Influence of ocean acidification on the complexation of iron and copper by organic ligands in estuarine waters

Southern Ocean phytoplankton physiology in a changing climate

“…However, to date, studies using diatom cultures and natural assemblages from the SO have shown that Fe bioavailability was decreased under the OA scenario (Shi et al, 2010;Hoppe et al, 2013;. This indicates that, while changes to physico-chemical conditions in the future are reasonably well characterised for inorganic Fe species, it is not the case for in-situ organic species (Gledhill et al, 2015). Given that more than 99% of Fe is associated with loosely characterised organic ligands, many uncertainties remain with respect to understanding changes to Fe bioavailability based on its chemistry.…”

“…First, changes in Fe input rates in the SO could be related to changes in important current sources, including precipitation, atmospheric dust deposition and sea ice melting (e.g., Lizotte, 2001;Lannuzel et al, 2008;Moore and Braucher, 2008;Boyd and Ellwood, 2010). Secondly, warmer temperatures and ocean acidification (OA) will directly affect Fe chemistry, namely its solubility and strength of complexation with organic ligands (Millero, 2009;Breitbarth et al, 2010;Hassler et al, 2013;Gledhill et al, 2015). In artificial seawater (pH 8.1) Fe solubility decreased from 0.5 nM at 5 • C to 0.03 nM at 25 • C (Liu and Millero, 1999).…”

“…As oceans become more acidic, both the hydroxide (OH − ) and carbonate (CO 3 2− ) ions that form strong complexes with Fe, are expected to decrease, dropping by up to 80% by the end of the millennium (Millero, 2009). Therefore, a decrease in pH would contribute not only to an increase in the concentration of dissolved inorganic Fe, Fe (II) concentrations, and Fe (II) half-life times, but also to a weakening of Fe binding with ligands (Millero, 2009;Breitbarth et al, 2010;Gledhill et al, 2015), all of which should result in increased Fe bioavailability. However, to date, studies using diatom cultures and natural assemblages from the SO have shown that Fe bioavailability was decreased under the OA scenario (Shi et al, 2010;Hoppe et al, 2013;.…”

“…Furthermore, both OA and temperature can affect biological growth and generation of organic ligands, potentially favouring growth of specific phytoplankton species and inducing a shift in the community structure unrelated to Fe (e.g., Tortell et al, 2008a;Trimborn et al, 2014). As different biological communities excrete different iron-binding ligands (Trick and Wilhelm, 1995;Maldonado et al, 2002;Hassler et al, 2015;Norman et al, 2015), a shift in community structure or changes in Fe-stress could have a greater impact on Fe chemistry and bioavailability than those associated with changes in temperature and pH (Gledhill et al, 2015). However, the effect that the modulation of the excretion of organic ligands associated with basal biological activity or the change in the nature of organic ligands associated with a shift in community will have on Fe chemistry and bioavailability is yet to be investigated.…”

“…In the second scenario (Fig. 4b), climate-induced physical and chemical changes to the SO increase the bioavailability of Fe due to warming (Byrne et al, 1998) and lowered pH (Millero, 2009;Breitbarth et al, 2010;Gledhill et al, 2015) and favour the increase in the prevalence of large diatoms. In addition, the intensification of westerly winds, due to the increasing positive SAM index (Fig.…”