Meeting Documents

ENSO-Related Rossby Waves Modulate the Upper-Ocean Stratification in the Tropical Pacific Ocean

Abstract

Upper-ocean stratification profoundly influences mass and energy exchange between the surface and deep ocean, impacting ventilation, mixed layer entrainment, oceanic dynamics, and air-sea interactions. This, in turn, has broad implications for the cycling of heat, oxygen, and carbon, as well as primary productivity. While surface forcing (heat, precipitation, wind stress) is often cited as the primary driver of stratification changes, subsurface processes can also play a significant role, particularly in the dynamically active tropical Pacific Ocean. This study investigates the interannual variability of upper-ocean stratification in the tropical Pacific Ocean, with a focus on the contribution of subsurface processes, using gridded Argo products and the ECCOv4 ocean state estimate. We identified regions, such as east of the Philippines and southeast of Papua New Guinea, where upper-ocean stratification anomalies are mainly affected by subsurface density anomalies that are related to the vertical displacement of the pycnocline. These pycnocline displacements are strongly linked to large-scale oceanic dynamics, with ENSO-induced first baroclinic Rossby waves serving as a principal driver. These waves induce substantial vertical fluctuations in subsurface density, thereby modifying upper-ocean stratification. Our findings highlight the critical importance of subsurface processes in shaping upper-ocean stratification variability in the tropical Pacific. A deeper understanding of the influence of Rossby waves and pycnocline displacements offers novel perspectives on the mechanisms governing upper-ocean stratification in the tropical regions.View Document (OSM26) »