Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

3H-leucine and thymidine incorporation of North Atlantic subseafloor sediments collected on cruise KN223 on R/V Knorr in November 2014.

All samples used in this work were collected as part of the North Atlantic long-coring expedition in Oct.-Dec. 2014 (R/V Knorr, Cruise KN223); this project focuses on sediments from 4 sites (2, 3, 11, 12) exhibiting variations in the depth to which oxygen penetrates. The sediment subsamples were collected from long piston cores or shorter gravity cores. While oxygen penetrates through the full long core depth at sites 11 and 12, oxygen was consumed in the sediment column at site 3 and especially at site 2. All samples were collected anaerobically in order to perform on-board culture enrichments via the most probable number (MPN) method. Sediments were placed in sterile serum vials, capped with butyl rubber stoppers and flushed with N2 for 2 min and maintained at 4 degrees C for immediate shipboard MPN inoculation work (see MPN dataset). Parallel samples were similarly collected from these and additional core sections and maintained at 4 degrees C for later determination of microbial production rates (this dataset).

We assessed microbial production on selected core sections at sites 11 and 12 using proxies for DNA synthesis (incorporation of methyl-3H thymidine) and protein synthesis (incorporation of 4,5-3H leucine). Core material was retained at 4 degrees C under an N2 atmosphere prior to slurry preparation. Aerobic slurry was prepared 1:1 by volume with 0.2 um-filtered deep seawater and incubations began immediately thereafter. Incubations (n=4 live treatments, n=4 TCA-killed controls) of 0.5 ml slurry each were conducted in sterile microfuge tubes for each label addition. Seawater-only blanks incubated and processed along with samples exhibited near background levels of activity. 50 ul of working 3H-Thy or 3H-Leu stock was added at time zero. This equates to 3.75 uCi Leu or 4.4375 uCi Thy per sample at concentrations of appx. 114 nmol label compound per liter slurry final. Incubations were carried out at 4 degrees C in the dark.

Incubations were terminated at 18-24 hr; a time-course experiment confirmed linearity of incorporation out to at least 24 hr. Live incubations were terminated with TCA and an extraction protocol modified from Dixon & Turley (2001, Microb. Ecol. 42:549) was used to isolate the protein + DNA fraction, which was analyzed by liquid scintillation counting for 3H-Leu incorporation; the DNA fraction alone was isolated and similarly analyzed for 3H-Thy incorporation. Rates are reported as pmol leucine or thymidine incorporated per ml of sediment per day (based on mean treatment minus mean control). Errors were calculated by propagating the standard deviations of treatments and controls.

These data represent short-term rates of label incorporation at the stated levels of addition. No corrections for potential isotope dilution were attempted, given the overall low metabolic rates of the system. Rates are reported as determined; therefore, where mean controls exceeded mean treatments, negative rates are reported.

BCO-DMO Processing:
- modified parameter names to conform with BCO-DMO naming conventions;
- re-formatted date to yyyy-mm-dd;
- replaced "R/V Knorr" with "RV_Knorr" in data.

Abstract from C-DEBI:

Deep marine sediments harbor an abundance of microbial cells that, if active, are likely to exert a strong influence on element biogeochemical cycling. Despite decades of study, our understanding of the fraction of cells that are active in situ and the metabolic processes that sustain them remain under-explored. We propose an integrated set of analyses aimed at unraveling the links between geochemical heterogeneity, cellular viability and synthesis, and metabolism along a vertical depth profile in four sediment cores collected during the North Atlantic long coring expedition. These sediment columns exhibit varying levels of organic carbon and differences in the degree of oxygen penetration along the depth profile which we hypothesize exert strong influence on the extent and nature of microbial life. Most probable number assays containing nine different selective enrichment conditions were initiated using subsamples from these cores in Nov. 2014. Separate subsamples were preserved for use in measuring rates of secondary production. Multivariate modeling tools will be applied to integrate these measurements with co-registered geochemical measurements, cell counts, and molecular data provided by collaborators. This work will provide new insight into the dynamic interplay between O2 and organic carbon and microbial activity, viability, and productivity in deep marine sediments.

NOTE: This project follows the C-DEBI program Data Management Plan (PDF).

The mission of the Center for Dark Energy Biosphere Investigations (C-DEBI) is to explore life beneath the seafloor and make transformative discoveries that advance science, benefit society, and inspire people of all ages and origins.

C-DEBI provides a framework for a large, multi-disciplinary group of scientists to pursue fundamental questions about life deep in the sub-surface environment of Earth. The fundamental science questions of C-DEBI involve exploration and discovery, uncovering the processes that constrain the sub-surface biosphere below the oceans, and implications to the Earth system. What type of life exists in this deep biosphere, how much, and how is it distributed and dispersed? What are the physical-chemical conditions that promote or limit life? What are the important oxidation-reduction processes and are they unique or important to humankind? How does this biosphere influence global energy and material cycles, particularly the carbon cycle? Finally, can we discern how such life evolved in geological settings beneath the ocean floor, and how this might relate to ideas about the origin of life on our planet?

C-DEBI's scientific goals are pursued with a combination of approaches:
(1) coordinate, integrate, support, and extend the research associated with four major programs—Juan de Fuca Ridge flank (JdF), South Pacific Gyre (SPG), North Pond (NP), and Dorado Outcrop (DO)—and other field sites;
(2) make substantial investments of resources to support field, laboratory, analytical, and modeling studies of the deep subseafloor ecosystems;
(3) facilitate and encourage synthesis and thematic understanding of submarine microbiological processes, through funding of scientific and technical activities, coordination and hosting of meetings and workshops, and support of (mostly junior) researchers and graduate students; and
(4) entrain, educate, inspire, and mentor an interdisciplinary community of researchers and educators, with an emphasis on undergraduate and graduate students and early-career scientists.

Note: Katrina Edwards was a former PI of C-DEBI; James Cowen is a former co-PI.

Data Management:
C-DEBI is committed to ensuring all the data generated are publically available and deposited in a data repository for long-term storage as stated in their Data Management Plan (PDF) and in compliance with the NSF Ocean Sciences Sample and Data Policy. The data types and products resulting from C-DEBI-supported research include a wide variety of geophysical, geological, geochemical, and biological information, in addition to education and outreach materials, technical documents, and samples. All data and information generated by C-DEBI-supported research projects are required to be made publically available either following publication of research results or within two (2) years of data generation.

To ensure preservation and dissemination of the diverse data-types generated, C-DEBI researchers are working with BCO-DMO Data Managers make data publicly available online. The partnership with BCO-DMO helps ensure that the C-DEBI data are discoverable and available for reuse. Some C-DEBI data is better served by specialized repositories (NCBI's GenBank for sequence data, for example) and, in those cases, BCO-DMO provides dataset documentation (metadata) that includes links to those external repositories.