Since half a century ago, the number and area of dead zones (dissolved oxygen (DO) < 2 mg L–1 or 30% saturation) in the coastal oceans has increased dramatically. As widely recognized, the increased terrestrial nutrient and organic matter inputs are the two main factors causing the eutrophication of many coastal oceans. Here we show with decadal observed time series data from stations off the Pearl River Estuary and in the northern South China Sea (nSCS) that a strong intrusion into the nSCS of the West Philippine Sea (WPS) seawater in the form of Kuroshio branch occurred during the warm phase of the Pacific Decadal Oscillation (PDO) around 2003–2004 and 2015–2016 (also a strong El Niño event). Consequently, the DO concentration increased but NO3– and PO43– concentrations decreased in the subsurface layers of the nSCS. The WPS seawater was observed to reach the hypoxic area off the Pearl River Estuary in 2003–2004. Likely, due to the oxygen supply carried by the Kuroshio, little hypoxia developed. Yet, anoxic condition developed in the cold phase of PDO or strong La Niña years with weak Kuroshio intrusions.

中文翻译：

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黑潮的入侵有助于减轻南海北部海岸的沿海缺氧

自半个世纪前以来，沿海海洋死区（溶解氧 (DO) < 2 mg L–1 或 30% 饱和度）的数量和面积急剧增加。众所周知，陆地养分和有机物质输入的增加是导致许多沿海海洋富营养化的两个主要因素。在这里，我们展示了来自珠江口和南海北部 (nSCS) 站点的十年观测时间序列数据，在此期间发生了以黑潮分支的形式对西菲律宾海 (WPS) 海水 nSCS 的强烈入侵。 2003-2004 年和 2015-2016 年太平洋年代际振荡 (PDO) 的暖期（也是强厄尔尼诺事件）。因此，在 nSCS 的地下层中，DO 浓度增加，但 NO3– 和 PO43– 浓度降低。2003-2004 年观测到 WPS 海水到达珠江口外缺氧区。很可能，由于黑潮携带的氧气供应，几乎没有发生缺氧。然而，缺氧条件在 PDO 的寒冷阶段或强拉尼娜年与弱黑潮入侵发展。