Biological Impact of Typhoon Wipha in the Coastal Area of Western Guangdong: A Comparative Field Observation Perspective

The impact of typhoons on the ecology of the ocean has been observed using high-accuracy satellite remote sensing data. However, few field observations in the ocean have been conducted to understand the effect of typhoons on the biogeochemistry because typhoon is furious, dangerous, and unpredictable. Here, we investigated the impact of Typhoon Wipha on the biogeochemistry of the coastal area of western Guangdong, northwest South China Sea. Our results show that the typhoon triggered phytoplankton blooms (the level of Chl a increased 3.25 times after the typhoon) nearshore (water depths <23 m); however, there was little change in the nutrients and Chl a offshore (water depths between 23 and 60 m). Terrestrial runoff and vertical seawater mixing were identified as the main processes that bring nutrients into the nearshore area and thus triggering phytoplankton blooms after the typhoon. Moreover, the positive apparent oxygen utilization (AOU) and unsaturated DO contents during the posttyphoon period suggest significant oxygen consumption (i.e., degradation process and biological respiration) caused by Typhoon Wipha in both nearshore and offshore areas. The internal nutrient recirculation and biological respiration are responsible for little change in POC, PN and nutrients in the offshore area between the pre- and posttyphoon periods and thus did not cause phytoplankton blooms. Our results suggest that the potential oxygen consumption (i.e., decomposition and biological respiration) after the typhoon are important biogeochemical impacts induced by Typhoon Wipha in coastal waters.