Carbonaceous nanoparticles in Zibo hot springs: Implications for the cycling of carbon and associated elements

Carbon (C) is major element of most hot springs, yet knowledge on carbonaceous compounds in hot springs and their role in the cycle of elements are limited. Here we analyzed carbonaceous compounds in Zibo hot springs, China, by electron microscopy and chemical analysis. Results display spherical and irregular C-bearing nanoparticles from 50 to 150 nm. Nanoparticles typically contain, in wt%, 40.4–77.6 C, 8.12–15.9 N, 4.27–13.8 O, 0.12–0.13 Mg, 1.47–2.67 Si, 0.09–0.16 S, 0.04–0.20 Cl, and 0.63–34.7 Fe. These findings reveal the occurrence of C nanoparticles in hot springs, accompagnied by several other elements. The biophilic elements N and Fe and biomimetic morphology of nanoparticles suggest a biological origin. We discuss implications for carbon cycling and for the possible use of C-bearing nanoparticles to prospect geothermal resources in the deep Earth.