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.