Abiotic synthesis of graphite in hydrothermal vents

Emily R Estes,Debora Berti,Andrew S Wozniak,George W Luther,Michael F Hochella,Nicole R Coffey

doi:10.1038/s41467-019-13216-z

Abstract

Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge in understanding the dynamics of the marine carbon cycle. In particular, the composition of aged organic carbon and what allows its persistence in the deep ocean and in sediment is unresolved. Here, we observe that both high and low temperature hydrothermal vents at the 9° 50′ N; 104° 17.5 W East Pacific Rise (EPR) vent field are a source for (sub)micron-sized graphite particles. We demonstrate that commonly applied analytical techniques for quantification of organic carbon detect graphite. These analyses thereby classify graphite as either dissolved or particulate organic carbon, depending on the particle size and filtration method, and overlook its relevance as a carbon source to the deep ocean. Settling velocity calculations indicate the potential for these (sub)micron particles to become entrained in the buoyant plume and distributed far from the vent fields. Thus, our observations provide direct evidence for hydrothermal vents acting as a source of old carbon to the deep ocean.

Highlights

Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge in understanding the dynamics of the marine carbon cycle
Deep marine organic carbon is a mixture of fresh material delivered from the surface and an aged component, the origin of which is undetermined[1,2,3,4]
The black carbon described in these previous studies is hypothesized to derive from the terrestrial combustion of biomass, additional evidence exists for a hydrothermal contribution to deep DOC and POC2,6 and to sedimentary black carbon[12]

Summary

Introduction

Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge in understanding the dynamics of the marine carbon cycle. A maximum estimated Stokes settling velocity for each particle was calculated from the longest measured dimension We identify (sub)micron-sized graphite particles emanating from five different focused and low temperature hydrothermal vent sites at the EPR 9° 50′ N vent field, providing an alternate source of old carbon to the deep ocean reservoir of DOC and POC.

Results

Conclusion