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51.
Development of a modelling methodology for simulation of long-term morphological evolution of the southern Baltic coast 总被引:1,自引:1,他引:0
The Darss–Zingst peninsula at the southern Baltic Sea is a typical wave-dominated barrier island system which includes an
outer barrier island and an inner lagoon. The formation of the Darss–Zingst peninsula dates back to the Littorina Transgression
onset about 8,000 cal BP. It originated from several discrete islands, has been reshaped by littoral currents, wind-induced
waves during the last 8,000 years and evolved into a complex barrier island system as today; thus, it may serve as an example
to study the coastal evolution under long-term climate change. A methodology for developing a long-term (decadal-to-centennial)
process-based morphodynamic model for the southern Baltic coastal environment is presented here. The methodology consists
of two main components: (1) a preliminary analysis of the key processes driving the morphological evolution of the study area
based on statistical analysis of meteorological data and sensitivity studies; (2) a multi-scale high-resolution process-based
model. The process-based model is structured into eight main modules. The two-dimensional vertically integrated circulation
module, the wave module, the bottom boundary layer module, the sediment transport module, the cliff erosion module and the
nearshore storm module are real-time calculation modules which aim at solving the short-term processes. A bathymetry update
module and a long-term control function set, in which the ‘reduction’ concepts and technique for morphological update acceleration
are implemented, are integrated to up-scale the effects of short-term processes to a decadal-to-centennial scale. A series
of multi-scale modelling strategies are implemented in the application of the model to the research area. Successful hindcast
of the coastline change of the Darss–Zingst peninsula for the last 300 years validates the modelling methodology. Model results
indicate that the coastline change of the Darss–Zingst peninsula is dominated by mechanisms acting on different time scales.
The coastlines of Darss and the island of Hiddensee are mainly reshaped by long-term effects of waves and longshore currents,
while the coastline change of the Zingst peninsula is due to a combination of long-term effects of waves and short-term effects
caused by wind storms. 相似文献
52.
Cyrus Karas Dirk Nürnberg Ralf Tiedemann Dieter Garbe-Schönberg 《Earth and Planetary Science Letters》2011,301(1-2):117-124
The transition from the early Pliocene “Warmhouse” towards the present “Icehouse” climate and the role of Gateway dynamics are intensively debated. Both, the constrictions of the Central American Seaway and the Indonesian Gateway affected ocean circulation and climate during the Pliocene epoch. Here, we use combined δ18O and Mg/Ca ratios of planktonic foraminifera (marine protozoa) from surface and subsurface levels to reconstruct the thermal structure and changes in salinities from the Southwest Pacific Deep Sea Drilling Project (DSDP) Site 590B from 6.5 to 2.5 Ma. Our data suggest a gradual cooling of ~ 2 °C and freshening of the sea surface during ~ 4.6–4 Ma with an increased meridional temperature gradient between the West Pacific Warm Pool and the Southwest Pacific when the closing of the Central American Seaway reached a critical threshold. After ~ 3.5 Ma, the restricted Indonesian Gateway might have amplified the East Australian Current, allowing enhanced heat transport towards the Southwest Pacific with reduced meridional temperature gradients when the global climate gradually cooled. At the same time our data suggest a cooling and freshening of Subantarctic Mode Water (SAMW) or/and an increased northward flow of SAMW towards Site 590B, possibly a first step towards the present Antarctic Frontal System. 相似文献
53.
Katia Sanhueza-Pino Oliver Korup Ralf Hetzel Henry Munack Johannes T. Weidinger Stuart Dunning Cholponbek Ormukov Peter W. Kubik 《Quaternary Research》2011,76(3):295-304
Numerous large landslide deposits occur in the Tien Shan, a tectonically active intraplate orogen in Central Asia. Yet their significance in Quaternary landscape evolution and natural hazard assessment remains unresolved due to the lack of "absolute" age constraints. Here we present the first 10Be exposure ages for three prominent (> 107 m3) bedrock landslides that blocked major rivers and formed lakes, two of which subsequently breached, in the northern Kyrgyz Tien Shan. Three 10Be ages reveal that one landslide in the Alamyedin River occurred at 11–15 ka, which is consistent with two 14C ages of gastropod shells from reworked loess capping the landslide. One large landslide in Aksu River is among the oldest documented in semi-arid continental interiors, with a 10Be age of 63–67 ka. The Ukok River landslide deposit(s) yielded variable 10Be ages, which may result from multiple landslides, and inheritance of 10Be. Two 10Be ages of 8.2 and 5.9 ka suggest that one major landslide occurred in the early to mid-Holocene, followed by at least one other event between 1.5 and 0.4 ka. Judging from the regional glacial chronology, all three landslides have occurred between major regional glacial advances. Whereas Alamyedin and Ukok can be considered as postglacial in this context, Aksu is of interglacial age. None of the landslide deposits show traces of glacial erosion, hence their locations and 10Be ages mark maximum extents and minimum ages of glacial advances, respectively. Using toe-to-headwall altitude ratios of 0.4–0.5, we reconstruct minimum equilibrium-line altitudes that exceed previous estimates by as much as 400 m along the moister northern fringe of the Tien Shan. Our data show that deposits from large landslides can provide valuable spatio-temporal constraints for glacial advances in landscapes where moraines and glacial deposits have low preservation potential. 相似文献
54.
Nutrient dynamics in estuaries are temporally variable in response to changing physical–chemical conditions and biogeochemical
processes involving primary producer groups such as phytoplankton, microphytobenthos, seagrass and macroalgae. In order to
reveal intra-annual changes in the biomass of primary producer groups and associated changes in estuarine nutrient dynamics,
we developed a box model, coupling water inflows and outflows and nitrogen dynamics in Wilson Inlet, a large, central-basin-dominated,
intermittently closed estuary exposed to a Mediterranean climate in Western Australia. The model is calibrated and validated
with monitoring data, aquatic plant biomass estimates and biogeochemical rate measurements. Macrophytes and their microalgal
epiphytes appear to rapidly assimilate nutrients from the first flush from the catchment in winter, but this buffer capacity
then ceases, and a phytoplankton ‘bloom’ develops in response to subsequent river runoff events in spring. Significant amounts
of bioavailable nitrogen are exported to the ocean because phytoplankton predominance occurs while the sand bar is breached.
Surface sediments play a key role for nitrogen dynamics: In late spring to autumn, high light availability at the sediment
surface stimulates high primary production by microphytobenthos, leading to reduced benthic ammonium fluxes particularly in
the deep basin. Microphytobenthos contributes about 60% of annual whole-system primary production. Despite high benthic primary
production, nitrogen release from sediments is the biggest nitrogen source to the estuary. 相似文献
55.
Wolf Uwe Reimold Iain McDonald Ralf‐Thomas Schmitt Birgit Hansen Juliane Jacob Christian Koeberl 《Meteoritics & planetary science》2013,48(9):1531-1571
Suevite and melt breccia compositions in the boreholes Enkingen and Polsingen are compared with compositions of suevites from other Ries boreholes and surface locations and discussed in terms of implications for impact breccia genesis. No significant differences in average chemical compositions for the various drill cores or surface samples are noted. Compositions of suevite and melt breccia from southern and northeastern sectors of the Ries crater do not significantly differ. This is in stark contrast to the published variations between within‐crater and out‐of‐crater suevites from northern and southern sectors of the Bosumtwi impact structure, Ghana. Locally occurring alteration overprint on drill cores—especially strong on the carbonate‐impregnated suevite specimens of the Enkingen borehole—does affect the average compositions. Overall, the composition of the analyzed impact breccias from Ries are characterized by very little macroscopically or microscopically recognized sediment‐clast component; the clast populations of suevite and impact melt breccia are dominated consistently by granitic and intermediate granitoid components. The Polsingen breccia is significantly enriched in a dioritic clast component. Overall, chemical compositions are of intermediate composition as well, with dioritic‐granodioritic silica contents, and relatively small contributions from mafic target components. Selected suevite samples from the Enkingen core have elevated Ni, Co, Cr, and Ir contents compared with previously analyzed suevites from the Ries crater, which suggest a small meteoritic component. Platinum‐group element (PGE) concentrations for some of the enriched samples indicate somewhat elevated concentrations and near‐chondritic ratios of the most immobile PGE, consistent with an extraterrestrial contribution of 0.1–0.2% chondrite‐equivalent. 相似文献
56.
Long-period natural-source electromagnetic data have been recorded using portable three-component magnetometers at 39 sites in 1998 and 2002 across the southern Eyre Peninsula, South Australia that forms part of the Gawler Craton. Site spacing was of order 5 km, but reduced to 1 km or less near known geological boundaries, with a total survey length of approximately 50 km. A profile trending east – west was inverted for a 2D electrical resistivity model to a depth of 20 km across the southern Eyre Peninsula. The main features from the models are: (i) on the eastern side of the Gawler Craton, the Donington Suite granitoids to the east of the Kalinjala Shear Zone are resistive (>1000 Ωm); (ii) the boundary between the Donington Suite granitoids and the Archaean Sleaford Complex, which has much lower resistivity of 10 – 100 Ωm, is almost vertical in the top 10 km and dips slightly westwards; and (iii) two very low resistivity (<1 Ωm) arcuate zones in the top 3 km of Hutchison Group sediments correlate with banded iron-formations, and are probably related to biogenic-origin graphite deposits concentrated in fold hinges. Such features suggest an extensional regime during the time period 2.00 – 1.85 Ga. We suggest that the resistivity boundary between the Donington Suite and the Archaean Sleaford Complex represents a growth fault, typical for rift systems that evolve into a half-graben structure. In the graben basin, low-resistivity shallow-marine Hutchison Group sediments were deposited. Folding of the sediments during the Kimban Orogeny between 1.74 and 1.70 Ga has led to migration of graphite to the fold hinges resulting in linear zones of very low resistivity that correlate with banded iron-formation magnetic anomalies. 相似文献
57.
58.
Macarena Bravo Mª de los ngeles Gallardo Guillermo Luna-Jorquera Paloma Núez Nelson Vsquez Martin Thiel 《Marine pollution bulletin》2009,58(11):1718-1726
Anthropogenic marine debris (AMD) is an ubiquitous problem, which has motivated public participation in activities such as beach surveys and clean-up campaigns. While it is known that beaches in the SE Pacific are also affected by this problem, the quantities and types of AMD remain largely unknown. In the context of an outreach project, volunteers (1500 high-school students) participated in a nation-wide survey of AMD on 43 beaches distributed randomly along the entire Chilean coast (18°S to 53°S). The mean density of AMD was 1.8 items m−2 and the major types were plastics, cigarette butts and glass. Densities in central Chile were lower than in northern and southern Chile, which could be due to different attitudes of beach users or to intense beach cleaning in central regions. We suggest that public participation in surveys and cleaning activities will raise awareness and thereby contribute to an improvement of the situation. 相似文献
59.
Daniele Norbiato Marco Borga Ralf Merz Günther Blschl Alberto Carton 《Journal of Hydrology》2009,375(3-4):312-325
Analyses of event runoff coefficients provide essential insight on catchment response, particularly if a range of catchments and a range of events are compared by a single indicator. In this study we examine the effect of climate, geology, land use, flood types and initial soil moisture conditions on the distribution functions of the event runoff coefficients for a set of 14 mountainous catchments located in the eastern Italian Alps, ranging in size from 7.3 to 608.4 km2. Runoff coefficients were computed from hourly precipitation, runoff data and estimates of snowmelt. A total of 535 events were analysed over the period 1989–2004. We classified each basin using a “permeability index” which was inferred from a geologic map and ranged from “low” to “high permeability”. A continuous soil moisture accounting model was applied to each catchment to classify ‘wet’ and ‘dry’ initial soil moisture conditions. The results indicate that the spatial distribution of runoff coefficients is highly correlated with mean annual precipitation, with the mean runoff coefficient increasing with mean annual precipitation. Geology, through the ‘permeability index’, is another important control on runoff coefficients for catchments with mean annual precipitation less than 1200 mm. Land use, as indexed by the SCS curve number, influences runoff coefficient distribution to a lesser degree. An analysis of the runoff coefficients by flood type indicates that runoff coefficients increase with event snowmelt. Results show that there exists an intermediate region of subsurface water storage capacity, as indexed by a flow–duration curve-based index, which maximises the impact of initial wetness conditions on the runoff coefficient. This means that the difference between runoff coefficients characterised by wet and dry initial conditions is negligible both for basins with very large storage capacity and for basins with small storage capacity. For basins with intermediate storage capacities, the impact of the initial wetness conditions may be relatively large. 相似文献
60.
by Ralf Köber Götz Hornbruch Carsten Leven Lars Tischer Jochen Großmann Peter Dietrich Holger Weiß Andreas Dahmke 《Ground water》2009,47(4):536-546
Most established methods to characterize aquifer structure and hydraulic conductivities of hydrostratigraphical units are not capable of delivering sufficient information in the spatial resolution that is desired for sophisticated numerical contaminant transport modeling and adapted remediation design. With hydraulic investigation methods based on the direct-push (DP) technology such as DP slug tests, DP injection logging, and the hydraulic profiling tool, it is possible to rapidly delineate hydrogeological structures and estimate their hydraulic conductivity in shallow unconsolidated aquifers without the need for wells. A combined application of these tools was used for the investigation of a contaminated German refinery site and for the setup of hydraulic aquifer models. The quality of DP investigation and the models was evaluated by comparisons of tracer transport simulations using these models and measured breakthroughs of two natural gradient tracer tests. Model scenarios considering the information of all tools together showed good reproduction of the measured breakthroughs, indicating the suitability of the approach and a minor impact of potential technical limitations. Using the DP slug tests alone yielded significantly higher deviations for the determined hydraulic conductivities compared to considering two or three of the tools. Realistic aquifer models developed on basis of such combined DP investigation approaches can help optimize remediation concepts or identify flow regimes for aquifers with a complex structure. 相似文献