F. Schütte et al.: Hidden vortices: near-equatorial low-oxygen extremes driven by high-baroclinic-mode vortices 131 
Table 1. Low-DO events (below 60 umol kg 7!) found in the upper 200 m during meridional CTD-O ship sections along 23° W between 7 and 
12° N. Only those low-DO events are listed, where meridional sections of DO, hydrography and velocity were available (spanning a latitude 
range of minimum 3°). Columns from left to right denote DO minimum between 0 and 200 m, corresponding depth, latitude and research 
cmuise with date of the CTD-O profile. The last three columns denote type, core position and radius of related eddy, that was analyzed with 
the eddy identification method. ACE events are marked in bold (the abbreviation ACME stands for anticyclonic mode water eddy). As ap 
example, the event in the third row (Meteor 119/1, 17 September 2015) is presented in Fig. 4. 
DO Depth Latitude Cruise ID (date) Eddy Eddy core Radius 
ninimum Im] [°N] type position [km] 
"umolkg 1? 
17 
59 8.0 
37 63 115 
aa mn 8.0 
ru 45 10.0 
69 10.5 
ı 
77 11.5 
75 11.5 
2 
53 67 11.0 
54 93 7,0 
5 65 10.5 
Meteor 116/1 ACME 8.3°N 33 
(22 May 2015) 23.1° W 
Meteor 116/1 
(21 May 2015) 
Meteor 119/1 ACME 8.0°N 38 
17 Sep 2015) 23.3° W 
Ronald H. Brown PNE0O9 ACME 10.3°N 36 
24 Jul 2009) 23.2° W 
Polarstern PS88.2 ACE 10.3°N 37 
(8 Nov 2014) 23.2° W 
Ronald H. Brown PNE0O9 ACME 1L6°N 31 
(24 Jul 2009) 22.9° W 
L’ Atalante IFM-GEOMAR -— 
4 
(11 Mar 2008) 
Meteor 97/1 
(30 May 2013) 
Meteor 68/2 ACME 
(4 Jul 2006) 
Z1°N 20 
23.0°W 
Merian 18/3 
(25 Jun 2011) 
74 20 
57m 11.5 Meteor 130/1 
(3 Sep 2016) 
58 82 11.0 Meteor 105/1 ACME 1L0°N 60 
“10 Apr 2014) 23.2° W 
73 11.5 Merian 22/1 ACME 1L6°N 37 
15 Nov 2012) 23.0° W 
79 10.5 Meteor 106/1 ACME 10.4°N 33 
(24 Apr 2014) 23.2°W 
Both HBVVs were identified to be anticyclonic and subsur- 
face intensified, as shown by the anomalously weak stratifi- 
cation along 23° W at subsurface depth, which is indicated by 
the thickening of isothermal and isopycnal layers at the depth 
range of the DO minimum core (Fig. 6c). The vertical extent 
of the HBVs (characterized by displaced isopycnal surfaces 
or zonal velocity) reached at least down to about 250 m and 
https:/doi.org/10.5194/os-22-119-2024 
covered the vertical extent of the low-DO cores. The esti- 
mated radii are 36 and 31 km and thus considerably smaller 
than the first baroclinic Rossby radius of around 90km at 
these latitudes. For none of the 10 anticyclonic HBVs, we 
could identify any anticyclonic signature from satellite al- 
timetry observations (Fig. 6a). One reason might be that the 
resolution of gridded SLA from conventional altimetry (in 
Ocean Seci.. 22. 119-143. 2026