Cold-water coral growth under extreme environmental conditions, the Cape Lookout area, NW Atlantic
Cold-water coral growth under extreme environmental conditions, the Cape Lookout area, NW Atlantic
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大西洋西北角卢考特角地区极端环境条件下的冷水珊瑚生长
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发表时间：
2013
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通讯作者：
T. V. Weering
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作者：
F. Mienis;G. Duineveld;A. Davies;M. Lavaleye;S. Ross;H. Seim;J. Bane;H. Haren;M. Bergman;H. Haas;S. Brooke;T. V. Weering
北卡罗莱纳海岸外的望角冷水珊瑚区形成了西北大西洋布莱克高原上最浅、最北的冷水珊瑚丘区。靠近瞭望角的冷水珊瑚栖息地偶尔会沐浴在墨西哥湾流中，墨西哥湾流的特点是少营养温暖的海水和强烈的表面流。在这里，我们首次深入了解了该珊瑚区的海底登陆者所记录的土丘分布和形态、沉积环境和珊瑚覆盖以及近床环境条件。这些土丘位于水深320至550米之间，其特点是高声波后向散射，表明存在硬结构。观察到三种不同的土丘形态：(1)320 m处为顶部扁平的土丘，(2)该地区中部为泪滴状的多峰土丘，(3)水深540 m处为单个土丘。回声测深剖面显示，在形成土丘底部的所有土丘结构下方都存在一个强反射体。这个反射体出现在单个土丘的下游，由碳酸盐板组成。视频分析显示，所有的土丘都被Lophelia pertusa覆盖，而且有生命的蜂群只出现在靠近土丘的SSW一侧的山顶处，也就是面对最强洋流的一侧。离丘地区的特点是低后向散射和沉积物波纹，表明存在相对较强的底流。2009年12月至2010年5月期间，在珊瑚丘中部署了两个底部着陆器。两个着陆器都记录了突出的事件，其特点是海底附近以及上覆水柱的环境条件波动很大。12月至4月期间的特点是温度和盐度升高，与流量增加和近床声波反向散射相一致。在这些事件中，温度在一天内波动高达9°C，这是迄今为止在冷水珊瑚栖息地测量到的最大温度变化。暖流事件与墨西哥湾流弯曲有关，持续时间约为1周，暖流在此期间流向东北偏北。鉴于温度对冷水珊瑚新陈代谢的强烈影响，这些事件的后果一定很严重。此外，在这些事件期间还记录到声波后向散射值升高和质量通量高，表明可能影响珊瑚的第二个压力源。沙子的磨蚀性，加上强劲的水流，可能会把珊瑚炸成沙子。我们的结论是，望角附近的冷水珊瑚生活在极端条件下，目前限制了丘的生长。
The Cape Lookout cold-water coral area off the coast of North Carolina forms the shallowest and northernmost cold-water coral mound area on the Blake Plateau in the NW Atlantic. Cold-water coral habitats near Cape Lookout are occasionally bathed in the Gulf Stream, which is characterised by oligotrophic warm water and strong surface currents. Here, we present the first insights into the mound distribution and morphology, sedimentary environment and coral cover and near-bed environmental conditions as recorded by bottom landers from this coral area. The mounds occur between 320 and 550 m water depth and are characterised by high acoustic backscatter indicating the presence of hard structure. Three distinct mound morphologies were observed: (1) a mound with a flattened top at 320 m, (2) multi-summited mounds with a teardrop shape in the middle part of the area and (3) a single mound at 540 m water depth. Echosounder profiles show the presence of a strong reflector underneath all mound structures that forms the base of the mounds. This reflector cropped out at the downstream side of the single mound and consists of carbonate slabs. Video analysis revealed that all mounds are covered by Lophelia pertusa and that living colonies only occur close to the summits of the SSW side of the mounds, which is the side that faces the strongest currents. Off-mound areas were characterised by low backscatter and sediment ripples, indicating the presence of relatively strong bottom currents. Two bottom landers were deployed amidst the coral mounds between December 2009 and May 2010. Both landers recorded prominent events, characterised by large fluctuations in environmental conditions near the seabed as well as in the overlying water column. The period between December and April was characterised by several events of increasing temperature and salinity, coinciding with increased flow and near-bed acoustic backscatter. During these events temperature fluctuated by up to 9 °C within a day, which is the largest temperature variability as measured so far in a cold-water coral habitat. Warm events, related to Gulf Stream meanders, had the duration of roughly 1 week and the current during these events was directed to the NNE. The consequences of such events must be significant given the strong effects of temperature on the metabolism of cold-water corals. Furthermore, elevated acoustic backscatter values and high mass fluxes were also recorded during these events, indicating a second stressor that may affect the corals. The abrasive nature of sand in combination with strong currents might sand blast the corals. We conclude that cold-water corals near Cape Lookout live under extreme conditions that limit mound growth at present.