Oxygen Pathways and Budget for the Eastern South Pacific Oxygen Minimum Zone. Issue 3 (2nd March 2018)

• Record Type: Journal Article
• Authors: Llanillo, P. J.; Pelegrí, J. L.; Talley, L. D.; Peña‐Izquierdo, J.; Cordero, R. R.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 3(2018)
• Page Start: 1722
• Page End: 1744
• Publication Date: 2018-03-02
• Subjects: eastern South Pacific Oxygen Minimum Zone -- ventilation -- subtropical cell -- oxygen budget -- subtropical pathway -- dianeutral advection; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2017JC013509
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Ventilation of the eastern South Pacific Oxygen Minimum Zone (ESP‐OMZ) is quantified using climatological Argo and dissolved oxygen data, combined with reanalysis wind stress data. We (1) estimate all oxygen fluxes (advection and turbulent diffusion) ventilating this OMZ, (2) quantify for the first time the oxygen contribution from the subtropical versus the traditionally studied tropical‐equatorial pathway, and (3) derive a refined annual‐mean oxygen budget for the ESP‐OMZ. In the upper OMZ layer, net oxygen supply is dominated by tropical‐equatorial advection, with more than one‐third of this supply upwelling into the Ekman layer through previously unevaluated vertical advection, within the overturning component of the regional Subtropical Cell (STC). Below the STC, at the OMZ's core, advection is weak and turbulent diffusion (isoneutral and dianeutral) accounts for 89% of the net oxygen supply, most of it coming from the oxygen‐rich subtropical gyre. In the deep OMZ layer, net oxygen supply occurs only through turbulent diffusion and is dominated by the tropical‐equatorial pathway. Considering the entire OMZ, net oxygen supply (3.84 ± 0.42 µmol kg −1 yr −1 ) is dominated by isoneutral turbulent diffusion (56.5%, split into 32.3% of tropical‐equatorial origin and 24.2% of subtropical origin), followed by isoneutral advection (32.0%, split into 27.6% of tropical‐equatorial origin and 4.4% of subtropical origin) and dianeutral diffusion (11.5%). One‐quarter (25.8%) of the net oxygen input escapes through dianeutral advection (most of it upwelling) and, assuming steady state, biological consumption is responsible for most of the oxygen loss (74.2%). Plain Language Summary: Large oceanic volumes with very low dissolved oxygen concentrations are a natural feature of the world ocean. Their existence is explained as a combination of weak water renewal plus large biological oxygen consumption. These low‐oxygen regions are expected to expand due to climate change, which will likely damage marine habitats and threaten the sustainability of important fisheries. Here we describe the mean state of the world's second most intense low‐oxygen volume, located in the tropical eastern South Pacific. For this purpose, we consider and quantify the physical processes oxygenating this low‐oxygen volume, including the contribution of vertical oxygen transport. We find that turbulence provides two‐thirds of the overall oxygen supply whereas mean currents contribute with one‐third. Regarding the pathway of origin, almost two‐thirds of the total oxygen supply takes place from the tropical‐equatorial region while a previously unaccounted subtropical pathway provides for about one‐quarter of the oxygen. Remarkably, one‐quarter of all the oxygen supplied to the low‐oxygen volume escapes through vertical transport, most of it upwelling into the Ekman layer. This study provides a necessary comparative baseline for future studies of how climate change may disrupt the mean‐state of this important low‐oxygen oceanic volume. Key Points: Upper OMZ layer is mainly ventilated by mean circulation inside the Subtropical Cell (STC). Below the STC, turbulence dominates ventilation One‐way dianeutral entrainment accounts for 25.8% of the oxygen lost in this OMZ, most of it upwelling into the Ekman layer within the STC The tropical‐equatorial pathway provides 59.9% of the net oxygen supply while the subtropical pathway contributes with 28.6%