Iron oxides, divalent cations, silica, and the early earth phosphorus crisis

Biosilicification Drives a Decline of Dissolved Si in the Oceans through Geologic Time

“…It should be noted that the formation of Si-rich precipitates would also impact cycling of other elements especially in the Precambrian oceans, including iron, trace metals and phosphorus (e.g., Konhauser et al, 2007;Jones et al, 2015). In addition, the rise to ecological prominence of the diatoms is a relevant landmark in the history of the Earth system with a probable increase in the strength and efficiency of the biological pump and its impact on C (Renaudie, 2016).…”

Early phosphorus redigested

“…This leads them to argue that P-limitation supported low levels of O 2 for most of Earth's history. Estimates from the shale record are based on the suggestion 4 that P concentrations prior to 800 million years ago were similar to those defined by ref 8. Upwards black arrows indicate minimum estimates; downwards black arrows represent maximum estimates.…”

“…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. 1).…”

“…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.…”

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

“…The model employs Fe(II) oxidation rates from modern photoferrotrophs under a range of reasonable mixing rates in the ocean. It is also likely that photoferrotrophs flourishing at depth could have exhausted dissolved phosphorous in upwelling waters, thus outcompeting cyanobacteria for a key nutrient, and by extension limiting their activity in overlying waters (Jones et al, 2015 A potential limitation with the approach of Kappler et al (2005) is that in many settings advection can be the dominant transport process (e.g., upwelling zones). As a simple test to assess the required thickness of a photoferrotrophic bacterial layer to oxidise both upwelling and diffusive 11).…”