Germanium in mid-ocean ridge flank hydrothermal fluids

Seawater interaction with the oceanic lithosphere crucially impacts on global geochemical cycles, controls ocean chemistry over geologic time, changes the petrophysical properties of the oceanic lithosphere, and regulates the global heat budget. Extensive seawater circulation is expressed near oceanic ridges by the venting of hydrothermal fluids through chimney structures. These vent fluids vary greatly in chemistry, from the metal-rich, acidic fluids that emanate from “black smokers” at temperatures up to 400 °C to the metal-poor, highly alkaline and reducing fluids that issue from the carbonate–brucite chimneys of ultramafic-hosted systems at temperatures below 110 °C. Mid-ocean ridge hydrothermal systems not only generate signifi-cant metal resources but also host unique life forms that may be similar to those of early Earth.

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Mantle-derived 40Ar in mid-ocean ridge hydrothermal fluids: implications for the source of volatiles and mantle degassing rates

Chemical Geology ◽

10.1016/s0009-2541(97)00173-3 ◽

1998 ◽

Vol 147 (1-2) ◽

pp. 77-88 ◽

Cited By ~ 19

Author(s):

Finlay M. Stuart ◽

Grenville Turner

Keyword(s):

Hydrothermal Fluids ◽

Mid Ocean Ridge ◽

Ocean Ridge

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Provenance, Stratigraphic Architecture, and Hydrogeologic Influence of Turbidites on the Mid-Ocean Ridge Flank of Northwestern Cascadia Basin, Pacific Ocean

Journal of Sedimentary Research ◽

10.2110/jsr.2005.012 ◽

2005 ◽

Vol 75 (1) ◽

pp. 149-164 ◽

Cited By ~ 48

Author(s):

M. B. Underwood ◽

K. D. Hoke ◽

A. T. Fisher ◽

E. E. Davis ◽

E. Giambalvo ◽

...

Keyword(s):

Pacific Ocean ◽

Stratigraphic Architecture ◽

Mid Ocean Ridge ◽

Ocean Ridge ◽

Ridge Flank

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Mixing-Driven Mean Flows and Submesoscale Eddies over Mid-Ocean Ridge Flanks and Fracture Zone Canyons

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0174.1 ◽

2020 ◽

Vol 50 (1) ◽

pp. 175-195 ◽

Cited By ~ 3

Author(s):

Xiaozhou Ruan ◽

Jörn Callies

Keyword(s):

Numerical Experiments ◽

Water Mass ◽

Mixing Layers ◽

Global Ocean ◽

Mid Ocean Ridge ◽

Mixing Rates ◽

Ocean Ridge ◽

Ridge Flank ◽

Abyssal Mixing ◽

Water Mass Transformation

AbstractTo close the abyssal overturning circulation, dense bottom water has to become lighter by mixing with lighter water above. This diapycnal mixing is strongly enhanced over rough topography in abyssal mixing layers, which span the bottom few hundred meters of the water column. In particular, mixing rates are enhanced over mid-ocean ridge systems, which extend for thousands of kilometers in the global ocean and are thought to be key contributors to the required abyssal water mass transformation. To examine how stratification and thus diabatic transformation is maintained in such abyssal mixing layers, this study explores the circulation driven by bottom-intensified mixing over mid-ocean ridge flanks and within ridge-flank canyons. Idealized numerical experiments show that stratification over the ridge flanks is maintained by submesoscale baroclinic eddies and that stratification within ridge-flank canyons is maintained by mixing-driven mean flows. These restratification processes affect how strong a diabatic buoyancy flux into the abyss can be maintained, and they are essential for maintaining the dipole in water mass transformation that has emerged as the hallmark of a diabatic circulation driven by bottom-intensified mixing.

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Magnetostratigraphic effects and artifacts of an inverse redox zonation in bottom-up oxygenated East Pacific mid-ocean ridge flank sediments

10.5194/egusphere-egu21-9458 ◽

2021 ◽

Author(s):

Adrian Höfken ◽

Tilo von Dobeneck ◽

Sabine Kasten

Keyword(s):

Pore Water ◽

Planetary Science ◽

Ex Situ ◽

Sediment Geochemistry ◽

Magnetic Minerals ◽

Diagenetic Alteration ◽

Mid Ocean Ridge ◽

Redox Zonation ◽

Ocean Ridge ◽

Ridge Flank

Shipborne ex-situ oxygen measurements in mid-ocean ridge flank sediment cores from the eastern low-latitude North Pacific (Clarion-Clipperton Zone) revealed a downward increase of pore-water oxygen above the sediment-crust interface (Mewes et al., 2016, Kuhn et al., 2017). This inverse redox zonation is caused by an upward diffusion of oxygen (and other solutes) from fluids circulating through the underlying 20 Mio. Year old and still cooling ocean crust. In consequence, these sediments experience a cyclic change in redox-conditions from oxic seafloor conditions at the top through mostly suboxic conditions throughout the sediment column back to oxygen-rich pore water in the last few sediment meters above the rock basement. We studied paleomagnetic records and bulk magnetic properties of three gravity cores from such settings that were collected during RV Sonne expedition SO-240 in 2015 and obtained high-quality magnetostratigraphic records covering the past 3.2 Ma. The generally very good preservation and interpretability of our reversal and RPI records, however, conflicts with a well-defined, but irregular &#8216;ghost event&#8217; of normal polarity within the upper Gilbert reversed C2Ar section. This magnetic polarity and intensity artifact cannot be explained by sediment tectonics, but coincides with the present depth of the lower suboxic-to-oxic redox boundary. Although chemical overprinting could be considered as an obvious explanation of such findings, bulk magnetic analyses (FORCs, thermomagnetics) infer no diagenetic alteration of the magnetic minerals. Over the entire paleomagnetic record, bacterial magnetite appears to be the predominant NRM carrier. We therefore introduce a novel conceptual model of secondary biogenic magnetite formation at crustal depth, hypothesizing that microaerophilic magnetotactic bacteria live and biomineralize not only in the shallow subsurface, but also near the deep oxygen above the sediment-crust interface.&#160;References Mewes, K., Mogoll&#243;n, J.M., Picard, A., R&#252;hlemann, C., Eisenhauer, A., Kuhn, T., Ziebis, W., Kasten, S., 2016. Diffusive transfer of oxygen from seamount basaltic crust into overlying sediments: An example from the Clarion-Clipperton Fracture Zone. Earth and Planetary Science Letters 433, 215-225.Kuhn, T., Versteegh, G.J.M., Villinger, H., Dohrmann, I., Heller, C., Koschinsky, A., Kaul, N., Ritter, S., Wegorzewski, A.V., Kasten, S., 2017. Widespread seawater circulation in 18-22 Ma oceanic crust: Impact on heat flow and sediment geochemistry. Geology 45, 799-802.&#160;&#160;&#160;

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Seawater dissolved gases associated with hydrothermal fluids in convergent margins (Brandsfield-South Shetland, Antarctica) and mid-ocean ridge and intraplate settings (Azores, Portugal)

10.5194/egusphere-egu2020-11991 ◽

2020 ◽

Author(s):

María Asensio-Ramos ◽

Cecilia Amonte ◽

Esther Santofimia ◽

Gladys V. Melián ◽

Enrique López ◽

...

Keyword(s):

Water Column ◽

Sea Water ◽

Volcanic Eruptions ◽

Isotopic Signature ◽

Hydrothermal Systems ◽

Hydrothermal Fluids ◽

Convergent Margins ◽

Dissolved Gases ◽

Mid Ocean Ridge ◽

Ocean Ridge

The occurrence of hydrothermal emissions implies the existence of heat sources related to magma reservoirs both in convergent margins (Bransfield-South Shetland) and in mid-ocean ridge and intra-plate settings (Azores). The importance of these systems lies in (a) producing important mineralizations,&#160; (b) favouring extremophilic ecosystems, (c) being precursors of underwater volcanic eruptions, (d) playing a major role they play in the matter and energy exchange between the geosphere and the hydrosphere and (d) their impact on the geochemistry of the oceans. In subduction margins, rifts, transforming faults or volcanic buildings in hot spots, emissions of hot fluids related to magmas and/or circulation in hydrothermal systems can occur. The fluids associated with magmas are fundamentally gases (CO2, H2O, H2, SO2, H2S, He, etc.). Hydrothermal fluids constitute a complex system where seawater percolates through fissures and fractures in sediments and rocks at different depths and heats up upon contact with magmas and hot volcanic rocks, leaching a large amount of chemical elements. The identification of acoustic plumes in the water column is the first step in the exploration of unknown underwater emissions. The new acoustic detection technologies, which operate with a wide frequency range, are one of the most innovative tools for detecting gas plumes and other fluids in the water column, especially in deep waters. Once detected, physical-chemical parameters (temperature, salinity, turbidity, cations, anions, dissolved gases, isotopic signature, etc.) that allow their characterization and classification will be determined. This type of studies is particularly useful when it is not possible to collect free gases, fumarolic and/or bubbling gases, as in the case of submarine activity. In this work, we show the results obtained regarding the chemical composition of dissolved gases (He, H2, CO2 (aq), O2, N2, CH4 and He) and isotopic signature of the dissolved CO2 (&#948;13C-CO2) in sea water sampled in sites of hydrothermal interest. With this purpose, we carried out two oceanographic surveys (EXPLOSEA1 and EXPLOSEA2) in 2019: the first in Antarctica aboard the Spanish Research Vessel (RV) Hesp&#233;rides and the second in North Atlantic Ocean aboard the Spanish RV Sarmiento de Gamboa. To do so, 13 and 10 water vertical profiles were studied in the RV Hesp&#233;rides and the RV Sarmiento de Gamboa, respectively, using a SBE 911plus CTD system where there was evidence of acoustic plumes or where appropriate, emission buildings of fluids were present. Water samples were kept in glass bottles for subsequent analysis. The establishment of the physicochemical characteristics of volcanic hydrothermal fluids and the characterization of the nature and origin of the different types of fluid emissions will help to classify the hydrothermal fluids in order to understand the phenomena that take place in them and their surroundings.

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