Geochemical Fingerprinting of Coltan Ores by Machine Learning on Uneven Datasets

Two modern machine learning techniques, Linear Programming Boosting (LPBoost) and Support Vector Machines (SVMs), are introduced and applied to a geochemical dataset of niobium–tantalum (“coltan”) ores from Central Africa to demonstrate how such information may be used to distinguish ore provenance, i.e., place of origin. The compositional data used include uni- and multivariate outliers and elemental distributions are not described by parametric frequency distribution functions. The “soft margin” techniques of LPBoost and SVMs can be applied to such data. Optimization of their learning parameters results in an average accuracy of up to c. 92%, if spot measurements are assessed to estimate the provenance of ore samples originating from two geographically defined source areas. A parameterized performance measure, together with common methods for its optimization, was evaluated to account for the presence of uneven datasets. Optimization of the classification function threshold improves the performance, as class importance is shifted towards one of those classes. For this dataset, the average performance of the SVMs is significantly better compared to that of LPBoost.     

Implications of the principle of effective stress

Acta Geotechnica - While Terzaghi justified his principle of effective stress for water-saturated soil empirically, it can be derived by means of the neutrality of the mineral with respect to...     

Biogeochemistry of a River-Dominated Estuary Influenced by Drought and Storms

Increased frequency and severity of droughts, as well as growing human freshwater demands, in the Apalachicola-Chattahoochee-Flint River Basin are expected to lead to a long-term decrease in freshwater discharge to Apalachicola Bay (Florida). To date, no long-term studies have assessed how river discharge variability affects the Bay’s phytoplankton community. Here a 14-year time series was used to assess the influence of hydrologic variability on the biogeochemistry and phytoplankton biomass in Apalachicola Bay. Data were collected at 10 sites in the bay along the salinity gradient and include drought and storm periods. Riverine dissolved inorganic nitrogen and phosphate inputs were correlated to river discharge, but chlorophyll a (Chl a) was similar between periods of drought and average/above-average river discharge in most of the Bay. Results suggest that the potentially negative impact of decreased riverine nutrient input on Bay phytoplankton biomass is mitigated by the nutrient buffering capacity of the estuary. Additionally, increased light availability, longer residence time, and decreased grazing pressures may allow more Chl a biomass to accumulate during drought. In contrast to droughts, tropical cyclones and subsequent increases in river discharge increased flushing and reduced light penetration, leading to reduced Chl a in the Bay. Analysis of the time series revealed that Chl a concentrations in the Bay do not directly mirror the effect of riverine nutrient input, which is masked by multiple interacting mechanisms (i.e., nutrient loading and retention, grazing, flushing, light penetration) that need to be considered when projecting the response of Bay Chl a to changes in freshwater input.     

Jesenice—A new meteorite fall from Slovenia

Abstract– On April 9, 2009, at 3:00 CEST, a very bright fireball appeared over Carinthia and the Karavanke Mountains. The meteoroid entered the atmosphere at a very steep angle and disintegrated into a large number of objects. Two main objects were seen as separate fireballs up to an altitude of approximately 5 km, and witnesses reported loud explosions. Three stones were found with a total weight of approximately 3.611 kg. The measured activity of short‐lived cosmogenic radionuclides clearly indicates that two specimens result from a very recent meteorite fall. All cosmogenic radionuclide concentrations suggest a rather small preatmospheric radius of <20 cm; a nominal cosmic‐ray exposure age based on ²¹Ne is approximately 4 Ma, but the noble gas and radionuclide results in combination indicate a complex irradiation. Jesenice is a highly recrystallized rock with only a few relic chondrules visible in hand specimen and thin section. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivines and pyroxenes clearly indicate that Jesenice is a L6 chondrite. The bulk composition of Jesenice is very close to the published average element concentration for L ordinary chondrites. The chondrite is weakly shocked (S3) as indicated by the undulatory extinction in olivine and plagioclase and the presence of planar fractures in olivine. Being weakly shocked and with gas retention ages of >1.7 Ga (⁴He) and approximately 4.3 Ga (⁴⁰Ar), Jesenice seems not to have been strongly affected by the catastrophic disruption of the L‐chondrite parent body approximately 500 Ma ago.     

Ancient harbors and Holocene morphogenesis of the Ras Ibn Hani peninsula (Syria)

Ras Ibn Hani peninsula, a wave-dominated tombolo (800 × 1000 m) on the Syrian coast, provides evidence for significant Holocene changes that can be linked to geological inheritance, rising post-glacial sea level, sediment supply and human impacts. Initial development of Ras Ibn Hani's coastal system began ~ 8000 years ago when shallow marine environments formed in a context of rising post-glacial sea level. Following relative sea-level stabilization ~ 6000 cal yr BP, beach facies trace the gradual formation of a wave-dominated sandbank fronted by a ~ 2300 × ~ 500 m palaeo-island whose environmental potentiality was attractive to Bronze Age societies. A particularly rapid phase of tombolo accretion is observed after ~ 3500 cal yr BP characterised by a two- to fourfold increase in sedimentation rates. This is consistent with (i) a pulse in sediment supply probably driven by Bronze Age/Iron Age soil erosion in local catchments, and (ii) positive feedback mechanisms linked to regionally attested neotectonics. Archaeological remains and radiocarbon datings confirm that the subaerial tombolo was probably in place by the Late Bronze Age. These data fit tightly with other eastern Mediterranean tombolo systems suggesting that there is a great deal of predictability to their geology and stratigraphy at the regional scale.     

Interpretation of SOFIE PMC measurements: Cloud identification and derivation of mass density,particle shape,and particle size

The Solar Occultation For Ice Experiment (SOFIE) was launched onboard the Aeronomy of Ice in the Mesosphere (AIM) spacecraft to measure polar mesospheric clouds (PMCs) and their environment. This work describes methods for identifying PMCs in SOFIE observations and determining mass density, particle shape, particle effective radius, and the parameters of a Gaussian size distribution. Results using SOFIE measurements from the northern summer of 2007 are compared with concurrent observations by the ALOMAR lidar in northern Norway. Ice particle properties determined from SOFIE are in good agreement with the lidar results, considering the differences in instrument characteristics.     

Observations of bedforms on a dissipative macrotidal beach

Field measurements of wave ripples and megaripples were made with a Sand Ripple Profiler in the surf and shoaling zones of a sandy macrotidal dissipative beach at Perranporth, UK in depths 1–6 m and significant wave heights up to 2.2 m. A frequency domain partitioning approach allowed quantification of height (η), length (λ) and migration rate of ripples and megaripples. Wave ripples with heights up to 2 cm and wavelengths ～20 cm developed in low orbital velocity conditions (u _m?<?0.65 m/s) with mobility number ψ?<?25. Wave ripple heights decreased with increasing orbital velocity and were flattened when mean currents were >0.1 m/s. Wave ripples were superimposed on top of megaripples (η?=?10 cm, λ?=?1 m) and contributed up to 35 % of the total bed roughness. Large megaripples with heights up to 30 cm and lengths 1–1.8 m developed when the orbital velocity was 0.5–0.8 m/s, corresponding to mobility numbers 25–50. Megaripple heights and wavelengths increased with orbital velocity but reduced when mean current strengths were >0.15 m/s. Wave ripple and megaripple migrations were generally onshore directed in the shoaling and surf zones. Onshore ripple migration rates increased with onshore-directed (+ve) incident wave skewness. The onshore migration rate reduced as offshore-directed mean flows (undertow) increased in strength and reached zero when the offshore-directed mean flow was >0.15 m/s. The migration pattern was therefore linked to cross-shore position relative to the surf zone, controlled by competition between onshore-directed velocity skewness and offshore-directed mean flow.     

Episodic and Long-Term Sediment Transport Capacity in The Hudson River Estuary

A tidally averaged model of estuarine dynamics is used to estimate sediment transport in the Hudson River estuary over the period 1918 to 2005. In long-term and seasonal means, along-channel gradients in sediment flux depend on the estuarine salinity gradient and along-channel depth profile. Lateral depth variation across the estuary affects the near-bottom baroclinic circulation and consequently the direction of net sediment flux, with generally up-estuary transport in the channel and down-estuary transport on the shoals. Sediment transport capacity in the lower estuary depends largely on river discharge, but is modified by the timing of discharge events with respect to the spring–neap cycle and subtidal fluctuations in sea level. Sediment transport capacity also depends on the duration of high-discharge events relative to the estuarine response time, a factor that varies seasonally with discharge and estuarine length. Sediment fluxes are calculated with the assumption that over long periods, the system approaches morphological equilibrium and sediment accumulation equals sea level rise. The inferred across- and along-channel distributions of sediment erodibility correspond with observations of bed properties. Equilibrium is assumed at long time scales, but at annual to decadal time scales the estuary can develop an excess or deficit of sediment relative to equilibrium. On average, sediment accumulates in the estuary during low- and high-discharge periods and is exported during moderate discharge. During high-discharge periods, maximum export coincides with maximum sediment supply from the watershed, but the nearly cubic discharge dependence of fluvial sediment supply overwhelms the roughly linear increase in estuarine transport capacity. Consequently, sediment accumulates in the estuary during the highest flow conditions. Uncertainty remains in the model, particularly with sediment properties and boundary conditions, but the results clearly indicate variability in the sediment mass balance over long time scales due to discharge events.