Evaluation of phosphate-uptake mechanisms by Fe(III) (oxyhydr)oxides in Early Proterozoic oceanic conditions

Abstract

Environmental contextReconstructing the Precambrian oceanic P cycle, in conjunction with the As cycle, is critical for understanding the rise of atmospheric O2 in Earth’s history. Bioavailable phosphorus (P) has been found to regulate photosynthetic activity, whereas dissolved arsenic (As) maxima correlate with photosynthetic minima. New data on empirical adsorption and coprecipitation models with Fe(III) (oxyhydr)oxides suggest coprecipitation is a more efficient method of P sorption than is adsorption in Precambrian surface ocean conditions. AbstractBanded iron formations (BIF) are proxies of global dissolved inorganic phosphate (DIP) content in Precambrian marine waters. Estimates of Precambrian DIP rely on constraining the mechanisms by which Fe(III) (oxyhydr)oxides scavenge DIP in NaCl solutions mimicking elevated Precambrian marine Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are (1) surface attachment on pre-formed Fe(III) (oxyhydr)oxides (adsorption), and (2) incorporation of P into actively growing Fe(III) (oxyhydr)oxides (coprecipitation) during the oxidation of Fe(II) to Fe(III) (oxyhydr)oxides in the presence of DIP. It has been suggested that elevated Si concentrations, such as those suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III) (oxyhydr)oxides; however, recent coprecipitation experiments show that DIP is scavenged by Fe(III) (oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In the present study, we show that the DIP uptake onto Fe(III) (oxyhydr)oxides by adsorption is less than 5 % of DIP uptake by coprecipitation. Differences in surface attachment and the possibility of structural capture within the Fe(III) (oxyhydr)oxides are inferred from the robust influence Si has on DIP binding during adsorption, meanwhile the influence of Si on DIP binding is inhibited during coprecipitation when As(III) and As(V) are present. In the Early Proterozoic open oceans, Fe(III) (oxyhydr)oxides precipitated when deep anoxic Fe(II)-rich waters rose and mixed with the first permanently oxygenated ocean surface waters. Our data imply that, DIP was removed from surface waters through coprecipitation with those Fe(III) (oxyhydr)oxides, rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III) (oxyhydr)oxides, and by the partial release of DIP into the anoxic bottom waters and buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters, both of which would have most likely decreased the productivity of cyanobacteria and O2 production.

Arsenic and high affinity phosphate uptake gene distribution in shallow submarine hydrothermal sediments

“…There is therefore a general consensus that where Fe(III)(oxyhydr)oxides form, they coprecipitate As in its +3 and +5 oxidation states (Cullen and Reimer 1989; Smedley and Kinniburgh 2002; Henke et al 2009; Kilias et al 2013; Chi Fru et al 2015a; Hemmingsson et al 2018). The increase in Fe(III)(oxyhydr)oxides precipitation from the white-capped hydrothermal center to the bordering sand-capped sediment, counterbalanced by a drop in sulfide production (Fig.…”

“…Crucially, most shallow submarine hydrothermal vent fluids are generally depleted in P, implying that unlike As, hydrothermal fluids are not a major P source but rather a strong seawater P sink (Wheat et al 1996; Edmonds and German 2004; Poulton and Canfield 2006; Hawkes et al 2014). Indeed, significant variation in As and P concentrations through Earth’s geological history have been linked to changing levels of submarine hydrothermal influence, Fe(III)(oxyhydr)oxide precipitation and sulfide content (Poulton and Canfield 2011; Chi Fru et al 2015a; Reinhard et al 2017; Chi Fru et al 2016a; Hemmingsson et al 2018). Importantly, shallow submarine hydrothermal activity in the modern oceans are suggested to account for up to 57% of global hydrothermal P removal from the ocean via Fe(III)(oxyhydr)oxide precipitation (Hawkes et al 2014).…”

“…Fe(III)(oxyhydr)oxides on their part are a well described As sink, resulting in their widespread application in the remediation of As-impacted waters (Cullen and Reimer 1989 ; Smedley and Kinniburgh 2002 ; Dixit and Hering 2003 ; Henke et al 2009 ). There is therefore a general consensus that where Fe(III)(oxyhydr)oxides form, they coprecipitate As in its +3 and +5 oxidation states (Cullen and Reimer 1989 ; Smedley and Kinniburgh 2002 ; Henke et al 2009 ; Kilias et al 2013 ; Chi Fru et al 2015a ; Hemmingsson et al 2018 ). The increase in Fe(III)(oxyhydr)oxides precipitation from the white-capped hydrothermal center to the bordering sand-capped sediment, counterbalanced by a drop in sulfide production (Fig.…”

The rise of oxygen-driven arsenic cycling at ca. 2.48 Ga

“…As 5+ As 3+ would have led to a simultaneous buildup of As(V) and depletion of P in seawater that would have negatively impacted marine primary productivity (Chi Fru et al, 2016b;Hemmingsson et al, 2018). The rise in As-S and As(V) appears some 30 m.y.…”

Foreword to the research front on ‘Biogeochemical Cycles across Spatial and Temporal Scales

“…Ling et al explore the importance of microbes in iron and sulfur cycling in coastal acid sulfate soils, [1] while Hemmingsson et al investigate the role of iron(oxyhydr) oxides in scavenging dissolved inorganic phosphate from oceanic waters under changing physiochemical conditions and elemental composition. [2] Such information is essential for understanding ocean productivity and atmospheric gas composition.…”