Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust
Abstract The permeability, connectivity, and reactivity of fluid reservoirs in oceanic crust are poorly constrained, yet these reservoirs are pathways for about a quarter of the Earth's heat loss, and seawater‐rock exchange within them impact ocean chemical cycles. We present results from the s...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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Wiley
2020-01-01
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| Series: | Geochemistry, Geophysics, Geosystems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2019GC008804 |
| _version_ | 1797638115401138176 |
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| author | C. Geoffrey Wheat Keir Becker Heinrich Villinger Beth N. Orcutt Trevor Fournier Anne Hartwell Claudia Paul |
| author_facet | C. Geoffrey Wheat Keir Becker Heinrich Villinger Beth N. Orcutt Trevor Fournier Anne Hartwell Claudia Paul |
| author_sort | C. Geoffrey Wheat |
| collection | DOAJ |
| description | Abstract The permeability, connectivity, and reactivity of fluid reservoirs in oceanic crust are poorly constrained, yet these reservoirs are pathways for about a quarter of the Earth's heat loss, and seawater‐rock exchange within them impact ocean chemical cycles. We present results from the second ever cross‐hole tracer experiment within oceanic crust and the first conducted during a single expedition and in slow‐spreading crust west of the Mid‐Atlantic Ridge at North Pond. Here we employed boreholes that were drilled by the Integrated Ocean Drilling Program (Sites U1382 and U1383) that were instrumented and sealed. A cesium salt solution and bottom seawater tracer experiment provided a measure of the minimum Darcy fluid velocity (2 to 41 m/day) within the upper volcanic crust, constraining the minimum permeability of 10−11 to 10−9 m2. We also document chemical heterogeneities in crustal fluid compositions, rebound from drilling disturbances, and nitrification within the basaltic crust, based on systematic differences in borehole fluid compositions over a 5‐year period. These results also show heterogeneous fluid compositions with depth in the borehole, indicating that hydrothermal circulation is not vigorous enough to homogenize the fluid composition in the upper permeable basaltic basement, at least not on the time scale of 5 years. Our work verifies the potential for future manipulative experiments to characterize hydrologic, biogeochemical, and microbial process within the upper basaltic crust. |
| first_indexed | 2024-03-11T12:58:58Z |
| format | Article |
| id | doaj.art-e26cd23b225440f1a4c3eeddf8e19822 |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-11T12:58:58Z |
| publishDate | 2020-01-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-e26cd23b225440f1a4c3eeddf8e198222023-11-03T16:55:55ZengWileyGeochemistry, Geophysics, Geosystems1525-20272020-01-01211n/an/a10.1029/2019GC008804Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic CrustC. Geoffrey Wheat0Keir Becker1Heinrich Villinger2Beth N. Orcutt3Trevor Fournier4Anne Hartwell5Claudia Paul6Institute of Marine Studies University of Alaska Fairbanks Moss Landing CA USADepartment of Marine Geosciences, RSMAS University of Miami Coral Gables FL USADepartment of Geoscience University of Bremen Bremen GermanyDeep Biosphere Laboratory Bigelow Laboratory for Ocean Sciences East Boothbay Maine USAInstitute of Marine Studies University of Alaska Fairbanks Moss Landing CA USACenter for Coastal and Ocean Mapping University of New Hampshire Durham NH USAInstitute of Marine Studies University of Alaska Fairbanks Moss Landing CA USAAbstract The permeability, connectivity, and reactivity of fluid reservoirs in oceanic crust are poorly constrained, yet these reservoirs are pathways for about a quarter of the Earth's heat loss, and seawater‐rock exchange within them impact ocean chemical cycles. We present results from the second ever cross‐hole tracer experiment within oceanic crust and the first conducted during a single expedition and in slow‐spreading crust west of the Mid‐Atlantic Ridge at North Pond. Here we employed boreholes that were drilled by the Integrated Ocean Drilling Program (Sites U1382 and U1383) that were instrumented and sealed. A cesium salt solution and bottom seawater tracer experiment provided a measure of the minimum Darcy fluid velocity (2 to 41 m/day) within the upper volcanic crust, constraining the minimum permeability of 10−11 to 10−9 m2. We also document chemical heterogeneities in crustal fluid compositions, rebound from drilling disturbances, and nitrification within the basaltic crust, based on systematic differences in borehole fluid compositions over a 5‐year period. These results also show heterogeneous fluid compositions with depth in the borehole, indicating that hydrothermal circulation is not vigorous enough to homogenize the fluid composition in the upper permeable basaltic basement, at least not on the time scale of 5 years. Our work verifies the potential for future manipulative experiments to characterize hydrologic, biogeochemical, and microbial process within the upper basaltic crust.https://doi.org/10.1029/2019GC008804hydrothermal circulationMid‐Atlantic Ridgeridge flanksnitrification |
| spellingShingle | C. Geoffrey Wheat Keir Becker Heinrich Villinger Beth N. Orcutt Trevor Fournier Anne Hartwell Claudia Paul Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust Geochemistry, Geophysics, Geosystems hydrothermal circulation Mid‐Atlantic Ridge ridge flanks nitrification |
| title | Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust |
| title_full | Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust |
| title_fullStr | Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust |
| title_full_unstemmed | Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust |
| title_short | Subseafloor Cross‐Hole Tracer Experiment Reveals Hydrologic Properties, Heterogeneities, and Reactions in Slow‐Spreading Oceanic Crust |
| title_sort | subseafloor cross hole tracer experiment reveals hydrologic properties heterogeneities and reactions in slow spreading oceanic crust |
| topic | hydrothermal circulation Mid‐Atlantic Ridge ridge flanks nitrification |
| url | https://doi.org/10.1029/2019GC008804 |
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