Collaborative Research: Observations of Three-dimensional Transport Pathways and Biogeochemical Fluxes in the Southern Ocean using Autonomous Gliders

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The Southern Ocean is often referred to as the window to the deep ocean. This vast ocean around Antarctica is the primary location where the waters that fill the deep ocean are brought to the surface where they interact with the atmosphere and with sea ice. Because of this unique role in the global climate system, the physical and biological processes that occur in the Southern Ocean have a disproportionately large impact on the properties of the global ocean, including the amount of heat and carbon dioxide that is trapped in the deep ocean for hundreds to thousands of years. Extremely sparse observations of both the Southern Ocean?s circulation structure and biological properties, such as nutrient and biomass concentrations, have presented a significant barrier to understanding the modification of near surface waters and their subsequent exchange with the deep ocean. In recent years, the SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling) project has used innovative robotic technologies, namely autonomous profiling floats, to provide observations of biogeochemical properties in the Southern Ocean with unprecedented coverage in space and time. This advance marks a step change in our ability to mechanistically understand the Southern Ocean?s role in the global carbon cycle but many of the physical and biological processes responsible for generating the observed biogeochemical distributions are not adequately captured by the floats because of their relatively coarse sampling interval (10 days). In this project, two ocean gliders will be piloted to track individual floats in order to measure the oceanic circulation features that impact exchange between the surface and interior ocean. Gliders sample the upper 1000 meters of the ocean once every 4 to 5 hours and are able to resolve variations in fluid motion on time scales of about a day. On these scales, the variability of vertical velocities are quite large and thus the circulation at these shorter temporal and smaller spatial scales significantly influences the vertical transport of ocean properties. An improved characterization of motions at these scales, and their impact on heat and carbon transport, will lead to a better understanding of the role the Southern Ocean plays in the global carbon cycle.Two autonomous ocean gliders will be deployed in the Indian sector of the Antarctic Circumpolar Current, coincident with one or more semi-Lagrangian Argo floats equipped with biogeochemical sensors through the SOCCOM project. The gliders will be piloted to track the Argo float for a period of at least four months, resolving the mesoscale and submesoscale structure surrounding the float as well as variability occurring at periods shorter than the float?s 10-day sampling interval. Measurements of the upper ocean hydrographic and velocity fields will permit an analysis of hydrodynamical instabilities within the mixed layer and their impact on vertical transport and exchange across the base of the mixed layer. The glider data will also be combined with the float observations and remote sensing products to derive vertical tracer fluxes, with the goal of quantifying the partitioning of export between sinking and advective pathways. Ultimately, this project will provide observations of the physical processes that contribute to high-frequency spatial and temporal variability in Southern Ocean tracer distributions and will provide a significant step towards describing the mechanisms that influence physical and biogeochemical distributions and transport pathways in the Southern Ocean.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.