Mesoscale Variability in the Boundaries of the Oxygen Minimum Zone in the Eastern South Pacific: Influence of Intrathermocline Eddies

Abstract

Oxygen minimum zones (OMZs) are oxygen-deficient bodies of water that occupy large volumes of intermediate-depth waters in the eastern tropical and subtropical oceans (

Strong Habitat Compression by Extreme Shoaling Events of Hypoxic Waters in the Eastern Pacific

“…We identify AEs with a vertical density structure typical for ACMEs (e.g., Schütte et al., 2016) as drivers of THREEs on both hemispheres where the mean HI is steeply slanted and located between 250 and 500 m depth, that is, along the edges of the core EP ODZs (Section 3.3.2, Figures 8 and 9). The horizontal positions of AE associated THREEs agree with the westward and slightly equatorward pathways of the ACMEs identified and tracked in previous model simulations (Frenger et al., 2018) and observations (Auger et al., 2021; Pegliasco et al., 2015) in both hemispheres. The fact that AEs dominate over CEs in driving THREEs in this depth range (see e.g., the dominance of AE associated THREEs between 100 and 90°W in Figure 9) is linked to the subsurface intensification of ACMEs, for which the cores are observed at ∼400 m depth in the ETSP (Chaigneau et al., 2011).…”

“…(2018)), they effectively displace the HI along their trajectories and generate THREEs. Hence, in the region dominated by AE associated THREEs, THREEs are a manifestation of how ACMEs contribute to shaping the vertical/lateral boundaries of the EP ODZs (Auger et al., 2021; Bettencourt et al., 2015; Frenger et al., 2018).…”

“…Hence, as non-linear ACMEs trap hypoxic water and transport it along isopycnals out of the core ODZs ("cannonball effect", Chelton et al (2011);Frenger et al (2018)), they effectively displace the HI along their trajectories and generate THREEs. Hence, in the region dominated by AE associated THREEs, THREEs are a manifestation of how ACMEs contribute to shaping the vertical/lateral boundaries of the EP ODZs (Auger et al, 2021;Bettencourt et al, 2015;Frenger et al, 2018).…”

“…On subseasonal to seasonal time scales, subsurface hypoxic volumes are further affected by variability in wind‐driven upwelling (Adams et al., 2016; Prakash et al., 2012), up‐ or downwelling Rossby and Kelvin waves (Graco et al., 2017; Lüdke et al., 2020; Vergara et al., 2016) or subsurface current variability (Pizarro‐Koch et al., 2019). On even shorter time scales, mesoscale eddy variability (Auger et al., 2021; Bettencourt et al., 2015; Frenger et al., 2018; Vergara et al., 2016) is complemented by tropical instability vortices (Eddebbar et al., 2021), submesoscale variability (Bertrand et al., 2010; Grados et al., 2016), synoptic wind variability (Duteil, 2019) or internal gravity waves (Bertrand et al., 2014; Booth et al., 2012; Grados et al., 2016) in inducing HI variability. While all of the above processes go along with changes in circulation or mixing, they can also be associated with changes in biological oxygen production and consumption.…”

Oxygen Variability in the Offshore Northern Benguela Upwelling System From Glider Data

“…Subsurface eddies in the BenUS were previously detected in Argo temperature and salinity profiles (McCoy et al., 2020 ), however, to our knowledge, hypoxia within a subsurface eddy shedding from the BenUS undercurrent has not previously been observed in situ. There is an abundance of literature studying the physical properties and biogeochemistry of such eddies in other upwelling systems based on in‐situ and model data (e.g., Chaigneau et al., 2011 ; Schütte, Karstensen, et al., 2016 ; Fiedler et al., 2016 ; Karstensen et al., 2017 ; Frenger et al., 2018 ; Auger et al., 2021 ) which have found that low‐oxygen anomalies trapped and further intensified within subsurface eddies generated along the shelf are transported toward the middle of the gyre, where they shape the large‐scale O 2 gradient of mid‐latitudes. In the tropical North Atlantic, a satellite‐based study estimated these structures constituted 9% of the eddy population (Schütte, Brandt, & Karstensen, 2016 ).…”