Meeting Documents

Vertical Motions in the Southern Ocean

Abstract

Vertical motions (i.e., upwelling and downwelling) are crucial for the Southern Ocean's role in global ocean circulation and climate, as they govern the transport of heat, carbon, and nutrients. However, a comprehensive analysis of their variability is still needed. This study investigates the spatial and temporal variability of vertical velocities in the Southern Ocean using the ECCOv4 ocean state estimate. At the surface, our analysis reveals a large-scale pattern of upwelling south of approximately 55°S and downwelling to the north, consistent with conventional wind-driven patterns. At intermediate and deep layers, this pattern becomes less uniform. Topography emerges as a key driver, with intense (magnitudes of 4 to 5 × 10^-6 m/s) vertical velocities (both positive and negative) found near major bathymetric features like the Kerguelen Plateau. Notably, strong, persistent upwelling is observed across all depths in the Drake Passage. We also find significant temporal variability on interannual scales, particularly in regions with large-scale topographic features. To understand the drivers of their interannual variability, we examined their correlations with two major climate modes: the Southern Annular Mode (SAM) and the El Niño-Southern Oscillation (ENSO). A positive SAM phase is moderately correlated with enhanced upwelling south of ~60°S and increased downwelling to the north. A moderate negative correlation exists between the Niño 3.4 Index and vertical velocity across most of the Pacific sector south of 50°S, indicating that El Niño conditions tend to suppress upwelling in this region. These findings suggest that SAM and ENSO can exert opposing influences on vertical mass transport in the Southern Ocean. By detailing the critical role of both large-scale wind forcing and localized topographic interactions, this research provides a clearer picture of the vertical motions and mechanisms controlling vertical exchange in this climatically vital region.View Document (OSM26) »