Relationship between waterfowl and American coot abundance with submersed macrophytic vegetation in Currituck Sound,North Carolina

Waterfowl and American coot data collected from aerial censusing on Currituck Sound were compared during three periods: before Eurasian watermilfoil (Myriophyllum spicatum) colonization (1961–1965); during Eurasian watermilfoil infestation (1968–1977); and following the near absence of submersed macrophytic vegetation after Eurasian watermilfoil decline (1981–1990). Numbers of dabbling ducks (Anas rubripes, Anas platyrhynchos, Anas acuta, Anas americana, Anas crecca), ring-necked ducks (Aythya collaris), and American coot (Fulica americana) were significantly different in Currituck Sound (p<0.05) in at least two of these periods and were highest during Eurasian watermilfoil infestation. These species also constituted higher percentages of the Atlantic Flyway counts during Eurasian watermilfoil infestation. than in periods before or after. Numbers of snow geese (Chen caerulescens), Canada geese (Branta canadensis), and canvasbacks (Aythya valisneria) were significantly different between periods; however, these birds exhibited a consistent decline from the early to the late period. This study suggests that submersed macrophytes, specifically Eurasian watermilfoil, support increased numbers of dabbling ducks, ring-necked ducks, and American coot.     

River stabilisation due to changing climate and vegetation during the late Quaternary in western Tasmania, Australia

The Stanley River in western Tasmania, Australia, contains sub-fossil rainforest logs within the channel and floodplain. Of the more than 85 radiocarbon dates obtained, all but 3 date from 17 ka to the present and permit an interpretation of fluvial and related environmental changes over this period. Particular attention is focused on the interactive relationship between the river and its riparian rainforest. Following the Last Glacial Maximum, the Stanley River was a laterally active gravel-load system reworking most of its valley floor in the upstream reaches. With ameliorating conditions at the end of the Pleistocene, climate became less seasonal and flow regimes less energetic. Huon pines already present in the catchment, re-asserted themselves in the form of dense tree cover along the river banks and floodplains with basal floodplain deposition shifting from gravels to coarse sands and granules. By about 3.5 ka, a further change in climate reduced stream discharges substantially. As a result the channel reduced in size, transported finer sediment, became laterally stable, and the floodplain accreted with overbank deposits of sand and silt. Huon pines falling into the channel formed obstructions of woody debris, some surviving for 2 ka. These have reduced stream power and boundary shear stress, further contributing to channel stability. Generational sequences of Huon pines on the river banks, some extending back 1–2 ka, are additional evidence of this stability. Since the Pleistocene, changing climate and the re-establishment of dense riparian rainforest appear to have stabilised the river channels and floodplains of western Tasmania.     

The effect of horizontal resolution on ocean surface heat fluxes in the ECMWF model

Annual mean ocean surface heat fluxes have been studied as a function of horizontal resolution in the ECMWF model (cycle 33) and compared with Oberhuber's COADS (1959–1979) based empirical estimates. The model has been run at resolutions of T21, T42, T63 and T106 for 15 months with prescribed monthly varying climatological SST and sea ice. The T42 simulation was extended to 2 years, which enabled us to determine that many differences between the resolution runs were significant and could not be explained by the fact that individual realizations of an ensemble of years can be expected to give different estimates of the annual mean climate state. In addition to systematic differences between the modeled and the observed fluxes, the simulated fields of surface shortwave and longwave radiation showed much more spatial variability than the observed estimates. In the case of the longwave radiation this may be attributable more to deficiencies in the observations than to errors in the model. The modeled latent and sensible heat fields were in better agreement with observations. The primary conclusion concerning the dependence of ocean surface fluxes on resolution is that the T21 simulation differed significantly from the higher resolution runs, especially in the tropics. Although the differences among the three higher resolution simulations were generally small over most of the world ocean, there were local areas with large differences. It appears, therefore, that in relation to ocean surface heat fluxes, a resolution greater than T42 may not be justified for climate model simulations, although the locally large differences found between the higher resolution runs suggest that convergence has not been achieved everywhere even at T106.     

Quaternary evolution of Cedar Creek alluvial fan, montana

Cedar Creek alluvial fan is a textbook example of an alluvial fan because of its fan shape with smooth, concentric contours and excellent symmetry. Similar planimetric shapes have been used to infer uniform fan deposition; however, Cedar Creek alluvial fan is composed of four fan deposits of Quaternary age, Qf1 (oldest) to Qf4 (youngest), indicating that fan deposition was nonuniform in both time and space. Field studies indicate that deposition of Cedar Creek alluvial fan is related to glaciofluvial outwash activity during the Pleistocene and upper-fan entrenchment and lower-fan deposition during the Holocene.Qf1 and Qf2 deposits are sub-horizontally bedded, clast-supported sandy gravels uniformly imbricated upfan. Comparison of soil profiles developed in these deposits to radiogenically-dated chronosequences within the region indicates that Qf1 and Qf2 are correlative with Bull Lake and Pinedale-age deposits, respectively. These relationships are substantiated by physical correlation of Qf1 and Qf2 with Bull Lake and Pinedale moraines, respectively, in the Cedar Creek drainage basin. The sedimentology and timing of Qf1 and Qf2 indicate deposition in high-energy, proglacial, braided streams. Furthermore, the present morphology of Cedar Creek alluvial fan was established largely during aggradation of Qf1 and Qf2 when sediment supply to the fan was sufficient to activate 60% to greater than 90% of the total fan area. During Bull Lake glaciation, the apex of Qf1 deposition formed the apex of Cedar Creek alluvial fan as Qf1 covered more than 90% of the present fan area. During Pinedale glaciation, Qf2 deposition shifted downfan; Qf2 is inset into Qf1 above the intersection point, but below the intersection point it eroded and/or buried Qf1 as it activated as much as 60% of the fan area.Qf3 and Qf4, comprising 21% of the fan area, are inset into Qf2 in the lower fan area. Soil development in Qf3 and Qf4 deposits indicate episodic deposition and entrenchment beginning in early Holocene and continuing to present. A post-glacial decrease in sediment supply to Cedar Creek alluvial fan is indicated by sediment storage within the Cedar Creek drainage basin. Decreased sediment supply to the fan resulted in upper-fan entrenchment of Qf2 and deposition of Qf3 and Qf4 in the lower-fan area.     

Use of GIS in Optimizing Timber Thinning Strategies in the Eastern Sierra Nevada*

This paper demonstrates the use of a Geographic Information System (GIS) to develop timber thinning strategies on the Kyburz Planning Area of the Tahoe National Forest in northeastern California. The primary criteria used in an assessment of selective thinning potential were forest health and fire hazard ratings. By eliminating environmentally sensitive, economically unfeasible, or low fire hazard areas from consideration, the use of GIS reduced the area that was considered appropriate for thinning by approximately 58%. GIS offers considerable potential for improving resource management strategies.     

Shape preferred orientation of object populations: automatic analysis of digitized images

An automatic technique is presented for systematic shape preferred orientation (SPO) analysis of crystal fabrics in rocks. This technique is based on digitization of an image with a CCD camera and separation of an object population from its matrix. The image is analysed globally using a rotating grid that is superimposed on the square pixel grid of the computer screen. The parametric method is based on counting intercepts in all directions. The interceps rose provides information on both the orientation and strength of the SPO. Problems of hardware-related counting noise anisotropy are avoided using an original method of filtering the intercept function with a linear, sliding mask on the counting grid. The technique was tested both on single objects of different shapes and on different populations of identical objects. A very high degree of accuracy was obtained for orientation measurements. Fabric shape parameters are introduced which are specific to this intercept technique; they compare favourably with shape parameters used in axial fabric analysis.     

国际古植物学1989年研究进展

古植物学是一个日新月异发展着的学科。每年,都有一些新的方法问世,它们结合地质学和生物学方法来研究地史时期植物的生活。其研究广度可以从1989年7月在美国首都华盛顿召开的第28届国际地质大会上明显看出。古植物学家们报告了他们关于“古气候”、“前寒武纪/寒武纪的过渡”、“泥炭和煤的来源”、“适应辐射”、“埋藏过程”、“特异埋藏”及南极地质等方面的研究成果;关于晚石炭世植物群的生物地理方面的文章也很多。 由Gastaldo(1989)编辑的《植物埋藏学——有机沉积过程》论文专辑是将更多的地质     

High-resolution garnet chronometry and the rates of metamorphic processes

Garnets in an amphibolite-facies metasediment from Sulitjelma, North Norway yield precise and concordant SmNd, UPb and RbSr ages that relate directly to the pressure (P) and temperature (T) conditions of mineral growth. Differential mineral reaction between graphitic and non-graphitic layers within this sample preserves a record of theP-T and time (t) history experienced during Barrovian regional metamorphism. Garnets in graphitic layers grew during prograde metamorphism at462 ± 16°C and5.2 ± 0.5 kbar under conditions of lowaH₂O, and yield indistinguishable¹⁴⁷Sm¹⁴³Nd and²³⁸U²⁰⁶Pb ages of434.1 ± 1.2 Ma and433.9 ± 1.0 Ma, respectively. In contrast, garnet growth in adjacent graphite-free layers did not occur untilP-T conditions of540 ± 18°C and8.0 ± 1.0 kbar were attained, with continued growth in response to minor heating and decompression with final matrix equilibration at544 ± 16°C and7.0 ± 1.0 kbar. The inclusion-free garnet rims in this assemblage record indistinguishable¹⁴⁷Sm¹⁴³Nd and²³⁸U²⁰⁶Pb ages of424.6 ± 1.2 Ma and423.4± 1.7 Ma, respectively. These results provide precise estimates for average heating and burial rates during prograde metamorphism of 8.6_−4.4^+7.5°C Ma⁻¹ and 0.8_−0.5^+0.9 km Ma⁻¹, respectively. Rb and Sr exchange between coexisting silicates in the graphite-free assemblage continued for some 37 Ma after the “peak” of metamorphism, and require an average cooling rate of about 4.0°C Ma⁻¹ during uplift. These results illustrate a clear relationship between reaction history and the timing of mineral growth and provide definitive constraints on the rates of thermal and tectonic processes accompanying regional metamorphism.     

Planktonic dimethylsulfide and cloud albedo: An estimate of the feedback response

Partial control of climate by the biosphere may be possible through a chain of processes that ultimately links marine plankton production of dimethylsulfide (DMS) with changes in cloud albedo (Charlson et al., 1987). Changes in cloud optical properties can have profound impacts on atmospheric radiation transfer and, hence, the surface environment. In this study, we have developed a simple model that incorporates empirically based parameterizations to account for the biological control of cloud droplet concentration in a first attempt to estimate the strength of the DMS-cloud albedo feedback mechanism. We find that the feedback reduces the global climatic response to imposed perturbations in solar insolation by less than 7%. Likewise, it modifies the strength of other feedbacks affecting surface insolation over oceans by roughly the same amount. This suggests that the DMS-cloud albedo mechanism will be unable to substantially reduce climate sensitivity, although these results should be confirmed with less idealized models when more is known about the net production of DMS by the marine biosphere and its relation to aerosol/cloud microphysics and climate.