Role of subsurface eddies in nitrate and organic carbon transport in the
Peru-Chile eastern boundary upwelling system
Abstract
The Southeast Pacific coast is renowned as the world’s most productive
regions, primarily due to upwelling of nutrient-rich subsurface water.
While numerous studies have emphasized the importance of surface eddies,
subsurface eddies such as Peru-Chile Undercurrent (PCUC) eddy, Puddies,
remain largely underexplored. This study utilizes a high-resolution
two-level nesting simulation coupled with a biogeochemical model to
elucidate roles of eddies at two distinct layers, the surface (upper 50
m) and subsurface layer (σθ=25.5-26.5 kgm−3). A Lagrangian particle
tracking was used to understand the fate of nitrate transported by
subsurface eddies. Our results reveal that cyclones dominate the surface
layer, while anticyclonic Puddies, prevail in the subsurface. The roles
of subsurface eddy-driven nitrate flux vary in space. In the southern
Peruvian region (16.5◦S-18.5◦S and 71◦ W-81◦ W), we show that more
predominant onshore subsurface eddy fluxes directed northeast as opposed
to the offshore flux caused by surface eddies. Meridionally averaged
onshore nitrate flux in the offshore region is driven almost entirely by
subsurface eddy-induced flux in the middle of the characteristic PCUC
density, σθ = 26-26.25 kgm−3. Subsurface eddy flux of nitrate averaged
within subsurface layers accounts for ≅10-20% of total onshore and
offshore transport in latitude range 16.5◦S-18.5◦S and from 18.5◦S to
the south, respectively. Furthermore, the Lagrangian particle tracking
shows that Puddies originated in the southernmost area travelled to the
northwestern regions, resupply nitrate onshoreward that is otherwise
flown away poleward by the PCUC. This Puddy- induced nitrate resupply
contributes 15.4% to the nitrate that reaches coastal upwelling zone.