Aerobic iron and manganese cycling in a redox-stratified Mesoarchean epicontinental sea

Abstract

This is a repository copy of Aerobic iron and manganese cycling in a redox-stratified Mesoarchean epicontinental sea.

Evidence for local carbon‐cycle perturbations superimposed on the Toarcian carbon isotope excursion

“…Assuming that the δ 13 C values of Phanerozoic [DIC] sw is near to zero (Shields & Veizer, 2002 and references therein), [DIC] org (equals to ([DIC] total × δ 13 C total )/δ 13 C org ) varies between 13% and 28% [DIC] total (average of 20%) (Table 2), while [DIC] sw has an average of 80%. This estimate can be translated by the δ 13 C carb versus δ 18 O cross‐plots (Figure 10b; Konhauser et al, 2017; Ossa Ossa et al, 2018). The samples of the interval 2a have δ 13 C carb values between −8.8 and −4.2‰ and almost all of them plot above the line of C org : C sw = 1:1 (Figure 10b).…”

“…Heimann et al, 2010;Konhauser et al, 2017 (Table 2), while [DIC] sw has an average of 80%. This estimate can be translated by the δ 13 C carb versus δ 18 O cross-plots ( Figure 10b; Konhauser et al, 2017;Ossa Ossa et al, 2018). The samples of the interval 2a have δ 13 C carb values between −8.8 and −4.2‰ and almost all of them plot above the line of C org : C sw = 1:1 (Figure 10b).…”

“…This implies that carbon components of these carbonates are contributed by ~80% of DIC and only ~20% of remineralized organic carbon (Figure 10b). The remineralization of organic matter occurs through anaerobic or microaerophilic microbial processes that require electron acceptors (e.g., Heimann et al, 2010;Konhauser et al, 2017 and references therein), which here are sulfate and possibly Mn-oxyhydroxides (see Section 5.2). These processes produce carbonates with lighter δ 13 C carb values compared to the ambient DIC composition.…”

“…(a) The interval 2a (black shales) and 2b (Unterer Stein and black shales) show strong correlations between δ 13 C carb and Δ 13 C. (b) An model showing the carbonate carbon contribution between organic matter oxidation (C org ) and seawater inorganic carbon (C sw ) (cf. Heimann et al, 2010;Konhauser et al, 2017). The isotope composition of early Jurassic seawater calcites during Toarcian OAE were estimated from the belemnites (δ 13 C bel : ~0 to +2‰ and δ 18 O bel : ~−6 to 0‰: Ullmann, Thibault, Ruhl, Hesselbo, & Korte, 2014) and platform limestone (δ 13 C limestone : ~+1 to +2‰ and δ 18 O limestone : ~−8 to −5‰; Han, Hu, Kemp, & Li, 2018) (a)…”

Microbial helpers allow cyanobacteria to thrive in ferruginous waters

“…At around 2.3 Ga, the Great Oxidation Event (GOE) resulted in the initial oxygenation of the atmosphere and surficial biosphere, which ultimately led to the modern dominance of aerobic organisms on Earth’s surface (Bar-On et al, 2018; Luo et al, 2016). Although biological O 2 production was a prerequisite for the GOE (Haqq-Misra et al, 2011; Holland, 2002), oxygenic photosynthesis may have emerged in cyanobacteria hundreds of millions of years prior to the initial accumulation of O 2 in Earth’s atmosphere (Cardona et al, 2019; Lalonde and Konhauser, 2015; Ossa Ossa et al, 2018; Planavsky et al, 2014). The delay between the emergence of cyanobacterial O 2 production and O 2 accumulation in the atmosphere may have been modulated by geophysical drivers (Catling et al, 2001; Holland, 2009; Lee et al, 2016), but may also reflect the time required for metabolic innovations to appear in early cyanobacteria or for the emergence of ecological linkages with other microbes facilitating the success of cyanobacteria (Blank and Sanchez-Baracaldo, 2010; Johnston et al, 2009; Lyons et al, 2014; Ozaki et al, 2019).…”