Variability of bottom dissolved oxygen on the southern Senegalese shelf at intraseasonal to interannual time scales using a modelling approach

IF 2.3 3区地球科学 Q2 OCEANOGRAPHY

Deep-sea Research Part Ii-topical Studies in Oceanography Pub Date : 2025-02-27 DOI:10.1016/j.dsr2.2025.105464

Abdoul Wahab Tall , Vincent Echevin , Xavier Capet , Eric Machu

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引用次数: 0

Abstract

Recent in-situ measurements on the west African continental shelf have shown that the bottom waters undergo episodic hypoxia and even anoxia. In this study, we investigate the variability of bottom dissolved oxygen (DO) over the southern Senegalese shelf at seasonal, intraseasonal and interannual time scales over the period 2015–2019 using a high-resolution (2 km) regional coupled dynamical-biogeochemical model. The model is forced by daily winds to represent synoptic variability during the upwelling-favourable cold season (November-May). Near-bottom DO evaluation using data from the Melax mooring located over the mid shelf indicates that the model represents well the seasonal and intraseasonal variability. A bottom DO budget shows that advection of deep, low-oxygenated waters over the shelf edge during the upwelling season generates a DO loss, which is overcompensated by ventilation of the entire shelf due to vertical mixing. Biogeochemical processes compensate this DO supply: DO is consumed by organic matter and zooplankton respiration, slightly compensated by regenerated and new primary production. Because of a sluggish shelf circulation during the summer season (July–September, JAS), oxygen concentration declines in parts of the outer shelf bottom layer, in spite of a weaker surface primary production and organic matter export than during the heart of the cold season (February–April, FMA). Analysis of the synoptic variability reveals the complexity of the DO response to the duration and intensity of upwelling and relaxation events, with the largest DO decrease of

\sim 110 μ m o l O_{2} L^{- 1}

associated with a strong upwelling event (cumulative upwelling index

\sim 2 {Nm}^{- 2} d a y

) obtained in 2016. Year to year variability indicates two periods of enhanced hypoxia in FMA 2017 and JAS 2016 characterized by a high retention of bottom waters over the shelf.

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利用建模方法研究塞内加尔南部大陆架海底溶解氧在季节内到年际时间尺度上的变化情况

最近在西非大陆架的现场测量表明，底部水域经历了间歇性的缺氧甚至缺氧。在这项研究中，我们使用高分辨率（2 km）区域耦合动力-生物地球化学模型，研究了2015-2019年期间塞内加尔南部大陆架底部溶解氧（DO）在季节、季节内和年际时间尺度上的变化。该模式受日风的影响，在有利于上升流的冷季（11月至5月）表现天气变化。利用位于大陆架中部的Melax系泊数据进行的近底部DO评估表明，该模型很好地代表了季节和季节内的变化。底部DO预算显示，在上升流季节，深层低氧水在陆架边缘的平流产生了DO损失，由于垂直混合，整个陆架的通风过度补偿了DO损失。生物地球化学过程补偿了这种DO供应：DO被有机物和浮游动物呼吸消耗，由再生和新的初级产物略微补偿。由于夏季（7 - 9月，JAS）大陆架环流缓慢，尽管表面初级生产和有机物输出较冷季中心（2 - 4月，FMA）弱，但外大陆架底层部分氧浓度下降。对天气变率的分析揭示了DO对上升流和弛缓事件的持续时间和强度的响应的复杂性，2016年获得的最大DO减少约110μmolO2L−1与强上升流事件（累积上升流指数约2Nm−2day）有关。每年的变化表明，FMA 2017和JAS 2016有两个阶段的缺氧增强，其特征是底部水在大陆架上的高保留。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Deep-sea Research Part Ii-topical Studies in Oceanography 地学-海洋学

CiteScore

6.40

自引率

16.70%

发文量

115

审稿时长

3 months

期刊介绍： Deep-Sea Research Part II: Topical Studies in Oceanography publishes topical issues from the many international and interdisciplinary projects which are undertaken in oceanography. Besides these special issues from projects, the journal publishes collections of papers presented at conferences. The special issues regularly have electronic annexes of non-text material (numerical data, images, images, video, etc.) which are published with the special issues in ScienceDirect. Deep-Sea Research Part II was split off as a separate journal devoted to topical issues in 1993. Its companion journal Deep-Sea Research Part I: Oceanographic Research Papers, publishes the regular research papers in this area.