Abstract: Chlorophyll a (Chl a), as the main pigment of phytoplankton photosynthesis, is often used to indicate the existing amount of phytoplankton in water column. The concentration of Chl a in Beibu Gulf from August to September 2021 was analyzed and its spatial distribution characteristics and influencing factors were discussed based on the summer cruise of the Shiptime Sharing Program on 2020 Beibu Gulf Scientific Research Expedition. The results showed that the mass concentration of Chl a ranged from 0.03 to 10.59 μg/L with an average value of 0.84 μg/L, among which the surface layer mass concentration ranged from 0.08 to 10.59 μg/L (average 0.97 μg/L) and the bottom layer mass concentration ranged from 0.03 to 4.69 μg/L (average 0.99 μg/L). Combined with the analysis of remote sensing data, the spatial distribution of Chl a mass concentration in Beibu Gulf was generally high in the nearshore and low in the offshore area. The high value area was mostly distributed in the nearshore area of Guangxi, namely the northern part of Beibu Gulf, while the mass concentration in the central and southern part of Beibu Gulf was relatively low. The correlation analysis between water environmental parameters and Chl a indicated that water nitrogen limitation was an important factor affecting the mass concentration of Chl a in Beibu Gulf from August to September.

Key words: Beibu Gulf, chlorophyll a, nitrogen limitation, water mass