Table of Contents

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

Solid samples were obtained from the 2018 Return to Lost City and four previous expeditions in 2015, 2005, 2003, and 2000 (Kelley et al., 2001; Kelley et al., 2005; Früh-Green et al., 2018). In all years except 2015, chimney and local rock materials were gathered as grab samples by the manipulators of either the ROV or Human Occupied Vehicle (HOV) Alvin and stowed in rock boxes. In 2015, rock samples were recovered with seabed rock drills as part of International Ocean Discovery Program (IODP) Expedition 357, which drilled a series of shallow boreholes across the Atlantis Massif (Früh-Green et al., 2018). In 2015 and 2018, samples were wrapped in Teflon sheeting and stored at -20°C. In previous years, samples were dried and stored at room temperature. 

The solid rock samples were analyzed for uranium (Ur) and thorium (Thr) concentrations by a Thermo Element 2 inductively coupled plasma mass spectrometer (ICP-MS). Approximately 40 mg of sample and approximately 80 mg of an Sm-Nd (145Nd) spike were weighed into a Teflon vial. The samples were digested for four days in a 4 mL dissolution mixture (3:1 concentrated HF: concentrated HNO3) in a closed beaker at 100°C. The digest was dried, 1 mL of concentrated HNO3 added, and the sample dried again. This was repeated three times. The digestion was brought into solution with 2.2 mL of 7N HNO3 and 4.8 mL of water and stored overnight. The contents were transferred to a 50 mL tube and diluted with an additional 33 mL of water. A 1:1 dilution (1 mL of sample and 1 ml of 2% HNO3) was distributed into 4 mL omnivials, and the samples were analyzed by ICP-MS.

Analyses of Ra in the solid samples (Rar) were conducted on seven carbonates, 19 serpentinites, four gabbro. The carbonates were crushed with a mortar and pestle while the other rocks were crushed with an impact mortar. An aliquot of dry, crushed sample (2 – 10 g) was then measured for 227Ac, 226Ra, 228Ra and 228Th via gamma spectrometry.

Data Processing:
226Ra, 238U and 232Th activities are reported in dpm kg-1.
226Ra was determined by gamma spectrometry.
238U and 232Th were determined by ICP-MS, except for samples marked *, which were determined by gamma spectrometry.
"bdl" indicates measurements that were below detection.
Expected 1σ errors are <10%.

HYPERMET software (Phillips and Marlow, 1976) was used in data processing.

BCO-DMO Processing:
- Adjusted field/parameter names to comply with BCO-DMO naming conventions;
- Missing data identifier ‘--’ replaced with 'nd' (BCO-DMO's default missing data identifier);
- Added a conventional header with dataset name, PI names, version date;
- Converted dates to format: YYYY-MM-DD.

NSF Award Abstract:
The vast majority of deep seafloor sediments are inhabited by microbial communities that survive under extreme energy limitation, with apparent generation times of centuries to millennia. Hydrothermal systems are a stark contrast to these energy-starved environments and may represent important, high-activity, 'population centers' in the oceanic subsurface. When rocks from the Earth's mantle are uplifted and exposed to water, the resulting reactions lead to acidic fluids with high concentrations of hydrogen. Under certain circumstances, small organic molecules such as methane can also form in the absence of biology. These compounds can provide energy to subseafloor microbial communities and, given the ubiquity of mantle rocks, such reactions may fuel a significant proportion of the active subsurface biosphere. The current project will characterize the microbial communities inhabiting an iconic example of this type of system, the Lost City Hydrothermal Field, using a remotely operated vehicle. The ghostly spires of Lost City are highly telegenic and have been featured in professional documentaries. The high definition underwater video footage collected during the expedition will provide the raw material for an 8 week educational training program in digital media focused on kindergarten through 12th grade high school students and undergraduate students. The resulting short documentaries will be published on YouTube and the Utah Education Network.

Mantle rocks comprise significant portions of the seafloor, and microbial communities hosted within them may be important mediators of carbon and energy exchange between the deep Earth and the surface biosphere. Upon tectonic uplift and exposure to water, the serpentinization of these materials releases potential energy in the form of hydrogen, methane, and heat, and further reaction of these products can sustain the abiogenic synthesis of small organic molecules. Recent studies have highlighted, however, the lack of alkalithermophiles that are capable of survival at the high pH (9-11) and elevated temperatures found in these systems. The almost complete lack of carbon dioxide (CO2) represents a second, and possibly more significant, limitation to growth. To better understand the extent of the serpentinite subsurface, this project will address the question: What limits biological activity in the serpentinite subsurface? Specifically, the proposed work will test the hypotheses: (1) microbial diversity spans a wider range of temperature-pH conditions than currently recognized and (2) the scarcity of CO2 is a key biological limitation to serpentinization-driven ecosystems that can be overcome by the metabolic activity of one or a few foundation species. These hypotheses will be tested during a 20 day (10 days on site) expedition to the Lost City Hydrothermal Field, focusing on fluids as windows to the subsurface biosphere. The sampling approach will capitalize on the differences in temperature, carbon availability, and microbial activity across the field. The analytical approach will integrate multidisciplinary techniques performed on replicate subsamples and feature the application of next-generation sequencing technologies to these marine serpentinizing fluids for the first time. This study will generate extensive sequence data from environmental DNA, environmental mRNA, and single-cell genomes, allowing us to identify the in situ expression of metabolic pathways and the genomics of active single cells. These efforts will be closely linked with a thorough characterization of carbon in these fluids that will focus on identifying available substrates (e.g. methane, CO2, organic acids) and on characterizing biomarkers that reflect specific metabolic pathways (e.g. lipids, amino acids).