Ocean Modelling ( IF 3.2 ) Pub Date : 2021-01-06 , DOI: 10.1016/j.ocemod.2021.101751 Wenxia Zhang , Julia M. Moriarty , Hui Wu , Yang Feng
The formation and maintenance of low oxygen offshore of the Changjiang River Estuary have occurred with high frequency in certain regions, which are defined as bottom hypoxia hotspots. The two major hotspots are the southern shallow bank (Yangtze Bank) and the submarine canyon. For this study, a high resolution ecosystem model was used to simulate dissolved oxygen dynamics over the continental shelf and to investigate the sensitivity of bottom hypoxia extent to multiple factors. Scenario simulations that varied the river discharge (both freshwater amount and nutrient loads), riverine nutrient concentration, shelf wind speed, and strength of the Kuroshio subsurface water intrusion and intrusion-introduced oceanic nutrient concentration were examined and the extent to which these processes regulated the bottom hypoxia extent was analyzed. Model results indicated that the spatial extent of bottom hypoxia is markedly sensitive to riverine inputs, which have larger impacts on hypoxia over the shallow bank than over the submarine canyon. The simulated bottom hypoxia is more responsive to changes in river discharge than riverine nutrient concentration, because discharge has a dual control on the shelf vertical stratification as well as primary production. The increased wind speed enhanced vertical mixing and thus reduced the spatial extent as well as the total volume of bottom hypoxic water. Weakened Kuroshio intrusion resulted in prolonged near-bottom water residence time, which can cause increase in bottom hypoxia extent. Increasing Kuroshio-introduced nutrient concentration by 30% resulted in enhanced primary production, which caused larger increase in hypoxia extent over the submarine canyon and offshore regions, compared to the shallow bank.
中文翻译:
长江口底部低氧对多种因素的响应:数值研究
长江口近海低氧的形成和维持在某些区域以高频率发生,这些区域被定义为底部缺氧热点。两个主要热点是南部浅滩(长江银行)和海底峡谷。对于本研究,使用高分辨率的生态系统模型来模拟大陆架上的溶解氧动力学,并研究底部缺氧程度对多种因素的敏感性。情景模拟研究改变了河流排放量(淡水量和养分含量),河流养分浓度,架子风速以及黑潮地下水入侵和入侵引入的海洋养分浓度的强度,并且这些过程在多大程度上调节了分析了底部缺氧程度。模型结果表明,底部缺氧的空间范围对河流输入明显敏感,这对浅岸的缺氧影响比对海底峡谷的影响大。模拟的底部缺氧比河流中的养分浓度对河流流量的变化更敏感,因为流量对架子垂直分层和初级生产具有双重控制。增加的风速增强了垂直混合,因此减小了空间范围以及底部缺氧水的总量。黑潮入侵减弱导致近水底停留时间延长,这可能导致底部缺氧程度增加。黑潮引入的养分浓度提高30%可以提高初级产量,