The T/B ratio decreases in-shore in Kunene and Lüderitz, indicating that
coastal locations display more non-thermal influences (i.e. biological
imprints) on p CO2 gradients than offshore
locations. In Walvis Bay however, the ratio exhibits a slight decrease
seaward but remains very low. The T/B = 1 indicates an equilibrium
between thermal and non-thermal processes (Takahashi et al., 2002).
Therefore, our results indicate the strong dominant influence of
non-thermal effects in the area (biological production and consumption
of p CO2, and mixing processes), which controls
the variation in p CO2 gradients.
During our seasonal campaigns, we also observed no significant
relationship between CT and salinity. This lack of
correlation suggests that other factors than simple dilution are likely
governing the fluctuations of CT (Cai, 2003; Chou et
al., 2013). Our results show a strong positive correlation between
normalized AT (AT35) and normalized
CT (CT35) within the hypoxic deep
waters, characterized by oxygen ≤ 20.00 µmol kg-1,
indicating a significant production of AT and
CT in these waters. In these hypoxic-anoxic deep waters,
the linear regression model produced a
AT/CT ratio slightly > 1
(Figure 7), implying the influence of CaCO3 dissolution
(given that CaCO3 dissolution results in a
AT/CT ratio of 2:1) (Zeebe and
Wolf-Gladrow, 2001). Moreover, anaerobic processes of organic matter
degradation likely occur, as the AT/CTratio produced by sulfate reduction (0.9) and denitrification (0.8)
closely align with the values observed in these hypoxic-anoxic waters
(Figure 7). On the contrary, the well-oxygenated waters represented the
lowest CT and intermediate AT,
reflecting CT consumption by primary production and
CO2 outgassing in the surface waters over the seasons
(e.g. Zeebe and Wolf-Gladrow, 2001; Chou, et al., 2013; Cai et al.,
2020). The data are predominantly situated on the left side when
CT levels are low, however, there is a minor adjustment
in AT accompanying this low CT range,
indicating that the processes of CO2 uptake and
outgassing have only a limited impact on AT (Figure 7).