The contribution of water radiolysis to marine sedimentary life

Justine F. Sauvage,Ashton Flinders,Richard W. Murray,Steven D’Hondt,Ann G. Dunlea,David C. Smith,Robert Pockalny,Arthur J. Spivack,Chloe H. Anderson

doi:10.1038/s41467-021-21218-z

Abstract

Water radiolysis continuously produces H2 and oxidized chemicals in wet sediment and rock. Radiolytic H2 has been identified as the primary electron donor (food) for microorganisms in continental aquifers kilometers below Earth’s surface. Radiolytic products may also be significant for sustaining life in subseafloor sediment and subsurface environments of other planets. However, the extent to which most subsurface ecosystems rely on radiolytic products has been poorly constrained, due to incomplete understanding of radiolytic chemical yields in natural environments. Here we show that all common marine sediment types catalyse radiolytic H2 production, amplifying yields by up to 27X relative to pure water. In electron equivalents, the global rate of radiolytic H2 production in marine sediment appears to be 1-2% of the global organic flux to the seafloor. However, most organic matter is consumed at or near the seafloor, whereas radiolytic H2 is produced at all sediment depths. Comparison of radiolytic H2 consumption rates to organic oxidation rates suggests that water radiolysis is the principal source of biologically accessible energy for microbial communities in marine sediment older than a few million years. Where water permeates similarly catalytic material on other worlds, life may also be sustained by water radiolysis.

Highlights

Water radiolysis continuously produces H2 and oxidized chemicals in wet sediment and rock
The extent to which most subsurface ecosystems rely on radiolytic products has been unclear because (i) radiolytic chemical yields in natural environments have been poorly constrained and (ii) organic matter and oxidants from the surface photosynthetic world are pervasive in many subsurface environments
Our results show that for pure water, seawater, and marine sediment slurries, H2 production increases linearly with absorbed α- and γ-ray dose

Summary

Introduction

Water radiolysis continuously produces H2 and oxidized chemicals in wet sediment and rock. Our estimates of radiolytic H2 and oxidant production are based on (i) spatial integration of a previously published model of sedimentary water radiolysis[2], (ii) our dataset of experimentally constrained radiolytic H2 yields for the principal marine sediment types, and (iii) the global distribution of sediment properties (details in “Methods”). Calculated radiolytic production rates of H2 and oxidants in the cored sediment of individual sites.

Results

Conclusion