Abstract
The biochemical composition of particulate organic matter (POM) mainly originates from phytoplankton. Transparent exopolymer particles (TEPs) depend on environmental conditions and play a role in the food web and biogeochemical cycle in marine ecosystems. However, little information on their characteristics in the Southern Ocean is available, particularly in winter. To investigate the seasonal characteristics of POM and TEPSs, seawater samples were collected once every two weeks from November 2017 to October 2018 at Jang Bogo Station (JBS) located on the coast of Terra Nova Bay in the Ross Sea. The total chlorophyll-a (Chl-a) concentrations increased from spring (0.08 ± 0.06 μg L−1) to summer (0.97 ± 0.95 μg L−1) with a highest Chl-a value of 2.15 μg L−1. After sea ice formation, Chl-a rapidly decreased in autumn (0.12 ± 0.10 μg L−1) and winter (0.01 ± 0.01 μg L−1). The low phytoplankton Chl-a measured in this study was related to a short ice-free period in summer. Strong seasonal variations were detected in the concentrations of proteins and lipids (one-way ANOVA test, p < 0.05), whereas no significant difference in carbohydrate concentrations was observed among different seasons (one-way ANOVA test, p > 0.05). The phytoplankton community was mostly composed of diatoms (88.8% ± 11.6%) with a large accumulation of lipids. During the summer, the POM primarily consisted of proteins. The composition being high in lipids and proteins and the high caloric content in summer indicated that the phytoplankton would make a good food source. In winter, the concentrations of proteins decreased sharply. In contrast, relatively stable concentrations of carbohydrates and lipids have been utilized for respiration and long-term energy storage in the survival of phytoplankton. The TEPS values were significantly correlated with variations in the biomass and species of the phytoplankton. Our study site was characterized by dominant diatoms and low Chl-a concentrations, which could have resulted in relatively low TEP concentrations compared to other areas. The average contributions of TEP-C to the total POC were relatively high in autumn (26.9% ± 6.1%), followed by those in summer (21.9% ± 7.1%), winter (13.0% ± 4.2%), and spring (9.8% ± 3.1%).
Highlights
The Ross Sea is one of the most productive regions in the Southern Ocean, with strong seasonal variations in the biomass and production of phytoplankton [1]
The seasonal Conditions variations in temperature and salinity at the Jang Bogo Station (JBS) were lower than those The previously reported from studies and in the Antarctic coastal environment seasonal variations in other temperature salinity at the JBS were lower than those
Relatively large variations in temperature and salinity were previously reported from other studies in the Antarctic coastal environment [52,53].obIn served the melting of sea ice, but they were stable and during the winter period, spring with and summer, relatively large variations in nearly temperature salinity were observed with the melting of sea ice, but they were nearly stable during the winter period, as expected
Summary
The Ross Sea is one of the most productive regions in the Southern Ocean, with strong seasonal variations in the biomass and production of phytoplankton [1]. Sea ice concentration has increased significantly in the Ross Sea [9] and the annual ice-free period has shortened [10], which could potentially reduce water stratification and irradiance throughout the surface water. These changes can influence the composition and biomass of phytoplankton [11,12] and the biogeochemical cycles and the food web structure in the Southern Ocean [13]
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