Hydrography of a shelf ecosystem inshore of a major Western Boundary Current
Hydrography of a shelf ecosystem inshore of a major Western Boundary Current
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主要西部边界流近岸陆架生态系统的水文学
DOI：
10.1016/j.ecss.2019.106363
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
R. Barlow
中科院分区：
文献类型：
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作者：
C. Russo;T. Lamont;G.C.O. Tutt;M. Berg;R. Barlow
阿古拉斯流是南半球最大的西边界流，它强烈地影响着邻近陆架系统的海洋条件。由于有限的社会驱动因素，如大规模渔业和海洋采矿，位于伊丽莎白港和谢普斯通港之间的南非东南大陆架是非洲南部研究最少和采样不足的大陆架系统之一。本研究描述了该地区前两次全大陆架高分辨率调查（2017年1月/ 2月和7月/ 8月）的水文条件。这些数据提供了大陆架上环境条件和水文过程的基线。观察到，阿古拉斯流以及沿该流近岸边缘的气旋中尺度涡旋强烈地驱动了大陆架上的条件。这些气旋涡旋的影响存在明显差异，1月/ 2月较小的不太强烈的涡旋诱导的上升流比7月/ 8月较大的更强烈的涡旋诱导的上升流强得多。表层温度、盐度和叶绿素-a具有明显的季节性特征。地表水1 / 2月比7 / 8月升温4 °C。由于高降雨量和随后的河流流量增加，1月/ 2月观测到的盐度明显降低（33.77 g kg−1）。上升流机制，如辐散诱导的上升流、底部边界层的Ekman转向、与气旋涡旋相关的Ekman泵送，被观察到将较冷、富含营养的水从较深的地层抬升到中营养大陆架上。由于风驱动的埃克曼运输和垂直混合，这些较冷的水最终到达地表。在陆架上观测到热带地表水、亚热带地表水和南印度中央水。除了气旋漩涡将中间水抬升到陆架上外，红海水和南极中间水一般占据斜坡区。整个大陆架的溶解氧水平（>3 ml l−1）表明，氧气的可用性足以促进现有大陆架生物的生存。
The Agulhas Current, the largest Western Boundary Current in the Southern Hemisphere, strongly influences the oceanographic conditions of its adjacent shelf system. As a result of limited societal drivers, such as large-scale fisheries and marine mining, the South African southeast shelf, between Port Elizabeth and Port Shepstone, is one of the least studied and under-sampled shelf systems in Southern Africa. This study describes hydrographic conditions from the first two shelf-wide high-resolution surveys (January/February and July/August 2017) of this region. These data provide a baseline of environmental conditions and hydrographic processes across the shelf. The Agulhas Current, as well as cyclonic mesoscale eddies along the inshore edge of the Current, were observed to strongly drive conditions on the shelf. Substantial differences in the impacts of these cyclonic eddies were evident, with the smaller less intense January/February eddy inducing much stronger upwelling than the larger more intense July/August eddy. Indications of seasonality in temperature, salinity and chlorophyll-a were observed in the surface layers. Surface waters were 4 °C warmer in January/February than in July/August. Considerably lower salinities (33.77 g kg−1) were observed in January/February as a result of high rainfall and subsequent increased river outflow. Upwelling mechanisms such as divergence-induced upwelling, Ekman veering in the bottom boundary layer, Ekman pumping associated with cyclonic eddies, were observed to uplift colder, nutrient-rich water from deeper layers onto the mesotrophic shelf. These colder waters ultimately reached the surface as a result of wind-driven Ekman transport and vertical mixing. Tropical Surface Water, Subtropical Surface Water and South Indian Central Water were observed on the shelf. Red Sea Water as well as Antarctic Intermediate Water generally occupied the slope regions except where cyclonic eddies uplifted intermediate waters onto the shelf. The shelf-wide dissolved oxygen levels (>3 ml l−1) suggested that oxygen availability adequately facilitated the survival of the existing shelf biology.