Phosphate availability and implications for life on ocean worlds

Abstract

Several moons in the outer solar system host liquid water oceans. A key next step in assessing the habitability of these ocean worlds is to determine whether life’s elemental and energy requirements are also met. Phosphorus is required by all known life and is often limited to biological productivity in Earth’s oceans. This raises the possibility that its availability may limit the abundance or productivity of Earth-like life on ocean worlds. To address this potential problem, here we calculate the equilibrium dissolved phosphate concentrations associated with the reaction of water and rocks—a key driver of ocean chemical evolution—across a broad range of compositional inputs and reaction conditions. Equilibrium dissolved phosphate concentrations range from 10−11 to 10−1 mol/kg across the full range of carbonaceous chondrite compositions and reaction conditions considered, but are generally > 10−5 mol/kg for most plausible scenarios. Relative to the phosphate requirements and uptake kinetics of microorganisms in Earth’s oceans, such concentrations would be sufficient to support initially rapid cell growth and construction of global ocean cell populations larger than those observed in Earth’s deep oceans.

Quantifying Uncertainty in Sustainable Biomass and Production of Biotic Carbon in Enceladus' Notional Methanogenic Biosphere

“…Critical nutrients such as iron and sulfur have not been directly detected without ambiguity on Enceladus, but their presence is expected (Cockell et al., 2021; Glein & Waite, 2020; Hao et al., 2022; Magee & Waite, 2017; Ray et al., 2021; Roche et al., 2023; Waite et al., 2017). Phosphorus was recently detected from Cassini E ring measurements (Postberg et al., 2023), and recent geochemical modeling analyses predict that it is unlikely to be a limiting nutrient (Hao et al., 2022; Randolph‐Flagg et al., 2023). The effectiveness of microbial models to predict the cell‐specific limiting effects of individual nutrients requires rigorous empirical study and key parameters are often unavailable (Higgins & Cockell, 2020).…”

“…How these factors can be quantitatively incorporated into habitability and biomass estimates remains an open question. For nutrients, one could generate turnover distributions similar to those presented here to estimate the flux required of key nutrients and heavy metals (e.g., CHNOPS + TM; Cockell et al., 2021) to support the biosphere, or ideally model their production directly and incorporate those fluxes (e.g., for phosphorus: Hao et al., 2022; Randolph‐Flagg et al., 2023). For toxicity and spatial factors, laboratory experiments could help constrain half‐saturation constants for methanogenic growth in Enceladus‐like conditions.…”

Differential Adsorption of Dissolved Organic Matter and Phosphorus on Clay Mineral in Water-Sediment System

“…Phosphates (P) and dissolved organic matter (DOM) are fundamental elements in lake ecosystems, playing crucial roles in nutrient cycling and carbon sequestration. − P, a limiting nutrient in various freshwater ecosystems, significantly influences primary production and the timing of algal blooms . Conversely, DOM serves as a source of organic carbon (OC) and energy for microorganisms, impacting aquatic food web dynamics .…”