Modelling the advance–retreat cycle of a tidewater glacier with simple sediment dynamics

We present a simple coupled glacier-sediment model to simulate the evolution of a tidewater glacier. The model is based on a consideration of the total mass budget of a glacier, whereas ice mechanics are fully parameterized. The calving rate at the glacier terminus is assumed to be proportional to the water depth. We show that the formation of a morainic shoal has a profound influence on the response of a tidewater glacier to climatic forcing. For a slow periodic forcing of the equilibrium-line altitude, the model glacier advances steadily into the estuary, builds up a submarine terminal moraine, and then retreats rapidly when a critical point is hit. For a slowly increasing equilibrium-line altitude, at a rate as low as 1 m per 5 years, we find terminus retreat rates of up to 10 km in 50 years. Our model suggests that, although the response of tidewater glaciers to external forcing is strongly nonlinear, the onset of retreat is controlled by climate change.     

Discrete displacement analysis for geographic linear features and the application to glacier termini

The extent of glacier terminus displacement is instrumental in investigations of natural or artificial geographic changes. Its importance to earth science and engineering is reflected in the considerable efforts that have been devoted to the development of several boundary displacement analysis methods. Among the methods, the buffering-based approach compares favorably with other approaches in objectivity and robustness. However, it does not consider the relative positions of boundaries, because its buffering operation cannot determine features' relative directions. This limitation incurs inaccurate calculation results – underestimation of mean shifts and overestimation of shape variations, especially when the two compared boundaries intersect. Discrete displacement analysis (DDA), an alternative method that considers given geographic objects as a set of a finite number of points, is proposed here. In a series of tests carried out, including Jakobshavn glacier's calving front, DDA was found to correctly calculate mean shift and shape variation even in cases where the conventional buffering-based method failed. Moreover, this approach is independent of the dimension of space in which it is implemented, and thus is expected to be utilized for analysis of 3D geographic object displacement.     

Atlantic humpback dolphins Sousa teuszii in the Saloum Delta (Senegal): distribution,relative abundance and photo-identification

During October and November 2015, the first systematic survey of Sousa teuszii was carried out in the Saloum Delta (Senegal, West Africa), comprising 1 617.5 km of boat-based survey coverage. Thirty sightings were recorded in the Saloum and Diomboss rivers, and along the southern coastline. Dolphins were also observed entering the Bandiala and Djinack channels, and travelling across the border into Gambia. The initial sighting locations were 0.043–1.192 km from shore, and tracked dolphins did not move more than 2.082 km from shore. Groups comprised 1–29 animals (mean 9.3 animals), and at least three neonate calves were observed during November. The overall relative abundance was 0.018 sight. km^?1 and 0.175 ind. km^?1. Sightings were concentrated in the Diomboss where relative abundance reached 0.037 sight. km^?1 and 0.331 ind. km^?1. Non-intensive photo-identification produced a minimum population size of 103 animals, the highest recorded for S. teuszii anywhere in its range. Photo-identification also confirmed a movement of individuals between different parts of the Saloum Delta. Combined travel–forage dominated the behaviour. Dolphins were photographed capturing mullet (Mugil sp.) on three occasions. The distribution, population size and movements of S. teuszii are discussed in relation to management.     

Glacier Changes at Svartisen,Northern Norway,during the Last 125 Years:Influence of Climate and Other Factors

The two ice caps of Svartisen,at the latitude of the Arctic Circle in Norway,supply 60 glaciers,ranging in size from >50 to <1 km2.Until the last two decades of the 19th century,the glaciers remained close to their maximum recent(Little Ice Age) size.In response to the prevailing 20th century climate,they have become smaller,but the changes have varied between glaciers.Climatic factors have not been the sole control of the variations.The response times of small,steep glaciers are shorter than those of the l...     

利用EnviSat ASAR数据监测南极冰架崩解

利用欧洲环境卫星(EnviSat)所携带的先进合成孔径雷达(ASAR)数据高时间、高空间分辨率的特点,实现了全南极范围内冰架年崩解面积的高精度估算和崩解类型的解译。利用40期重复覆盖全南极海岸线的EnviSatASAR数据探测了冰架崩解的位置、类型和发生时间,统计分析了2005年8月到2011年8月连续6年南极冰架崩解频率和面积的时空变化。结果显示:(1)2005年—2011年平均崩解面积为2969.7km2,年崩解面积变化幅度较大,年崩解频率略呈下降的趋势;(2)南极冰架崩解主要发生1—3月,其中2月崩解最频繁;(3)东南极威尔克斯地区域是当前南极冰架崩解最活跃的区域,冰架罗斯、龙尼-菲尔希纳及埃默里等3大冰架很稳定且鲜有崩解发生,东南极毛德皇后地区域冰架相对稳定;(4)空间尺度小于100km2的崩解频率占到总频率的94.1%,忽略它们将导致南极年崩解面积低估20.7%—92.9%;(5)以内部冰川应力为主要驱动力的开裂型(Rift-opening)崩解较以外部大气和海洋因素为主要驱动力的融水型(Melt-related)崩解发生更为频繁,但是两者在量上的差异不大(约10%)。     

Calving retreat and proglacial lake growth at Hooker Glacier,Southern Alps,New Zealand

Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (～2.14 km) during the last two centuries. High retreat rates (51 m a^?1 1986–2001, 43 m a^?1 2001–2011) have produced a large (1.22 km²) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate.     

Streamflow response to the rapid retreat of a lake‐calving glacier

There has been increasing attention over the last decade to the potential effects of glacier retreat on downstream discharge and aquatic habitat. This study focused on streamflow variability downstream of Bridge Glacier in the southern Coast Mountains of BC between 1979 and 2014, prior to and during a period in which the glacier experienced enhanced calving and rapid retreat across a lake‐filled basin. Here we combined empirical trend detection and a conceptual‐parametric hydrological model to address the following hypotheses: (1) streamflow trends in late summer and early autumn should reflect the opposing influences of climatic warming (which would tend to increase unit‐area meltwater production) and the reduction in glacier area (which would tend to reduce the total volume of meltwater generated), and (2) winter streamflow should increase because of displacement of lake water as ice flows past the grounding line and calves into the lake basin. In relation to the first hypothesis, we found no significant trends in monthly discharge during summer. However, applying regression analysis to account for air temperature and precipitation variations, weak but statistically significant negative trends were detected for August and melt season discharge. The HBV‐EC model was applied using time‐varying glacier cover, as derived from Landsat imagery. Relative to simulations based on constant glacier extent, model results indicated that glacier recession caused a decline in mean monthly streamflow of 9% in August and 11% in September. These declines in late‐summer streamflow are consistent with the results from our empirical analysis. The second hypothesis is supported by the finding of positive trends for December, January, and February discharge. Despite the modelled declines in late‐summer mean monthly streamflow, recorded discharge data exhibited neither positive nor negative trends during the melt season, suggesting that Bridge Glacier may currently be at or close to the point of peak water. Further analysis of the impact of lake‐terminating glaciers on downstream discharge is needed to refine the peak water model. Copyright © 2016 John Wiley & Sons, Ltd.     

Terminus recession,proglacial lake expansion and 21st century calving retreat of Tasman Glacier,New Zealand

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 (U_r) 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 (U_r) from 2000 to 2008. U_r varies temporally, with mean U_r of 54 m/a from 2000 to 2006 and a mean U_r 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.     

The origin and flux of icebergs released into the Last Glacial Maximum Northern Hemisphere oceans: the impact of ice‐sheet topography

The precipitation fields of a palaeoatmospheric general circulation model are used to derive estimates of the geographical distribution, and flux, of icebergs from the Laurentide, Fennoscandinavian and eastern Siberian ice‐sheets at the Last Glacial Maximum (LGM). The atmospheric model fields from LGM simulations using CLIMAP or Peltier (ICE‐4G) ice orography were studied, to test the sensitivity of the predicted flux. The estimated Northern Hemispheric LGM iceberg flux is 3500–4000 km³ yr^?1, of which about 60% issued directly into the North Atlantic. The iceberg flux from the St Lawrence area is of similar significance to that issuing from Hudson Strait in all estimates. Both the North Pacific and the Arctic received substantial iceberg fluxes (ca. 700 km³ yr^?1), with relatively minor differences occurring between the two ice‐sheet reconstructions. Apparent discrepancies between Arctic deep‐sea core samples of ice‐rafted debris and our estimates of mean glacial iceberg flux may be ascribed to coastal trapping of bergs, the existence of floating ice tongues or a rapid exit of icebergs from the Arctic basin into the Greenland Sea through the Fram Strait. Copyright © 2001 John Wiley & Sons, Ltd.