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1.
Feature tracking of orthorectified pairs of Advanced Spaceborne Thermal Emission and Reflection Radiometer satellite images is used to calculate velocities for the Tasman Glacier, New Zealand (2002–2014) and the Khumbu Glacier, Nepal (2001–2008). Velocities in the middle and upper ablation zones of both glaciers show a long‐term decrease of ～10–20%, while the terminus of Khumbu Glacier has remained near stagnation throughout the study period. In contrast, there has been a recent acceleration of the lower terminus of Tasman Glacier, from ～5 m a–1 in 2002 to 40 m a–1 in 2014. Both of these glaciers have an extensive supraglacial debris cover across their lower ablation regions, with the Khumbu Glacier terminating on land and the Tasman Glacier terminating in a proglacial lake. The rapid recent increase in velocity of the terminus of Tasman Glacier is closely correlated with the increase in size of its proglacial lake. These results indicate the complex dynamic changes that mountain valley glaciers may undergo in response to long‐term negative mass balance.  相似文献   

2.
Glacier Benito is a temperate outlet glacier on the west side of the North Patagonian Icefield. Rates of thinning and ablation were obtained using data collected by the British Joint Services Expedition in 1972/73 and subsequent data collected in 2007 and 2011. Ice‐front recession rates were based on dendrochronological dating for the terminal moraines and aerial and satellite imagery of the ice front in 1944, 1998 and 2002. Between the first Benito survey in 1973 and 2007, the lower glacier thinned by nearly 150 m at an average rate of 4.3 m yr?1 with the rate increasing to 6.1 m yr?1 between 2007 and 2011, a 28.7% increase during the latter period. Increases in ice movement and ablation were negligible: ice movement for 1973 and 2007 averaged 0.45 m day?1 and ablation averaged 0.05 m day?1. Ice front recession along the glacier's centre line from 1886 to 2002 was approximately 1860 m. Retreat rates between 1886 and 1944 averaged 8.9 m yr?1. Thereafter glacier asymmetry makes measurement along the glacier centre line unrepresentative of areal change until 1998 when symmetry was restored; retreat between 1944 and 1998 was 15.4 m yr?1. From 1998 to 2002 the rate increased dramatically to 127.2 m yr?1. Recession from the southern end of Benito's terminal moraine in the 1850s supports an early date for initial retreat of the Icefield's glaciers.  相似文献   

3.
The Tasman Glacier is the largest glacier in New Zealand. Although 20th century warming caused down-wastage, it remained at its Little Ice Age terminus until the late 20th century. Since then, rapid calving retreat (Ur) has occurred, allowing a large (5.96 × 106 m2) proglacial lake to form (maximum depth ∼240 m). From sequential satellite image analysis and echo sounding of Tasman Lake, we document (Ur) from 2000 to 2008. Ur varies temporally, with mean Ur of 54 m/a from 2000 to 2006 and a mean Ur of 144 m/a from 2007 to 2008. Consistent with global data sets, calving rate appears closely associated with lake depth at the calving terminus.  相似文献   

4.
大同-阳原盆地古泥河湾湖的岸线变化   总被引：8，自引：0，他引：8  
夏正楷 《地理研究》1992,11(2):52-59
本文通过大同-阳原盆地古湖岸线遗迹的分析,阐述第四纪古泥河湾湖的出现、发展和消亡,指出湖泊变迁是构造运动和气候变化等因素共同作用的结果,构造运动是主要因素。  相似文献   

5.
The Corinth rift (Greece) is one of the world's most active rifts. The early Plio‐Pleistocene rift is preserved in the northern Peloponnese peninsula, south of the active Corinth rift. Although chronostratigraphic resolution is limited, new structural, stratigraphic and sedimentological data for an area >400 km2 record early rift evolution in three phases separated by distinct episodes of extension rate acceleration and northward fault migration associated with major erosion. Minimum total N–S extension is estimated at 6.4–7.7 km. The earliest asymmetrical, broad rift accommodated slow extension (0.6–1 mm a?1) over >3 Myrs and closed to the west. North‐dipping faults with throws of 1000–2200 m defined narrow blocks (4–7 km) with little footwall relief. A N‐NE flowing antecedent river system infilled significant inherited relief (Lower group). In the earliest Pleistocene, significant fluvial incision coincided with a 15 km northward rift margin migration. Extension rates increased to 2–2.5 mm a?1. The antecedent rivers then built giant Gilbert‐type fan deltas (Middle group) north into a deepening lacustrine/marine basin. N‐dipping, basin margin faults accommodated throws <1500 m. Delta architecture records initiation, growth and death of this fault system over ca. 800 ka. In the Middle Pleistocene, the rift margin again migrated 5 km north. Extension rate increased to 3.4–4.8 mm a?1. This transition may correspond to an unconformity in offshore lithostratigraphy. Middle group deltas were uplifted and incised as new hangingwall deltas built into the Gulf (Upper group). A final increase to present‐day extension rates (11–16 mm a?1) probably occurred in the Holocene. Fault and fault block dimensions did not change significantly with time suggesting control by crustal rheological layering. Extension rate acceleration may be due to strain softening or to regional tectonic factors.  相似文献   

6.
Terminus geometry, ice margins, and surface elevations on Rabots glaciär were measured using differential GPS during summer 2011 and compared with those similarly measured in 2003. Glacier length over the eight years decreased by ～105 m corresponding to 13 m a?1, a rate consistent with ice recession over the last several decades. Measured changes in surface elevations show that between 2003 and 2011 the glacier's volume decreased by ～27.6 ± 2.6 × 106 m3, or 3.5 ± 0.3 × 106 m3 a?1. This compares favorably with an estimate of ?28.1 ± 2.6 × 106 m3 based on a mass‐balance approach. The rate of volume loss appears, however, to have significantly increased after 2003, being substantially greater than rates determined for the intervals 1959–80, 1980–89, and 1989–2003. This increase corresponds to a sustained interval of more negative summer balances. Previous work suggests that as of 2003 Rabots glaciär had not yet completed its response to a ～1°C warming that occurred c. 1900, and thus the current marked increase rate of ice loss might reflect the effect of recent, or accelerated regional warming that occurred during the last decade superimposed on its continued response to that earlier warming.  相似文献   

7.
Eutrophication, prompted by anthropogenic activities and climate change has led to multiple adverse effects in freshwater systems across the world. As instrumental measurements are typically short, lake sediment proxies of aquatic primary productivity (PP) are often used to extend the observational record of eutrophication back in time. Sedimentary pigments provide specific information on PP and major algal communities, but the records are often limited in the temporal resolution. Hyperspectral imaging (HSI) data, in contrast, provide very high seasonal (sub-varve-scale) resolution, but the pigment speciation is limited. Here, we explore a combined approach on varved sediments from the Ponte Tresa basin, southern Switzerland, taking the advantages of both methods (HSI and high performance liquid chromatography, HPLC) with the goal to reconstruct the recent eutrophication history at seasonal to interannual resolution. We propose a modified scheme for the calibration of HSI data (here: Relative Absorption Band Depth between 590 and 730 nm RABD590–730) and HPLC-inferred pigment concentrations (here: ‘green pigments’ {chlorophyll a and pheophytin a}) and present a calibration model (R2?=?0.82; RMSEP?~?12%). The calibration range covers >?98% of the spectral index values of all individual pixels (68 µm?×?68 µm) in the sediment core. This allows us to identify and quantify extreme pigment concentrations related to individual major algal blooms, to identify multiple algal blooms within one season, and to assess interannual variability of PP. Prior to the 1930s, ‘green pigment’ concentrations and fluxes (~?50 µg g?1;?~?2 µg cm?2a?1, chlorophyll a and pheophytin a) and interannual variability was very low. From the 1930s to 1964, chlorophyll a and pheophytin a increased by a factor of ~?4, and ββ-carotene appeared in substantial amounts (~?0.4 µg cm?2a?1). Interannual variability increased markedly and a first strong algal bloom with ‘green pigment’ concentrations as high as 700 µg g?1 is observed in 1958. Peak eutrophication (~?12 µg cm?2a?1 chlorophyll a and pheophytin a) and very high interannual variability with extreme algal blooms (‘green pigment’ concentrations up to 1400 µg g?1) is observed until ca. 1990, when eutrophication decreases slightly. Maximum PP values after 2009 are likely the result of internal nutrient cycling related to repeated deep mixing of the lake.  相似文献   

8.
The Imja Glacier Lake (Imja Tsho) (1.03 km2 in 2007) is repeatedly cited as one of the most dangerous glacial lakes in the Himalaya with a glacial lake outburst flood (GLOF) claimed to be imminent. Knowledge of lake development and its dynamics, however, is limited and forecasts of a possible outburst are not scientifically based. Nevertheless, prospects for such a catastrophe are repeatedly exaggerated, attracting alarmist mass media coverage. The paper provides an assessment of the lake expansion rates from 1956 to 2007. Stage 1 (1956–1975), slowest: coalescence of several small supra-glacial ponds; Stage 2 (1975–1978), a short period of most rapid expansion; Stage 3 (1978–1997), slow: gradual expansion of single lake; and Stage 4 (1997–2007), renewed acceleration: mainly eastward expansion into the glacier surface. The lake's water level has fallen from 5041 m to 5004 m (1964–2006). The results show that there is no immediate danger of catastrophic outburst although the dynamics of up-glacier and down-valley lake expansion, fluctuation of lake water level, and dead-ice morphology changes should be continuously and comprehensively monitored. Alarmist prognostications based solely upon rapid areal expansion are counterproductive.  相似文献   

9.
Geografisk Tidsskrift, Danish Journal of Geography 108(1):121–136, 2008

SnowModel, a physically-based snow evolution modeling system that includes four submodels—MicroMet, EnBal, SnowPack, and SnowTran-3D—was used to simulate eight full-year (1998/99 through 2005/06) evolutions of snow accumulation, blowing snow sublimation, evaporation, snow and ice surface melt, runoff, and mass changes on the entire Mittivakkat Glacier (31 km2) in southeast Greenland. Meteorological observations from two meteorological stations inside the glacier catchment were used as model input, and glaciological mass balance observations were used for model calibration (1998/99 through 2001/02) and validation (2002/03 through 2005/06) of winter snow simulations. As confirmed by observations, the spatially modeled end-of-winter snow water equivalent (SWE) accumulation increased with elevation up to 700–800 m a.s.l. in response to elevation, topography, and dominating wind direction, and maximum snow deposition occurred on the lee side of the ridge east and south of the glacier. Simulated end-of-summer cumulative runoff decreased with elevation and minimum runoff occurred on the shadowed side of the ridge east and south of the glacier. The modeled test period averaged annual mass balance was 65 mm w. eq. y?1 or ～8% more than the observed. For the simulation period, the glacier net mass balance varies from -199 to -1,834 mm w.eq. y?1, averaging -900 (±470) mm w.eq.y?1. The glacier averaged annual modeled precipitation ranged from 1,299 to 1,613 mm w.eq. y?1, evaporation and sublimation from 206 to 289 mm w.eq., and runoff from 1,531 to 2,869 mm w.eq. y?1. The model simulated Mittivakkat Glacier net loss of900 mm w.eq. y?1 contributes approximately 42% to the average simulated runoff of 2,140 mm w.eq. y?1, indicating a mean specific runoff of 67.8 l s?1 km?2.  相似文献   

10.
Average sea-level rise in the northern part of the Danish Wadden Sea has been 1.3 mm a?1 during the last 100 years but during the last 25 years a rise of 4.2 mm a?1 was observed. Concurrent with the recent sea-level rise the Skallingen barrier spit has migrated landward by 3–5 m a?1. Long term sediment budgets for each of the morphological units involved in the migration are reviewed (e.g. onshore in the shore face +90.000 m3 a?1, longshore -641.000 m3 a?1, foredunes +65,000 m3 a?1, overwash fan including shorenormal dunes +11,000 m3 a?1, spit terminus -96,000 m3 a?1, tidal flat + 10,000 m3 a?1 and backbarrier salt marsh +33,000 m3 a?1) and used to establish the relative importance of sediment transport processes involved in barrier migration. Strong interannual variations exist in the long term budget making evaluation of barrier behaviour based on short term measurements doubtful. In a cross shore sense the barrier spit is accreting in spite of the sea level rise. This is specially pronounced at an active overwash fan. However, due to substantial sediment losses to longshore transport the barrier, gets narrower and shorter during its transgressive behaviour. This may indicate that preservation of barriers in the geological record during rapid sea level rise is promoted when sediment loss to longshore transport is insignificant.  相似文献   

11.
In this paper, we will present the stratigraphic evolution, internal facies architecture and geomorphology of the Middle Pleistocene Emme delta, controlled by rapid high‐amplitude lake‐level change. The Emme delta was deposited on the northern margin of glacial Lake Weser, located in north‐west Germany. Rates of lake‐level rise were probably >50 mm year?1 and rates of lake‐level fall 30–50 m within a few days or weeks, due to the opening of lake outlets. We use digital elevation models, sedimentology and shear wave seismics to improve earlier reconstructions and investigate the influence of rapid base‐level change on delta development. Shear wave seismic data resolve architectural elements in the range of metres and bridge the common gap between outcrop and conventional compression wave seismic data. The radial delta complex is about 2 km long, 1.8 km wide and up to 70 m thick, overlying a concave, up to 13° steep dipping ramp surface. It consists of vertically and laterally stacked delta lobes, caused by lobe switching during base‐level change. During the lake‐level rise, vertically stacked (Gilbert‐type) delta systems formed. The decrease in thickness and lateral extent indicates a rapid upslope shift of depocentres. A high rate and magnitude of lake‐level fall (50 m) promoted the development of a single incised valley and the deposition of forced regressive coarse‐grained delta lobes in front of the valley. The incised valley was filled during decreasing rates of lake‐level fall and low base‐level, because the alluvial gradient was larger than the emergent lake profile. Attached sand‐rich forced regressive aprons formed during lower magnitudes of lake‐level falls in the range of 30–35 m. Valley incision occurred, but was limited to the uppermost portion of the delta, controlled by the steep slope. The incised valley related to the final lake drainage is associated with long‐wavelength (60–90 m) bedforms at the downslope end, attributed to the formation of standing waves as a result of a hydraulic jump. Estimated palaeoflow depth during standing wave formation was ～9–14 m and flow velocity was 10–12 m s?1. Because subsidence, waves or tides did not play a major role, the Emme delta can be used as an analogue‐based predictive stratigraphical and sedimentological model for steep glacigenic deltas controlled by rapid base‐level change and can help to understand better the facies distribution and three‐dimensional geometry of these depositional systems.  相似文献   

12.
Mass changes of Blue Glacier, USA are calculated from topographic maps made from vertical aerial photography in late summer of 1939, 1952, 1957, and 1987, along with laser altimetry flown in June 1996. Changes in elevation between maps were adjusted for seasonal variations in the snow cover, and to account for the ablation between the date of photography and 1 October. Topography obtained from the laser altimetry was adjusted for snow thickness and glacier motion to estimate topography of 1 October 1995. The mass of Blue Glacier has changed less than 7 m (water equivalent) during this 56 year period which is minor compared with other glaciers in the region and elsewhere in the world. Glacier-average annual mass balances, beginning in 1956, have been calculated either from stake measurements and probing of late-season snow, or from a regression analysis using late-season measurements of the equilibrium line altitude. A comparison with the changes derived from surface maps shows values obtained from field measurements are too positive by about 0.4 m a?1 , indicating that considerable caution is needed when interpreting time series of mass balance. Two alternative time series of mass balance consistent with the long-term mass changes are created by making simple adjustments: (1) a single constant is subtracted from each value so that the series is consistent with the 1957–95 mass change; (2) one constant is subtracted from each value over 1957–87 and another is subtracted from each value over 1987-95 so that the series is consistent with both the 1957–87 and 1987–95 mass changes. The mass balance of Blue Glacier was generally positive until the mid-1970s and negative since. The fluctuations of mass balance closely resemble those of snowfall on the glacier as estimated from the joint distribution of temperature and precipitation. The climate in western Washington was cooler and wetter during the decade before the mid-1970s, but the trend since has been towards warmer and drier conditions.  相似文献   

13.
Glacier mass balance is a key component of glacier monitoring programs. Information on the mass balance of Sawir Mountains is poor due to a dearth of in-situ measurements. This paper introduces the applicability of an ultra-long-range terrestrial laser scanner(TLS) to monitor the mass balance of Muz Taw Glacier, Sawir Mountains, China. The Riegl VZ?-6000 TLS is exceptionally well-suited for measuring snowy and icy terrain. Here, we use TLS to create repeated high spatiotemporal resolution DEMs, focusing on the annual mass balance(June 2, 2015 to July 25, 2016). According to TLS-derived high spatial resolution point clouds, the front variation(glacier retreat) of Muz Taw Glacier was 9.3 m. The mean geodetic elevation change was 4.55 m at the ablation area. By comparing with glaciological measurements, the glaciological elevation change of individual stakes and the TLS-derived geodetic elevation change of corresponding points matched closely, and the calculated balance was-3.864±0.378 m w.e.. This data indicates that TLS provides accurate results and is therefore suitable to monitor mass balance evolution of Muz Taw Glacier.  相似文献   

14.
The Bunger Hills in East Antarctica occupy a land area of approximately 400 km2. They have been exposed by Holocene retreat of the Antarctic ice sheet and its outlet glaciers. The accompanying sea level rise flooded the marine inlets that now separate the northern islands and peninsulas from the major part of the hills. During deglaciation the continental ice sheet margin retreated south‐eastwards with several temporary halts, during which ice‐dammed lakes were formed in some valleys. These lakes were maintained long enough to permit formation of beaches of sand and gravel, and for the erosion of shore platforms and low cliffs in bedrock. Around the western end of Fish Tail Bay impressive shoreline features 20 m above sea level define a former ice‐dammed lake that was 5.5 km long. A similar 7 km long former ice‐dammed lake was formed at Lake Dolgoe. The more extensive and deeper glacial lake is revealed by well‐developed and preserved shoreline features cut at 29 m which is 16 m above present lake level. In addition, several small ice‐dammed lakes existed temporarily near Lake Shchel and in the valley to the west. Lake Fish Tail existed more than 6,900 14C years ago and Lake Shchel probably more than 6,680 14C years ago. It is inferred that the shore platforms and beaches were formed by lake ice and wave action over considerable periods when the lakes were impounded by steep cold ice margins. There appears to have been a balance between meltwater input and evaporative loss from the lakes in the cold dry continental climate. There is no evidence for rapid lake level fluctuations, and there was very little input of clastic sediment. This resulted in poor development of deltaic and rhythmically laminated lake floor deposits. It is suggested that such deposits are more characteristic of ice‐dammed lakes formed in association with wet‐based temperate ice than those associated with dry‐based polar ice.  相似文献   

15.
Swath bathymetry, single‐channel seismic profiling, gravity and box coring, 210Pb down‐core radiochemical analyses and sequence stratigraphic analysis in the Gulf of Alkyonides yielded new data on the evolution of the easternmost part of the Gulf of Corinth. Three fault segments, the South Strava, West Alkyonides and East Alkyonides faults, dipping 45, 30 and 45°, respectively, northwards, form the southern tectonic boundary of the Alkyonides Basin. Two 45° southwards dipping segments, the Domvrena and Germeno Faults, form the northern tectonic margin. The Alkyonides Basin architecture is the result of a complex interaction between fault dynamics and the effects of changes in climate and sea/lake level. Chrono‐stratigraphic interpretation of the seismic stratigraphy through correlation of the successive seismic packages with lowstands and highstands of the Late Quaternary indicates that the evolution of the basin started 0.40–0.45 Ma BP and can be divided in two stages. Subsidence of the basin floor during the early stage was uniform across the basin and the mean sedimentation rate was 1.0 m kyear?1. Vertical slip acceleration on the southern tectonic margin since 0.13 Ma BP resulted in the present asymmetric character of the basin. Subsidence concentrated close to the southern margin and sedimentation rate increased to 1.4 m kyear?1 in the newly formed depocentre of the basin. Actual (last 100 year) sedimentation rates were calculated to >2 mm year?1, but are significantly influenced by the presence of episodic gravity flow deposits. Total vertical displacement of 1.1 km is estimated between the subsiding Alkyonides Basin floor and the uplifting Megara Basin since the onset of basin subsidence at a mean rate of 2.4–2.75 m kyear?1, recorded on the East Alkyonides Fault. Gravity coring in the Strava Graben and in the lower northern margin of Alkyonides Basin proved the presence of whitish to olive grey laminated mud below thin marine sediments. Aragonite crystals and absence of the marine coccolithophora Emiliania huxleyi indicate sedimentation in lacustrine environment during the last lowstand glacial interval.  相似文献   

16.
Surface-process models (SPMs) have the potential to become an important tool in predicting sediment flux to basins, but currently suffer from a lack of quantitative understanding of their controlling parameters, as well as difficulties in identifying landscape properties that can be used to test model predictions. We attempt to constrain the parameter values that enter a SPM by comparing predictions of landscape form (as expressed by hypsometric and fractal measures) and process rates obtained for different parameter sets with observations from the south-eastern Australian highlands, a rifted margin mountain belt that has remained tectonically stable during Cenozoic times. We map the hypsometry and fractal characteristics of south-eastern Australia and find that the roughness amplitude (G) correlates well with local relief, whereas the hypsometric integral (H ) correlates slightly better with elevation than with relief. The fractal dimension (D) does not correlate with any other morphometric measure and varies randomly throughout the region. Variograms generally show three kinds of scaling behaviour of topography with increasing wavelength, with topography only being truly self-affine at wavelengths between ～1 and 10 km. From a review of the available data on long-term denudation rates in south-eastern Australia, we infer that these have been 1–10 m Myr?1, and average escarpment retreat rates 0.2–1.0 km Myr?1, throughout the Cenozoic. Model predictions, using a SPM that includes hillslope diffusion and long-range fluvial transport, suggest that landscape form evolves with time; after an initial phase where D, G and relief increase, all morphometric measures decrease with increasing denudation. The behaviour of GandH in the models is qualitatively compatible with the observations; D, however, varies predictably in the models, in contrast with its random behaviour in the real world. The observed present-day morphology of SE Australia does not impose quantitative constraints on parameter values. The fractal analyses do impose general conditions of relative parameter values that have to be met in order to create ‘realistic’ topographies. They also suggest that there is no theoretical basis for including hillslope diffusion in SPMs with a spatial resolution coarser than 1 km. A comparison of the observed denudation and retreat rates with model predictions places order-of-magnitude constraints on parameter values. Thus, data pertaining to landscape evolution are much more valuable than static present-day topography data for calibrating SPMs.  相似文献   

17.
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18.
Glacier retreat is not only a symbol of temperature and precipitation change, but a dominating factor of glacial lake changes in alpine regions, which are of wide concern for high risk of potential outburst floods. Of all types of glacial lakes, moraine-dammed lakes may be the most dangerous to local residents in mountain regions. Thus, we monitored the dynamics of 12 moraine-dammed glacial lakes from 1974 to 2014 in the Poiqu River Basin of central west Himalayas, as well as their associated glaciers with a combination of remote sensing, topographic maps and digital elevation models (DEMs). Our results indicate that all monitored moraine-dammed glacial lakes have expanded by 7.46 km2 in total while the glaciers retreated by a total of 15.29 km2 correspondingly. Meteorological analysis indicates a warming and drying trend in the Nyalam region from 1974 to 2014, which accelerated glacier retreat and then augmented the supply of moraine-dammed glacial lakes from glacier melt. Lake volume and water depth changed from 1974 to 2014 which indicates that lakes Kangxico, Galongco, and Youmojanco have a high potential for outburst floods and in urgent need for continuous monitoring or artificial excavation to release water due to the quick increase in water depths and storage capacities. Lakes Jialongco and Cirenmaco, with outburst floods in 1981 and 2002, have a high potential risk for outburst floods because of rapid lake growth and steep slope gradients surrounding them.  相似文献   

19.
Anthropogenic mercury accumulation in lake sediments has been studied extensively, but natural processes that controlled mercury accumulation in the past are still poorly understood. We present a 17,300-year record of mercury accumulation in the sediments of Lake Hambre, southernmost Patagonia, Chile (53°S, 70°W), in combination with an investigation of environmental changes in the region. Mercury accumulation in the remote pristine lake varied appreciably, as much as 16×, exceeding the anthropogenic forcing of atmospheric mercury fluxes by a factor of 3–5. Principal Component Analysis revealed that short-term variations were not related to changes in atmospheric mercury deposition or to fluxes of mineral soil into the lake. Instead, there was significant covariation between short-term changes in mercury and catchment-derived trace elements, e.g. copper and yttrium, throughout the past 17,000 years. Covariation between mercury and carbon concentration in some parts of the record suggests that fluxes of particulate and dissolved organic matter from the catchment to the lake account for short-term variations in mercury accumulation. Nevertheless, over the long term, there is no common trend for mercury accumulation and organic matter flux. The median mercury accumulation rate was rather constant (29 μg m?2 a?1), whereas the flux of terrestrial organic matter into the lake increased through time. We hypothesize that this was a consequence of a progressive decrease in the input of terrestrial organic matter-bound mercury through time. Whereas production of terrestrial organic matter increased over the long term because of development of catchment vegetation and soils, following glacier retreat, amounts of mercury, copper and yttrium provided by atmospheric deposition and bedrock weathering remained relatively constant. As a consequence, despite increased fluxes of terrestrial organic matter to the lake, fluxes of mercury remained constant.  相似文献   

20.
1978-2015年喀喇昆仑山克勒青河流域冰川变化的遥感监测   总被引：1，自引：1，他引：0  
本文采用1978、1991、2001和2015年的Landsat MSS、TM、ETM+和OLI遥感影像,通过遥感图像计算机辅助分类和目视解译等方法提取冰川边界,分析喀喇昆仑山克勒青河流域冰川在1978-2015年间的进退变化。结果表明：1978-2015年间研究区冰川面积由1821.70 km2减少至1675.92 km2,减少145.78 km2,占1978年冰川总面积的8.00%;冰川消融率较低,在气候变暖的背景下反而呈现出退缩速率由快变慢的趋势。研究区东南向冰川退缩率明显高于西北向,冰川退缩率随冰川规模的增大而减小。研究区内有27处冰川在1978-2015年间发生过特殊的前进现象,面积与长度显著增加。其中,木斯塔冰川西侧冰川末端在1996-1998年间前进速度为904 m/a,乔戈里冰川东侧冰川末端在2007-2009年间前进速度为446 m/a,5Y654D0097冰川末端在1978-1990年间前进速度为238 m/a,初步判定这三条冰川为跃动冰川。以10 a为滞后期分析研究区周边气象站点资料发现：研究区气温持续升高,降水量以1981年为分界点呈现“先减后增”趋势是冰川退缩速率减慢的原因之一;此外,亚大陆型冰川性质、巨大山势条件和高山冷储作用,也可能是冰川退缩幅度较小的原因。  相似文献   

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