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Hydrothermal exploration of the southern Chile Rise: sediment‐hosted venting at the Chile Triple Junction (2022)

German, Christopher R. ; Baumberger, Tamara ; Lilley, Marvin D. ; [et al.]

American Geophysical Union

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Publication Date: 2022-10-26

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in German, C., Baumberger, T., Lilley, M., Lupton, J., Noble, A., Saito, M., Thurber, A., & Blackman, D. Hydrothermal exploration of the southern Chile Rise: sediment‐hosted venting at the Chile Triple Junction. Geochemistry Geophysics Geosystems, 23(3), (2022): e2021GC010317, https://doi.org/10.1029/2021gc010317.

Description: We report results from a hydrothermal plume survey along the southernmost Chile Rise from the Guamblin Fracture Zone to the Chile Triple Junction (CTJ) encompassing two segments (93 km cumulative length) of intermediate spreading-rate mid-ocean ridge axis. Our approach used in situ water column sensing (CTD, optical clarity, redox disequilibrium) coupled with sampling for shipboard and shore based geochemical analyses (δ3He, CH4, total dissolvable iron (TDFe) and manganese, (TDMn)) to explore for evidence of seafloor hydrothermal venting. Across the entire survey, the only location at which evidence for submarine venting was detected was at the southernmost limit to the survey. There, the source of a dispersing hydrothermal plume was located at 46°16.5’S, 75°47.9’W, coincident with the CTJ itself. The plume exhibits anomalies in both δ3He and dissolved CH4 but no enrichments in TDFe or TDMn beyond what can be attributed to resuspension of sediments covering the seafloor where the ridge intersects the Chile margin. These results are indicative of sediment-hosted venting at the CTJ.

Description: We acknowledge University of California Ship Funds for their support of that shiptime and the NOAA Ocean Exploration and Research Grant NA08OAR4600757 which supported the research presented here. Finally, we thank two anonymous reviewers whose important contributions helped to improve the final version of this paper. This is PMEL contribution number 5341.

Keywords: Hydrothermal ; Geochemistry ; Chile Rise ; Chile Triple Junction ; Sediment hosted

Repository Name: Woods Hole Open Access Server

Type: Article

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Shallow calcium carbonate cycling in the North Pacific Ocean (2022)

Subhas, Adam V. ; Dong, Sijia ; Naviaux, John D. ; [et al.]

American Geophysical Union

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Publication Date: 2022-11-06

Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(5), (2022): e2022GB007388, https://doi.org/10.1029/2022gb007388.

Description: The cycling of biologically produced calcium carbonate (CaCO3) in the ocean is a fundamental component of the global carbon cycle. Here, we present experimental determinations of in situ coccolith and foraminiferal calcite dissolution rates. We combine these rates with solid phase fluxes, dissolved tracers, and historical data to constrain the alkalinity cycle in the shallow North Pacific Ocean. The in situ dissolution rates of coccolithophores demonstrate a nonlinear dependence on saturation state. Dissolution rates of all three major calcifying groups (coccoliths, foraminifera, and aragonitic pteropods) are too slow to explain the patterns of both CaCO3 sinking flux and alkalinity regeneration in the North Pacific. Using a combination of dissolved and solid-phase tracers, we document a significant dissolution signal in seawater supersaturated for calcite. Driving CaCO3 dissolution with a combination of ambient saturation state and oxygen consumption simultaneously explains solid-phase CaCO3 flux profiles and patterns of alkalinity regeneration across the entire N. Pacific basin. We do not need to invoke the presence of carbonate phases with higher solubilities. Instead, biomineralization and metabolic processes intimately associate the acid (CO2) and the base (CaCO3) in the same particles, driving the coupled shallow remineralization of organic carbon and CaCO3. The linkage of these processes likely occurs through a combination of dissolution due to zooplankton grazing and microbial aerobic respiration within degrading particle aggregates. The coupling of these cycles acts as a major filter on the export of both organic and inorganic carbon to the deep ocean.

Description: This work was funded by NSF OCE-1220301 to W.B., NSF OCE-1220600 to J.F.A., and startup funding for A.V.S.

Description: 2022-11-06

Keywords: Calcium carbonate ; Dissolution ; Carbon cycle