Particle transport and distribution on the Mars Science Laboratory mission: Effects of triboelectric charging

We report on the nature of fine particle (<150 μm) transport under simulated martian conditions, in order to better understand the Mars Science Laboratory’s (MSL) sample acquisition, processing and handling subsystem (SA/SPaH). We find that triboelectric charging due to particle movement may have to be controlled in order for successful transport of fines that are created within the drill, processed through the Collection and Handling for In situ Martian Rock Analysis (CHIMRA) sample handing system, and delivered to the Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments. These fines will be transferred from the surface material to the portioner, a 3 mm diameter, 8 mm deep distribution center where they will drop ∼2 cm to the instrument inlet funnels. In our experiments, movement of different material including terrestrial analogs and martian soil simulants (Mars Mojave Simulant - MMS) resulted in 1-7 nanocoulombs of charge to build up for several different experimental configurations. When this charging phenomenon occurs, several different results are observed including particle clumping, adherence of material on conductive surfaces, or electrostatic repulsion, which causes like-charged particles to move away from each other. This electrostatic repulsion can sort samples based upon differing size fractions, while adhesion causes particles of different sizes to bind into clods. Identifying these electrostatic effects can help us understand potential bias in the analytical instruments and to define the best operational protocols to collect samples on the surface of Mars.     

The diverse nature of optical emission lines in brightest cluster galaxies: IFU observations of the central kiloparsec

We present integral field spectroscopy of the nebular line emission in a sample of nine brightest cluster galaxies (BCGs). The sample was chosen to probe both cooling flow and non-cooling flow clusters, as well as a range of cluster X-ray luminosities. The line emission morphology and velocity gradients suggest a great diversity in the properties of the line emitting gas. While some BCGs show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and MKW 3s), others have extended emission (Abell 1204, Abell 2199), while still others have centrally concentrated emission (Abell 2052). We examine diagnostic line ratios to determine the dominant ionization mechanisms in each galaxy. Most of the galaxies show regions with active galactic nucleus like spectra, however, for two BCGs, Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which can be described by the emission from young stellar populations. The diversity of emission-line properties in our sample of BCGs suggests that the emission mechanism is not universal, with different ionization processes dominating different systems. Given this diversity, there is no evidence for a clear distinction of the emission-line properties between cooling flow and non-cooling flow BCGs. It is not always cooling flow BCGs which show emission (or young stellar populations), and non-cooling flow BCGs which do not.     

Landscape variations in stream water SO4 and δSSO4 in a boreal stream network

Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO₄²⁻ and δ³⁴S_SO4 in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (<2% wetland cover) S-SO₄²⁻ concentrations in stream water averaged 1.7 mg L⁻¹ whereas in wetland dominated catchments (>30% wetland cover) the concentrations averaged 0.3 mg L⁻¹. A significant negative relationship was observed between S-SO₄²⁻ and percentage wetland coverage (r² = 0.77, p < 0.001) and the annual export of stream water SO₄²⁻ and wetland coverage (r² = 0.76, p < 0.001). The percentage forest coverage was on the other hand positively related to stream water SO₄²⁻ concentrations and the annual export of stream water SO₄²⁻ (r² = 0.77 and r² = 0.79, respectively). The annual average δ³⁴S_SO4 value in wetland dominated streams was +7.6‰ and in streams of forested catchments +6.7‰. At spring flood the δ³⁴S_SO4 values decreased in all streams by 1‰ to 5‰. The δ³⁴S_SO4 values in all streams were higher than the δ³⁴S_SO4 value of +4.7‰ in precipitation (snow). The export of S ranged from 0.5 kg S ha⁻¹ yr⁻¹ (wetland headwater stream) to 3.8 kg S ha⁻¹ yr⁻¹ (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha⁻¹ yr⁻¹ (2002-2006) the mass balance results in a net export of S from all catchments, except in catchments with >30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.     

Spatial and temporal dynamics of nitrogen exchange in an upwelling reach of a groundwater-fed river and potential response to perturbations changing rainfall patterns under UK climate change scenarios

We report the complex spatial and temporal dynamics of hyporheic exchange flows (HEFs) and nitrogen exchange in an upwelling reach of a 200 m groundwater-fed river. We show how research combining hydrological measurement, geophysics and isotopes, together with nutrient speciation techniques provides insight on nitrogen pathways and transformations that could not have been captured otherwise, including a zone of vertical preferential discharge of nitrate from deeper groundwater, and a zone of rapid denitrification linking the floodplain with the riverbed. Nitrate attenuation in the reach is dominated by denitrification but is spatially highly variable. This variability is driven by groundwater flow pathways and landscape setting, which influences hyporheic flow, residence time and nitrate removal. We observed the spatial connectivity of the river to the riparian zone is important because zones of horizontal preferential discharge supply organic matter from the floodplain and create anoxic riverbed conditions with overlapping zones of nitrification potential and denitrification activity that peaked 10–20 cm below the riverbed. Our data also show that temporal variability in water pathways in the reach is driven by changes in stage of the order of tens of centimetres and by strength of water flux, which may influence the depth of delivery of dissolved organic carbon. The temporal variability is sensitive to changes to river flows under UK climate projections that anticipate a 14%–15% increase in regional median winter rainfall and a 14%–19% reduction in summer rainfall. Superimposed on seasonal projections is more intensive storm activity that will likely lead to a more dynamic and inherently complex (hydrologically and biogeochemically) hyporheic zone. We recorded direct evidence of suppression of upwelling groundwater (flow reversal) during rainfall events. Such flow reversal may fuel riverbed sediments whereby delivery of organic carbon to depth, and higher denitrification rates in HEFs might act in concert to make nitrate removal in the riverbed more efficient.     

The effects of floods on the temperature of riparian groundwater

The transition area between rivers and their adjacent riparian aquifers, which may comprise the hyporheic zone, hosts important biochemical reactions, which control water quality. The rates of these reactions and metabolic processes are temperature dependent. Yet the thermal dynamics of riparian aquifers, especially during flooding and dynamic groundwater flow conditions, has seldom been studied. Thus, we investigated heat transport in riparian aquifers during 3 flood events of different magnitudes at 2 sites along the same river. River and riparian aquifer temperature and water‐level data along the Lower Colorado River in Central Texas, USA, were monitored across 2‐dimensional vertical sections perpendicular to the bank. At the downstream site, preflood temperature penetration distance into the bank suggested that advective heat transport from lateral hyporheic exchange of river water into the riparian aquifer was occurring during relatively steady low‐flow river conditions. Although a small (20‐cm stage increase) dam‐controlled flood pulse had no observable influence on groundwater temperature, larger floods (40‐cm and >3‐m stage increases) caused lateral movement of distinct heat plumes away from the river during flood stage, which then retreated back towards the river after flood recession. These plumes result from advective heat transport caused by flood waters being forced into the riparian aquifer. These flood‐induced temperature responses were controlled by the size of the flood, river water temperature during the flood, and local factors at the study sites, such as topography and local ambient water table configuration. For the intermediate and large floods, the thermal disturbance in the riparian aquifer lasted days after flood waters receded. Large floods therefore have impacts on the temperature regime of riparian aquifers lasting long beyond the flood's timescale. These persistent thermal disturbances may have a significant impact on biochemical reaction rates, nutrient cycling, and ecological niches in the river corridor.     

The pulsating hydrogen-deficient star LSS 3184 (BX Cir)

We present extensive photometry and spectroscopy of the extremely hydrogen-deficient star, LSS 3184, recently discovered to be a rapid variable (period ∼0.1066 d) strikingly similar to V652 Her. Over 95 h of photometry confirms the reported variability, which is of rather low amplitude (Δ V ∼0.03 mag), defines the light curve with greater precision and establishes a much more accurate ephemeris (period ∼0.106 578 4 d) to form a basis for detecting period change. Attention is drawn to the usefulness of a period-finding technique that fits harmonic components to the photometric observations. Spectroscopy shows a peak-to-peak variation in radial velocity of about 30 km s⁻¹, which, when combined with the photometric observations, confirms the pulsational nature of the variability and strongly indicates that the pulsations are radial in nature.