Environmental drivers of phytoplankton crops and taxonomic composition in northeastern Antarctic Peninsula adjacent sea area

The ecosystem of the sea region adjacent to the Antarctic Peninsula is undergoing remarkable physical and biological changes, in the context of global warming. However, understanding of the dynamics of phytoplankton taxonomic composition in this marginal ice zone remains unclear. In this study, seawater samples collected from 36 stations in the northeastern Antarctic Peninsula were analyzed for nutrients and phytoplankton pigments. Combining with CHEMTAX analysis, remote sensing data, and physicochemical measurements, we investigated the relationships between phytoplankton crops, taxonomic composition, and marine environmental drivers. Integrated chlorophyll a (Chl a ) concentrations (200 m) varied from 8.9 mg/m 2 to 64.2 mg/m 2 , with an average of (23.2±12.0) mg/m 2 and higher phytoplankton biomass concentrated in the coastal region of South Orkney Island and South Shetland Island. Diatoms were the dominant functional group (63%±21%). Higher proportions of diatoms were associated with higher Chl a ( r =0.40, p <0.01), stable water columns ( r =0.20, p <0.01), higher Si/P ratios ( r =0.34, p <0.01), higher photosynthetically active radiation intensity ( r =0.64, p <0.01), and higher sea ice melt water contributions (MWC, r =0.20, p <0.01). Conversely, Phaeocystis antarctica contributed a smaller overall proportion (31%±18%) and was more concentrated in the offshore water masses (e.g., Philip Ridge and South Scotia Ridge) with lower light levels ( r =−0.58, p <0.01), deeper mixed layer depths ( r =0.17, p <0.05), higher nutrient concentrations (e.g., N, P, and Si, r >0.35, p <0.01), and lower MWC ( r =−0.20, p <0.01). In comparison, the total contribution from green flagellates (4%±5%), cryptophyta (1%±3%), dinoflagellates (1%±4%), and cyanobacteria (1% ± 5%) was only 6%. In offshore regions with well-mixed water, less varied taxonomic composition and lower crops with a higher proportion of nanophytoplankton were observed. In contrast, significantly decreasing crops below the mixed layer depth was observed in water columns with strong stratification, where the dominant phytoplankter changed from diatoms to P. antarctica . These findings have important implications for better understanding the future dynamics of marine ecosystems in the sea area adjacent to the Antarctic Peninsula.