Large scale patterns and size distributions of marine particles across the African and Pacific Sectors of the Southern Ocean

Marine particles play an important role in the transfer of carbon, nutrients, and trace elements into the deep ocean. However, the large scale distributions of marine particles remain poorly described, limiting our understanding of the large scale features of the biological carbon pump and their impact on biogeochemistry and climate. Using a CTD-mounted underwater imaging system, the Underwater Vision Profiler 5 (UVP5), we observed the depth-resolved concentrations and size distributions of large marine particles (0.1 - 2.5 mm equivalent spherical diameter (ESD)) across two large scale GO-SHIP repeat hydrography transects in the Pacific and African sectors of the Southern Ocean. We find that large marine particles penetrate into deep waters in several Southern Ocean regions. The regions with elevated particle concentrations in deep waters are characterized by larger particles (0.2 – 2.5 mm ESD) at higher latitudes, 62 - 70 degrees south, and smaller particles (0.1 – 0.2 mm ESD) at lower latitudes, 33 - 42 degrees south. Additionally, a mid-depth particle concentration maximum was observed in the African sector from 1000-2000 meters depth from 52 – 62 degrees south, mostly consisting of smaller particles (0.1 – 0.2 mm ESD). These results shed light on the patterns, drivers, and role of the biological carbon pump in the Southern Ocean where observations are limited, and where the strength and nature of the biological carbon pump plays a large role in global biogeochemical cycles.