8
Figure 5.11: Relationships between pZn, pMn, pFe, pCu, pCo and BSi export fluxes at Eq. In the graph
showing pZn and BSi exports, the green dashed line represents the averaged Zn/Si ratio measured in
diatom phytoplankton cells (i.e. 2 × 10
-4
mol.mol
-1
; Twining et al., 2004). .......................................... 217
Figure 5.12: Relationship between pFe, pCo, pMn, pZn and CaCO
3
export fluxes at Eq. ................ 220
Chapter 6:
Figure 6.1: Surface Chlorophyll-a concentrations (mg.m
-3
) at the beginning (19/10/2011) and at the end
(17/11/2011) of the KEOPS2 cruise. Filled circles represent the location of stations. The station F-L,
represented by a dotted circle, was sampled between these two dates (06/11/2011). The thick dotted
line represents the approximate location of the Polar Front while the thick black arrows indicating the
Antarctic Circumpolar Current (ACC) and the Fawn Trough Current (FTC; adapted from Park et al.,
2008). ................................................................................................................................................... 234
Figure 6.2: Vertical profiles of BSi, PN (µmol.L
-1
) and PFe (nmol.L
-1
) concentrations for the different
stations. ............................................................................................................................................... 244
Figure 6.3: Vertical profiles of elemental ratios of a) BSi:
234
Th, b) PN:
234
Th, c) PFe:
234
Th. Large (> 53
µm) particles are represented by filled symbols while small particles (1-53 µm) are represented by open
symbols. PFe concentrations for small particles are discussed in van der Merwe et al. (2015), PN
concentrations for small particles can be found in Table S2. Sediment trap ratios (from Laurenceau et
al., 2015; Bowie et al., 2015) at 200 m are represented by thick black surrounded symbols. Bottom
depths are indicated by the zebra lines and Eq depths are indicated by the light green lines. .......... 246
Figure 6.4: Elemental ratios of PN, BSi and PFe to
234
Th for the >53 µm size fraction calculated at the
Eq depth using different interpolation/averaging methods being: linear interpolation; average around Eq;
power interpolation; depth-weighted average. The ratios obtained from sediment traps are also indicated
with the BSi:
234
Th and PN:
234
Th ratios from Laurenceau et al. (2015) and the PFe:
234
Th ratios from Bowie
et al. (2015). ........................................................................................................................................ 249
Figure 6.5: Range of calculated PN, BSi (mmol.m
-
².d
-1
) and PFe (µmol.m
-
².d
-1
) export fluxes at the Eq
depth from in-situ pumps (box plots) and export fluxes obtained by sediment traps at 200 m (circles;
Laurenceau et al., 2015 and Bowie et al., 2015) during KEOPS2. The heights of the boxes correspond
to the lowest and the highest values determined by the 4 different interpolation/averaging methods. The
plain line inside the box represents the median value. ....................................................................... 252
Figure 6.6: Vertical profiles of BSi:POC, BSi:PN, BSi:PFe and POC:PN molar ratios in large particles
(> 53 µm) collected in the Kerguelen area. Close to the surface, green surrounded symbols represent
Si:C ratios specific to diatoms as reported by Lasbleiz (2014). These ratios were obtained from the
carbon biomass and the BSi concentration. The latter may be overestimated by taking into
account the
living and dead cells. At 200 m, ratios measured in sediment traps by Laurenceau et al. (2015) and
Bowie et al. (2015) are represented by the black surrounded symbols. The dashed line represents the
typical value of the C:N ratio (6.6) reported by Redfield et al. (1963). ................................................ 260
Figure 6.7: POC versus PN fluxes (mmol.m
-2
.d
-1
) for all stations. ...................................................... 262
Figure 6.8: Schematic of the main variations of export fluxes determined in this study, in line with other
parameters studied during KEOPS2 cruise, including ThE
PN
, ThE
BSi
, estimated POC (grey circles), PN
(white squares), BSi (grey stars; mmol.m
-2
.d
-1
), and PFe (orange triangles; µmol.m
-2
.d
-1
) export fluxes.
PN export fluxes are multiplied by 6.6 to examine directly the variations of the C:N Redfield ratio.
a
primary production data (mmol C.m
-2
.d
-1
) from Cavagna et al. (2015).
b
dFe concentrations (nmol.L
-1
)
from Quéroué et al. (2015).
c
N uptake data (mmol N.m
-2
.d
-1
) from Cavagna et al. (2015).
d
Si uptake
data (mmol Si.m
-2
.d
-1
) from Closset et al. (2014).
e
total mesozooplankton biomass data (g C.m
-2
) from
Carlotti et al. (2015).
f
bacterial respiration rates (µmol C.L
-1
.d
-1
) from Christaki et al. (2014).
g
taxonomic
data from Lasbleiz et al. (2016).
h
POC export fluxes (mmol.m
-2
.d
-1
) from Planchon et al. (2015). .... 264