Fig. 4: Potential role of different humic materials and carbohydrates in the in situ Fe biogeochemistry.
From: Marine biogenic humic substances control iron biogeochemistry across the Southern Ocean
a Iron-binding ligands (Fe-L) calculated from electroactive humic substances (eHS) assuming that eHS behave as Suwannee river humics (HA), fulvics (FA), exopolymeric substances (EPS) either as in situ EPS (EPSin), EPS from bacteria (EPSbact), EPS from phytoplankton (EPSphyto) or hydrolysable carbohydrates (Carb). b In situ complexing capacity for these different humics is used to assess their potential role in Fe biogeochemistry. The complexing capacity was calculated using the measured excess ligands and the iron-binding-conditional stability constants for HA, FA, EPS and Carb (see “Methods” section). Data were compared to the measured in situ Fe-L (a) and in situ complexing capacity (b). The red regions coincide with the bulk of the in situ observations and aid in visualising the potential role of the different humics considered, with humics ≥ than in situ Fe-L potentially strongly contributing to Fe-L and controlling Fe biogeochemistry. Data are represented as box plots with mean and 5th and 95th percentiles. Standard deviations are shown as error bars.
