Signals of intense primary production in response to Ulva prolifera bloom in the Yellow Sea during summer 2021

Abstract

The variability in changing climate has been predicted to lead to significant changes in the world's oceans primary productivity. Recent years have experienced more intense algal blooms during the spring-summer months in many coastal waters. Here we present results from the analysis of satellite ocean color products from MODIS-Terra datasets during June 2 to July 20, 2021, corresponding to the most intense period of the Enteromorpha (Ulva) prolifera algae (U. prolifera) bloom in the Yellow Sea. Because the studies on sea surface temperature (SST) variability over the U. prolifera bloom have not yet been fully explored by satellite measurements in the offshore waters of Qingdao, China, we analyzed the MODIS SST and their relationship with the U. prolifera blooms in the 2021 summer months. Analysis of SST showed a variation in the range of 18–24 °C in near-shore waters in response to the bloom of green algae. We find that a significant thermal front with a gradient magnitude of 0.03 °C/km was developed over the shelf and offshore regions during the algal bloom period. The observed changes in thermal fronts are driven by high-wind speed and Ekman pumping-velocity processes. We concluded that the changes in SSTs with a range of 20–23 °C, high-magnitude thermal fronts and wind speed, and Ekman pumping velocity resulted in the intensification of the largest bloom of U. prolifera in the Yellow Sea during the study period.