The Southern Ocean Observing System 2021-2025 Science and Implementation Plan

The Southern Ocean plays a central role in the Earth System by connecting the Earth’s ocean basins, and it is a crucial link between the deep ocean, surface ocean and atmosphere. Hence, the ongoing changes in the Southern Ocean impact global climate, rates of sea level rise, biogeochemical cycles and ecological systems. Yet, understanding of the causes and consequences of these changes is limited by the short and incomplete nature of observations. To address this issue, sustained, integrated and multidisciplinary observations are needed. Due to the size of the Southern Ocean, this requires international agreement on the priority observations to be collected, and also internationally coordinated data management and delivery. The Southern Ocean Observing System (SOOS) was initiated in 2011 to support these efforts. In the last decade, SOOS has enhanced regional coordination and observing system capabilities through network development, data curation and publication, development of data discovery and coordination tools, and providing strong advocacy mechanisms for the Southern Ocean community. Significant data gaps remain in observations of the ice-affected ocean, sea ice habitats, the ocean at depths >2000 m, the air-ocean-ice interface, biogeochemical and biological variables, and for seasons other than summer. This Science and Implementation Plan articulates the scientific priorities for SOOS through the identification of these key gaps in the observational network and by identifying the priorities in addressing these gaps. This Plan covers the five year period 2021-2025, with emphasis on the capabilities required to support data collection and delivery, and the objectives and actions that SOOS will implement. Five Science Themes have been identified, each encompassing a number of Key Science Challenges. These Themes and Challenges incorporate many scientific drivers that are cross-disciplinary, reflecting the highly-interconnected nature of the Southern Ocean, and Theme 5 is cross-cutting and highlights a number of linkages amongst Themes 1-4. The Themes provide a framework for enhancing the coordination of international data collection and delivery efforts that will contribute to understanding and quantifying the state and variability of: Theme 1: Southern Ocean cryosphere Theme 2: Southern Ocean circulation Theme 3: Southern Ocean carbon and biogeochemical cycles Theme 4: Southern Ocean ecosystems and biodiversity Theme 5: Southern Ocean-sea ice-atmosphere fluxes Addressing the data gaps across these inherently interconnected Themes sustainably and systematically requires parallel advances in coordination networks, cyberinfrastructure and data management tools, observational platform and sensor technology, and development of internationally agreed sampling and analytical standards and data requirements of key variables. In recognition of this, SOOS has also identified a number of Foundational Capabilities that will need to be developed or expanded.