3.1 Physical conditions at the depth of the sediment trap
The average depth of the sediment trap was 293 ± 2 m (n=3152) with a few
short and episodic deepening events below 300 m (Fig. 2A). The mean
inclination angle of the sediment trap was 0.8° ± 1° (Fig. 2B).
Inclination angles above 2° were rare and associated with deepening
events of the trap and current speeds exceeding 0.2 m
s-1. The mean current speed was 0.13 ± 0.07 m
s-1. The short-term variability of current speed and
direction (Fig. 2C and 2D) was driven by tide (see Rembauville et al.
2015a) for a detailed study at the same site and depth) and a window of
26 h is adequate for filtering this short-term variability.
3.2 Seasonal changes of mass flux and biological export .
The seasonal variations of export fluxes were determined for particle
mass, total POC and PON, for CaCO3 and BSi. POC was
further partitioned between different biological carrier phases that are
total diatoms (POCdiat), separated into diatom spores
(POCspore) and diatom vegetative cells
(POCveg), and fecal pellets (POCfp)(Fig.
3). Seasonal variations of particle mass, POC, POCdiat,
and BSi fluxes are characterised by two peaks of export. The first
export event occurred between 12 Nov 2016 and 15 Dec 2016 and was
recorded in cups #3 to #5. A second export event occurred between 17
Jan 2017 and 08 Feb 2017 and was recorded in cups #9 and #10. The
export of POCspore took place largely during the first
event, while POCveg and CaCO3 exports
were mainly observed during the second event. High export fluxes of
POCfp were also observed during these two main events
(cups #4, #5 and #9). On a seasonal basis, the POC export was largely
dominated by fecal pellets (89 %) while the relative contribution of
diatoms (vegetative cells and spores) to total POC never exceeded 11%.
To better understand the seasonal variability of the export viadifferent biological carrier phases we used principal component analysis
(PCA) (Fig. 4). The first two principal components (PC) explained
respectively 72.1 % and 20.8 % of the total variance. The first PC
separated the cups in two categories. Positive values of PC1 correspond
to cups with material collected during both major export events (#3,
#4, #5 and #9, #10), and negative values of PC1 were related to the
other cups. The highly correlated variables (mass, BSi, POC, PON,
POCfp, POCdiat and
POCspore) (Figure S1) mainly contribute to PC1. The
second component (PC2) separated mainly the first (negative values, #3,
#4, #5) from the second export event (positive values, #9, #10). The
variables contributing mainly to PC2 are POCsporeassociated with the first export event and POCveg and
CaCO3 associated with the second export event.