FLUCTUATIONS OF CRILLON GLACIER SYSTEM,SOUTHEAST ALASKA     

RICHARD P. GOLDTHWAIT  IAN C. Mc KELLAR  CASPAR CRONK 《水文科学杂志》2013,58(1):62-74

Abstract

Crillon Glacier system (Lat. 58° 37′ N, Long. 137° 23′w) consisting of two long feeding arms and a common T-shaped ending along the Fairweather Fault, with two cliffed termini, has been advancing. La Perouse's sketch map in 1786 suggests that North and South Crillon Glaciers were back far enough to have separate termini in Lituya Bay, so they must have advanced at about 30 m/yr for 150 years. More detailed maps and photos show that North Crillon terminus did advance 28 m/yr into open water positions from 1894 to 1933. Some of this 4.5 km advance may well be just the result of consolidation of two long calving ice cliffs into one deep water front.

South Crillon front in the other arm of the “T”, where no junction of fronts is involved, also advanced into Crillon Lake 10 m/yr between 1929 and 1961. This implies that the basic cause was some increased snowfall on the high mountains. At the same time glaciers from lower peaks just to the east of Glacier Bay lost nearly all accumulation by a rising snowline and receded 5 to 11 km.

Since 1926 the Lituya Bay terminus has been more or less stable where it lies in water; however, the land portion has advanced 25 m/yr since 1948. Between about 1920 and 1961 a large gravel delta appeared and grew to 145 × 10⁶ m³, so this slow ice advance on one side of the front may be due to ice shearing over the new land of the fan where ablation is slower than watercliff calving.

Prehistoric advances of Crillon Glacier system are recorded in stratigraphic deposits dated by C-14. Trees buried in the prominent extensive outer moraine system around Crillon Lake and Lituya Bay were annihilated in the maximal push of the Little Ice Age 400 to 1000 years ago. The first advance came 1500 to 1800 years ago when logs became buried in glacial outwash, now under Little Ice Age till. Because it is regional, this was a climatic event involving a lowering snowline due to cooler summers.

Still further back, in hypsithermal time, these Crillon Glacier termini were probably as retracted as today, because many outcrops of buried forest 3000 to 9000 years old occur in alluvial deposits in Lituya Bay. Underneath all these is outwash gravel and till recording the last push of Wisconsin ice, ending at least 9000 years ago. Still earlier Wisconsin advances of North Crillon Glacier carried the Lituya Bay ice tongue a little further to sea, yet all through the pleistocene, unglaciated refugia endured between the ice streams.  相似文献   

Geographic variations in spring and autumn phenology of white ash in a common garden     

Liang Liang 《自然地理学》2013,34(6):489-509

Geographic variations in plant phenology are known to be affected by climatic differences over space, but the role of adaptation variability of plant populations is less well understood. In this study, I examined the geographic variations in spring and autumn phenology of white ash (Fraxinus americana L.) in a common garden and related observations over a 2-year period (2013 and 2014) to climatic and geographic factors of their provenances. Spring leaf-out of trees with northern provenances occurred later in 2013, but slightly earlier in 2014, than those with southern provenances. This difference was potentially caused by the counterbalancing effect of chilling and forcing in response to interannual temperature fluctuations. In both years, leaf senescence of white ash occurred significantly earlier for trees with northern than southern provenances, reflecting strong adaptation to a photoperiod gradient. The growing season length for white ash, therefore, is constrained by spring and fall phenology through different environmental cues. Spring phenology exerted a greater influence on the interannual variability of growing season length. Identifying these detailed adaptive patterns facilitates a better understanding of phenological change over space and allows development of genotype-sensitive phenological models to predict the ecological impact of climate change.  相似文献   

Agent-based simulation for a dual-diffusion process of influenza and human preventive behavior     

Liang Mao  Ling Bian 《International journal of geographical information science》2013,27(9):1371-1388

Influenza disease diffuses from one individual to another through their close contacts, while preventive behavior propagates through inter-personal influences. These two diffusion processes take place simultaneously and interact with one another in opposite directions. Many current influenza studies consider the diffusion of influenza, but few of them have incorporated the diffusion of human preventive behavior. This article proposes an original dual-diffusion model to couple these two diffusion processes. The conceptual framework of the model incorporates these two opposite processes into a human contact network. An agent-based approach, network theory, disease model, and behavioral model are integrated to formulate the conceptual framework. Model implementation simulates an influenza epidemic in an urbanized area of one million individuals. The simulation results suggest that the proposed model offers a close representation of the observed data. The research findings will provide a more rational basis for influenza control.  相似文献   

Seasonality indices for regionalizing low flows   总被引：2，自引：0，他引：2  

G. Laaha  G. Blschl 《水文研究》2006,20(18):3851-3878

In this study we examine three seasonality indices for their potential in regionalizing low flows. The indices are seasonality histograms (SHs) that represent the monthly distribution of low flows, a cyclic seasonality index (SI) that represents the average timing of low flows within a year, and the seasonality ratio (SR), which is the ratio of summer and winter low flows. The rationale of examining these indices is the recognition that summer and winter low flows are subject to important differences in the underlying hydrological processes. We analyse specific low flow discharges q₉₅, i.e. the specific discharge that is exceeded on 95% of all days at a particular site. Data from 325 subcatchments in Austria, ranging in catchment area from 7 to 963 km², are used in the analysis. In a first step, three seasonality indices are compared. Their spatial patterns can be interpreted well on hydrological grounds. In a second step, the indices are used to classify the catchments into two, three, and eight regions based on different combinations of the indices. In a third step, the value of the seasonality indices for low flow regionalization is examined by comparing the cross‐validation performance of multiple regressions between low flows and catchment characteristics. The regressions make use of the three seasonality‐based classifications. The results indicate that grouping the study area into two regions and three regions and separate regressions in each region gives the best performance. A global regression model yields the lowest performance and a global regression model that uses different calibration coefficients in each of the eight regions only performs slightly better. This suggests that separate regression models in each of the regions are to be preferred over a global model in order to represent differences in the way catchment characteristics are related to low flows. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity     

Rob Westaway 《地球表面变化过程与地形》2006,31(12):1480-1509

Many studies have highlighted the role of coupling between surface processes and flow in the lower continental crust in deforming the crust and creating topographic relief over Quaternary timescales. On the basis of the rheological knowledge gained, it is suggested that intraplate seismicity can also be caused by coupling between surface processes and flow in the lower continental crust. This view is shown to be a natural consequence of the modern idea that isostatic equilibrium is maintained by flow in the weak lower crust in response to erosion and sedimentation. It is supported by a general correlation between the vigour of surface processes and rates of intraplate seismicity, and by instances of seasonal seismicity that correlates with seasonal climate. Human interference in the environment can affect surface loading: for instance, deforestation for agriculture or urban development can cause increased erosion rates; global warming is expected to cause increased storminess (and thus increased erosion rates) and/or global sea‐level rise. The possibility of increased rates of seismicity resulting from these processes should thus be considered in future hazard assessment. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Seasonal Variation in the Covering ­Behaviour of the Echinoid Paracentrotus lividus (Lamarck)     

Anne C. Crook  & David K. A. Barnes 《Marine Ecology》2001,22(3):231-239

Abstract. Covering behaviour is displayed by several regular echinoid species but its functional significance has yet to be quantified. Some of the most popular theories have interpreted this behaviour as an adaptive response to avoid over-exposure to light and/or as an anti-predator strategy. Since both predation pressure and light intensity may be seasonal as well as diurnal in nature, the aim of the present study was to quantitatively examine, in situ , the potential seasonality of covering behaviour in the purple sea urchin, Paracentrotus lividus (Lamarck). Data were collected over a one-year period at Lough Hyne, Co. Cork in Ireland. A peak in covering activity was observed over the summer months. Predator density and light intensity (sunlight hours) were also shown to vary seasonally at Lough Hyne. Covering behaviour in P. lividus , as in other echinoids, may be a response to a number of simultaneously interacting factors. At Lough Hyne, however, light intensity and covering item availability appear to be particularly important factors.  相似文献   

Water fluxes through the Barents Sea   总被引：14，自引：2，他引：14  

Loeng  Harald; Ozhigin  Vladimir; Adlandsvik  Bjorn 《ICES Journal of Marine Science》1997,54(3):310-317

  相似文献   

Fluctuations and Variations in Coastal Marine Environments   总被引：2，自引：0，他引：2  

Ferdinando  Boero 《Marine Ecology》1994,15(1):3-25

Abstract. The manifold aspects of variability of coastal marine ecosystems are reviewed, with special reference to the response of species and communities. Fluctuations are defined as recurrent modifications in community structure, for instance due to seasonality, whereas variations are defined as changes permanently leading from a given community to a different one. Both patterns are described and linked to the interaction between life history traits and environmental factors. Resting stages are proposed to play a still underestimated role in the dynamics of coastal communities, especially for plankton. Rare species are considered as an essential constant of communities, being the source of potential variation and alternance in the contribution to the standing biomass.  相似文献   

Day–night variations in the demersal nekton assemblage on the Mediterranean shelf-break     

P. Carpentieri  F. Colloca  G.D. Ardizzone 《Estuarine, Coastal and Shelf Science》2005,63(4):577-588

The composition of the demersal nekton assemblage inhabiting the Mediterranean shelf-break of west-central Italy was examined to investigate the diel variation in species composition and abundance. Fish were obtained during four 24-h sampling periods that represented the four annual seasons. Thirty-two hauls (eight in each season) were conducted in a shelf-break area at 140–160 m depth. The density of fish, crustaceans, and decapods exhibited differences on short- and long-term time scales: multidimensional scaling suggested that season and light intensity may be important factors influencing fish assemblage composition.At the diel scale two main assemblages separating nocturnal and diurnal hauls were identified. The typical assemblage structure of shelf-break bottoms was represented during daylight by species such as Merluccius merluccius, Capros aper, Serranus hepatus, Macroramphosus scolopax and Trisopterus minutus capelanus. At night, the assemblage showed a drastic change due to the increase of small nektobenthic species, Argentina sphyraena and Glossanodon leioglossus, together with cave-dwelling fish (Gnathophis mystax, Chlopsis bicolor, Nettastoma melanurum) and nektobenthic crustaceans (i.e., Parapenaeus longirostris and Solenocera membranacea).The above-mentioned differences in species composition may be related to changes in vertical distribution for trophic needs (M. merluccius) and/or in the shoal structure (A. sphyraena and G. leioglossus). The lack of data on the pattern of trawl catchability of Mediterranean species during the day may lead to an inaccurate estimation of species abundance when only diurnal trawl survey data are used.  相似文献   

Zonation and Evolution of a Rocky Bottom Hydroid Community*     

FERDINANDO BOERO  EUGENIO FRESI 《Marine Ecology》1986,7(2):123-150

Abstract. .The distribution in space and time of a hydroid community on a vertical rocky substratum is studied from the surface to 20 m depth. The role of the major environmental factors (light, water movement, temperature) in determining the zonation is evaluated. The results are compared with the main zonation models of Mediterranean benthos. The autecology of the collected species is briefly described.  相似文献