical time-scale for the critical interval of major evolutionary and oceanic events in the Spathian. delta C-13(carb) documents eccentricity modulation of carbon cycling through the period and a strong obliquity signal. A shift in phasing between short and long eccentricity modulation, and amplification of obliquity, is nearly coincident with a 2% decrease in seawater delta C-13(DIC), the last of a longer-term stepped decrease through the Spathian. The mid-Spathian shift in seawater delta C-13(DIC) to typical thermocline values is interpreted to record a major oceanic reorganization with global climate amelioration. Coincidence of the phasing shift with the first occurrence of marine reptiles (248.81 Ma), suggests that their invasion into the sea and the onset of a complex ecosystem were facilitated by restoration of deep ocean ventilation linked mechanistically to a change in the response of the oceanic carbon reservoir to astronomical forcing. Together these records place the first constraints on the duration of the post-extinction recovery to 3.35 myr.National Natural Science Foundation of China [40920124002, 41372016]; State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) [123102]; Research Fund for the Doctoral Program of Higher Education [20120001110072]; National Geographic grant [8669-09]; China Scholarship Council (CSC); National Science Foundation [EAR-1024737]; U.S. National Science Foundation [EAR-1151438]SCI(E)[email protected]; [email protected]

Siberian larch forests and the ion content of thaw-lakes form a geochemically functional entity

Siberian larch forests growing on shallow permafrost soils have not, until now, been considered as controlling the abiotic and biotic characteristics of the vast number of thaw-lake ecosystems. We show, using four independent data-sets (a modern data-set from 201 lakes from tundra to taiga, and three lake-core records), that lake-water geochemistry in Yakutia is highly correlated with vegetation. Alkalinity increases with catchment forest density. We postulate that in this arid area, higher evapotranspiration in larch forests compared to tundra vegetation leads to local salt accumulation in soils. Solutes are transported to nearby thaw-lakes during rain-events and snow-melt, but are not fully transported into rivers because there is no continuous groundwater-flow within permafrost soils. This implies that potentially large shifts in the chemical characteristics of aquatic ecosystems to known warming are absent because of the slow response of catchment forests to climate change