Ocean productivity before about 1.9 Gyr ago limited by phosphorus adsorption onto iron oxides

Abstract

After the evolution of oxygen-producing cyanobacteria at some time before 2.7 billion years ago, oxygen production on Earth is thought to have depended on the availability of nutrients in the oceans, such as phosphorus (in the form of orthophosphate). In the modern oceans, a significant removal pathway for phosphorus occurs by way of its adsorption onto iron oxide deposits. Such deposits were thought to be more abundant in the past when, under low sulphate conditions, the formation of large amounts of iron oxides resulted in the deposition of banded iron formations. Under these circumstances, phosphorus removal by iron oxide adsorption could have been enhanced. Here we analyse the phosphorus and iron content of banded iron formations to show that ocean orthophosphate concentrations from 3.2 to 1.9 billion years ago (during the Archaean and early Proterozoic eras) were probably only approximately 10-25% of present-day concentrations. We suggest therefore that low phosphorus availability should have significantly reduced rates of photosynthesis and carbon burial, thereby reducing the long-term oxygen production on the early Earth--as previously speculated--and contributing to the low concentrations of atmospheric oxygen during the late Archaean and early Proterozoic.

Early anaerobic metabolisms

“…10 13 mol yr K1 of ferric iron. Analysis of Archaean BIFs shows Fe 3C : Fe 2C ratios of 0.4-0.6 (see summary in Bjerrum & Canfield 2002). If we assume that these ratios apply to early-Earth sedimentary iron in general, then we need an input of around 2.2!10 13 mol yr K1 of reactive iron, i.e.…”

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…Iron formations are among the most widely used lithologies to investigate the composition of the ancient oceans because their precursor minerals, such as Fe(III)-oxyhydroxides, are likely to retain the chemical signature of seawater (e.g., Bau and Dulski, 1996;Jacobsen and Pimental-Klose, 1988b;Bjerrum and Canfield, 2002;Bolhar et al, 2004;Robbins et al, 2015Robbins et al, , 2016 However, at present, there is no conclusive evidence in the Transvaal IF for either the primary oxidative mechanism for episodic Mn sequestration (i.e., aerobic versus photoferrotrophic), nor for the relative role of Mn(II) incorporation into carbonates directly as Mn(II) from porefluid or indirectly through diagenetic bacterial reduction of Mn(IV) oxyhydroxides.…”

“…Based on the low P/Fe ratios in Archaean and Palaeoproterozoic IFs, it was proposed that seawater at that time contained limited marine phosphorous. This, in turn, would have reduced levels of photosynthesis and carbon burial, thereby inhibiting long-term oxygen production on the early Earth (Bjerrum and Canfield, 2002). This model was based on partitioning coefficients (K D ) derived for P to Fe(III) oxyhydroxides associated with modern hydrothermal plumes.…”

Early phosphorus redigested

“…e-mail: s.poulton@leeds.ac.uk 6,7,8 . Reinhard and colleagues 4 compile P concentrations from shales, and identify a 4-fold increase in P concentrations around 800 million years ago.…”

“…Reconstructing P concentrations in the ancient oceans is, however, notoriously difficult. Previously the approach has been to measure the P content of iron-rich chemical sediments such as banded iron formations 6,7 , which are thought to reflect dissolved concentrations in the ocean at their time of formation. This has led to wildly variable results [6][7][8] , dependent on the precise way in which dissolved phosphate concentrations are back-calculated from total P contents in the rocks (Fig.…”