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This study reports the first inventory of physical properties of individual plastic debris in the North Atlantic. We analyzed 748 samples for size, mass, and material composition collected from surface net tows on 11 expeditions from Cape Cod, Massachusetts to the Caribbean Sea between 1991 and 2007. Particles were mostly fragments less than 10 mm in size with nearly all lighter than 0.05 g. Material densities ranged from 0.808 to 1.24 g ml−1, with about half between 0.97 and 1.04 g ml−1, a range not typically found in virgin plastics. Elemental analysis suggests that samples in this density range are consistent with polypropylene and polyethylene whose densities have increased, likely due to biofouling. Pelagic densities varied considerably from that of beach plastic debris, suggesting that plastic particles are modified during their residence at sea. These analyses provide clues in understanding particle fate and potential debris sources, and address ecological implications of pelagic plastic debris.  相似文献   
2.
The Humber Estuary, UK, divides into the Ouse and Trent estuaries at the so-called Apex within its upper reaches. Remotely sensed Compact Airborne Spectrographic Imager (CASI) images and boat measurements were used to observe a strong turbidity maximum in the upper Humber and Ouse during a spring tide in November 1995. Surface suspended particulate matter (SPM) concentrations during the late ebb, as estimated from the CASI data, increased from approximately 6 to 13 g I−1 moving up-estuary into the Ouse. Greater SPM concentrations (∼10 g I−1) were evident in the deeper channels of the Ouse, compared with shallower areas, possibly due to faster ebb currents there and differential down-estuary advection of the turbidity maximum. Ribbons, or streaks, of lower SPM and slightly cooler waters were observed. It appears that slightly cooler and lower turbidity waters from the confluent Trent estuary remained fairly distinct for distances of approximately 2 km down-stream of its confluence with the upper Humber and Ouse. These waters eventually broke into ribbon-like or streak-like structures within the higher SPM-laden and slightly warmer waters of the Humber. They were discernible for more than 5 km down-estuary of the confluence of the Humber, Ouse, and Trent. Boat measurements showed that the turbidity maximum occurred over a fairly restricted region of the upper Humber, between about 20 to 50 km from the tidal limit at high water. The turbidity maximum’s sediment load was largely suspended in the water column during stronger currents. SPM rapidly settled close to the bed during high water and low water slack periods. At these times, SPM concentrations in a thin, near-bed layer were >60 g I−1 in the turbidity maximum region of the Ouse and >30 g 1−1 in the upper Humber (where channel volumes were much greater). SPM within the turbidity maximum comprised very fine-grained material and its low organic content demonstrated that the SPM was essentially mineral, clastic sediment derived originally from erosion and decay of crustal rocks.  相似文献   
3.
Natural Hazards - There are several different estimates of the observed cyclone damage potential of tropical cyclones based on observations of size, intensity and track. For the analysis of climate...  相似文献   
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The ability of General Circulation Models (GCMs) to generate Tropical Cyclones (TCs) over the North Atlantic Main Development Region (MDR; 10–20°N, 20–80°W; Goldenberg and Shapiro in J Clim 9:1169–1187, 1996) is examined through a subset of ocean–atmosphere coupled simulations from the World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel data set and a high-resolution (0.5°) Sea Surface Temperature (SST)-forced simulation from the Australian Conformal-Cubic Atmospheric Model GCM. The results are compared with National Center for Environmental Prediction (NCEP-2) and European Center for Medium Range Weather Forecasts Re-Analysis (ERA-40) reanalyses over a common period from 1980 to 1998. Important biases in the representation of the TC activity are encountered over the MDR. This study emphasizes the strong link in the GCMs between African Easterly Waves (AEWs) and TC activity in this region. However, the generation of AEWs is not a sufficient condition alone for the models to produce TCs. Precipitation over the Sahel, especially rainfall over the Fouta Djallon highlands (cf. Fig.?1), is playing a role in the generation of TCs over the MDR. The influence of large-scale fields such as SST, vertical wind shear and tropospheric humidity on TC genesis is also examined. The ability of TC genesis indices, such as the Genesis Potential Index and the Convective Yearly Genesis Potential, to represent TC activity over the MDR in simulations at low to high spatial resolutions is analysed. These indices are found to be a reasonable method for comparing cyclogenesis in different models, even though other factors such as AEW activity should also be considered.  相似文献   
5.
The XXIst International Congress of Photogrammetry and Remote Sensing was held at the Beijing International Convention Centre, China, from 3rd to 11th July 2008. Reports are given on the Congress as a whole, including the General Assembly, some Technical Commission activities and the Congress Exhibition. Papers from the Congress are published in Volume XXXVII of the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences.  相似文献   
6.
Over the past 40 years there have been significant changes in Australian rainfall with increases in the north-west and decreases in the east. Tropical cyclones (TCs) and other closed low pressure systems are important synoptic systems that provide a large proportion of Australia’s annual rainfall. This study examines the proportion of rainfall that can be attributed to TCs over the 1970–2009 period, and to TCs combined with other closed lows over the 1989–2009 period. The contribution of these systems to Australian rainfall trends is also analysed. Tropical cyclones are found to have little influence on rainfall trends over the full time period. However, when the more recent 21-year period is considered, TCs and other closed low pressure systems can partially explain the positive rainfall trend in the north-west. Similarly, other closed low pressure systems, such as cut-off lows and east coast lows, can explain some of the negative rainfall trend in the south-east. The contribution of TCs and other closed low pressure systems to rainfall trends in the north and south-east is found to be predominantly due to respective increases and decreases in the rainfall producing efficiency of the systems. An understanding of the influence of these synoptic systems on Australian rainfall in the current climate is vital for evaluating how Australia's water budget may change in future climates.  相似文献   
7.
An important goal in ocean colour remote sensing is to accurately detect different phytoplank- ton groups with the potential uses including the validation of multi-phytoplankton carbon cycle models; synoptically monitoring the health of our oceans, and improving our understanding of the bio-geochemical interactions between phytoplankton and their environment. In this paper a new algorithm is developed for detecting three dominant phytoplankton size classes based on distinct differences in their optical signatures. The technique is validated against an independent cou- pled satellite reflectance and in situ pigment dataset and run on the 10-year NASA Sea viewing Wide Field of view Sensor (SeaWiFS) data series. Results indicate that on average 3.6% of the global oceanic surface layer is dominated by microplankton, 18.0% by nanoplankton and 78.4% by picoplankton. Results, however, are seen to vary depending on season and ocean basin.  相似文献   
8.
Satellite derived sea surface temperature (SST) and chlorophyll data are used to characterise the period of upwelling during a cruise on which two Lagrangian drift experiments were conducted off the Iberian Atlantic coast in August 1998. During the cruise there was a prolonged period of equator-ward winds which favour upwelling; three distinct maxima were observed in the meteorological data interspersed with periods of relaxation. The SST and chlorophyll imagery show upwelling to be active with distinct offshore filaments that are cooler and of higher chlorophyll concentration than the surrounding oceanic water; these filaments represent an important cross-shelf transport mechanism. A front detection methodology has been applied to satellite images and suggests that these filaments are distinct, long-lived features, characterised by enhanced primary production.  相似文献   
9.
Detection of tropical lows is performed in a suite of climate model simulations using objectively-determined detection thresholds that are resolution-dependent. It is found that there is some relationship between model resolution and tropical cyclone formation rate even after the resolution-dependent tropical cyclone detection threshold is applied. The relationship is investigated between model-simulated tropical cyclone formation and a climate-based tropical cyclone Genesis Potential Index (GPI). It is found that coarser-resolution models simulate the GPI better than they simulate formation of tropical cyclones directly. As a result, there appears to be little relationship from model to model between model GPI and the directly-simulated cyclone formation rate. Statistical analysis of the results shows that the main advantage of increasing model resolution is to give a considerably better pattern of cyclone formation. Finer resolution models also simulate a slightly better pattern of GPI, and for these models there is some relationship between the pattern of GPI simulated by each model and that model’s pattern of simulated tropical cyclone formation.  相似文献   
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