Seasonal Variations in the Biochemical Compositions of Phytoplankton and Transparent Exopolymer Particles (TEPs) at Jang Bogo Station (Terra Nova Bay, Ross Sea), 2017–2018

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%).

Environmental driving forces and phytoplankton diversity across the Ross Sea region during a summer–autumn transition

“…In this regard, the prevalence and high relative contributions of dinoflagellate in this study and other metabarcoding surveys (Liu et al 2022) would be partially due to the high number of gene copies in this group (Gong et al 2013). However, the increase in dinoflagellates abundance from summer to autumn in the Ross Sea observed with metabarcoding data is in good agreement with previous reports based on pigments (Park et al 2021).…”

Vertical distributions of organic matter components in sea ice near Cambridge Bay, Dease Strait, Canadian Archipelago

“…Kim et al (2021) noted that during the Antarctic polar night at Jang Bogo Station (JBS) in the Ross Sea in 2015, CHO constituted the predominant component (73.0%) of POM, followed by LIP (20.9%), and PRT (6.1%). A similar observation of elevated proportions of CHO and LIP in under-ice phytoplankton was made by Park et al (2021) at JBS. While these investigations pertain to the Antarctic region, they suggest a prevalent composition of CHO and LIP in the polar region phytoplankton during the dark winter.…”

Marine Nitrogen Fixation and Phytoplankton Ecology

“…In this Special Issue, we present a total of 11 articles offering ecological and biogeochemical baselines as indicators for the changes in marine environments and ecosystems driven by global climate changes. In particular, articles on the compositions of intracellular biochemical components such as proteins, lipids, and carbohydrates of phytoplankton could provide important information for their physiological conditions and the nutritional value of organic matter available to grazers [17,18]. Recently, phytoplankton-derived transparent exopolymer particles (TEPs) are known for making a considerable contribution to the organic matter pools and thus marine biogeochemical cycles in aquatic environments [19].…”

“…Over a year at Jang Bogo Station (JBS) in Antarctica, ref. [18] measured bi-weekly biochemical compositions of particulate organic matter (POM) and concentrations of TEPs. The high composition of lipids and proteins indicated a good food source in summer, whereas stably low concentrations of carbohydrates and lipids were utilized for long-term energy storage in the survival of phytoplankton in winter.…”