Soda lake phosphorus fluxes controlled by biological uptake imply abundant phosphate in plausible origin-of-life environments

Phosphate is crucial for the origin of life but typical environmental concentrations are too low for prebiotic synthesis of essential biomolecules like nucleic acids. However, evaporative, sodium-carbonate rich “soda” lakes can accumulate extreme phosphate levels sufficient for prebiotic synthesis. In modern soda lakes, this presumably requires small biological and inorganic (apatite mineral formation) sinks, but the relative importance of these sinks is unclear because studies on phosphorus fluxes in soda lakes are lacking. Here, we quantified phosphorus source and sink fluxes in the extremely phosphate-rich Last Chance Lake (LCL), Canada, and neighboring, moderately phosphate-rich, Goodenough Lake (GL). Within the total phosphorus (0.1 wt%) in LCL sediments, sequential extraction showed 61 % detrital apatite, ∼19 % dissolved phosphate, ∼11 % organic-bound phosphorus (P org ), 6 % carbonate-bound P, and ∼2 % authigenic apatite. Combining these measurements with hydrological fluxes, we demonstrate that evapo-concentration of dilute inflow sufficed to accumulate tens of millimolar phosphate on a millennial timescale due to small sinks. Low apatite formation rates directly confirmed a previously hypothesized mechanism allowing extreme phosphate solubility at high carbonate concentrations. Yet, it is its 18 × lower P org formation rates that mainly distinguish LCL from the less phosphate-rich, more biologically active GL. Because low productivity is key, evaporative soda lakes on prebiotic Earth should have commonly attained millimolar phosphate levels. Consequently, we identify soda lakes as the only known natural environments with sufficiently high phosphate levels for critical phosphorylation and catalysis in prebiotic synthesis.