‚Z06 
Q. Devresse et al.: Eddy-enhanced primary production sustains heterotrophic microbial activities 
24.33° W and around — 50m from 22.78 to 20.3° W, up 
to 0.68 ug L7! (Fig. 4a). At the coastal stations, the Chl a 
maximum was found between 30-40 m depth with values 
ap to 0.96 ug L7!. Integrated biomass of autotrophic pico- 
and nanoplankton (Table 1) ranged between 1.6 and 7.8 
and between 3.6 and 6.1 g Cm”? in the open ocean and at 
he coastal stations, respectively. In the open ocean waters, 
the depth distribution of autotrophic pico- and nanoplankton 
biomass (Fig. 4b) showed a gradient from west to east with a 
concentration maximum at — 75m from 23.61 to 24.33° W, 
a concentrations maximum at — 50m from 22 to 22.78° W, 
and a concentrations maximum between 5-25 m from 21.13 
co 20.3° W. Concentrations reached up to 166 ug CL7!. At 
che coastal stations, the maximum autotrophic pico- and 
1anoplankton biomass was found between 30-40 m depth 
with values up to 117 ug CL7!. Both Chl a concentration 
and autotrophic pico- and nanoplankton biomass did not vary 
significantly between the open ocean and the coastal stations 
(Tukey, p>0.05). Integrated total and dissolved primary pro- 
duction (PPrTorT; PPpoc; Table 1) remained fairly constant 
with ranges of 101-137 and 42.8-78 mmolC m”? d7!, re- 
spectively, at the coastal and the open ocean stations. An ex- 
ception was the station furthest offshore (24.33° W), where 
rates decreased sharply to 25.8 mmol C m”? a7! for PProrT 
and to 12.3 mmolC m”? d7! for PPpoc. The integrated per- 
centage of extracellular release (PER; Table 1) ranged be- 
tween 42.3 % and 67.5 %. PPpoc and PER did not vary 
significantly between the open ocean and the coastal sta- 
tions (Tukey, p>0.05). PPror and PPpoc decreased with 
depth except for station E2 (Fig. 4c), while PER increased 
(Fig. 4d). 
In the CE (core and periphery) and at the frontal zone, inte- 
grated Chl a concentration ranged from 17.2 to 225 mg m”? 
(Table 1). The Chl a distribution (Fig. 3a) showed a clear 
spatial separation with the highest values (98.7-225 mg m 7?) 
in the western and northern (148 mg m7?) parts of the CE 
and lowest values (26.8-37.5mg m?) in the southern and 
eastern parts. Depth distribution of Chl a concentration also 
differed across the eddy, with values >0.5 ug L7! reaching 
down to 45 m depth at the frontal zone and the western part 
of the CE and down to 30 m depth in the eastern part of the 
CE (Fig. 4a). The highest concentrations were detected in the 
western part of the eddy with 8.7 ug L7! at station EDZ-1 at 
27 m. Within the upper 30 m, Chl a concentration within the 
CE was significantly higher than at the open ocean and the 
coastal stations (ANOVA, p<0.05). Integrated autotrophic 
pico- and nanoplankton biomass ranged between 0.3 and 
4.7 g Cm”? in the CE (Table 1). Depth distribution of au- 
cotrophic pico- and nanoplankton biomass (Fig. 4b) showed 
low biomass in the upper 40m (<25 ug CL7') from 18.83 
co 19.11° W. In contrast, higher biomass (>25 ug CL7!) oc- 
curred in the more eastern stations of the CE (17.11 to 
18.54° W) and westwards from the frontal zone (19.55° W). 
In the eddy, autotrophic pico- and nanoplankton biomass 
reached higher concentrations mainly within the upper 40m, 
with values up to 191 ug C L7!. Depth-integrated PPror and 
PPpoc rates were significantly higher in the CE and at the 
frontal zone than in the open ocean and the coastal sta- 
tions (Tukey, p<0.05) with values ranging from 245 to 
687 mmol C m—* d7! and from 95.9 to 238 mmol Cm? d—!, 
respectively (Table 1). PPror rates (Fig. 4c; Table 2) 
were fairly constant across the CE’s surface (5m depth), 
ranging between 11.2 and 13.7 umol1CL7! d7!, but varied 
strongly between 15-40 m depth (0.2-14.5 umol CL7! a7. 
The highest PPror rates were found in the frontal zone 
with up to 25.0umol1CL7! d7! at the surface. The range 
of PPpoc rates (Table 2; Fig. 4d) was larger in the 
CE (0.2-4.9 umolCL7! a7!) and the frontal zone (0.7- 
7.8 umol CL7! d7!) than in the open ocean and at the coastal 
stations. Integrated PER had a range of 29.4 %-—40.8 % (Ta- 
ble 1). Compared to open ocean and coastal stations, a 
slightly lower PER was observed within the upper 40m 
(Fig. 4e) for the CE and frontal zone. 
3.3 Bacterial abundance and activities 
Heterotrophic bacterial abundance decreased with depth and 
was highest in the upper 50m at all stations (Fig. 5a). At 
the coastal and open ocean stations, integrated (0-100 m) 
heterotrophic bacteria abundance ranged between 12.9-14.7 
and 5.4-16.9 x 10! cells m7?, respectively (Table 1). No 
significant differences in heterotrophic bacterial abundance 
were observed between the open ocean and coastal stations 
(Tukey, p>0.05). In the open ocean waters, the lowest in- 
tegrated BR and CR rates were observed at the station fur- 
thest offshore (E1), with 6.3 and 19.7 mmol Cm”? d7!, re- 
spectively (Table 1). At the other open ocean stations, in- 
tegrated BR and CR rates ranged between 148-168 and 
346-348 mmol Cm? d7!, respectively, which was higher 
than at the coastal station with BR rates of 32 and CR 
rates of 98 mmolC m7? d7!. Overall, BR and CR rates were 
higher in the open ocean stations than in the coastal ones 
with the highest rates (>1 and >2.5 umol1C L7! d7!, respec- 
tively) in the top 60 m (Figs. 5b, S4a). Integrated BP, in con- 
trast, was generally higher at the coastal stations with 5.6— 
10.8 mmolC m”? d7! compared to the open ocean ones with 
1.4-8.2 mmol C m7? d7! (Table 1). However, volumetric BP 
rates were not significantly different from the open ocean 
(Tukey, p>0.05), where BP rates were more variable. At the 
coastal stations, the highest BP rates were observed either at 
the surface (5 m) or at around — 40 m depth, while in the open 
ocean, the highest rates were constantly found in the surface 
samples (Fig. 5c). BGE was determined for the upper 50m 
and showed little variability with depth (Table 2; Fig. 5d). 
However, BGE was significantly higher (Tukey, p<0.05) at 
the coastal stations (9.6 +3.7% to 14.1 + 1.7 %) compared 
to the open ocean ones (1.7 + 0.1 % to 4.2 + 0.04 %). We es- 
timated the predominance of autotrophy or heterotrophy in 
the system by dividing the PPror rates by CR (Mourifo- 
Carballido and MceGillicuddy, 2006). Heterotrophic condi- 
Biogeosciences, 19, 51995219. 202. 
https://doi.org/10.5194/bg-19-5199-2022