Quasi-geostrophic vertical motion from satellite and in-situ observations: Impact on South East Pacific nitrate distribution through a Lagrangian simulation

Abstract

The objective of this study is to improve our understanding of the influence of mesoscale vertical exchanges on ecosystem dynamics. In particular, we aim to investigate the influence of vertical velocity on ocean tracer distributions in the South East Pacific. Previous remote sensing studies in this region have revealed that chlorophyll distributions within mesoscale eddies are characterised by dipole-like patterns, with extreme values found at the eddy peripheries. An observation-based product, ARMOR3D, is used to obtain an estimate of 3D currents. Horizontal velocities are derived from application of the geostrophic equations to 3D fields of temperature and salinity obtained from the ARMOR3D reanalysis that combines satellite (SST and altimetry) and in-situ (Argo profiling floats, XBTs, CTDs and moorings) data. Vertical velocities are estimated from quasi-geostrophic (QG) dynamics by integrating the QG Omega equation with ARMOR3D fields. Finally, a Lagrangian particle tracking model, forced by the derived 3D currents, is used to study passive tracer dispersion and its influence on the distribution of biochemical properties such as nitrates. The Lagrangian results show that the impact of vertical advection on nitrate distribution is non-negligible as they account for about 30% of the contribution of horizontal advection.