The oxidation state of nanophase Fe particles in lunar soil: Implications for space weathering

We report measurements of the oxidation state of Fe nanoparticles within lunar soils that experienced varied degrees of space weathering. We measured >100 particles from immature, submature, and mature lunar samples using electron energy‐loss spectroscopy (EELS) coupled to an aberration‐corrected transmission electron microscope. The EELS measurements show that the nanoparticles are composed of a mixture of Fe⁰, Fe²⁺, and Fe³⁺ oxidation states, and exhibit a trend of increasing oxidation state with higher maturity. We hypothesize that the oxidation is driven by the diffusion of O atoms to the surface of the Fe nanoparticles from the oxygen‐rich matrix that surrounds them. The oxidation state of Fe in the nanoparticles has an effect on modeled reflectance properties of lunar soil. These results are relevant to remote sensing data for the Moon and to the remote determination of relative soil maturities for various regions of the lunar surface.     

Global distribution of volcanic centers and mountains on Io: Control by asthenospheric heating and implications for mountain formation

Jupiter's moon Io possesses numerous tectonic mountains in addition to its ubiquitous volcanoes and volcanic features. Remarkably, a distinct global anticorrelation exists between the spatial distribution of mountains and volcanic centers on Io. This relationship indicates an explicit connection between volcanism and mountain formation, even though the mountains are tectonic in origin (predominantly upthrusted crustal blocks). Spherical harmonic analysis shows the distribution of mountains and volcanic centers have statistically significant power at degree 2; this result is especially striking for the volcanic center distribution, and directly implicates models of asthenospheric tidal heating. The latter predict enhanced heat flux along the equator in a degree-two pattern that matches observations. Mountain formation on Io appears to be a form of dominantly vertical tectonism unique in the modern Solar System: continual burial by widespread volcanism drives the crust inward, which leads to strong compression, and at discrete locations, mountains. Correlation coefficients between the volcanic and mountain distributions indicate statistically meaningful anticorrelation at low spectral degrees (l = 1, 2, 4, and 6); the anticorrelation is especially significant between the longitudinal (sectorial) l = 2 components when considered on their own. We compare this anticorrelation with published models that link volcano and mountain formation. While consistent in part with l = 2 convection models, which predict such an anticorrelation (in principle), such low degree anticorrelations are also (if not more) compatible with mountain formation due to, or influenced by, thermal expansion of Io's crust, and deep compression and thrust faulting in regions of lower than average volcanic heat-piping. Positive correlations between mountain and volcanic center distributions at high spectral degree may reflect structural links between a good fraction of mountain blocks and adjacent volcanic paterae, whereas the anticorrelation at low degree implies that most volcanic features (which are far more numerous overall) form independently of mountains.     

Constraints on Jalisco Block Motion and Tectonics of the Guadalajara Triple Junction from 1998�C2001 Campaign GPS Data

A GPS campaign network in the state of Jalisco was occupied for?~36?h per station most years between 1995 and 2005; we use data from 1998?C2001 to investigate tectonic motion and interseismic deformation in the Jalisco area with respect to the North America plate. The twelve stations used in this analysis provide coverage of the Jalisco Block and adjacent North America plate, and show a pattern of motion that implies some contribution to Jalisco Block boundary deformation from both tectonic motion and interseismic deformation due to the offshore 1995 earthquake. The consistent direction and magnitude of station motion on the Jalisco Block with respect to the North America reference frame,?~2?mm/year to the southwest (95% confidence level), perhaps can be attributed to tectonic motion. However, some station velocities within and across the boundaries of the Jalisco Block are also non-zero (95% confidence level), and the overall pattern of station velocities indicates both viscoelastic response to the 1995 earthquake and partial coupling of the subduction interface (together termed ??interseismic deformation??). Our results show motion across the northern Colima rift, the eastern boundary of the Jalisco Block, which is likely to be sinistral oblique extension rather than pure extension. We constrain extension across both the Colima rift and the northeastern boundary of the Jalisco Block, the Tepic-Zacoalco rift, to???8?mm/year (95% confidence level), slow compared to relative rates of motion at nearby plate boundaries.     

Linear trends in sea surface temperature of the tropical Pacific Ocean and implications for the El Niño-Southern Oscillation

A principal component decomposition of monthly sea surface temperature (SST) variability in the tropical Pacific Ocean demonstrates that nearly all of the linear trends during 1950–2010 are found in two leading patterns. The first SST pattern is strongly related to the canonical El Niño-Southern Oscillation (ENSO) pattern. The second pattern shares characteristics with the first pattern and its existence solely depends on the presence of linear trends across the tropical Pacific Ocean. The decomposition also uncovers a third pattern, often referred to as ENSO Modoki, but the linear trend is small and dataset dependent over the full 61-year record and is insignificant within each season. ENSO Modoki is also reflected in the equatorial zonal SST gradient between the Niño-4 region, located in the west-central Pacific, and the Niño-3 region in the eastern Pacific. It is only in this zonal SST gradient that a marginally significant trend arises early in the Northern Hemisphere spring (March–May) during El Niño and La Niña and also in the late summer (July–September) during El Niño. Yet these SST trends in the zonal gradient do not unequivocally represent an ENSO Modoki-like dipole because they are exclusively associated with significant positive SST trends in either the eastern or western Pacific, with no corresponding significant negative trends. Insignificant trends in the zonal SST gradient are evident during the boreal wintertime months when ENSO events typically mature. Given the presence of positive SST trends across much of the equatorial Pacific Ocean, using fixed SST anomaly thresholds to define ENSO events likely needs to be reconsidered.     

Holocene development of maritime ombrotrophic peatlands of the St. Lawrence North Shore in eastern Canada

Macrofossil analyses were used to reconstruct long-term vegetation successions within ombrotrophic peatlands (bogs) from the northern shorelines of the St. Lawrence Estuary (Baie-Comeau) and the Gulf of St. Lawrence (Havre-St-Pierre). Over the Holocene, the timing and the ecological context of peatland inception were similar in both regions and were mainly influenced by fluctuations in relative sea level. Peat accumulation started over deltaic sands after the withdrawal of the Goldthwait Sea from 7500 cal yr BP and above silt–clay deposits left by the Laurentian marine transgression after 4200 cal yr BP. In each region, the early vegetation communities were similar within these two edaphic contexts where poor fens with Cyperaceae and eastern larch (Larix laricina) established after land emergence. The rapid transitions to ombrotrophy in the peatlands of Baie-Comeau are associated with particularly high rates of peat accumulation during the early developmental stage. The results suggest that climate was more propitious to Sphagnum growth after land emergence in the Baie-Comeau area. Macrofossil data show that treeless Sphagnum-dominated bogs have persisted over millennia and that fires had few impacts on the vegetation dynamics. This study provides insight into peatland vegetation responses to climate in a poorly documented region of northeastern America.     

Model constraints on the opening rates of bands on Europa

A mid-ocean-ridge spreading analog is used to constrain the opening rates and brittle-ductile transition depths for two axisymmetric ridged bands on Europa. Estimates of brittle-ductile transition depth based on the morphologies of Yelland and Ino Lineae are combined with a conductive cooling model based on a mid-ocean ridge analog to estimate the opening rates and active lifetimes of the bands. This model limits local strain rates to ∼¹⁰⁻¹⁵-¹⁰⁻¹² s⁻¹, opening rates to 0.2-40 mm yr⁻¹, and active lifetimes of the bands to 0.1-30 Myr. If the observed structures in the outer portions of ridged bands are indeed normal faults, the estimated range for the tensile strength of ice on Europa is 0.4-2 MPa, consistent with nonsynchronous rotation as the dominant driving mechanism for band opening.     

Living on the Edge: Increasing Patch Size Enhances the Resilience and Community Development of a Restored Salt Marsh

Foundation species regulate communities by reducing environmental stress and providing habitat for other species. Successful restoration of biogenic habitats often depends on restoring foundation species at appropriate spatial scales within a suitable range of environmental conditions. An improved understanding of the relationship between restoration scale and environmental conditions has the potential to improve restoration outcomes for many biogenic habitats. Here, we identified and tested whether inundation/exposure stress and spatial scale (patch size) can interactively determine (1) survival and growth of a foundation species, Spartina alterniflora and (2) recruitment of supported fauna. We planted S. alterniflora and artificial mimics in large and small patches at elevations above and below local mean sea level (LMSL) and monitored plant survivorship and production, as well as faunal recruitment. In the first growing season, S. alterniflora plant survivorship and stem densities were greater above LMSL than below LMSL regardless of patch size, while stem height was greatest in small patches below LMSL. By the third growing season, S. alterniflora patch expansion was greater above LMSL than below LMSL, while stem densities were higher in large patches than small patches, regardless of location relative to LMSL. Unlike S. alterniflora, which was more productive above LMSL, sessile marine biota recruitment to mimic plants was higher in patches below LMSL than above LMSL. Our results highlight an ecological tradeoff at ~LMSL between foundation species restoration and faunal recruitment. Increasing patch size as inundation increases may offset this tradeoff and enhance resilience of restored marshes to sea-level rise.     

Pathways for adaptive and integrated disaster resilience

The GIS-multicriteria decision analysis (GIS-MCDA) technique is increasingly used for landslide hazard mapping and zonation. It enables the integration of different data layers with different levels of uncertainty. In this study, three different GIS-MCDA methods were applied to landslide susceptibility mapping for the Urmia lake basin in northwest Iran. Nine landslide causal factors were used, whereby parameters were extracted from an associated spatial database. These factors were evaluated, and then, the respective factor weight and class weight were assigned to each of the associated factors. The landslide susceptibility maps were produced based on weighted overly techniques including analytic hierarchy process (AHP), weighted linear combination (WLC) and ordered weighted average (OWA). An existing inventory of known landslides within the case study area was compared with the resulting susceptibility maps. Respectively, Dempster-Shafer Theory was used to carry out uncertainty analysis of GIS-MCDA results. Result of research indicated the AHP performed best in the landslide susceptibility mapping closely followed by the OWA method while the WLC method delivered significantly poorer results. The resulting figures are generally very high for this area, but it could be proved that the choice of method significantly influences the results.