Impacts of Agulhas Current meanders on intermediate water masses along the adjacent continental slope and shelf.

IF 2.1 3区地球科学 Q2 OCEANOGRAPHY

Continental Shelf Research Pub Date : 2024-03-01 DOI:10.1016/j.csr.2024.105197

T. Lamont , I. Halo , C.S. Russo

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Abstract

Variability in the Agulhas Current system is dominated by meanders, which constitute cyclonic eddies along the inshore edge of the Current on the southeast coast of South Africa. Few studies have investigated the influence of these meanders on hydrographic variability on the adjacent shelf and slope and to date only a handful have been sampled in situ. This study used available in situ data and GLORYS12v1 model output to investigate the impact of meanders on the distribution of Intermediate waters, namely Red Sea Water (RSW) and Antarctic Intermediate Water (AAIW), as well as mechanisms driving these variations. We focussed on four eddies, sampled in situ during July 1998, April 2010, January–February 2017, and July–August 2017. RSW dominated along the inshore edge of the Agulhas Current in the absence of meanders, but larger proportions of AAIW occurred in the presence of cyclonic eddies. During eddy events, the kinematic steering level was raised above the lower boundary of Intermediate waters, increasing cross-frontal mixing of waters at depths of 800–1800 m. Eddy-induced upwelling of Central and Intermediate waters onto the shelf appeared to be inhibited by bands of strong positive relative vorticity (>0.4 × 10⁻⁴ s⁻¹), which likely promoted downwelling conditions inshore of the July 1998, April 2010, and July–August 2017 eddies. Weak positive relative vorticity (<0.2 × 10⁻⁴ s⁻¹) inshore of the January–February 2017 eddy was associated with enhanced water mass exchange between the shelf and deeper (>1000 m) ocean. GLORYS12v1 was consistently comparable with satellite and in situ data, and simulated the overall distribution of water masses on the continental shelf and slope despite its inability to reflect the influence of river discharge in nearshore regions during austral summer. The model is thus suitable to investigate the influence of Agulhas Current meanders on the hydrography of South Africa's southeast coast.

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阿古哈斯洋流蜿蜒曲折对邻近大陆坡和大陆架中间水团的影响。

阿古哈斯洋流系统的变化主要受蜿蜒流的影响，这些蜿蜒流构成了南非东南海岸洋流近岸边缘的旋涡。很少有研究调查这些蜿蜒流对邻近陆架和斜坡水文变化的影响，迄今为止，只有少数研究对其进行了取样。本研究利用现有数据和 GLORYS12v1 模型输出结果，调查了蜿蜒流对中间水域（即红海水域（RSW）和南极中间水域（AAIW））分布的影响，以及这些变化的驱动机制。我们重点研究了 1998 年 7 月、2010 年 4 月、2017 年 1-2 月和 2017 年 7-8 月期间取样的四个漩涡。在没有蜿蜒流的情况下，RSW 在阿古哈斯洋流近岸边缘占主导地位，但在有气旋漩涡的情况下，AAIW 的比例较大。在漩涡事件期间，运动转向水平高于中层水域的下边界，增加了 800-1800 米深处水域的跨锋面混合。漩涡引起的中央和中层水域上涌到陆棚似乎受到强正相对涡度带（>0.4 × 10 s）的抑制，这可能促进了 1998 年 7 月、2010 年 4 月和 2017 年 7-8 月漩涡沿岸的下沉条件。弱正相对涡度（1000 米）海洋。GLORYS12v1 与卫星和数据具有一致的可比性，模拟了大陆架和斜坡上水团的总体分布，尽管它无法反映夏季澳大利亚近岸区域河流排水量的影响。因此，该模型适用于研究阿古哈斯洋流蜿蜒对南非东南海岸水文地理的影响。

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来源期刊

Continental Shelf Research 地学-海洋学

CiteScore

4.30

自引率

4.30%

发文量

136

审稿时长

6.1 months

期刊介绍： Continental Shelf Research publishes articles dealing with the biological, chemical, geological and physical oceanography of the shallow marine environment, from coastal and estuarine waters out to the shelf break. The continental shelf is a critical environment within the land-ocean continuum, and many processes, functions and problems in the continental shelf are driven by terrestrial inputs transported through the rivers and estuaries to the coastal and continental shelf areas. Manuscripts that deal with these topics must make a clear link to the continental shelf. Examples of research areas include: Physical sedimentology and geomorphology Geochemistry of the coastal ocean (inorganic and organic) Marine environment and anthropogenic effects Interaction of physical dynamics with natural and manmade shoreline features Benthic, phytoplankton and zooplankton ecology Coastal water and sediment quality, and ecosystem health Benthic-pelagic coupling (physical and biogeochemical) Interactions between physical dynamics (waves, currents, mixing, etc.) and biogeochemical cycles Estuarine, coastal and shelf sea modelling and process studies.