Near-surface Heating of Young Rift Sediment Causes Mass Production and Discharge of Reactive Dissolved Organic Matter

Abstract

Ocean margin sediments have been considered as important sources of dissolved organic carbon (DOC) to the deep ocean, yet the contribution from advective settings has just started to be acknowledged. Here we present evidence showing that near-surface heating of sediment in the Guaymas Basin, a young extensional depression, causes mass production and discharge of reactive dissolved organic matter (DOM). In the sediment heated up to ~100 °C, we found unexpectedly low DOC concentrations in the pore waters, reflecting the combined effect of thermal desorption and advective fluid flow. Heating experiments suggested DOC production to be a rapid, abiotic process with the DOC concentration increasing exponentially with temperature. The high proportions of total hydrolyzable amino acids and presence of chemical species affiliated with activated hydrocarbons, carbohydrates and peptides indicate high reactivity of the DOM. Model simulation suggests that at the local scale, near-surface heating of sediment creates short and massive DOC discharge events that elevate the bottom-water DOC concentration. Because of the heterogeneous distribution of high heat flow areas, the expulsion of reactive DOM is spotty at any given time. We conclude that hydrothermal heating of young rift sediments alter deep-ocean budgets of bioavailable DOM, creating organic-rich habitats for benthic life.

Generation and Utilization of Volatile Fatty Acids and Alcohols in Hydrothermally Altered Sediments in the Guaymas Basin, Gulf of California

“…DOC concentrations generally increased with depth (Figures a, c, and e). In contrast, a decrease in DOC with increasing depth and temperature was observed at some hot sites (>60 °C; Figures b and f), and this could be indicative of inhibition of biological DOC production under elevated temperature or reduced DOC production at these sites due to previous prolonged exposure of the sediment to elevated temperature, which had resulted in increased abiotic DOC production and subsequent loss by advection (Lin et al, ).…”

“…Energy‐laden fluids are transported subsequently through the sediment column, providing organic substrates to fuel microbial activity and growth and promote microbial diversity. Near‐surface heating of sediments also facilitates production and discharge of reactive dissolved organic carbon (Lin et al, ). Guaymas Basin surficial sediments provide a rare and accessible window for investigating the impact of microbially mediated processes on carbon and other elemental (e.g., sulfur and nitrogen) cycles.…”

Dissolved organic carbon compounds in deep-sea hydrothermal vent fluids from the East Pacific Rise at 9°50′N

“…Hydrothermal fluids also contain hydrocarbons generated during thermal alteration of microbial biomass (Dittmar, 2008;Konn et al, 2011;Reeves et al, 2014). In addition to biogenic sources, dissolved organic compounds may be derived from thermal alteration of dissolved organic matter initially present in circulating seawater (Hawkes et al, 2016;Rossel et al, 2017) and abiotic processes that occur during hydrothermal circulation (Lang et al, 2010;Lin et al, 2017;McCollom and Seewald, 2007;McDermott et al, 2015a;Proskurowski et al, 2008). We posit that information on the composition of organic compounds delivered to the water column by hydrothermal fluids can help identify the source of these compounds, and the roles that they play in deep-sea carbon cycling.…”

Comparative Study of Guaymas Basin Microbiomes: Cold Seeps vs. Hydrothermal Vents Sediments

“…Based on genomecentric metagenomic, members of these taxa have been proposed as potential degraders of organic matters in marine sediments, degrading aromatic compounds (Wasmund et al, 2016), scavenging dead cells (Lloyd et al, 2013;Robbins et al, 2016;Lazar et al, 2017) or fermenting various carbohydrates (Nobu et al, 2016). These heterotrophic microbial communities identified in both cold seep and hydrothermal sediments might be supported by the high sedimentary rates and the important microbial and meiofaunal biomass (Portail et al, 2015) likely generating the important organic carbon concentrations measured in the Guaymas Basin seafloor (Lin et al, 2017). Thus, these potential organic matter degraders might represent an important proportion of the "core microbiome" of the Guaymas Basin chemosynthetic areas.…”