130 F. Schütte et al.: Hidden vortices: near-equatorial low-oxygen extremes driven by high-baroclinic-mode vortices 
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Figure 6. (a) Current velocity (black arrows) and DO (colored dots) at 80 m depth along 23° W and between 8 and 12° N obtained from 
along-track shipboard ADCP observations and CTD-O observations between 23 and 25 July 2009 (cruise Ron Brown 2009, see Table 1). 
Grey arrows show geostrophic velocities and black contours show sea level anomalies from satellite altimetry data on 24 July 2009. Red 
circles denote positions and extent of the two eddies, identified and reconstructed from shipboard ADCP observations at 80 m. Latitude-depth 
sections of (b) DO, (c) conservative temperature, (d) zonal velocity, (e) meridional velocity and (f) PV between 8 and 12° N obtained from 
CTD-O observations along 23° W (same period to a). Black diamonds at the top of panels (b) and (c) denote actual latitudes of CTD-O 
profiles. Thin gray lines in panels (b)-(f) denote surfaces of potential density. In panels (d) and (e), solid black and dashed black lines denote 
0.15ms7! velocity intervals. Thick dark gray lines in panels (d)-(f) denote DO contours of 70 umol kg71. (g)-(1) are analog to (a)-(f), but 
caken from GFDL CM2.6 model simulation for model date 23 Mar 0197. Gray arrows in (g) denote surface velocity. Black arrows denote 
current velocity and colored contours show DO distribution both at 77 m depth along — 28° W. (h)-(1) show respective latitude-depth sections 
along — 28° W for the same model date. Thick dark grayv lines in panels (1}—(D denote DO contours of 90 umol ke-1. 
of 100km or more. Instead, these eddies have a confined 
paroclinic structure, which is associated to higher baroclinic 
modes and corresponding smaller Rossby radii of deforma- 
‘ion as is shown in detail in Sect. 4.4. The HB Vs’ horizontal 
core positions are estimated from the current velocities and 
closely match the meridional position of the low-oxygen ex- 
tremes (cf. 3rd and 6th column for bold marked events in 
Table 1; Fig. 6a and b). Note, that the derived HBVs’ zonal 
core position range between 23.3 and 22.9° W, whereas for 
Ocean Sei... 22. 119-143. 2026 
the low-oxygen extremes, only the meridional position along 
the 23° W section can be identified. Notable is the simulta- 
neous occurrence of two HBVs observed during one cruise 
in 2009 at positions 10.3° N/23.2°W and 11.6° N/22.9° W 
(Fig. 6a—f). These two HBVs were meridionally cut through 
their eastern and western flank, respectively, and were both 
observed with DO concentrations well below 50 umol kg”! 
(Fig. 6a and b). 
https://doi.org/10.5194/os-22-119-2026