Interstitial Water Studies, Leg 74

Gieskes, Joris M.; Johnston, K.; Boehm, M.

doi:10.2973/dsdp.proc.74.122.1984

Cited by 6 publications

(3 citation statements)

References 10 publications

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“…At this site, we noted nitrate enrichment in the crustal fluids at the sediment/basement interface relative to background seawater. In line with its representation, this geochemical signal has been detected in the few studied locations characterized by vigorous low-temperature hydrothermal circulation (e.g., the East Pacific Rise [44] and the Clarion-Clipperton Fracture Zone [45]). Such nitrate enrichment in the crust may result from (i) high-level downward nitrate flux from the overlying sediments (25) or (ii) a downward flux combined with in situ nitrification.…”

Section: Discussionsupporting

confidence: 62%

Indigenous Ammonia-Oxidizing Archaea in Oxic Subseafloor Oceanic Crust

et al. 2020

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Oceanic ridge flank systems represent one of the largest and least-explored microbial habitats on Earth. Fundamental ecological questions regarding community activity, recruitment, and succession in this environment remain unanswered. Here, we investigated ammonia-oxidizing archaea (AOA) in the sediment-buried basalts on the oxic and young ridge flank at North Pond, a sediment-filled pond on the western flank of the Mid-Atlantic Ridge, and compared them with those in the overlying sediments and bottom seawater. Nitrification in the North Pond basement is thermodynamically favorable and is supported by a reaction-transport model simulating the dynamics of nitrate in the crustal fluids. Nitrification rate is estimated to account for 6% to 7% of oxygen consumption, which is similar to the ratios found in marine oxic sediments, suggesting that aerobic mineralization of organic matter is the major ammonium source for crustal nitrifiers. Using the archaeal 16S rRNA and amoA genes as phylogenetic markers, we show that AOA, composed solely of Nitrosopumilaceae, are the major archaeal dwellers at North Pond. Phylogenetic analysis reveals that the crustal AOA communities are distinct from those in the bottom seawater and the upper oxic sediments but are similar to those in the basal part of the overlying sediment column, suggesting either similar environmental selection or the dispersal of microbes across the sediment-basement interface. Additionally, quantitative abundance data suggest enrichment of the dominant Nitrosopumilaceae clade (Eta clade) in the basement compared to the seawater. This study explored AOA and their activity in the upper oceanic crust, and our results have ecological implications for the biogeochemical cycling of nitrogen in the crustal subsurface. IMPORTANCE Ridge flanks represent the major avenue of chemical and heat exchange between the Earth’s oceans and the lithosphere and are thought to harbor an enormous and understudied biosphere. However, little is known about the diversity and functionality of the crustal biosphere. Here, we report an indigenous community of archaea specialized in ammonia oxidation (i.e., AOA) in the oxic oceanic crust at North Pond. These AOA are the dominant archaea and are likely responsible for most of the cycling taking place in the first step of nitrification, a feasible nitrogen cycling step in the oxic basement. The crustal AOA community structure significantly differs from that in deep ocean water but is similar to that of the community in the overlying sediments in close proximity. This report links the occurrence of AOA to their metabolic activity in the oxic subseafloor crust and suggests that ecological selection and in situ proliferation may shape the microbial community structure in the rocky subsurface.

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Section: Discussionsupporting

confidence: 62%

Indigenous Ammonia-Oxidizing Archaea in Oxic Subseafloor Oceanic Crust

et al. 2020

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“…At Sites 699, 700, and 702, the downhole gradients in Ca and Mg are linear with depth and reflect diffusional gradients between the overlying seawater and basalt-seawater reactions occurring in basement (McDuff, 1981;Gieskes, 1983;Gieskes et al, 1984). The calcium vs. magnesium relationship at these three sites is linear with a ΔMg/ΔCa slope of -0.5 ( Fig.…”

Section: Basalt Basement Reactions Vs Silicic Volcanic Ashmentioning

confidence: 89%

Interstitial-Water Chemistry: Abyssal South Atlantic and East Georgia Basins, Islas Orcadas and Meteor Rises

Froelich¹,

Mortlock²,

Mefferd³

et al. 1991

Proceedings of the Ocean Drilling Program

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Pore-water samples were recovered at five sites from ODP Leg 114 in the subantarctic South Atlantic Ocean and analyzed for pH, alkalinity, chloride, sulfate, fluoride, silica, magnesium, calcium, strontium, potassium, lithium, and barium. At sites in the East Georgia Basin and on the Islas Orcadas Rise, Ca increases and Mg decreases linearly downhole with a ΔMg/ΔCa ratio reflecting conservative diffusive exchange and basalt basement reactions. At sites on the west flank of the Mid-Atlantic Ridge and on the Meteor Rise, Ca gradients are nonlinear, and nonconservative ΔMg/ΔCa ratios reflect alteration reactions of abundant silicic volcanic ash in the sediment. K decreases linearly downhole at all sites, reflecting uptake by basement and the absence of significant sediment-hosted reactions. SO 4 decreases and alkalinity increases downhole are due to a slight sulfate reduction at all sites except at Site 701. Sr increases downhole at all sites except Site 701, with ΔSr/ΔCa ratios reflecting diffusive exchange with basement. At Site 704 on the Meteor Rise, there is intense Sr production during carbonate recrystallization in the upper 200 mbsf. Below 200 mbsf at Site 704, the ion concentration product of SrSO 4 is constant, suggesting Sr control by celestite solubility. Li and F concentrations display complex behavior related to sedimentary reactions, probably calcite recrystallization (Li uptake and F release).

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“…Studies of interstitial waters from accretionary convergent plate margins revealed the importance of element transfer by fluid flow in accretionary wedges. These studies include those during n DSDP Legs 66 and 67 (Harrison et al, 1982;Gieskes et al, 1985) and Leg 84 (Hesse et al, 1985) in the Middle America Trench, during ODP Leg 110 on the Barbados Ridge (Shipboard Scientific Party, 1988a), and during ODP Leg 112 at the Peru continental margin (Shipboard Scientific Party, 1988b). The principal characteristics of these forearc fluids are low chlorinities and the presence of hydrocarbons, especially methane, which form gas hydrates, given appropriate temperatures, pressures, and partial pressure of the hydrocarbons.…”

Section: Chemical Fluxes In Forearc Terranesmentioning

confidence: 99%

Introduction

1990

Proceedings of the Ocean Drilling Program

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Interstitial Water Studies, Leg 74

Cited by 6 publications

References 10 publications

Indigenous Ammonia-Oxidizing Archaea in Oxic Subseafloor Oceanic Crust

Indigenous Ammonia-Oxidizing Archaea in Oxic Subseafloor Oceanic Crust

Interstitial-Water Chemistry: Abyssal South Atlantic and East Georgia Basins, Islas Orcadas and Meteor Rises

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