Association of abnormal Yantai-Weihai coastal front with large-scale algal bloom in winter in the northern Shandong peninsula coastal waters

• A large-scale HAB persisted in northern Shandong Peninsula during winter 2021. • YWCF played crucial role in sustaining the HAB by creating a stable marine environment with increased nutrient. • Significant SST gradient and Chl- a anomalies coincide with HAB development. • Freshwater discharge, PAR levels and wind supported HAB evolution and persistence. The coastal waters in the northern Shandong Peninsula experienced a significant and persistent harmful algal bloom (HAB) event during the winter of 2021. This study aims to investigate the persistence and extent mechanisms of this large-scale HAB using the satellite-derived and reanalysis datasets, with a focus on the role of sea surface temperature (SST) fronts, known to influence nutrient accumulation and act as physical barriers that prevent the dispersion of algal blooms. The results showed the HAB in the winter of 2021 began in the coastal waters of the northern Dongying on October 27th near the Yellow River estuary and expanded southeastward, reaching the Yantai-Weihai coastal waters before subsiding by December 28. The anomalous intensification and early onset of the Yantai-Weihai Coastal Front (YWCF) played a crucial role in sustaining the HAB by creating a stable marine environment with enhanced nutrient concentrations. The HAB was first detected near the Yellow River estuary and subsequently spread along the coast, influenced by prevailing northwesterly winds, southeastward currents, and the impact of the YWCF. Our findings highlight the significant impact of the front on the development and persistence of HAB, suggesting that such oceanographic features could serve as key indicators for predicting future algal blooms in this region.