Carbon Biomass Assessment for Microbial Plankton Groups Across a Young Anticyclonic Loop Current Eddy and Surrounding Waters in the Gulf of Mexico

Carbon biomass assessments are useful in quantifying carbon stored in key planktonic functional groups involved in biogeochemical processes in marine ecosystems. The microbial community inhabiting the open-ocean Gulf of Mexico comprises organisms that regulate carbon fluxes within this mesoscale-dominated ecosystem. The anticyclonic Loop Current Eddies (LCEs) are highly dynamic structures that harbor and transport significant microbial players in the ocean carbon cycle. This study focuses on characterizing the vertical and horizontal high-resolution carbon biomass distribution of the microbial community within the euphotic zone of a young LCE and the surrounding waters during a cruise conducted in the oceanic region of the Gulf of Mexico in November 2022. Carbon estimates were performed using cell abundance and variable carbon conversion factors per microbial group. The prevailing mesoscale dynamics modulated the biomass vertical distribution inside the LCE and at the external region. Sinking and rising of the microbial carbon to deeper and upper layers were discernible at the LCE center and edges, respectively. Upwelling and increase of carbon were evidenced in the cyclonic-influenced external region. Biotic factors, including habitat preferences, nutritional strategies, and ecological interactions among microorganisms, also shaped the biomass composition and distribution within the euphotic zone of mesoscale structures. Remarkably, the combined impact of the deep vertical mixing and the eddy interaction with strong northerly winds during the study period promoted phytoplankton vertical redistribution and carbon stock enhancement inside the LCE. The study's findings situate the LCEs as important dynamic structures regulating the microbial carbon pool within this open-ocean ecosystem.