High‐resolution modeling of the Eastern Tropical Pacific oxygen minimum zone: Sensitivity to the tropical oceanic circulation

Abstract

The connection between the equatorial mean circulation and the oxygen minimum zone (OMZ) in the Eastern Tropical Pacific is investigated through sensitivity experiments with a high-resolution coupled physical-biogeochemical model. A validation against in situ observations indicates a realistic simulation of the vertical and horizontal oxygen distribution by the model. Two sets of climatological openboundary conditions for the physical variables, which differ slightly with respect to the intensity and vertical structure of the Equatorial Current System, are shown to lead to contrasting characteristics of the simulated OMZ dynamics. From a Lagrangian perspective, the mean differences near the coast originate to a large extent from the different transport of deoxygenated waters by the secondary Tsuchiya Jet (secondary Southern Subsurface Countercurrent, sSSCC). The O 2 budget further indicates a large difference in the balance between tendency terms, with advection exhibiting the largest difference between both simulations, which is shown to result from both linear and nonlinear advection. At regional scale, we also find that the variability of the physical contribution to the rate of O 2 change is one order of magnitude larger than the variability associated with the biogeochemical contribution, which originates from internal highfrequency variability. Overall our study illustrates the large sensitivity of the OMZ dynamics to the equatorial circulation.

On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic

“…The increase in the resolution of ocean circulation models improves the tropical circulation and associated oxygen distribution in the Atlantic (Duteil et al, 2014) and Pacific OMZs (Montes et al, 2014), suggesting that deficiencies in model physics largely contribute to the oxygen bias in coarser-resolution models. However, particularly the intermediate circulation (below 250 m) is still underestimated by these high-resolution simulations in realistic settings.…”

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

“…Regional coupled biogeochemical modeling nonetheless has provided a complementary approach to gain insight in the dynamics of OMZ and its relationship with climate (Resplandy et al, 2012;Gutknecht et al, 2013a). One recent modeling effort to understand the dynamics behind the OMZ in the eastern tropical Pacific comes from Montes et al (2014). This study provided a first regional simulation of the OMZ in the SEP and summarized the elements involved in maintaining the OMZ found off the coast of Peru as the result of a delicate balance of (i) the equatorial current system dynamics -the relatively oxygen-rich waters carried by the Equatorial Undercurrent (EUC), the relatively oxygen-poor and nutrientrich waters carried by the primary and secondary Tsuchiya Jets (primary and secondary southern subsurface countercurrents) -and (ii) the high surface productivity rates induced by the coastal upwelling, which in turn triggers an intense oxygen consumption in the subsurface.…”

“…The study by Montes et al (2014) established a benchmark in terms of numerical modeling of the OMZ in the SEP, focusing on its permanent regime and connection with the equatorial current dynamics. In the present study, we also take advantage of the regional modeling approach in order to investigate the mechanisms associated with the seasonal cycle of DO within the OMZ.…”

Impact of mesoscale eddies on water mass and oxygen distribution in the eastern tropical South Pacific

“…9a, b) reflecting the characteristics of the oxygen-depleted ESSW. The ESSW is carried poleward by the secondary southern subsurface countercurrent (Montes et al, 2014), feeds the subsurface PCUC (Hormazabal et al, 2013) and is then transported along the Peruvian and Chilean coast where anticyclonic eddies are likely 25 generated (Chaigneau et al, 2011). (Fig.…”