Momentum and sensible heat exchange are studied in an Arctic fjord system in Spitsbergen, Svalbard (Norway), based on tower
measurements taken in January–June 2008. Due to ice-free conditions, the surface layer was unstable for most of the time,
occasionally very unstable. The shape of the fjord and the surrounding topography have a large influence on the wind field.
Low frequency eddies are mainly responsible for occasionally large crosswind momentum transfer that, together with upward
momentum transfer (occurring in 9% of the data), invalidate conventional stability and scaling parameters. When the flow is
along the fjord with moderate or high wind speeds, the Monin–Obukhov similarity theory is applicable. However, the momentum
and the sensible heat exchange in the fjord system differs from the exchange taking place over the open ocean, mainly due
to topographic effects. 相似文献
The lowermost units of the nappe pile of the Lepontine Alps crop out in the Antigorio valley in the footwall of the Simplon
Fault. The whole orthogneiss section of the Antigorio Unit is exposed on both sides of the valley, sandwiched between the
Mesozoic metasedimentary sequences of the Baceno unit below and the Tèggiolo unit above. The petrography and mineral composition
of tremolite–calcite veins occurring in dolomite marble in both metasedimentary sequences were investigated. Tremolite–calcite
(with lesser talc and minor phlogopite) veins have rhythmic banded texture. Banding is due to cyclic differences in modal
abundances and fabric of tremolite and calcite. These veins are very similar to those occurring in dolomite rafts within the
Bergell granite and it is inferred that they formed by the same “fracture-reaction-seal” mechanism. Veins formed by reaction
of a silica-rich aqueous fluid with the host dolomite marble along fractures. According to thermo-barometric calculations,
based on electron microprobe analyses, reaction occurred at temperatures between 450 and 490°C and minimum pressure of 2–3 kbar.
Such temperature conditions occurred in this footwall region of the Simplon Fault Zone around 15 Ma, during exhumation and
cooling of the nappe pile and a transition to brittle behaviour. Aqueous, silica-rich fluids concentrated along fractures,
forming tremolite–calcite veins in the dolomite marbles and quartz veins in the orthogneiss. 相似文献
In the eastern United States, the use of prescribed fire as a silvicultural technique to manage for desirable upland tree species is increasing in popularity. Bark physical properties such as thickness, density, and porosity have known associations with fire tolerance among species. These physical properties simultaneously influence rainfall interception and canopy storage and thus are of interest across a range of disciplines. Furthermore, while these characteristics are innate to a species, it is unknown whether repeated exposure to fire facilitates physical change in bark structure and whether these changes are consistent among species. To answer these questions, bark samples were collected from mature pine (Pinus taeda L.) and oak (Quercus montana Willd.) trees from sites across the Bankhead National Forest in Alabama, USA under three different burn regimes: 3-year cycle, 9-year cycle, and no fire. Samples were analysed in the laboratory for bulk density, porosity, water storage capacity, and hygroscopicity (the amount of atmospheric water vapour absorbed by bark during non-rainfall conditions). Drying rates of saturated samples under simulated wetting conditions were also assessed. Oak bark had higher bulk density, lower porosity, and dried slower than pine bark. Interestingly, bark from both species had lower bulk density, higher porosity, greater water storage capacity, and dried faster in stands that were burned every 3 years compared to other fire regimes (p < 0.001). In summary, this study demonstrates that prescribed fire regimes in an eastern US forest alter bark structure and thus influence individual tree control on hydrological processes. The increase in bark water storage capacity, coupled with faster bark evaporation times may lead to less water inputs to the forest floor and drier overall conditions. Further investigation of this fire-bark-water feedback loop is necessary to understand the extent of these mechanisms controlling landscape-scale conditions. 相似文献
In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ? ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal bp. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment. 相似文献
The mineral water of Vilajuïga village in Alt Empordà (NE Catalonia, Spain) owes its uniqueness to an emanation of geogenic CO2 that modifies groundwater hydrochemistry to produce a differentiated HCO3–Na- and CO2-rich groundwater among the usual Ca–HCO3 type found in this region. A hydrogeological conceptual model attributes its occurrence to the intersection of two faults: La Valleta and Garriguella-Roses. The former provides a thrust of metamorphic over igneous rocks, formed during the Paleozoic, over a layer of ampelitic shale that, from a hydrogeological perspective, acts as a confining layer. The Garriguella-Roses normal fault, which originated during the Neogene, permits the degassing of geogenic CO2 that is attributed to volcanic activity occurring in the Neogene. Groundwater mixing from the metamorphic and igneous rock units plus the local occurrence of CO2 creates a HCO3–Na water that still holds free-CO2 in solution. Interaction with the gas phase is restricted at the intersection of the two faults. Radiocarbon dating, after correcting for geogenic dead carbon, estimates an age of 8,000 years BP. The low tritium content (0.7 TU) indicates that Vilajuïga water is a mix of “older” groundwater recharged in the metamorphic rocks of the Albera range and “younger” groundwater from the igneous rocks of the Rodes range, over a recharge area of 45 km2 and a maximum elevation of 600 m. Given its origin as rare groundwater in the southern slope of the Eastern Pyrenees, purposeful monitoring is necessary to evaluate the groundwater vulnerability and anticipate impacts from nearby wells and climate-change effects.