Understanding Manganese Fluxes in the Southern Ocean: Contributions to Climate Adaptation and Ocean Sustainability

Dissolved manganese, despite its subnanomolar concentrations, plays a crucial role in co-limiting primary production in the Southern Ocean, yet the physical supply mechanisms during winter—critical for biological consumption in spring and summer—remain underexplored. This study addresses the urgent need to understand how manganese dynamics relate to the broader context of ocean health and climate adaptation. During the austral winter and spring of 2019, two research cruises were conducted in the Atlantic sector of the Southern Ocean to investigate the distribution and supply mechanisms of dissolved manganese in the upper water column. The findings revealed that winter entrainment accounted for an overwhelming majority of the total dissolved manganese flux, averaging 97.26 ± 5.28%, while diapycnal diffusion contributed a mere 4.92 ± 5.14%. Mean dissolved manganese concentrations in the upper water column (<500 m) were consistently low (≤0.34 nmol kg⁻¹; p-value > 0.05), with seasonal mixed layer reservoir sizes averaging 65.21 ± 12.93 μmol m⁻² in winter and 21.64 ± 19.32 μmol m⁻² in spring. Notably, winter supply rates exceeded estimated consumption rates during spring, thus fulfilling phytoplankton’s biological demands and enhancing ecosystem resilience. Conversely, in the subtropical zone, supply rates were insufficient to meet consumption needs, indicating the potential influence of additional mechanisms such as coastal upwelling. These insights into manganese fluxes highlight their importance in sustaining marine ecosystems and their implications for equitable and effective climate adaptation strategies in response to oceanic changes driven by climate variability.