The importance of tidewater glaciers for marine mammals and seabirds in Svalbard, Norway
The importance of tidewater glaciers for marine mammals and seabirds in Svalbard, Norway
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DOI：
10.1016/j.jmarsys.2013.09.006
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发表时间：
2014-01-01
影响因子：
2.8
通讯作者：
Zajaczkowski, Marek
中科院分区：
文献类型：
--
作者：
Lydersen, Christian;Assmy, Philipp;Zajaczkowski, Marek
目前，斯瓦尔巴特群岛大约60%的土地都被冰川覆盖。该群岛有超过1100个冰川（>1公里（2）），其中163个是“冰川”，即终止于海洋的冰川。人们早就知道，这些冰川前沿地区是海鸟和海洋哺乳动物的重要觅食区。在此，我们回顾目前的知识，这些地区的重要性，这些动物和反思的过程中，创造这些明显的“热点”。Kittiwakes里萨三趾鸥通常在斯瓦尔巴群岛冰川前的鸟类群落中占据主导地位，但管鼻蝠、象牙鸥Pagophila eburnea和蓝灰色海鸥Larus hyperboreus也对集群做出了贡献，有时集群可以由数千只组成。这种鸟经常在所谓的“棕色地带”被发现，这是一个位于冰川前面的区域，由于水流的原因，这里没有冰，由于悬浮的沉积物，这里很泥泞。在这些地方的动物通常有他们的胃充满了大型浮游动物或鱼类。这些棕色区域也是斯瓦尔巴群岛环斑海豹（Pusa hispida）和白色鲸（Delphinapterus leucas）觅食的热点。斯瓦尔巴群岛环斑海豹的主要繁殖栖息地位于峡湾深处，冰川前沿的冰块在那里被冻结成陆地固定的海冰，促进雪的积累达到适合环斑海豹雌性的深度，以便在冰中的呼吸孔上方挖掘出出生巢穴。这些幼熊区是春季北极熊（Ursus maritimus）的重要狩猎区，特别是在从冬季/分娩窝出现后的这段时间里带着幼崽的母熊。漂浮在沿海地区的冰川冰块对该区域所有海豹物种也很重要，因为它们是换羽期间的干燥平台，也是鸟类和海豹的一般休息平台。在过去的十年里，斯匹次卑尔根群岛西海岸沿着的许多峡湾有几年完全缺乏春季海冰。在这些年的春季，胡子海豹（Erignathus rectatus）已经用冰川冰取代了它们常规的海冰平台，将其作为分娩和哺乳以及一般休息的坚实基质。在冰川前沿形成觅食热点的机制与冰川前沿排出的大量地下淡水羽流有关。当这些羽状物向地表上升时，它们夹带着大量的环境水，是原始排放量的数十至数百倍。当烟羽上升时，这些水从各个深度水平被抽取。这种夹带确保了从峡湾外部向冰川前沿不断补充中等深度的沃茨，并极大地增强了一般河口环流。中间的水团将浮游生物从广阔的区域（包括外部峡湾）带入冰川前沿区域，在那里它们被卷入上升到表面的羽流中，并经常因淡水渗透冲击而昏迷或死亡。这些小动物很容易成为水面捕食者的猎物。大型、强壮的海洋浮游动物有时可以通过在流入的海水下面游泳来逃脱。但是，它们随后集中在靠近底部的水层中，使它们变得有趣并容易受到捕食者的影响。中间水团还将营养物质带到冰川前沿，在那里它们被运送到表层，随后可以用于开花后的初级生产。然而，这往往有最大的影响距离冰川前沿，当大部分流出的沉积物已经解决了。目前，斯瓦尔巴特群岛冰川的物质平衡是负面的，对未来气候变化的预测表明，气候将继续变暖，因此冰川将继续退缩。这将导致斯瓦尔巴特群岛的冰川崩解到海洋中的数量减少，以及群岛周围的崩解前沿的总长度减少。类似于北方海冰边缘的退缩（这是北极脊椎动物另一个觅食热点），气候变暖引起的冰川变化可能会导致许多北极物种的分布发生重大变化和丰度减少。(C)2013爱思唯尔有限公司版权所有。
Approximately 60% of Svalbard's land areas are glaciated at the present time. The Archipelago has more than 1100 glaciers (>1 km(2)) and 163 of these are "tidewater glaciers" that is glaciers that terminate (with their calving front) at the sea. It has been known for a long time that these glacier front areas are important feeding areas for seabirds and marine mammals. Herein, we review current knowledge regarding the importance of these areas for these animals and reflect upon the processes that create these apparent "hotspots". Kittiwakes Rissa tridactyla, routinely dominate avian assemblages in front of glaciers in Svalbard, but fulmars Fulmarus glacialis, ivory gulls Pagophila eburnea and glaucous gulls Larus hyperboreus also contribute to aggregations, which can sometimes comprise many thousands of individuals. The birds are often found in the so-called "brown zone", which is an area in front of tidewater glaciers that is ice-free due to currents and muddy due to suspended sediments. Animals at these sites typically have their stomachs full of large zooplankton or fish. These brown zones are also foraging hotspots for Svalbard's ringed seals (Pusa hispida) and white whales (Delphinapterus leucas). Prime breeding habitat for ringed seals in Svalbard occurs deep in the fjords where ice pieces calved from the glacier fronts become frozen into land-fast sea-ice, promoting the accumulation of snow to a depth suitable for ringed seal females to dig out birth lairs above breathing holes in the ice. These pupping areas are important hunting areas for polar bears (Ursus maritimus) in spring, especially female bears with cubs of the year during the period following emergence from the winter/birthing den. Glacier-ice pieces floating in coastal areas are also important for all seal species in the region as dry platforms during moulting and also as general resting platforms for both birds and seals. During the last decade there have been several years with a complete lack of spring sea ice in many of the fjords along the west coast of Spitsbergen. During the spring periods in these years, bearded seals (Erignathus barbatus) have replaced their regular sea-ice platform with glacier ice, using it as a solid substrate for both birthing and nursing as well as general resting. The mechanisms that create foraging hotspots at the fronts of tidewater glaciers are related to the massive subsurface plumes of freshwater discharged from the glacier fronts. As these plumes rise towards the surface they entrain large volumes of ambient water, tens to hundreds of times the original discharge volume. This water is drawn from all depth levels as the plume ascends. This entrainment ensures a continuous resupply of intermediate depth waters from the outer parts of the fjords towards the glacier front and greatly amplifies the general estuarine circulation. The intermediate water masses carry plankton from a broad area, including the outer fjord, into the glacier front area, where they get entrained in the plume rising towards the surface, and often become stunned or die from freshwater osmotic shock. These small animals fall as an easy prey to the surface feeding predators. Large, strong swimming marine zooplankton species can sometimes escape by swimming below the inflow of marine water. But, they then become concentrated in a water layer near the bottom, making them of interest and susceptible to predators.The intermediate water masses also bring nutrients towards the glacier fronts where they are transported up to the surface layer where they can subsequently be utilized for post-bloom primary production. However, this tends to have greatest influence some distance away from the glacier front, when much of the outflow sediment has settled out. Currently, the mass balance for Svalbard glaciers is negative and climate change predictions for the future suggest continued warming, and hence continued glacial retreat. This will result in a reduction in both the number of glaciers calving into the ocean in Svalbard and the total length of calving fronts around the Archipelago. Similar to the retraction of the northern sea-ice edge (which is another diminishing foraging hotspot for these same arctic vertebrates), the climate-warming-induced changes in glaciers will likely lead to substantial distributional shifts and abundance reductions for many arctic species. (C) 2013 Elsevier B.V. All rights reserved.