We examined the evolution of intermittent hypoxia off the Pearl River estuary based on three cruise legs conducted in July 2018: one during severe hypoxic conditions before the passage of a typhoon and two post-typhoon legs showing destruction of the hypoxia and its reinstatement. The lowest ever recorded regional dissolved oxygen (DO) concentration of 3.5 µmol kg⁻¹ (∼ 0.1 mg L⁻¹) was observed in bottom waters during leg 1, with an ∼ 660 km² area experiencing hypoxic conditions (DO < 63 µmol kg⁻¹). Hypoxia was completely destroyed by the typhoon passage but was quickly restored ∼ 6 d later, resulting primarily from high biochemical oxygen consumption in bottom waters that averaged 14.6 ± 4.8 µmol O₂ kg⁻¹ d⁻¹. The shoreward intrusion of offshore subsurface waters contributed to an additional 8.6 ± 1.7 % of oxygen loss during the reinstatement of hypoxia. Freshwater inputs suppressed wind-driven turbulent mixing, stabilizing the water column and facilitating the hypoxia formation. The rapid reinstatement of summer hypoxia has a shorter timescale than the water residence time, which is however comparable with that of its initial disturbance from frequent tropical cyclones that occur throughout the wet season. This has important implications for better understanding the intermittent nature of hypoxia and predicting coastal hypoxia in a changing climate.

中文翻译：

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珠江口附近南海沿海缺氧的破坏和恢复

我们基于2018年7月进行的三个巡航行程检查了珠江口附近间歇性缺氧的演变：一个在台风通过之前的严重低氧条件下，另外两个在台风后行程中显示了缺氧的破坏和恢复。3.5的最低有记录区域的溶解氧（DO）浓度 μ摩尔千克^-1（〜  0.1毫克的L ^-1）的底部水域中观察到腿1中，用〜  660公里²区域经历低氧条件（DO  <  63  μ mol kg ^-1）。缺氧被台风通过完全破坏，但很快恢复了 〜 6 d后，主要是由于底水中生化耗氧量很高，平均耗氧量为14.6  ±  4.8  µ mol O ₂  kg ^-1  d ^-1。近海地下水的向岸侵入增加了8.6  ± 恢复缺氧过程中的氧气损失为1.7％。淡水输入抑制了风驱动的湍流混合，稳定了水柱并促进了低氧的形成。夏季缺氧的快速恢复时间短于水的停留时间，但是，与整个潮湿季节频繁发生的热带气旋对水体的初始干扰相比，这是可比的。这对于更好地了解缺氧的间歇性以及预测气候变化中的沿海缺氧具有重要意义。