Abstract
The study of active microbial populations in deep, energy-limited marine sediments has extended our knowledge of the limits of life on Earth. Typically, microbial activity in the deep biosphere is calculated by transport-reaction modelling of pore water solutes or from experimental measurements involving radiotracers. Here we modelled microbial activity from the degree of D:L-aspartic acid racemization in microbial necromass (remains of dead microbial biomass) in sediments up to ten million years old. This recently developed approach (D:L-amino acid modelling) does not require incubation experiments and is highly sensitive in stable, low-activity environments. We applied for the first time newly established constraints on several important input parameters of the D:L-amino acid model, such as a higher aspartic acid racemization rate constant and a lower cell-specific carbon content of sub-seafloor microorganisms. Our model results show that the pool of necromass amino acids is turned over by microbial activity every few thousand years, while the turnover times of vegetative cells are in the order of years to decades. Notably, microbial turnover times in million-year-old sediment from the Peru Margin are up to 100-fold shorter than previous estimates, highlighting the influence of microbial activities on element cycling over geologic time scales.
Highlights
Marine sediments harbour a microbial ecosystem that vertically extends into the seafloor for more than two kilometres in certain regions of the World Ocean[1]
Together with data on the total nitrogen (TN) concentrations in the sediments, the data on the amino acid concentrations were used to evaluate the quality of marine sedimentary organic matter by the established diagenetic indicator %TAAN, which is the fraction of TN present as amino acid-nitrogen (THAA-N)[9, 10]
The relative abundance of Bacteria in the cores from the Labrador Sea (SA13-ST3-20G), the Godthåbsfjord (SA13-ST6-40G) and the Iceland Basin (DA12-11/2-GC01) were between 40% and 80%
Summary
Marine sediments harbour a microbial ecosystem that vertically extends into the seafloor for more than two kilometres in certain regions of the World Ocean[1]. It has been estimated that this ecosystem contains a total of 2.9–5.4 × 1029 vegetative cells[2, 3], the biomass of which is about equal to all microbial biomass in the ocean water[2,3,4] It appears that an equal amount of (dormant) bacterial endospores resides in the seabed[5, 6]. The microorganisms in this deep, buried biosphere feed on organic compounds deposited from the surface photosynthetic world. Together with data on the total nitrogen (TN) concentrations in the sediments, the data on the amino acid concentrations were used to evaluate the quality of marine sedimentary organic matter by the established diagenetic indicator %TAAN, which is the fraction of TN present as amino acid-nitrogen (THAA-N)[9, 10]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
