Using Small Craters to Determine the Erosion Rates of Martian Sedimentary Rock

Mars sedimentary rock erosion rates constrained using crater counts, with applications to organic matter preservation and to the global dust cycle

Authors:

Kite et al

Abstract:

Small-crater counts on Mars light-toned sedimentary rock are often inconsistent with any isochron; these data are usually plotted then ignored. We show (using an 18-HiRISE-image, >10^4 crater dataset) that these non-isochron crater counts are often well-fit by a model where crater production is balanced by crater obliteration via steady exhumation. For these regions, we fit erosion rates. We infer that Mars light-toned sedimentary rocks typically erode at ~10^2 nm/yr, when averaged over 10 km^2 scales and 10^7-10^8 yr timescales. Crater-based erosion-rate determination is consistent with independent techniques, but can be applied to nearly all light-toned sedimentary rocks on Mars. Erosion is swift enough that radiolysis cannot destroy complex organic matter at some locations (e.g. paleolake deposits at SW Melas), but radiolysis is a severe problem at other locations (e.g. Oxia Planum). The data suggest that the relief of the Valles Marineris mounds is currently being reduced by wind erosion, and that dust production on Mars older than 3 Gya greatly exceeds the modern reservoir of mobile dust.

The effect of dust on the martian polar vortices

The effect of dust on the martian polar vortices

Authors:

Guzewich et al

Abstract:

The influence of atmospheric dust on the dynamics and stability of the martian polar vortices is examined, through analysis of Mars Climate Sounder observations and MarsWRF general circulation model simulations. We show that regional and global dust storms produce “transient vortex warming” events that partially or fully disrupt the northern winter polar vortex for brief periods. Increased atmospheric dust heating alters the Hadley circulation and shifts the downwelling branch of the circulation poleward, leading to a disruption of the polar vortex for a period of days to weeks. Through our simulations, we find this effect is dependent on the atmospheric heating rate, which can be changed by increasing the amount of dust in the atmosphere or by altering the dust optical properties (e.g., single scattering albedo). Despite this, our simulations show that some level of atmospheric dust is necessary to produce a distinct northern hemisphere winter polar vortex.

Dust From the Kuiper Belt Produces Benzene in Titan's Atmosphere

Uptake of acetylene on cosmic dust and production of benzene in Titan's atmosphere

Authors:

Frankland et al

Abstract:

A low-temperature flow tube and ultra-high vacuum apparatus were used to explore the uptake and heterogeneous chemistry of acetylene (C2H2) on cosmic dust analogues over the temperature range encountered in Titan's atmosphere below 600 km. The uptake coefficient, γ, was measured at 181 K to be (1.6 ± 0.4) × 10-4, (1.9 ± 0.4) × 10−4 and (1.5 ± 0.4) × 10−4 for the uptake of C2H2 on Mg2SiO4, MgFeSiO4 and Fe2SiO4, respectively, indicating that γ is independent of Mg or Fe active sites. The uptake of C2H2 was also measured on SiO2 and SiC as analogues for meteoric smoke particles in Titan's atmosphere, but was found to be below the detection limit (γ < 6 × 10−8 and < 4 × 10-7, respectively). The rate of cyclo-trimerization of C2H2 to C6H6 was found to be 2.6 × 10-5 exp(-741/T) s−1, with an uncertainty ranging from ± 27 % at 115 K to ± 49 % at 181 K. A chemical ablation model was used to show that the bulk of cosmic dust particles (radius 0.02–10 µm) entering Titan's atmosphere do not ablate (< 1% mass loss through sputtering), thereby providing a significant surface for heterogeneous chemistry. A 1D model of dust sedimentation shows that the production of C6H6via uptake of C2H2 on cosmic dust, followed by cyclo-trimerization and desorption, is probably competitive with gas-phase production of C6H6 between 80 and 120 km.

The Sahara Fertilizes & Poisons the Caribbean

Dust from the Saharan desert is bringing needed iron and other nutrients to underwater plants in the Caribbean, but bacteria may be the first thing to prosper from that dust.

The dust is causing the bacteria to bloom and also become more toxic to humans and marine organisms.

"This has been going on for a long time, but nobody understood it," said Florida State University Professor of Chemical Oceanography William Landing, a co-author on a new paper outlining the effect of the dust. "It's a natural phenomenon."

The new research was published in the May 9 edition of the Proceedings of the National Academy of Sciences.

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Possible water lubricated grain movement in the circumpolar region of Mars

Possible water lubricated grain movement in the circumpolar region of Mars

Authors:

Kereszturi et al

Abstract:

In this work we evaluate a new model on the possibility, could microscopic liquid water supported grain movement on Mars happen at the circumpolar region (in Richardson crater) today, combined with the analysis of new HiRISE ESP images. We confirmed earlier (PSP images based) findings on the morphology, sequential growth and two separate phased formation method of flow features emanate from Dark Dune Spots (1: gas-jet driven streaks toward different directions, 2: flow-like streaks downward). We also identified that the gas-jet ejected and back fallen grains surrounded by water ice produce local enrichment of H2O, forming local water ice layer.

Several model scenarios were developed and evaluated to exploit the possibilities of liquid supported flow, including the increased thickness of interfacial liquid layer by salts and impurities, the collapse and movement of loose stratum of air-fallen dust-salt mixture with interbedded liquid layers, the mechanical force to kick-off the movement by hydration/dehydration cycles, and the migrating phase change plus the seeping of thin liquid film around interconnected grains. Selecting the most relevant elements among them, which are also compatible to our current knowledge of Mars, a comprehensive model was built that could be tested. This best model contains four interconnected and subsequent elements: 1. deposition of airfall dust in autumn and winter producing a loose surface layer, 2. spatial concentration of H2O ice by gas-jet activity during the CO2 sublimation phase, 3. mechanical kick-off by daily expansion/contraction cycles to mix the components, 4. engulfed hygroscopic salts and dust grains to enlarge the ratio of liquid to support the flow. The emerged self-amplifying process could produce daily movement in theory. The scenario contains realistic elements; it is in agreement with the observations, and also being testable by laboratory modelling. The analyzed locations are important because of the joint occurrence of concentrated water ice, elevated temperature and moving flow-features; and it also provides insight into the possible current action of liquid water on Mars.

Middle Eocene Climatic Optimum's Ocean Productivity Spiked Because of Increased Eolian Iron Fertilization

Environmental magnetic implications of magnetofossil occurrence during the Middle Eocene Climatic Optimum (MECO) in pelagic sediments from the equatorial Indian Ocean

Authors:

Savian et al

Abstract:

Magnetic properties of pelagic marine sediments that record the Middle Eocene Climatic Optimum (MECO) at ~ 40 Ma provide information about major environmental changes. The main variations observed during this transient warming event reflect a bacterial magnetofossil signal, but the cause of the linkage between bacterial production and climate remains unclear. We present an environmental magnetic study of middle Eocene deep-sea sediments from the northern edge of Madingley Rise (Ocean Drilling Program Hole 711A, equatorial Indian Ocean) to investigate the origin of the increased magnetic mineral concentration concomitant with subchron C18n.2n, which corresponds to the MECO interval in ODP Hole 711A. This magnetic mineral peak also coincides with a change in lithofacies from calcareous nannofossils to radiolarian ooze, and a slight increase in clay concentration. Magnetite is the main magnetic mineral in the MECO sediments, which occurs as magnetically non-interacting single domain biogenic particles. The increased magnetic mineral concentration across the MECO event is likely to have been caused by increased eolian iron fertilization. This is interpreted to have given rise to increased surface ocean productivity, where increased delivery of iron and nutrients to the seafloor enhanced magnetotactic bacterial populations during the MECO event.

Extreme Dust Storms Delivered Very Reactive Iron to the Late Paleozoic Oceans

Extreme eolian delivery of reactive iron to late Paleozoic icehouse seas

Authors:

Sur et al

Abstract:

The biogeochemical impacts of iron-rich dust to the oceans are known for Earth's recent record but unexplored for deep time, despite recognition of large ancient dust fluxes, particularly during the late Paleozoic. We report a unique Fe relationship for Upper Pennsylvanian mudrock of eolian origin that records lowstand (glacial) conditions within a carbonate buildup of western equatorial Pangaea (western United States) well removed from other detrital inputs. Here, reactive Fe unambiguously linked to dust is enriched without a corresponding increase in total Fe. More broadly, data from thick coeval loess deposits of western equatorial Pangaea show the same marked enrichment in reactive Fe. This enrichment—atypical compared to modern marine, fluvial, glacial, loess, and soil sediments—suggests an enhancement of the reactivity of the internal Fe pool that increased the bioavailability of the Fe for marine primary production. Regardless of the mechanism behind this enhancement, our data in combination with other evidence for high dust fluxes imply delivery of extraordinarily large amounts of biogeochemically reactive Fe to glacial-stage late Paleozoic seas, and modeling of this indicates major impacts on carbon cycling and attendant climatic feedbacks.