3.3 Seasonal changes of TE export
The individual TE fluxes varied by almost 7 orders of magnitude (Figure
5). The highest flux was recorded for Al with a maximum of 160 µmol
m-2 d-1 and the lowest for Th with a
minimum of 3.5 x 10-2 nmol m-2d-1. Examination of the seasonal changes revealed two
qualitatively different temporal patterns. High export fluxes of P, Cd,
Ba, Mo, Cu, Ni and V were associated with one or both of the main export
events described in the previous section. For most of these elements,
the export fluxes were higher during the first than during the second
event, but more subtle differences appear. For example, the flux of Cd
export was much more pronounced during the first than the second event,
whereas for V the fluxes were almost identical during both events. For
the other elements (Y, Mn, Zr, Co, Ti, Cr, Th, Fe and Al) the highest
fluxes were measured in the first cups (#1 to #5) and the lowest in
the remaining cups (#6 to #12).
For TE fluxes, a PCA confirms the partitioning between the two main
groups mentioned in the previous section based on the qualitative
analysis of the seasonal changes (Figure 6). The two first components of
the PCA explain 98.2 % of the seasonal variation of the TE export. For
PC1, positive scores correspond to the beginning of the season (#1 to
#5) and negative scores to the remaining cups (#6 to #12). The
highest positive scores for the PC2 are typical of cups corresponding to
the two export events (#4 #5 and #9 #10). Within the group of
elements characterised by two marked peaks of export (P, Cd, Ba, Mo, Cu,
Ni and V), the PCA shows three possible subgroups where seasonal
variations of these elements are highly correlated. These consist of P,
Cd and Ba, then Mo and Cu, and finally Ni and V (Figure S2).