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821.
Jin Li Andrew D. HeapAnna Potter Zhi HuangJames J. Daniell 《Continental Shelf Research》2011,31(13):1365-1376
Spatially continuous data of environmental variables is often required for marine conservation and management. However, information for environmental variables is usually collected by point sampling, particularly for the marine region. Thus, methods generating such spatially continuous data by using point samples to estimate values for unknown locations become essential tools. Such methods are, however, often data- or even variable-specific and it is difficult to select an appropriate method for any given dataset. In this study, 14 methods (37 sub-methods) are compared using samples of mud content with five levels of sample density across the southwest Australian margin. Bathymetry, distance-to-coast, slope and geomorphic province were used as secondary variables. Ten-fold cross validation with relative mean absolute error (RMAE) and visual examination were used to assess the performance of these methods. A total of 1850 prediction datasets are produced and used to assess the performance of the methods and the effects of other factors considered. Considering both the accuracy and the visual examination, we found that a combined method (i.e., random forest and ordinary kriging: RKrf) is the most robust method. This method is novel, with a RMAE up to 17% less than that of the control. No threshold in sample density was detected in relation to prediction accuracy. No consistent patterns are observed between the performance of the methods and data variation. The RMAE of three most accurate methods is about 30% lower than that of the best methods in previous publications, highlighting the robustness of the methods selected in this study. The implications and limitations of this study are discussed and a number of suggestions are provided for further studies. 相似文献
822.
823.
Chris Andrew Christopher R.C. Paul Stephen K. Donovan 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(1):34-46
Over 40 ammonites, mostly Promicroceras, with epifaunal worm tubes are described from the Lower Jurassic, Charmouth Mudstone Formation (Lias Group) of Dorset. Serpulids that were overgrown by the ammonites or responded to the ammonites’ growth attached to juvenile, living ammonites. Some epifaunal serpulids attached post-mortem, indicating oxygenated bottom water, which was rare in the lower Charmouth Mudstone Formation. Other serpulids do not conform to either pre- or post-mortem growth predictions and require individual assessment. The commonest pattern of growth for serpulids on live juvenile ammonites was attachment in the umbilical seam, with later growth onto, and finally around, the venter. Reconstructing this pattern shows that serpulids kept their aperture at 6 o’clock with respect to the orientation of the living ammonite (105-115° behind the ammonite aperture) throughout life. Reorientation of growth lines in serpulid worms just before the aperture suggests some worm tubes were fully grown. The 6 o’clock position of the aperture enabled feeding currents generated by the worms to parallel currents generated by swimming ammonites, thus maximizing food gathering and confirming that ammonites swam backwards. The mid-ventral position enabled the worm to deploy its branchia on both sides of the ammonite. Growth on ammonites was beneficial to the worms, but parasitic to the ammonites. Promicroceras with epifaunal worm tubes died at smaller sizes than unencumbered examples and size at death correlates inversely to extra weight of worm tubes. Uniformitarian comparisons suggest fossil serpulid worms grew in one season and that Promicroceras reached full size in two or three years. 相似文献
824.
Daniel Cossa Lars-Eric Heimbürger Stephen R. Rintoul Edward C.V. Butler Andrew R. Bowie Roslyn J. Watson 《Geochimica et cosmochimica acta》2011,75(14):4037-4052
We present here the first mercury speciation study in the water column of the Southern Ocean, using a high-resolution south-to-north section (27 stations from 65.50°S to 44.00°S) with up to 15 depths (0-4440 m) between Antarctica and Tasmania (Australia) along the 140°E meridian. In addition, in order to explore the role of sea ice in Hg cycling, a study of mercury speciation in the “snow-sea ice-seawater” continuum was conducted at a coastal site, near the Australian Casey station (66.40°S; 101.14°E). In the open ocean waters, total Hg (HgT) concentrations varied from 0.63 to 2.76 pmol L−1 with “transient-type” vertical profiles and a latitudinal distribution suggesting an atmospheric mercury source south of the Southern Polar Front (SPF) and a surface removal north of the Subantartic Front (SAF). Slightly higher mean HgT concentrations (1.35 ± 0.39 pmol L−1) were measured in Antarctic Bottom Water (AABW) compared to Antarctic Intermediate water (AAIW) (1.15 ± 0.22 pmol L−1). Labile Hg (HgR) concentrations varied from 0.01 to 2.28 pmol L−1, with a distribution showing that the HgT enrichment south of the SPF consisted mainly of HgR (67 ± 23%), whereas, in contrast, the percentage was half that in surface waters north of PFZ (33 ± 23%). Methylated mercury species (MeHgT) concentrations ranged from 0.02 to 0.86 pmol L−1. All vertical MeHgT profiles exhibited roughly the same pattern, with low concentrations observed in the surface layer and increasing concentrations with depth up to an intermediate depth maximum. As for HgT, low mean MeHgT concentrations were associated with AAIW, and higher ones with AABW. The maximum of MeHgT concentration at each station was systematically observed within the oxygen minimum zone, with a statistically significant MeHgTvs Apparent Oxygen Utilization (AOU) relationship (p < 0.001). The proportion of HgT as methylated species was lower than 5% in the surface waters, around 50% in deep waters below 1000 m, reaching a maximum of 78% south of the SPF. At Casey coastal station HgT and HgR concentrations found in the “snow-sea ice-seawater” continuum were one order of magnitude higher than those measured in open ocean waters. The distribution of HgT there suggests an atmospheric Hg deposition with snow and a fractionation process during sea ice formation, which excludes Hg from the ice with a parallel Hg enrichment of brine, probably concurring with the Hg enrichment of AABW observed in the open ocean waters. Contrastingly, MeHgT concentrations in the sea ice environment were in the same range as in the open ocean waters, remaining below 0.45 pmol L−1. The MeHgT vertical profile through the continuum suggests different sources, including atmosphere, seawater and methylation in basal ice. Whereas HgT concentrations in the water samples collected between the Antarctic continent and Tasmania are comparable to recent measurements made in the other parts of the World Ocean (e.g., Soerensen et al., 2010), the Hg species distribution suggests distinct features in the Southern Ocean Hg cycle: (i) a net atmospheric Hg deposition on surface water near the ice edge, (ii) the Hg enrichment in brine during sea ice formation, and (iii) a net methylation of Hg south of the SPF. 相似文献
825.
826.
827.
Thomas Alfred Schlacher Andrew Holzheimer Tim Stevens David Rissik 《Estuaries and Coasts》2011,34(5):937-949
Biological impacts of oil on sandy shore ecosystems remain incompletely understood, especially following smaller spills on
subtropical beaches. Here we quantified changes to benthic assemblages on a sandy beach following the 270-t spill of heavy
fuel oil from the Pacific Adventurer that occurred in March 2009 off Moreton Island in Eastern Australia. Assessments of ecological impacts are based on spatial
contrasts between multiple reference and impact sites sampled 1 week and 3 months after the spill. Benthic invertebrate assemblages
exposed to oil had significantly fewer individuals of fewer species 1 week after the spill, markedly changing their ecological
structure. Biological differences consistent with oil-related mortality were significant on the lower shore and in the swash
and remained so 3 months after the spill. This signals a lack of recovery of these communities in the short term, despite
the fairly rapid removal of oil. Results show that, despite the relatively small size of the spill, heavy fuel oil contamination
can cause substantial impacts on sandy beach ecosystems, and that recovery may be prolonged. 相似文献
828.
We describe and test a method for identifying alluvial fans likely to be affected by debris flows. It is based on identifying
catchment parameters by geographical information system interrogation of a digital elevation model, using the Melton ratio
as the discriminating parameter. The method was calibrated using data from debris-flow-generating catchments in Coromandel
and the adjacent Kaimai Ranges, North Island, NZ, and tested against data from the rest of New Zealand. The procedure is remarkably
(but not completely) reliable for identifying debris-flow-capable catchments, and thus fans, across the wide range of climates
and lithologies in New Zealand mountains. A case study illustrates the potential of the method for avoiding future hazards
and emphasises the need for a precautionary approach when field investigations do not detect evidence for past debris flows. 相似文献
829.
András A. Sipos Gábor Domokos Andrew Wilson Niels Hovius 《Mathematical Geosciences》2011,43(5):583-591
We use a simple, collision-based, discrete, random abrasion model to compute the profiles for the stoss faces in a bedrock
abrasion process. The model is the discrete equivalent of the generalized version of a classical, collision based model of
abrasion. Three control parameters (which describe the average size of the colliding objects, the expected direction of the
impacts and the average volume removed from the body due to one collision) are sufficient for realistic predictions. 相似文献
830.
Kirstin Dobbs Jon Day Hilary Skeat John Baldwin Fergus Molloy Laurence McCook Margaret Johnson Bruce Elliot Andrew Skeat Karen Vohland David Wachenfeld Richard Kenchington 《Marine Policy》2011
The Great Barrier Reef Outlook Report 2009 was the first produced in response to a newly legislated requirement for five-yearly reports on the status of and outlook for the Great Barrier Reef. It adopted an ecosystem approach, assessing all habitats and species, ecosystem processes and major uses. By then considering the factors affecting the ecosystem, coupled with an assessment of management effectiveness, it provided a risk-based forward-looking projection for the ecosystem. Rarely has such a comprehensive, ecosystem-based report been produced to guide government action. With no pre-determined path to follow for interpreting the legislative requirements, the Great Barrier Reef Marine Park Authority (GBRMPA) developed a repeatable structure and method for Great Barrier Reef Outlook Reports that impartially and consistently considers the evidence and clearly presents the findings. The GBRMPA worked closely with relevant Australian and Queensland Government agencies as well as researchers, industry representatives and the community while developing the report. That such a report must be produced every five years allows an overview of the effectiveness of management responses to be regularly assessed. It also provides a transparent means of highlighting and tracking emerging risks facing the Great Barrier Reef. 相似文献