Numerical study of mean flow patterns in the South China Sea and the Luzon Strait   总被引：2，自引：1，他引：1  

Ching-Sheng Chern  Sen Jan  Joe Wang 《Ocean Dynamics》2010,60(5):1047-1059

Previous investigations have suggested that wind stress curl, the balance of influx- and outflux-induced upwelling, as well as a positive vorticity source fed from the left flank of the Kuroshio are all possible mechanisms that contribute to a persistent cyclonic gyre in the South China Sea (SCS). Studies have also suggested that the loop current that forms from the Kuroshio intrusion in the Luzon Strait, similar to the Loop Current in the Gulf of Mexico (GOM), has rarely been observed in the northern SCS. In this research, an idealized numerical model driven by annual mean wind stress was adopted to investigate the relative importance of dynamic processes that control the mean flow pattern of Kuroshio in the Luzon Strait and regulate circulation in the SCS. An analysis of results drawn from numerical experiments suggests that the three mechanisms are of approximately equal importance in the formation of the persistent cyclonic gyre in the northern SCS. Unlike the Gulf Stream which enters the Gulf of Mexico through the Yucatan Channel, the two topographic ridges that align nearly meridionally in the Luzon Strait keep the Kuroshio flowing roughly northward without distinct intrusion into the SCS. Unsurprisingly, an anticyclonic loop current similar to the Gulf Stream pathway in the GOM was barely observed in the northern SCS.  相似文献   

Endemic avifaunal biodiversity and tropical forest loss in Makira, a mountainous Pacific island     

Finn Danielsen  Christopher E. Filardi  Knud A. Jønsson  Victor Kohaia  Niels Krabbe  Jan B. Kristensen  Robert G. Moyle  Patrick Pikacha  Michael K. Poulsen  Mikael K. Sørensen  Charles Tatahu  Joseph Waihuru  Jon Fjeldså 《Singapore journal of tropical geography》2010,31(1):100-114

Anthropogenic habitat changes and the introduction of pigs, dogs, cats and rats have caused a catastrophic decline in the terrestrial biodiversity of Pacific archipelagos. At present, economic globalization and an increased demand for timber are promoting industrial logging and plantation expansion. Commercial logging can be sustainable but in practice it more often leads to land degradation, especially on small flat islands. On large and mountainous islands, however, more modest impacts can be expected as the narrowly endemic species tend to inhabit montane forests where logging is difficult. In this study we use ornithological data collected at different elevations to assess the extent to which the avifauna of Makira, a large mountainous island in Melanesia, will be affected by deforestation of the lowlands, most of which are under timber concessions. Our data suggest that a majority of the endemic bird species use lowland forest to some extent and that this may even apply to species hitherto associated with montane forest. If current commercial forestry programmes are continued, the forest habitat may be disturbed or lost over large parts of Makira, potentially undermining the natural resource base for the local subsistence economy, exacerbating climate change and threatening the integrity of one of the most important areas for biodiversity conservation on earth. Our study highlights the importance of understanding the habitat requirements of endemic species and the urgency of establishing and effectively managing community-based protected areas in suitable lowland forests of the Pacific.  相似文献   

Diatom assemblage dynamics during abrupt climate change: the response of lacustrine diatoms to Dansgaard–Oeschger cycles during the last glacial period     

Linda Ampel  Barbara Wohlfarth  Jan Risberg  Daniel Veres  Melanie J. Leng  Päivi Kaislahti Tillman 《Journal of Paleolimnology》2010,44(2):397-404

The sedimentary record from the paleolake at Les Echets in eastern France allowed a reconstruction of the lacustrine response to several abrupt climate shifts during the last glacial period referred to as Dansgaard–Oeschger (DO) cycles. The high-resolution diatom stratigraphy has revealed distinct species turnover events and large fluctuations in stable oxygen isotope values in diatom frustules, as a response to DO climate variability. More or less identical species compositions became re-established during each DO stadial and interstadial phases, respectively. However, the relative abundance of the most dominant species within these assemblages varies and might indicate differences in climatic conditions. Interstadial phases are characterized by identical species successions. Transitions from stadial to interstadial conditions show a distinct Fragilaria–Cyclotella succession, which resembles the diatom regime shifts that have been recognized in some lakes in the Northern Hemisphere since the mid-nineteenth century.  相似文献   

The ecology of <Emphasis Type="Italic">Pediastrum</Emphasis> (Chlorophyceae) in subarctic lakes and their potential as paleobioindicators     

Kaarina Weckström  Jan Weckström  Linda-Marie Yliniemi  Atte Korhola 《Journal of Paleolimnology》2010,43(1):61-73

Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still among the least impacted lakes by humans. Hence they provide an excellent setting for studies on long-term climatic variability without the overriding effects of direct anthropogenic perturbation. On the other hand, these ecosystems are highly vulnerable to even moderate anthropogenic influence like long-distance airborne transport of nutrients and pollutants. The paleolimnological studies conducted in these areas usually include a multitude of different proxies, but so far only few have used the green algal group of Pediastrum Meyen. These algae, however, preserve well in sediments and can be identified to species level, which lends them potential as a paleo-proxy. In this study we analysed the present Pediastrum assemblages from surface-sediments of 16 subarctic lakes in Finnish Lapland as well as bottom samples from the same sediment cores, which are “spot” samples from the recent past. We found a total of 14 Pediastrum taxa, five of which occurred at moderate to high relative abundances. The majority of the taxa showed distinct relationships to environmental variables measured. Of these, pH and dissolved organic carbon (DOC) explained most of the variance in the distribution of Pediastrum and generally summarised the main environmental gradients in our data set well. Five of the studied lakes lacked Pediastrum taxa altogether, and Pediastrum occurred at low abundances in four additional lakes. All of these nine lakes have extremely low nutrient concentrations and generally lowest pH and DOC in the data set and were defined by barren catchment areas and scarce lake macrophyte growth. According to a top–bottom analysis of sediment cores, the Pediastrum assemblages of the study lakes have changed moderately, suggesting changed environmental conditions in the lakes. Although these changes appear to be climate-related, more studies are needed to confirm this hypothesis.  相似文献   

Local Seismic Events in the Area of Poland Based on Data from the PASSEQ 2006–2008 Experiment     

Marcin Polkowski  Beata Plesiewicz  Jan Wiszniowski  Monika Wilde-Piórko  Passeq Working Group 《Acta Geophysica》2016,64(6):2092-2113

PASSEQ 2006–2008 (Passive Seismic Experiment in TESZ; Wilde-Piórko et al. 2008) was the biggest passive seismic experiment carried out so far in the area of Central Europe (Poland, Germany, the Czech Republic and Lithuania). 196 seismic stations (including 49 broadband seismometers) worked simultaneously for over two years. During the experiment, multiple types of data recorders and seismometers were used, making the analysis more complex and time consuming. The dataset was unified and repaired to start the detection of local seismic events. Two different approaches for detection were applied for stations located in Poland. The first one used standard STA/LTA triggers (Carl Johnson’s STA/LTA algorithm) and grid search to classify and locate the events. The result was manually verified. The second approach used Real Time Recurrent Network (RTRN) detection (Wiszniowski et al. 2014). Both methods gave similar results, showing four previously unknown seismic events located in the Gulf of Gdańsk area, situated in the southern Baltic Sea. In this paper we discuss both detection methods with their pros and cons (accuracy, efficiency, manual work required, scalability). We also show details of all detected and previously unknown events in the discussed area.  相似文献   

A simple water balance model adapted for soil water repellency: application on Portuguese burned and unburned eucalypt stands   总被引：1，自引：0，他引：1       下载免费PDF全文

João Pedro Nunes  Maruxa Malvar  Akli Ait Benali  María Ermitas Rial Rivas  Jan Jacob Keizer 《水文研究》2016,30(3):463-478

Soil water repellency can impact soil hydrology, overland flow generation and associated soil losses. However, current hydrological models do not take it into account, which creates a challenge in repellency‐prone regions. This work focused on the adaptation for soil water repellency of a daily water balance model. Repellency is estimated from soil moisture content using site‐specific empirical relations and used to limit maximum soil moisture. This model was developed and tested using approximately 2 years of data from one long‐unburned and two recently burned eucalypt plantations in northern Portugal, all of which showed strong seasonal soil water repellency cycles. Results indicated important improvements for the burned plantations, with the Nash–Sutcliffe efficiency increasing from ?0.55 and ?0.49 to 0.55 and 0.65. For the unburned site, model performance was already good without the modification and efficiency only improved slightly from 0.71 to 0.74, mostly due to the better simulation of delayed soil wetting after dry periods. Results suggested that even a simple approach to simulate soil water repellency can markedly improve the performance of hydrological models in eucalypt forests, especially after fire. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Contaminants in cetaceans from UK waters: status as assessed within the Cetacean Strandings Investigation Programme from 1990 to 2008     

Law RJ  Barry J  Barber JL  Bersuder P  Deaville R  Reid RJ  Brownlow A  Penrose R  Barnett J  Loveridge J  Smith B  Jepson PD 《Marine pollution bulletin》2012,64(7):1485-1494

Since 1990, tissue samples from UK-stranded and -bycaught cetaceans have been available for study of contaminant burdens. These have been used to study spatial and temporal trends in concentrations in UK waters, and to investigate potential associations between contaminants and health status. We describe the current status of cetaceans (primarily harbour porpoises, Phocoena phocoena) in UK waters in relation to pollution. Concentrations of BDEs, HBCD, and the organochlorine pesticides are declining. In contrast, concentrations of CBs have plateaued following earlier reductions due to regulation of use, and further reductions are likely to take decades. Blubber PCB concentrations are still at toxicologically significant levels in many harbour porpoises and regularly occur at even higher levels in bottlenose dolphins and killer whales due to their higher trophic level in marine food chains. Further reductions in PCB inputs into the marine environment are needed to mitigate risk from PCB exposure in these species.  相似文献   

Plastic ingestion by the northern fulmar (Fulmarus glacialis) in Iceland     

Kühn S  van Franeker JA 《Marine pollution bulletin》2012,64(6):1252-1254

In 2011, northern fulmars (Fulmarus glacialis) from Iceland were used to test the hypothesis that plastic debris decreases at northern latitudes in the Atlantic when moving away from major human centres of coastal and marine activities. Stomach analyses of Icelandic fulmars confirm that plastic pollution levels in the North Atlantic tend to decrease towards higher latitudes. Levels of pollution thus appear to link to regions of intense human coastal and marine activities, suggesting substantial current inputs in those areas.  相似文献   

Classification of acoustically stable areas using empirical orthogonal functions   总被引：1，自引：1，他引：0  

Karl Thomas Hjelmervik  Jan Kristian Jensen  Petter ?stenstad  Atle Ommundsen 《Ocean Dynamics》2012,62(2):253-264

Sonar performance modeling is crucial for submarine and anti–submarine operations. The validity of sonar performance models is generally limited by environmental uncertainty, and particularly uncertainty in the vertical sound speed profile (SSP). Rapid environmental assessment (REA) products, such as oceanographic surveys and ocean models may be used to reduce this uncertainty prior to sonar operations. Empirical orthogonal functions (EOF) applied on the SSPs inherently take into account the vertical gradients and therefore the acoustic properties. We present a method that employs EOFs and a grouping algorithm to divide a large group of SSPs from an ocean model simulation into smaller groups with similar SSP characteristics. Such groups are henceforth called acoustically stable groups. Each group represents a subset in space and time within the ocean model domain. Regions with low acoustic variability contain large and geographically contiguous acoustically stable groups. In contrast, small or fragmented acoustically stable groups are found in regions with high acoustic variability. The main output is a map of the group distribution. This is a REA product in itself, but the map may also be used as a planning aid for REA survey missions.  相似文献   

Coseismic slip model of the 2007 August Pisco earthquake (Peru) as constrained by Wide Swath radar observations   总被引：1，自引：0，他引：1  

Mahdi Motagh  Rongjiang Wang  Thomas R. Walter  Roland Bürgmann  Eric Fielding  Jan Anderssohn  Jochen Zschau 《Geophysical Journal International》2008,174(3):842-848

The Pisco earthquake ( M _w 8.0; 2007 August 15) occurred offshore of Peru's southern coast at the subduction interface between the Nazca and South American plates. It ruptured a previously identified seismic gap along the Peruvian margin. We use Wide Swath InSAR observations acquired by the Envisat satellite in descending and ascending orbits to constrain coseismic slip distribution of this subduction earthquake. The data show movement of the coastal regions by as much as 85 cm in the line-of-sight of the satellite. Distributed-slip model indicates that the coseismic slip reaches values of about 5.5 m at a depth of ∼18–20 km. The slip is confined to less than 40 km depth, with most of the moment release located on the shallow parts of the interface above 30 km depth. The region with maximum coseismic slip in the InSAR model is located offshore, close to the seismic moment centroid location. The geodetic estimate of seismic moment is 1.23 × 10²¹ Nm ( M _w 8.06), consistent with seismic estimates. The slip model inferred from the InSAR observations suggests that the Pisco earthquake ruptured only a portion of the seismic gap zone in Peru between 13.5° S and 14.5° S, hence there is still a significant seismic gap to the south of the 2007 event that has not experienced a large earthquake since at least 1687.  相似文献