Physical transport processes in the fjords of South Georgia

Abstract. The Southern Ocean, typically characterized as a high-nutrient, low-chlorophyll region, exhibits recurring chlorophyll blooms downstream of South Georgia island fuelled by iron enrichment of near-surface water. To better understand the physical processes underpinning iron and nutrient transport from South Georgia fjords to the surrounding shelf, extensive data were collected during research cruise PS133.2 of RV Polarstern in late austral spring 2022. Here, we present analyses of these data to characterize water masses, circulation patterns and nutrient distribution inside Cumberland Bay East and King Haakon Bay including the adjacent shelf. Surface currents are influenced by westerly winds, particularly on the eastern side of the island. Fjord-shelf exchange in Cumberland Bay East exhibit weak export and residence times are on the order of days to months driven by a vertical overturning circulation. The highest temperature and chlorophyll values are measured at the mouth of King Haakon Bay. The results highlight the diverse local environment and the significant influence of bathymetry and orography on fjord systems at South Georgia. This study elucidates the physical transport processes of fjord-shelf exchange that may support transport of iron and nutrients as a source for the downstream chlorophyll blooms in the open ocean. Ongoing investigations will further explore the biological and geochemical aspects, providing a comprehensive understanding of the South Georgia system.