Impact of vertical and horizontal advection on nutrient distribution in the South East Pacific

An innovative approach is used to analyse the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the distribution of a passive nutrient tracer (nitrate) in the South East Pacific. Twelve years of vertical and horizontal currents are derived from an observation-based estimate of the ocean state. Horizontal velocities are obtained through application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG Omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents are coincident, with peaks in austral summer (November–December) in accord with published observations. Two ensembles of Lagrangian particle tracking experiments that differ according to vertical forcing (w = wQG vs. w = 0) enable a quantitative analysis of the impact of the vertical velocity. From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that the impact of vertical advection on nutrient distribution is 30 % of the contribution of horizontal advection. Despite being weaker by a factor of up to 10−4 than the horizontal currents, vertical velocity is demonstrated to make an important contribution to nutrient distributions in the region of studyThis work has been carried out as part of E-MOTION (CTM2012-31014) project funded by the Spanish National Research Program. Additional funding from the Local Government of the Balearic Islands (CAIB-51/2011 grant) is also acknowledged. Bàrbara Barceló-Llull is supported by a pre-doctoral grant from the Spanish National Research Program associated to the PUMP (CTM2012-33355) project. Evan Mason is supported by a post-doctoral grant from the Conselleria d’Educació, Cultura i Universitats del Govern de les Illes Balears (Mallorca, Spain) and the European Social FundPeer Reviewe