Oceanographic influences on seabirds and cetaceans of the eastern tropical Pacific: A review     

Lisa T. Ballance  Robert L. Pitman  Paul C. Fiedler 《Progress in Oceanography》2006,69(2-4):360

This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific, the oceanic region centered on the eastern Pacific warm pool, but also including the equatorial cold tongue and equatorial current system, and summarizes what is known about oceanographic influences on seabirds and cetaceans there. The eastern tropical Pacific supports on the order of 50 species of seabirds and 30 species of cetaceans as regular residents; these include four endemic species, the world’s largest populations for several others, three endemic sub-species, and a multi-species community that is relatively unique to this ecosystem. Three of the meso-scale physical features of the region are particularly significant to seabirds and cetaceans: the Costa Rica Dome for blue whales and short-beaked common dolphins, the Equatorial Front for planktivorous seabirds, and the countercurrent thermocline ridge for flocking seabirds that associate with mixed-species schools of spotted and spinner dolphins and yellowfin tuna. A few qualitative studies of meso- to macro-scale distribution patterns have indicated that some seabirds and cetaceans have species-specific preferences for surface currents. More common are associations with distinct water masses; these relationships have been quantified for a number of species using several different analytical methods. The mechanisms underlying tropical species–habitat relationships are not well understood, in contrast to a number of higher-latitude systems. This may be due to the fact that physical variables have been used as proxies for prey abundance and distribution in species–habitat research in the eastern tropical Pacific.Though seasonal and interannual patterns tend to be complex, species–habitat relationships appear to remain relatively stable over time, and distribution patterns co-vary with patterns of preferred habitat for a number of species. The interactions between seasonal and interannual variation in oceanographic conditions with seasonal patterns in the biology of seabirds and cetaceans may account for some of the complexity in species–habitat relationship patterns.Little work has been done to investigate effects of El Niño-Southern Oscillation cycles on cetaceans, and results of the few studies focusing on oceanic seabirds are complex and not easy to interpret. Although much has been made of the detrimental effects of El Niño events on apex predators, more research is needed to understand the magnitude, and even direction, of these effects on seabirds and cetaceans in space and time.  相似文献   

ENSO variability and the eastern tropical Pacific: A review   总被引：3，自引：0，他引：3  

Chunzai Wang  Paul C. Fiedler 《Progress in Oceanography》2006,69(2-4):239

El Niño-Southern Oscillation (ENSO) encompasses variability in both the eastern and western tropical Pacific. During the warm phase of ENSO, the eastern tropical Pacific is characterized by equatorial positive sea surface temperature (SST) and negative sea level pressure (SLP) anomalies, while the western tropical Pacific is marked by off-equatorial negative SST and positive SLP anomalies. Corresponding to this distribution are equatorial westerly wind anomalies in the central Pacific and equatorial easterly wind anomalies in the far western Pacific. Occurrence of ENSO has been explained as either a self-sustained, naturally oscillatory mode of the coupled ocean–atmosphere system or a stable mode triggered by stochastic forcing. Whatever the case, ENSO involves the positive ocean–atmosphere feedback hypothesized by Bjerknes. After an El Niño reaches its mature phase, negative feedbacks are required to terminate growth of the mature El Niño anomalies in the central and eastern Pacific. Four requisite negative feedbacks have been proposed: reflected Kelvin waves at the ocean western boundary, a discharge process due to Sverdrup transport, western Pacific wind-forced Kelvin waves, and anomalous zonal advections. These negative feedbacks may work together for terminating El Niño, with their relative importance being time-dependent.ENSO variability is most pronounced along the equator and the coast of Ecuador and Peru. However, the eastern tropical Pacific also includes a warm pool north of the equator where important variability occurs. Seasonally, ocean advection seems to play an important role for SST variations of the eastern Pacific warm pool. Interannual variability in the eastern Pacific warm pool may be largely due to a direct oceanic connection with the ENSO variability at the equator. Variations in temperature, stratification, insolation, and productivity associated with ENSO have implications for phytoplankton productivity and for fish, birds, and other organisms in the region. Long-term changes in ENSO variability may be occurring and are briefly discussed. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific.  相似文献   

A review of eastern tropical Pacific oceanography: Summary     

M.F. Lavín  P.C. Fiedler  J.A. Amador  L.T. Ballance  J. Frber-Lorda  A.M. Mestas-Nuez 《Progress in Oceanography》2006,69(2-4):391

The collection of articles in this volume reviewing eastern tropical Pacific oceanography is briefly summarized, and updated references are given. The region is an unusual biological environment as a consequence of physical characteristics and patterns of forcing – including a strong and shallow thermocline, the ITCZ and coastal wind jets, equatorial upwelling, the Costa Rica Dome, eastern boundary and equatorial current systems, low iron input, inadequate ventilation of subthermocline waters, and dominance of ENSO-scale temporal variability. Remaining unanswered questions are presented.  相似文献   

Side-scan and acoustic subbottom characterization of the sea floor near the Dry Tortugas, Florida     

Thomas F. Wever  Hannelore M. Fiedler  Gunther Fechner  Friedrich Abegg  Ingo H. Stender 《Geo-Marine Letters》1997,17(4):246-252

 Between 2 and 6 February, 1995, a 25 km² area at the Dry Tortugas (Florida Keys) was surveyed with a 100 kHz side-scan sonar system and 3.5-kHz subbottom profiler. The side-scan system revealed a pattern of alternating high and low backscatter. The subbottom profiler showed areas with no acoustic penetration between sediment troughs. The combination of both methods allowed delineation of the boundaries in high-backscatter regions, and sediment samples allowed correlations between high backscatter and coarser-grained sediments.  相似文献   

The use of MODIS data to derive acreage estimations for larger fields: A case study in the south-western Rostov region of Russia     

S. Fritz  M. Massart  I. Savin  J. Gallego  F. Rembold   《International Journal of Applied Earth Observation and Geoinformation》2008,10(4):453

Recent developments in remote sensing technology, in particular improved spatial and temporal resolution, open new possibilities for estimating crop acreage over larger areas. Remotely sensed data allow in some cases the estimation of crop acreage statistics independently of sub-national survey statistics, which are sometimes biased and incomplete. This work focuses on the use of MODIS data acquired in 2001/2002 over the Rostov Oblast in Russia, by the Azov Sea. The region is characterised by large agricultural fields of around 75 ha on average. This paper presents a methodology to estimate crop acreage using the MODIS 16-day composite NDVI product. Particular emphasis is placed on a good quality crop mask and a good quality validation dataset. In order to have a second dataset which can be used for cross-checking the MODIS classification a Landsat ETM time series for four different dates in the season of 2002 was acquired and classified. We attempted to distinguish five different crop types and achieved satisfactory and good results for winter crops. Three hundred and sixty fields were identified to be suitable for the training and validation of the MODIS classification using a maximum likelihood classification. A novel method based on a pure pixel field sampling is introduced. This novel method is compared with the traditional hard classification of mixed pixels and was found to be superior.  相似文献   

Channelized and hillslope sediment transport and the geomorphology of mountain belts     

Heinz Schneider  Marco Schwab  Fritz Schlunegger 《International Journal of Earth Sciences》2008,97(1):179-192

This paper uses the results of landscape evolution models and morphometric data from the Andes of northern Peru and the eastern Swiss Alps to illustrate how the ratio between sediment transport on hillslopes and in channels influences landscape and channel network morphologies and dynamics. The headwaters of fluvial- and debris-flow-dominated systems (channelized processes) are characterized by rough, high-relief, highly incised surfaces which contain a dense and hence a closely spaced channel network. Also, these systems tend to respond rapidly to modifications in external forcing (e.g., rock uplift and/or precipitation). This is the case because the high channel density results in a high bulk diffusivity. In contrast, headwaters where landsliding is an important sediment source are characterized by a low channel density and by rather straight and unstable channels. In addition, the topographies are generally smooth. The low channel density then results in a relatively low bulk diffusivity. As a consequence, response times are greater in headwaters of landslide-dominated systems than in highly dissected drainages. The Peruvian and Swiss case studies show how regional differences in climate and the litho-tectonic architecture potentially exert contrasting controls on the relative importance of channelized versus hillslope processes and thus on the overall geomorphometry. Specifically, the Peruvian example illustrates to what extent the storminess of climate has influenced production and transport of sediment on hillslopes and in channels, and how these differences are seen in the morphometry of the landscape. The Swiss example shows how the bedding orientation of the bedrock drives channelized and hillslope processes to contrasting extents, and how these differences are mirrored in the landscape. An erratum to this article can be found at  相似文献   

Phanerozoic tectonothermal history of the Arabian–Nubian shield in the Eastern Desert of Egypt: evidence from fission track and paleostress data     

Ana-Voica Bojar  Harald Fritz  Sabine Kargl  Wolfgang Unzog 《Journal of African Earth Sciences》2002,34(3-4)

To constrain the post-Pan-African evolution of the Arabian–Nubian Shield, macro-scale tectonic studies, paleostress and fission track data were performed in the Eastern Desert of Egypt. The results provide insights into the processes driving late stage vertical motion and the timing of exhumation of a large shield area. Results of apatite, zircon and sphene fission track analyses from the Neoproterozoic basement indicate two major episodes of exhumation. Sphene and zircon fission track data range from 339 to 410 Ma and from 315 to 366 Ma, respectively. The data are interpreted to represent an intraplate thermotectonic episode during the Late Devonian–Early Carboniferous. At that time, the intraplate stresses responsible for deformation, uplift and erosion, were induced by the collision of Gondwana with Laurussia which started in Late Devonian times. Apatite fission track data indicate that the second cooling phase started in Oligocene and was related to extension, flank uplift and erosion along the actual margin of the Red Sea. Structural data collected from Neoproterozoic basement, Late Cretaceous and Tertiary sedimentary cover suggest two stages of rift formation. (1) Cretaceous strike-slip tectonics with sub-horizontal σ1 (ENE/WSW) and σ3 (NNW/SSE), and sub-vertical σ2 resulted in formation of small pull-apart basins. Basin axes are parallel to the trend of Pan-African structural elements which acted as stress guides. (2) During Oligocene to Miocene the stress field changed towards horizontal NE–SW extension (σ3), and sub-vertical σ1. Relations between structures, depositional ages of sediments and apatite fission track data indicate that the initiation of rift flank uplift, erosion and plate deformation occurred nearly simultaneously.  相似文献   

A Simplified Analytical Procedure for the Determination of Organically Bound Halogens in Salt‐containing Water Samples     

Helko Borsdorf  Petra Fiedler  Dorit Wilke  Holger Weiß 《洁净——土壤、空气、水》2003,31(1):19-24

A method was developed for the determination of organic halogens in water samples with the aim of minimizing matrix effects and simplifying the sample preparation technique commonly used. The method is based on the adsorption of organic halogens in modified hydrophilic divinylbenzene polymer columns and their elution with methanol. The adsorbent used enables rapid adsorption and desorption due to comparatively high operating flow rates and minimized solvent amounts. Furthermore, no additional reconcentration steps are needed. The methanol extract obtained is combusted with a standard EOX (extractable organic halogen) analyzer and the concentration of organically bound halogens is determined by microcoulometric analysis. The matrix effects are considerably reduced compared to the standard procedure (EN 1485) commonly used. A detection limit of 13 μg/L was established.  相似文献   

Pleistocene/Holocene climate change, re-establishment of fluvial drainage network and increase in relief in the Swiss Alps   总被引：1，自引：0，他引：1  

Fritz Schlunegger  Matthias Hinderer 《地学学报》2003,15(2):88-95

ABSTRACT Data are presented about modern sediment discharge of the Swiss rivers and related to the size of catchments. The information reveals that the Central Alps have experienced denudation rates of ≈0.15 mm yr⁻¹ in the foreland, and ≈0.5 mm yr⁻¹ in the Alpine core. Mapping, however, indicates that modern erosion only affects 30–50% of the Alpine surface, and that fluvial and associated hillslope processes have focused erosion in 50–200-m-deep valleys. These valleys are incised into the glacial surface. If this limited spatial extent of erosion is considered, then effective erosion rates are significantly higher than average denudation rates. These effective rates equal or locally exceed modern rates of rock uplift. This implies that the modification of erosional processes related to the Pleistocene/Holocene climate change has resulted in an increase in the relief at a local scale. At a drainage basin scale, however, the relief appears not to change at present.  相似文献   

Regional effects of large-scale extreme wind events over orographically structured terrain     

N. Kalthoff  I. Bischoff-Gauß  F. Fiedler 《Theoretical and Applied Climatology》2003,74(1-2):53-67

Summary ?Above orographically structured terrain considerable differences of the regional wind field may be identified during large-scale extreme wind events. So far, these regional differences could not be resolved by climate models. To determine the relationships between large-scale atmospheric conditions, the influence of orography, and the regional wind field, data measured in the upper Rhine valley within the framework of the REKLIP Regional Climate Project were analyzed and calculations were made using the KAMM mesoscale model. In the area of the upper Rhine valley, ratios of the wind velocity in the Rhine valley at 10 m above ground level, ν_val, and the large-scale flow velocity, ν_lar, are between ν_val/ν_lar ≈ 0.1 and ν_val/ν_lar ≈ 1. The ν_val/ν_lar ratio exhibits a strong dependence on thermal stratification, δ, and decreases from ν_val/ν_lar ≈ 1 at δ = 0 K m⁻¹ to ν_val/ν_lar ≈ 0.2 at δ = 0.0075 K m⁻¹. In areas, where the lateral mountainous border of the Rhine valley is interrupted, the ν_val/ν_lar ratio increases again with increasing stability or decreasing Froude number. This is obviously due to flow around the Black Forest under stable stratification. It is demonstrated by model calculations that a complex wind field develops in the Rhine valley at small Froude numbers (Fr < 1) irrespective of the direction of large-scale flow. The ν_val/ν_lar ratio is characterized by small values in the direct lee side (ν_val/ν_lar ≈ 0.2) and high values on the windward side of the lateral mountainous border of the Rhine valley (ν_val/ν_lar ≈ 0.8). Received October 22, 2001; revised June 18, 2002; accepted June 23, 2002  相似文献