Ocean acidification affects iron speciation during a coastal seawater mesocosm experiment

Abstract

Abstract. Rising atmospheric CO 2 is acidifying the surface ocean, a process which is expected to greatly influence the chemistry and biology of the future ocean. Following the development of iron-replete phytoplankton blooms in a coastal mesocosm experiment at 350, 700, and 1050 µatm pCO 2 , we observed significant increases in dissolved iron concentrations, Fe(II) concentrations, and Fe(II) half-life times during and after the peak of blooms in response to CO 2 enrichment and concomitant lowering of pH, suggesting increased iron bioavailability. If applicable to the open ocean this may provide a negative feedback mechanism to the rising atmospheric CO 2 by stimulating marine primary production.

Southern Ocean phytoplankton physiology in a changing climate

“…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;.…”

“…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.…”

Rapid shifts in picoeukaryote community structure in response to ocean acidification

“…This will result in a significant reduction in the calcium carbonate saturation state, with potentially major impacts on both calcifying and non-calcifying marine organisms . The chemical speciation of many other elements, including those such as nitrogen (ammonia), phosphorus and iron that are required to support primary production, is also influenced by acidification, although the possible effects on marine ecosystems of these shifts in speciation largely remain to be assessed (Doney et al, 2009;Breitbarth et al, 2010).…”

Iron biogeochemistry across marine systems – progress from the past decade

“…We follow the structure of the workshop topics, which were: Natural Fe fertilization (Sect. 2, articles: Ardelan et al, 2010;Chever et al, 2010;Duggen et al, 2010;Ye et al, 2009); artificial Fe fertilization (3: Bucciarelli et al, 2010;Chever et al, 2010); Fe inputs into coastal and estuarine systems (4: Breitbarth et al, 2009); Colloidal iron and organic matter (5); Linking biological processes to iron chemistry (6: Breitbarth et al, 2009;Bucciarelli et al, 2010;Hassler and Schoemann, 2009;Steigenberger et al, 2010); and Iron and Climate Change (7: Breitbarth et al, 2010;Rose et al, 2009). Each section concludes with recommendations for future research.…”