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561.
CaCO3 and total organic carbon concentrations, organic matter C/N and carbon isotope ratios, and sediment accumulation rates in late Quaternary sediments from DSDP Site 594 provide information about glacial–interglacial variations in the delivery of organic matter to the Chatham Rise offshore of southeastern New Zealand. Low C/N ratios and nearly constant organic δ13C values of −23‰ indicate that marine production dominates organic matter supply in both glacial and interglacial times during oxygen isotope stages 1 through 6 (0–140 ka) and 17 through 19 (660–790 ka). Increased organic carbon mass accumulation rates in isotope stages 2, 4, 6, and 18 record enhanced marine productivity during glacial maxima. Excursions of organic δ13C values to ca. −29‰ in portions of isotope stage 2 suggest that the local concentration of dissolved CO2 was occasionally elevated during the last glacial maximum, probably as a result of short periods of lowered sea-surface temperature. Dilution of carbonates by clastic continental sediment generally increases at this location during glacial maxima, but enhanced delivery of land-derived organic matter does not accompany the increased accumulation of clastic sediments. 相似文献
562.
563.
The pollution effects of cage aquaculture represent an external cost to society, and the challenge for environmental economists has been to estimate the magnitude of these costs and to suggest ways in which they can be mitigated or ‘internalised’. One possible mitigation strategy involves the development of integrated production systems based on polyculture, and this paper examines the financial viability of such a system that integrates the farming of salmon and mussels. The results demonstrate the commercial potential of an integrated salmon–mussel production system under present market conditions, but highlight the critical role played by future price trends. 相似文献
564.
Fulton Elizabeth A.; Smith Anthony D.M.; Punt Andre E. 《ICES Journal of Marine Science》2005,62(3):540-551
565.
Shih-Nan Chen Lawrence P. Sanford Evamaria W. Koch Fengyan Shi Elizabeth W. North 《Estuaries and Coasts》2007,30(2):296-310
The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were investigated using a modified
Nearshore Community Model (NearCoM). The model was enhanced to account for cohesive sediment erosion and deposition, sediment
transport, combined wave and current shear stresses, and seagrass effects on drag. Expressions for seagrass drag as a function
of seagrass shoot density and canopy height were derived from published flume studies of model vegetation. The predicted reduction
of volume flux for steady flow through a bed agreed reasonably well with a separate flume study. Predicted wave attenuation
qualitatively captured seasonal patterns observed in the field: wave attenuation peaked during the flowering season and decreased
as shoot density and canopy height decreased. Model scenarios with idealized bathymetries demonstrated that, when wave orbital
velocities and the seagrass canopy interact, increasing seagrass bed width in the direction of wave propagation results in
higher wave attenuation, and increasing incoming wave height results in higher relative wave attenuation. The model also predicted
lower skin friction, reduced erosion rates, and higher bottom sediment accumulation within and behind the bed. Reduced erosion
rates within seagrass beds have been reported, but reductions in stress behind the bed require further studies for verification.
Model results suggest that the mechanism of sediment trapping by seagrass beds is more complex than reduced erosion rates
alone; it also requires suspended sediment sources outside of the bed and horizontal transport into the bed. 相似文献
566.
Elizabeth R. Jones 《The Australian geographer》2007,38(1):93-112
Protected areas that are created to safeguard environmental values such as Indigenous culturescapes may in fact significantly fail in this task. This study concerns such an instance in far north-west Tasmania, where the government adopted a multiple-use resource conservation-development management model for the Arthur–Pieman Conservation Area (APCA). The model offers protection of cultural heritage values whilst permitting numerous community recreational and commercial uses. One particular objective is to protect ‘an extraordinary richness of Aboriginal cultural heritage’ in one of Earth's great archaeological regions (DPIWE, Arthur–Pieman Conservation Area Management Plan, 2002, p. iii). Yet under the auspices of multiple use, Aborigine and others report unremitting damage and loss of ancestral values. To examine how this is so in an actively managed protected area, perceptions of 16 environmental professionals and local residents engaged in APCA planning and management are used to identify three major challenges for appropriate custodianship of the Aboriginal cultural landscape: Aboriginal–Eurocentric conflicts; limited community governance capacities; and deficient regulatory provisions. It is concluded that APCA multiple-use management of heritage conservation is ineffectual and that an alternative governance model is required urgently. The management challenges examined here offer insights for problematic Indigenous cultural heritage conservation in other jurisdictions of Australia and elsewhere. 相似文献
567.
Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution 总被引:4,自引:6,他引:4
Barnier Bernard Gurvan Madec Thierry Penduff Jean-Marc Molines Anne-Marie Treguier Julien Le Sommer Aike Beckmann Arne Biastoch Claus Böning Joachim Dengg Corine Derval Edmée Durand Sergei Gulev Elizabeth Remy Claude Talandier Sébastien Theetten Mathew Maltrud Julie McClean Beverly De Cuevas 《Ocean Dynamics》2006,56(5-6):543-567
Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4°) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy–enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10° resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current–topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution. 相似文献
568.
Warren J. De Bruyn Elizabeth Dahl Eric S. Saltzman 《Journal of Atmospheric Chemistry》2006,53(2):145-154
Dimethyl sulfide (DMS) and sulfur dioxide (SO2) mixing ratios were measured in the boundary layer on Oahu, Hawaii in April and May 2000. Average DMS and SO2 levels were 22 ± 7 (n = 488) pmol/mol and 23 ± 7 (n = 471) pmol/mol respectively. Anti-correlated DMS and SO2 diurnal cycles, consistent with DMS + OH oxidation were observed on most days. Photochemical box model simulations suggest that the yield of SO2 and total SO2 sink are ∼85% and ∼2 × 104 molec cm− 3 s− 1 respectively. On several days the rate of decrease in DMS and increase in SO2 levels in the early morning were larger that predicted by the model. Dynamical and chemical causes for the anomalous early morning data are explored. 相似文献
569.
570.
Elizabeth H. Hearn 《Geophysical Journal International》2003,155(3):753-777