Typhoons frequently induce algal blooms in the open ocean based on the satellite remote sensing data. However, the effects of typhoons on nearshore areas are not fully clarified due to the inaccessibility of in situ sampled data and the low accuracy of satellite data in the nearshore areas. To understand the biogeochemical and ecological changes in semi-enclosed bays under the influence of typhoons, physicochemical parameters and isotopic compositions of surface water were measured in Zhanjiang Bay during the super Typhoon Mujigae and nontyphoon periods. The results show that the chlorophyll a (Chl a) concentrations inside and outside the bay during these two periods were considerably different. During typhoon periods, the positive apparent oxygen utilization and unsaturated dissolved oxygen (DO) values suggested significant biological degradation in Zhanjiang Bay, rather than the algal blooms reported by previous studies. In contrast, during nontyphoon periods, particulate organic matter (POM: POC and PN) was mainly generated by in situ phytoplankton production, as indicated by a low POC/Chl a ratio (<99), low C/N ratio, and positive correlations between PN, POC, and Chl a. Isotopic analysis of the particulate N (PN) and nitrate (NO₃⁻) indicated that the ¹⁵N-enriched PN in both periods originally came from sewage-dissolved inorganic N. These results suggest that the typhoon-induced decomposition processes, rather than algal blooms, in this semi-enclosed bay in the northern South China Sea, providing new understanding of the impact of the typhoons on marine biogeochemistry and ecology.

中文翻译：

---

台风穆吉盖对南海北部半封闭海湾生物地球化学和生态的影响

根据卫星遥感数据，台风经常导致公海藻类大量繁殖。然而，由于近岸地区现场采样数据的不可获取性和卫星数据的准确性较低，台风对近岸地区的影响尚未完全阐明。为了了解台风影响下半封闭海湾的生物地球化学和生态变化，在超强台风木吉盖和非台风期间测量了湛江湾地表水的物理化学参数和同位素组成。结果表明，叶绿素a (Chl a) 这两个时期海湾内外的浓度差异很大。在台风期间，正的表观氧利用率和不饱和溶解氧 (DO) 值表明湛江湾发生了显着的生物降解，而不是先前研究报告的藻华。相比之下，在非台风期间，颗粒有机物（POM：POC 和 PN）主要由原位浮游植物产生，表现为低 POC/Chl a比值（<99）、低 C/N 比值和正相关PN、POC 和 Chl a 之间。微粒 N (PN) 和硝酸盐 (NO ₃ ^- ) 的同位素分析表明，¹⁵两个时期富含 N 的 PN 最初来自污水溶解的无机 N。这些结果表明，在南海北部的这个半封闭海湾中，台风引起的分解过程，而不是藻华，提供了对台风对海洋生物地球化学和生态的影响。