Mesoscale surface circulation and variability of Southern Indian Ocean derived by combining satellite altimetry and drifter observations

High resoultion Eulerian mean velocity field has been derived by combining the satellite tracked surface drifter data with satellite altimetry and ocean surface winds. The drifter data used in this study includes Argos and surface drifter data from Global Drifter Program. Maps of Sea Level Anomaly(MSLA) weekly files with a resolution of(1/3)° in both Latitude and Longitude for the period 1993–2012 have been used. The Ekman current is computed using ocean surface mean wind fields from scatterometers onboard ERS 1/2,Quikscat and ASCAT. The derived mean velocity field exhibits the broad flow of Antarctic Circumpolar Current with speeds up to 0.6 m/s.Anomalous field is quite significant in the western part between 20° and 40°E and in the eastern part between 80°E and 100°E with velocity anomaly up to 0.3 m/s. The estimated mean flow pattern well agrees with the dynamic topography derived from in-situ observations. Also,the derived velocity field is consistent with the in-situ ADCP current measurements. Eddy kinetic energy illustrates an increasing trend during 1993–2008 and is in phase coherence with the Southern Annular Mode by three month lag. Periodic modulations are found in the eddy kinetic energy due the low frequency Antarctic Circumpolar Wave propagation.     

Using Shoreline Video Assessment for coastal planning and restoration in the context of climate change in Kien Giang,Vietnam

Kien Giang, bordering Cambodia in the Mekong River Delta, is one of the two most vulnerable provinces in the region to coastal erosion and flooding. Coastal protection can conflict with current land use and economic development activities. The conditions of the mangrove forest and mainland coastline of the Kien Giang province were assessed using the Shoreline Video Assessment Method (SVAM) backed up with information from satellite images. Half of the 206 km Kien Giang coastline has been eroded or is being eroded. Protective mangrove forests naturally occurred in 74% of the coastline but have been under threat from illegal cutting, erosion and coastal retreat. Accurate information on the state of the coastline and mangrove forest health provided invaluable data for developing a new coastal rehabilitation plan to guard against future sea level rise. In contrast to the current boundary management of land and natural resources, this plan divided the provincial coastline into 19 sections based on the landscape condition and exposure to erosion. Priority strategic actions for erosion management, mangrove restoration and sustainable livelihood development for local communities for each section of coast were developed based on an integrated cross sectoral approach and practical experience in the Conservation and Development of the Kien Giang Biosphere Reserve Project.

     

Boron abundances and isotopic ratios of olivine grains on Itokawa returned by the Hayabusa spacecraft

We report the B abundances and isotopic ratios of two olivine grains from the S‐type asteroid Itokawa sampled by the Hayabusa spacecraft. Olivine grains from the Dar al Gani (DaG) 989 LL6 chondrite were used as a reference. Since we analyzed polished thin sections in both cases, we expect the contribution from the solar wind B (rich in ¹⁰B) to be minimal because the solar wind was implanted only within very thin layers of the grain surface. The Itokawa and DaG 989 olivine grains have homogeneous B abundances (~400 ppb) and ¹¹B/¹⁰B ratios compatible with the terrestrial standard and bulk chondrites. The observed homogeneous B abundances and isotopic ratios of the Itokawa olivine grains are likely the result of thermal metamorphism which occurred in the parent asteroid of Itokawa, which had a similar composition as LL chondrites. The chondritic B isotopic ratios of the Itokawa samples suggest that they contain little cosmogenic B (from cosmic‐ray spallation reactions) rich in ¹⁰B. This observation is consistent with the short cosmic‐ray exposure ages of Itokawa samples inferred from the small concentrations of cosmogenic ²¹Ne. If other Itokawa samples have little cosmogenic B as well, the enrichment in ¹⁰B found previously on the surface of another Itokawa particle (as opposed to the bulk grain study here) may be attributed to implanted solar wind B.     

Examining Fluvial Stratigraphic Architecture Using Ground‐Penetrating Radar at the Fanta Stream Fossil and Archaeological Site,Central Ethiopia

The Fanta Stream site is an archaeological and paleontological locality in Addis Ababa, Ethiopia. The site contains a rich assemblage of fossil mammals and Acheulean artifacts of approximately 600 ka located in a rare high‐altitude context. A ground‐penetrating radar (GPR) survey was conducted in order to provide three‐dimensional imaging of the subsurface, which the authors use to interpret the geometry and distribution of fossil‐containing stratigraphic units. Utilizing the stream's natural cut bank exposure, we calibrate GPR data to known geologic units through radar facies analysis. Shallow, high‐amplitude coherent reflection geometries are attributed to volcanic tuff deposits, as these units exhibit subparallel continuous reflections consistent with planar stratified sedimentary deposition. Deeper, discontinuous reflection packages are interpreted as conglomeritic, fossil‐containing deposits. The results of the GPR survey outline the location of the Fanta Stream's paleodepositional features as well as suggest the extent of fossiliferous stratigraphic units for use in future excavations.     

Optimal dynamos in the cores of terrestrial exoplanets: Magnetic field generation and detectability

A potentially promising way to gain knowledge about the internal dynamics of extrasolar planets is by remote measurement of an intrinsic magnetic field. Strong planetary magnetic fields, maintained by internal dynamo action in an electrically conducting fluid layer, are helpful for shielding the upper atmosphere from stellar wind induced mass loss and retaining water over long (Gyr) time scales. Here we present a whole planet dynamo model that consists of three main components: an internal structure model with composition and layers similar to the Earth, an optimal mantle convection model that is designed to maximize the heat flow available to drive convective dynamo action in the core, and a scaling law to estimate the magnetic field intensity at the surface of a terrestrial exoplanet. We find that the magnetic field intensity at the core surface can be up to twice the present-day geomagnetic field intensity, while the magnetic moment varies by a factor of 20 over the models considered. Assuming electron cyclotron emission is produced from the interaction between the stellar wind and the exoplanet magnetic field we estimate the cyclotron frequencies around the ionospheric cutoff at 10 MHz with emission fluxes in the range 10⁻⁴-10⁻⁷ Jy, below the current detection threshold of radio telescopes. However, we propose that anomalous boosts and modulations to the magnetic field intensity and cyclotron emission may allow for their detection in the future.     

Search for extinct aluminum‐26 and titanium‐44 in nanodiamonds from the Allende CV3 and Murchison CM2 meteorites

Abstract– We report Mg‐Al and Ca‐Ti isotopic data for meteoritic nanodiamonds separated from the Allende CV3 and Murchison CM2 meteorites. The goal of this study was to search for excesses in ²⁶Mg and ⁴⁴Ca, which can be attributed to the in situ decay of radioactive and now extinct ²⁶Al and ⁴⁴Ti, respectively. Previous work on presolar SiC and graphite had shown that ²⁶Al/²⁷Al and ⁴⁴Ti/⁴⁸Ti ratios in presolar grains can be used to discriminate between different types of stellar sources. Aluminum and Ti concentrations are low in the meteoritic nanodiamonds of this study. Murchison nanodiamonds have higher Al and Ti concentrations than the Allende nanodiamonds. This can be attributed to contamination and the presence of presolar SiC in the Murchison nanodiamond samples. ²⁶Mg/²⁴Mg and ⁴⁴Ca/⁴⁰Ca ratios are close to normal in Allende nanodiamonds with upper limits on the initial ²⁶Al/²⁷Al and ⁴⁴Ti/⁴⁸Ti ratios of approximately 1 × 10^?3. These ratios are factors of 10–1000 and, respectively, 1–1000 lower than those of presolar SiC and graphite grains from supernovae. The ²⁶Al/²⁷Al and ⁴⁴Ti/⁴⁸Ti data for nanodiamonds are compatible with an asymptotic giant branch star or solar system origin, but not with a supernova origin of a major fraction of meteoritic nanodiamonds. The latter possibility cannot be excluded, though, as the diamond separates may contain significant amounts of contaminating Al and Ti, which would lower the inferred ²⁶Al/²⁷Al and ⁴⁴Ti/⁴⁸Ti ratios considerably.     

The lunar rock and mineral characterization consortium: Deconstruction and integrated mineralogical,petrologic, and spectroscopic analyses of mare basalts

The lunar rock and mineral characterization consortium (LRMCC) has conducted coordinated mineralogy/petrography/spectroscopy analyses of a suite of pristine lunar basalts. Four basalt slabs (two low‐Ti, two high‐Ti) and paired thin sections were analyzed. Thin sections were analyzed for mineralogy/petrography, while the slabs were used to prepare particulate separates of major mineral phases and bulk samples. Mineral separates and particulate bulk samples were crushed to controlled grain sizes and their reflectance spectra measured in the NASA RELAB at Brown University. The resulting data set provides an essential foundation for spectral mixing models, offers valuable endmember constraints for space weathering analyses, and represents critical new ground truth results for lunar science and exploration efforts.