New thermochronometric constraints on the rapid Palaeogene exhumation of the Cordillera Darwin complex and related thrust sheets in the Fuegian Andes

Thermal modelling of new fission‐track and (U–Th–Sm)/He data from the Fuegian Andes reveals rapid cooling (～12–48 °C Ma^?1) during the middle and late Eocene followed by slow cooling ( ～ 1.5 °C Ma^?1) to the Recent. We interpret the rapid cooling as a result of exhumation from contractional uplift within the crystalline interior of the orogen. This interpretation is consistent with independent evidence of Eocene shortening, flexural subsidence and provenance changes in the study area, and is approximately coeval with marine geochemical evidence of the onset of Drake Passage opening. In light of the Palaeogene history of Nazca‐South American plate convergence and the differences in shortening magnitudes and exhumation histories between the Fuegian and Patagonian Andes, our data support Eocene development of the Patagonian orocline, which also provides a plausible explanation for early opening of Drake Passage.     

A down-valley low-level jet event during T-REX 2006

A prolonged down-valley flow and low-level jet were observed throughout the Enhanced Observing Period 4 (April 28–29) of the 2006 Terrain-induced Rotor Experiment, held in the Owens Valley of California near the town of Independence. The low-level jet was strongest during the nocturnal hours, and special field observations captured important details of the event lifecycle. High-resolution simulations using the Weather Research and Forecasting numerical weather prediction model were generated, with underlying assumptions being that model resolution, boundary layer physics, and nesting configuration would be dominant controlling factors in reproducing the jet. The large-scale conditions were dry throughout the event, so moist physics were not a significant forcing consideration. For the control simulation, a two-nest (4.5 and 1.5 km grid spacing) configuration with 90 vertical levels was applied. Additionally, the Quasi-Normal Scale Elimination planetary boundary and surface layer option were selected due to its published performance under conditions of stable stratification. Three other sensitivity simulations were run for comparison, differing from the control just in the choice of vertical resolution (60 versus 90 levels with Quasi-Normal Scale Elimination) and planetary boundary/surface layer physics (90 levels/Mellor-Yamada-Jancic; 90 levels/Yonsei State University). Although the gross evolution (location, height, and timing) of the low-level jet is captured by all model runs (with the 1.5 km inner nest providing the more accurate details), there were at times large underestimations of the nocturnal jet speed max in each simulation (approaching 100 % error, or up to almost 10 m s^?1). Overall, the variations of vertical resolution and planetary boundary/surface physics against the control seemed to (1) yield little overall improvement to statistical or subjective evaluations; (2) do little to improve deficiencies in reproducing the magnitude strength of the nocturnal down-valley low-level jet. Since the cold-start simulations spanned 36 h (including a 12-h spin-up period), it was suspected that the lateral boundary conditions imposed on the outermost 4.5 km nest might negatively impact the interior model solutions in the Owens Valley. To investigate this possibility, an additional simulation was executed by adding two extra nests to the control configuration: an outer 13.5 km and an inner 500 m. This simulation produced a better evolution of the nocturnal low-level jet and especially the speed max. The addition of the larger 13.5 km nest appears more critical to this improvement than that of the extra spatial resolution provided by the inner 500 m nest, which supports the idea that accurate capturing of the large-scale synoptic condition was critical in reproducing important details of this down-valley low-level jet event. The extra 500-m resolution did seem to improve the morning valley cold pool forecast.     

ENSO and Sea Surface Temperature Anomalies in Association with Canadian Wheat Yield Variability

Interannual variations of spring wheat yields in Canadian agricultural regions are analyzed, together with the associated sea surface temperature (SST) anomalies in the northern hemisphere tropics and extratropics, from 1961 to 2015. The cubic trend is calculated and used to represent the trend related to advances in agricultural technology over this time period. The correlations between Canadian wheat yields at regional scales and the tropical El Niño–Southern Oscillation (ENSO) variability are not robust at any stage of the evolution of ENSO. Based on the power spectrum and cross-spectrum analysis, the most prominent yield variance is found in the Canadian Prairies, with a significant power peak of 4.5 years but does not co-vary significantly with interannual ENSO variability. ENSO weakly affects temperature and precipitation anomalies in the Canadian Prairie Region in summer—two important agroclimatic conditions for crop growth—and hence insignificantly impacts wheat yields. This indicates that there would be little benefit to including tropical ENSO indices in the operational wheat yield forecasting system. For Canadian wheat yield forecasting, attention should be paid to the preceding winter and spring SST anomalies in the northern extratropics. The SST anomalies associated with yields in the Canadian Prairie region and Central Region are generally stronger than those associated with yields in the Canadian Pacific Coast Region and eastern Maritime Region. In association with the Prairie Region and Central Region yields, SST shows pronounced anomalies in the mid-high latitudes of the North Pacific from winter to summer. The non-linearity of the SST anomalies associated with the Canadian yields is also clearly evident. Stronger (weaker) SST anomalies in the extratropical North Pacific correspond to low wheat yields in the Prairie (Central) Region, while weaker (stronger) SST anomalies correspond to high yields in the Prairie (Central) Region.     

A new approach to soil characterisation for hydrology–stability analysis models

Landslide stability analysis increasingly utilises high-resolution coupled hydrology–slope stability models (CHASM) to improve stability assessments in areas subject to dynamic pore pressure regimes. In such environments, the estimation of soil hydraulic conductivity (K) is a key parameter but one which is not always readily available or determined with the required resolution. By using basic soil particle-size distribution (PSD) data, we evaluate the microscopic composition of the actual soil, and applying the analytical relations obtain by a Self-Consistent Method (SCM) approach, we determine an appropriate value of K. This is of importance in that it allows within-soil type variability to be reflected in terms of K and hence within the model structure. The SCM methodology is briefly reviewed and an illustrative application is undertaken for a slope typical of Hong Kong. The results show model output sensitivity in terms of moisture content and factor of safety (FOS) when comparing K values determined using the SCM approach and the conventional field determination. In attempting to determine slope hydrological processes and attendant stability conditions, we conclude that the application of SCM approach offers a novel methodology for potentially improving the parameterisation of hydrology–slope stability models.     

Establishing habitat-specific indicator species in Tierra del Fuego with freshwater macroinvertebrates

As a tool to understand Tierra del Fuego’s basic ecology and detect changes due to human pressures, this study develops habitat bioindicators. We compared the freshwater benthic macroinvertebrates at 61 study sites in six habitat types: grassland streams, urbanised streams, forested streams, beaver ponds, lakes and peat bog ponds. Forty-nine taxa were identified; insects were the most diverse group. Beaver pond, lake and grassland stream assemblages were similar, as were those from lakes, grassland streams and peat bog ponds. Fourteen taxa were habitat-specific. In forests, these included mayfly scrapers (Andesiops, Meridialaris) and blackfly filterers (Gigantodax). In lakes, two copepod filterers were indicators, and in urban streams, one shredder (Aphroteniella) and three collector-gatherers (springtail, earthworm, aquatic worm). Predators (Corixa, Aeshna) were characteristic of peat bog ponds. Beaver ponds had no indicator species. Establishing links between species and ecosystems constitutes the beginning of a broader effort to understand anthropogenic impacts to Fuegian watersheds.     

Effects of pollution on the benthos of the Firth of Forth

A long-term benthic study has been undertaken in the Firth of Forth to assess the environmental impact of a new sewage treatment scheme for the city of Edinburgh. The Sewage Scheme reduces the suspended solids content of the liquid effluent by approximately 60% and achieves a lowering of the concentration of materials in solution through more efficient dilution and dispersion. Marked changes in the intertidal benthic flora and fauna have been recorded along the Edinburgh coastal zone. These changes have been apparent as the decline and disappearance of populations of certain pollution indicator species and the appearance and establishment of several species previously unrecorded along the more polluted parts of the Edinburgh shoreline. Study of the sublittoral benthos has shown no deleterious effect arising from the new effluent outfall, although there does appear to be some enhancement of the fauna in the area.     

A study case of bioluminescence potential dynamics in the Delaware Bay with observations and modeling

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Marine electrical resistivity imaging of submarine groundwater discharge: sensitivity analysis and application in Waquoit Bay, Massachusetts, USA

Electrical resistivity imaging has been used in coastal settings to characterize fresh submarine groundwater discharge and the position of the freshwater/salt-water interface because of the relation of bulk electrical conductivity to pore-fluid conductivity, which in turn is a function of salinity. Interpretation of tomograms for hydrologic processes is complicated by inversion artifacts, uncertainty associated with survey geometry limitations, measurement errors, and choice of regularization method. Variation of seawater over tidal cycles poses unique challenges for inversion. The capabilities and limitations of resistivity imaging are presented for characterizing the distribution of freshwater and saltwater beneath a beach. The experimental results provide new insight into fresh submarine groundwater discharge at Waquoit Bay National Estuarine Research Reserve, East Falmouth, Massachusetts (USA). Tomograms from the experimental data indicate that fresh submarine groundwater discharge may shut down at high tide, whereas temperature data indicate that the discharge continues throughout the tidal cycle. Sensitivity analysis and synthetic modeling provide insight into resolving power in the presence of a time-varying saline water layer. In general, vertical electrodes and cross-hole measurements improve the inversion results regardless of the tidal level, whereas the resolution of surface arrays is more sensitive to time-varying saline water layer.