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Seafloor hydrothermal systems control long-term changes in seawater [Li⁺]: Evidence from fluid inclusions.

ABSTRACT: Secular variations in the major ion chemistry and isotopic composition of seawater on multimillion-year time scales are well documented, but the causes of these changes are debated. Fluid inclusions in marine halite indicate that the Li concentration in seawater [Li⁺]_SW declined sevenfold over the past 150 million years (Ma) from ~184 μmol/kg H₂O at 150 Ma ago to 27 μmol/kg H₂O today. Modeling of the lithium geochemical cycle shows that the decrease in [Li⁺]_SW was controlled chiefly by long-term decreases in ocean crust production rates and mid-ocean ridge and ridge flank hydrothermal fluxes without requiring changes in continental weathering fluxes. The decrease in [Li⁺]_SW parallels the 150 Ma increase in seawater Mg²⁺/Ca²⁺ and ⁸⁷Sr/⁸⁶Sr, and the change from calcite to aragonite seas, KCl to MgSO₄ evaporites, and greenhouse to icehouse climates, all of which point to the importance of plate tectonic activity in regulating the composition of Earth's hydrosphere and atmosphere.

SUBMITTER: Weldeghebriel MF

PROVIDER: S-EPMC10371017 | biostudies-literature | 2023 Jul

REPOSITORIES: biostudies-literature

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Seafloor hydrothermal systems control long-term changes in seawater [Li+]: Evidence from fluid inclusions.

Weldeghebriel Mebrahtu F MF Lowenstein Tim K TK

Science advances 20230726 30

Secular variations in the major ion chemistry and isotopic composition of seawater on multimillion-year time scales are well documented, but the causes of these changes are debated. Fluid inclusions in marine halite indicate that the Li concentration in seawater [Li+]SW declined sevenfold over the past 150 million years (Ma) from ~184 μmol/kg H2O at 150 Ma ago to 27 μmol/kg H2O today. Modeling of the lithium geochemical cycle shows that the decrease in ...[more]

PMID: 37494431

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Project description:Depressurization and sample processing delays may impact the outcome of shipboard microbial incubations of samples collected from the deep sea. To address this knowledge gap, we developed a remotely operated vehicle (ROV)-powered incubator instrument to carry out and compare results from in situ and shipboard RNA stable isotope probing (RNA-SIP) experiments to identify the key chemolithoautotrophic microbes and metabolisms in diffuse, low-temperature venting fluids from Axial Seamount. All the incubations showed microbial uptake of labeled bicarbonate primarily by thermophilic autotrophic Epsilonbacteraeota that oxidized hydrogen coupled with nitrate reduction. However, the in situ seafloor incubations showed higher abundances of transcripts annotated for aerobic processes, suggesting that oxygen was lost from the hydrothermal fluid samples prior to shipboard analysis. Furthermore, transcripts for thermal stress proteins such as heat shock chaperones and proteases were significantly more abundant in the shipboard incubations, suggesting that depressurization induced thermal stress in the metabolically active microbes in these incubations. Together, the results indicate that while the autotrophic microbial communities in the shipboard and seafloor experiments behaved similarly, there were distinct differences that provide new insight into the activities of natural microbial assemblages under nearly native conditions in the ocean.IMPORTANCE Diverse microbial communities drive biogeochemical cycles in Earth's ocean, yet studying these organisms and processes is often limited by technological capabilities, especially in the deep ocean. In this study, we used a novel marine microbial incubator instrument capable of in situ experimentation to investigate microbial primary producers at deep-sea hydrothermal vents. We carried out identical stable isotope probing experiments coupled to RNA sequencing both on the seafloor and on the ship to examine thermophilic, microbial autotrophs in venting fluids from an active submarine volcano. Our results indicate that microbial communities were significantly impacted by the effects of depressurization and sample processing delays, with shipboard microbial communities being more stressed than seafloor incubations. Differences in metabolism were also apparent and are likely linked to the chemistry of the fluid at the beginning of the experiment. Microbial experimentation in the natural habitat provides new insights into understanding microbial activities in the ocean.

Dataset Information

Seafloor hydrothermal systems control long-term changes in seawater [Li⁺]: Evidence from fluid inclusions.

Publications

Seafloor hydrothermal systems control long-term changes in seawater [Li<sup>+</sup>]: Evidence from fluid inclusions.

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