Spatial and temporal dynamics of taxonomic and functional diversity of microorganisms in the Southern Ocean with an emphasis on the carbon cycle

• Ano de defesa: 2025
• Autor(a) principal: Faria, Laiza Cabral de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Metabarcoding; Antarctica; Antártica; Biological Carbon Pump; Bomba Biológica de Carbono; Dinâmica Microbiana Multidomínios; Metagenômica; Metagenomics; Microbial Oceanography; Microbiologia Polar; Multidomain Microbial Dynamics; Oceanografia Microbiana; Polar Microbiology
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/21/21134/tde-11082025-160812/

Microbial communities play a fundamental role in the biogeochemical cycles of the Southern Ocean. However, their diversity, structure, and functionality remain poorly understood, especially in the context of climate change. This study investigates how oceanographic conditions influence microbial communities (bacteria, archaea, and microeukaryotes) across different spatial and temporal scales in the northwestern Antarctic Peninsula. To achieve this, 162 seawater samples were collected from depths ranging from 5 to 1,525 meters at 10 monitoring stations (M01 to M10) along the Antarctic Peninsula (southern Drake Passage, Bransfield Strait, and Gerlache Strait). Sampling took place during research expeditions conducted between 2013 and 2019 (spring, summer, and late summer) aboard the vessel Almirante Maximiano, as part of the Brazilian Antarctic Program. The samples were analyzed using amplicon sequencing (primers 515Y/926R) and metagenomics. Taxonomic composition and functional potential of the pelagic microbial community were integrated with environmental variables, including temperature, salinity, fluorescence, and dissolved organic carbon concentration. Overall, prokaryotic diversity was higher than that of microeukaryotes. Interannual and seasonal analyses revealed that while prokaryotic communities remained relatively stable - possibly due to their metabolic diversity and high dispersal potential - microeukaryotes exhibited pronounced fluctuations driven by environmental factors. Among these, the reduction in sea surface temperature was particularly notable, likely linked to rising atmospheric temperatures and increased ice melt associated with extreme climate events, such as the 2016 El Niño. Assessment of the water column structure indicate that surface microbial communities - dominated by diatoms, Alphaproteobacteria, Bacteroidia, and Gammaproteobacteria - responded rapidly to short-term environmental changes, particularly temperature variations driven by phenomena like El Niño. In contrast, deep-water communities - primarily composed of archaea and bacteria from the Flavobacteriales and Pseudomonadales groups - were more stable, likely influenced by physical factors and biological interactions, such as nutrient competition. Mesopelagic communities did not exhibit a clear pattern: in some areas, they resembled surface communities, while in others, they were more similar to deep-sea communities. Integrated amplicon and metagenomic analyses from 2015 and 2016 highlighted taxonomic and metabolic differences between surface and deep-water communities. While surface communities - rich in diatoms, Polaribacter, Rhodobacteraceae, and Sulfitobacter - responded to seasonal phytoplankton activity, deep-water communities - dominated by SAR11, Thioglobaceae, and Nitrosopumilaceae - played a key role in long-term carbon remineralization. These findings underscore the importance of microbial processes in regulating the carbon cycle and suggest potential impacts of climate change on microbial community functionality. Understanding these spatial and temporal patterns is crucial for predicting future changes in polar marine ecosystems, developing biodiversity conservation strategies, and implementing measures to mitigate the effects of climate change in the Southern Ocean