Glen Snyder

Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor

A deep sleep in coal beds Deep below the ocean floor, microorganisms from forest soils continue to thrive. Inagaki et al. analyzed the microbial communities in several drill cores off the coast of Japan, some sampling more than 2 km below the seafloor (see the Perspective by Huber). Although cell counts decreased with depth, deep coal beds harbored active communities of methanogenic bacteria. These communities were more similar to those found in forest soils than in other deep marine sediments. Science, this issue p. 420; see also p. 376 Coal beds more than 2 kilometers below the seafloor host methanogenic bacteria related to those found in forest soils. [Also see Perspective by Huber] Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from <10 to ~104 cells cm−3. Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.

Origin of iodine in volcanic fluids: 129I results from the Central American Volcanic Arc

Abstract The largest reservoir of crustal iodine is found in marine sediments, where it is closely associated with organic material. This presence, together with the existence of a long-lived, cosmogenic radioisotope 129I (t1/2 = 15.7 Ma), make this isotopic system well suited for the study of sediment recycling in subduction zones. Reported here are the results of 129I/I ratios in volcanic fluids, collected during a comprehensive study of fluids and gases in the Central American Volcanic Arc. 129I/I ratios, together with I, Br, and Cl concentrations, were determined in 79 samples from four geothermal centers and a number of crater lakes, fumaroles, hot springs, and surface waters in Costa Rica, Nicaragua, and El Salvador. Geothermal and volcanic fluids were found to have iodine concentrations substantially higher than values in seawater or meteoric waters. 129I/I ratios in most of the geothermal fluids are below the preanthropogenic input ratio of 1500 × 10−15, demonstrating that recent anthropogenic additions are largely absent from the volcanic systems. The majority of the 129I/I ratios are between 500 and 800 × 10−15. These ratios indicate minimum iodine ages between 25 and 15 Ma, in good agreement with the age of subducted sediments in this region. In all four geothermal systems, however, a few samples were found with iodine ages older than 40 Ma—that is, considerably below the expected age range for subducted sediments from the Cocos Plate. These samples probably reflect the presence of iodine derived from sediments in older accreted oceanic terraines. The iodine ages indicate that the magmatic end member for the volcanic fluids originates in the deeper parts of the subducted sediment column, with small additions from older iodine mobilized from the overlying crust. The high concentrations of iodine in geothermal fluids, combined with the observed iodine ages, demonstrate that remobilization in the main volcanic zone (and probably also in the forearc area) is an important part in the overall marine cycle of iodine and similar elements.

Iodine dating of pore waters associated with gas hydrates in the Nankai area, Japan

The Nankai hydrate field, Japan, is an example of gas-hydrate deposits associated with an active subduction zone. In order to determine the origin of gas hydrates in this area, 129I/I ratios together with halogen concentrations were measured in a set of pore-water samples collected from two boreholes in the Nankai hydrate field. Iodine concentrations are between 100 and 230 μM, i.e., strongly enriched compared to seawater, while Cl concentrations were found to be close to that of seawater. Except for one sample, 129I/I ratios are between 180 and 520 × 10−15, giving minimum ages between 24 and 48 Ma. Because these ages are considerably older than present host sediments (<2 Ma) and subducting marine sediments (<21 Ma) in this area, iodine (and, by association, methane in the gas hydrates) must have been derived from source formations located in the continental side of the subduction zone. The results do not support derivation of gas hydrates from present host sediments or currently subducting sediments, but could be related to release and long-time recycling of fluids from marine formations of early Tertiary age.

Origin and history of waters associated with coalbed methane: 129I, 36Cl, and stable isotope results from the Fruitland Formation, CO and NM

Abstract The Fruitland Formation of the San Juan Basin was deposited during the late Cretaceous and is associated with significant reservoirs of coalbed methane (CBM). The purpose of this study is to determine the origin and history of waters associated with the formation, using long-lived cosmogenic and stable isotope systems. Ratios of 129 I/I and stable isotope values (δD and δ 18 O) were determined in waters from close to 100 wells, 36 Cl/Cl ratios for a subset of these samples. A significant group of samples has 129 I/I ratios between 100 × 10 −15 and 200 × 10 −15 , indicating minimum iodine ages close to 60 Ma. If these ages are corrected for the addition of fissiogenic 129 I, they are compatible with the depositional age of the Fruitland Formation (Late Cretaceous). Several sets of waters are clearly present within the data. A group dominated by infiltration of recent surface waters is restricted to the uplifted basin margins, with a lateral extent of less than 5 km from outcrop, and is characterized by 129 I/I ratios in excess of 1500 × 10 −15 and meteoric δD, δ 18 O, and 36 Cl/Cl signatures. The rest of the basin is characterized by several subsets of formation waters which have undergone variable degrees of iodine enrichment through diagenesis as well as variable degrees of dilution. The first subgroup is found in coals of relatively low vitrinite reflectance and moderate enrichment of iodine. This subgroup predominantly consists of entrapped pore fluids, although it may also contain waters which infiltrated the coals at the time of the Laramide uplift, between 25 and 30 Ma. A second subgroup consists of formation waters associated with coals of high vitrinite reflectance. Despite subsequent uplift, the high iodine concentrations and low 129 I/I ratios of this subgroup, as well as a moderate depletion of deuterium relative to 18 O, suggest that these waters were not significantly altered since the time when diagenetic reactions occurred in the deepest portion of the basin. A third subgroup, with higher δD and δ 18 O values as well as higher 129 I/I ratios, extends roughly west to east at the New Mexico–Colorado state line and corresponds to a region of extensive fracturing of the coalbeds. In this case, the higher 129 I/I ratios are probably due to contributions of fissiogenic 129 I through fracture flow, perhaps from deeper formation waters. Our results do not support models of subsequent basin-wide groundwater migration in the Fruitland Formation. The combined use of 129 I and 36 Cl with stable isotope studies provides valuable information as to the hydrologic history of coalbed methane deposits, as well as their potential for commercial exploitation.

129I in the Southern Hemisphere: Global redistribution of an anthropogenic isotope

Determination of 129I concentrations and 129I/I ratios in surface waters collected in the Southern Hemisphere indicate the presence of anthropogenic 129I on a global scale. Although levels in the Southern Hemisphere are significantly below those in the Northern Hemisphere, they are still two orders of magnitude above natural levels. The most likely sources for anthropogenic 129I are releases from reprocessing plants located in the Northern Hemisphere. The results indicate a rapid redistribution of this radioisotope through atmospheric transport on a global scale. Mid-latitudes in both hemispheres have higher values than equatorial and polar regions, probably reflecting atmospheric transport and precipitation patterns.

Climate change and tectonic uplift triggered the formation of the Atacama Desert’s giant nitrate deposits

The giant nitrate deposits of the hyperarid Atacama Desert (Chile) are one of the most extraordinary, yet enigmatic, mineral occurrences on Earth. These deposits are complex assemblages of highly soluble nitrates, chlorides, sulfates, perchlorates, iodates, and chromates, and their preservation is the result of prevalent hyperarid climate conditions in the Atacama Desert since the late Miocene, with average rainfall rates of <10 mm/yr in the past ~3 m.y. Although several hypotheses have been proposed since the mid-1800s, the formation of these extensive deposits still remains highly controversial despite the fact that recent studies have argued toward an atmospheric source for the nitrate, sulfate, and perchlorate components. In this report, we focus on the often overlooked and poorly studied iodine and chromium components of Atacama’s nitrates. We present the fi rst cosmogenic iodine ( 129 I) and stable chromium (δ 53/52 Cr) isotope data of nitrates showing that groundwater has played an unforeseen role in the formation of these massive deposits. The isotopic signature of I in the nitrates ( 129 I/I ~150–600 × 10 –15 ) share similarities with deep sedimentary (marine) pore waters and shales, deviating signifi cantly from atmospheric iodine ( 129 I/I ~1500 × 10 –15 ), while the positive and highly fractionated δ 53/52 Cr SRM979 values (+0.7‰ to +3‰) are indicative of intense Cr redox cycling due to groundwater transport. Our evidence points toward a multi-source genetic model for the Atacama Desert nitrate deposits, where these extensive accumulations were the result of long-lived, near-surface mineral precipitation driven by groundwater (i.e., chromates, iodates) coupled with dry atmospheric deposition (i.e., nitrates, perchlorates) and sea spray inputs (i.e., sulfates, chlorides), triggered by increasing aridity and tectonic uplift.

New insights on the hydrocarbon system of the Fruitland Formation coal beds, northern San Juan Basin, Colorado and New Mexico, USA

The Fruitland Formation is the world’s largest known and most productive coalbed methane deposit, with 45 TCF of gas. This important hydrocarbon system originates from a unique combination of depositional environments, tectonic framework, and structural and landscape evolution. This system is more complex than recognized by previous workers. The presence of biogenic gas in the formation is recognized, and is thought to indicate contemporary meteoric recharge of the formation. We conclude recharge of the regolith is taking place, but that biogenic methane is probably sourced by microbes introduced to the formation 35 to 40 million years (Ma) ago. Previous discussions of the coal hydrology focused on meteoric waters thought to be recharging the coals today. Our work indicates that four distinct waters are present in the coals. Connate waters fill the formation in the center of the basin. Meteoric recharge is restricted to coal and regolith no more than a few kilometers from the outcrop. Meteoric water found farther down dip is fossil meteoric water and reflects recharge between 35 and 40 Ma. Waters from deeper formations also locally recharge fractures in the coals. The Paleozoic architecture of the basin continues to influence fluid flow in the coals. Fractures or faults in the coals may be contributory to the high permeabilities found in the high-rate fairway, a cluster of wells with larger recoverable reserves that produce at rates of up to 10,000 MCFPD; the structure could also explain the fairway’s abrupt southern boundary. The Cenozoic Rio Grande rift event imposed a second fracture set. Intersection of these fracture sets with the outcrop provides the locus for most methane seeps. Methane seeps at the coal outcrop have been active for decades. The presence of these seeps is due in part to continued weathering and breaching of biosome-scale reservoir compartments, a process which is more rapid along fracture systems. Our work finds that seep activity varies on a thirty-year cycle. We attribute this cyclicity to variations in the frequency of magnitude-3 or greater earthquakes, which also varies on a thirty-year cycle. The epicenters of these quakes closely correspond with the areas of most active seepage. As such, pulses in seep activity are due to the result of releases from deeper reservoirs whose seals are periodically breached. �

Acoustical surveys of Methane plumes using the quantitative echo sounder in Japan Sea

R&T/V Umitaka-maru(Tokyo Univ. of Marine Science and Technology) and R/V Natsushima(JAMSTEC) sailed to the methane seep area on a small ridge in the Naoetsu Basin, in the eastern margin of the Sea of Japan in 2004,2005 and 2006 to survey the ocean floor gas hydrate and related acoustic signatures of methane plumes by using a quantitative echo sounder and a multi beam SONER [1]. Detailed bathymetric profiles have revealed a number of mounds, pockmarks and collapse structures within 3 km times 4 km on the ridge at the water depth of 910 m to 980 m. We mapped minutely methane plumes by using a quantitative echo sounder with positioning data from GPS. We also measured averaged echo intensity from the methane plumes and sea bottoms both in every 100 m range and very one minute by the echo integrator. We obtained the following results from the present echo-sounder and SONER surveys. 1) We measured the averaged volume backscattering strength (SV) of each methane plume. The strongest SV, -33dB, of the plumes was stronger than SV of fish school. 2) Averaged SV of each methane plume tend to be related to the water temperature and the water pressure. 3) We recovered several fist-sized chunks of methane hydrate by piston coring at the area where we observed the methane plumes. 4) Using this method, we detected methane bubbles floating up points and revealed that the hydrate bubbles float upward until they reach warm waters at 300 m depth. 5) We revealed the hydrate bubbles in the conic container on the sea bottom. Because of results this acoustical method was effective to know the behaviors of the methane hydrate under water and to monitor the area of the methane seep. As a following up project, we are planning 1) to measure SV of methane hydrate bubbles and methane hydrate floating in water columns in situ, 2) to make a trial calculation of amount of floating methane bubbles and methane hydrates and 3) to study how to sample the acoustical data of methane plumes using the side scanning SONAR, called SeaBat.