A First Look at Dissolved Ge Isotopes in Marine Sediments

The removal of chemical species from seawater during the precipitation of authigenic minerals is difficult to constrain but may play a major role in the global biogeochemical cycles of some elements, including silicon (Si) and germanium (Ge). Here, we present Ge/Si, δ^(74)Ge, and supporting chemical data of pore waters and core incubations at three continental margin sites in California and the Gulf of Mexico. We used these data to partition Ge release and uptake by the various allogenic (delivered via sedimentation) and authigenic (formed in situ) phases in these sediments. About half of the pore water Ge (δ^(74)Ge_(pw) = 1.3–2.4‰) is supplied by biogenic silica dissolution (δ^(74)Ge ~ 3‰), with the other half contributed by lithogenic particulates (δ^(74)Ge ~ 0.6‰). The highest Ge/Si (~3μmol/mol) and lowest δ^(74)Ge (1.3–1.9‰) are observed at the Fe redox horizon, suggesting a supply from detrital Ge-rich Fe oxides. The precipitation of authigenic phases (most likely aluminosilicate clays) in deeper sediments preferentially incorporates Ge over Si, resulting in low pore water Ge/Si (~0.3μmol/mol). The lack of corresponding δ^(74)Ge_(pw) trend indicates negligible Ge isotope fractionation during this process. Ge fluxes measured via core incubations were variable and appeared strongly controlled by Fe redox behavior near the sediment-water interface. In some cases, reductive Fe oxide dissolution appeared to enhance the benthic Ge flux by over 100% and released fractionated low δ74Ge of ~−0.7‰, resulting in overall benthic δ^(74)Ge_(inc) between –0.2 and 3.6‰, depending on Fe oxide contribution to Ge flux. We estimate that detrital inputs supply 12–31% of total dissolved Ge to continental margin pore fluids globally, resulting in an average pore water and benthic flux δ^(74)Ge between 2.2 and 2.7‰. Assuming 10-60% of pore water Ge is captured by the authigenic aluminosilicate sink, the dissolved Ge flux to the ocean derived from terrigenous inputs should be roughly 2.5–6.6 Mmol/y, much higher than previously estimated. Our results imply that authigenic Si burial in continental margins should be in the range of 1–8 Tmol/y (best estimate 3.1 Tmol/y), sufficient to close the global marine Si budget

Distribution of extracellular flavins in a coastal marine basin and their relationship to redox gradients and microbial community members

The flavins (including flavin mononucleotide (FMN) and riboflavin (RF)) are a class of organic compounds synthesized by organisms to assist in critical redox reactions. While known to be secreted extracellularly by some species in laboratory-based cultures, flavin concentrations are largely unreported in the natural environment. Here, we present pore water and water column profiles of extracellular flavins (FMN and RF) and two degradation products (lumiflavin and lumichrome) from a coastal marine basin in the Southern California Bight alongside ancillary geochemical and 16S rRNA microbial community data. Flavins were detectable at picomolar concentrations in the water column (93–300 pM FMN, 14–40 pM RF) and low nanomolar concentrations in pore waters (250–2070 pM FMN, 11–210 pM RF). Elevated pore water flavin concentrations displayed an increasing trend with sediment depth and were significantly correlated with the total dissolved Fe (negative) and Mn (positive) concentrations. Network analysis revealed a positive relationship between flavins and the relative abundance of Dehalococcoidia and the MSBL9 clade of Planctomycetes, indicating possible secretion by members of these lineages. These results suggest that flavins are a common component of the so-called shared extracellular metabolite pool, especially in anoxic marine sediments where they exist at physiologically relevant concentrations for metal oxide reduction

A First Look at Dissolved Ge Isotopes in Marine Sediments

The removal of chemical species from seawater during the precipitation of authigenic minerals is difficult to constrain but may play a major role in the global biogeochemical cycles of some elements, including silicon (Si) and germanium (Ge). Here, we present Ge/Si, δ74Ge, and supporting chemical data of pore waters and core incubations at three continental margin sites in California and the Gulf of Mexico. We used these data to partition Ge release and uptake by the various allogenic (delivered via sedimentation) and authigenic (formed in situ) phases in these sediments. About half of the pore water Ge (δ74Gepw = 1.3–2.4‰) is supplied by biogenic silica dissolution (δ74Ge ~ 3‰), with the other half contributed by lithogenic particulates (δ74Ge ~ 0.6‰). The highest Ge/Si (~3μmol/mol) and lowest δ74Ge (1.3–1.9‰) are observed at the Fe redox horizon, suggesting a supply from detrital Ge-rich Fe oxides. The precipitation of authigenic phases (most likely aluminosilicate clays) in deeper sediments preferentially incorporates Ge over Si, resulting in low pore water Ge/Si (~0.3μmol/mol). The lack of corresponding δ74Gepw trend indicates negligible Ge isotope fractionation during this process. Ge fluxes measured via core incubations were variable and appeared strongly controlled by Fe redox behavior near the sediment-water interface. In some cases, reductive Fe oxide dissolution appeared to enhance the benthic Ge flux by over 100% and released fractionated low δ74Ge of ~−0.7‰, resulting in overall benthic δ74Geinc between –0.2 and 3.6‰, depending on Fe oxide contribution to Ge flux. We estimate that detrital inputs supply 12–31% of total dissolved Ge to continental margin pore fluids globally, resulting in an average pore water and benthic flux δ74Ge between 2.2 and 2.7‰. Assuming 10-60% of pore water Ge is captured by the authigenic aluminosilicate sink, the dissolved Ge flux to the ocean derived from terrigenous inputs should be roughly 2.5–6.6 Mmol/y, much higher than previously estimated. Our results imply that authigenic Si burial in continental margins should be in the range of 1–8 Tmol/y (best estimate 3.1 Tmol/y), sufficient to close the global marine Si budget

A First Look at Dissolved Ge Isotopes in Marine Sediments

The removal of chemical species from seawater during the precipitation of authigenic minerals is difficult to constrain but may play a major role in the global biogeochemical cycles of some elements, including silicon (Si) and germanium (Ge). Here, we present Ge/Si, δ74Ge, and supporting chemical data of pore waters and core incubations at three continental margin sites in California and the Gulf of Mexico. We used these data to partition Ge release and uptake by the various allogenic (delivered via sedimentation) and authigenic (formed in situ) phases in these sediments. About half of the pore water Ge (δ74Gepw = 1.3–2.4‰) is supplied by biogenic silica dissolution (δ74Ge ~ 3‰), with the other half contributed by lithogenic particulates (δ74Ge ~ 0.6‰). The highest Ge/Si (~3μmol/mol) and lowest δ74Ge (1.3–1.9‰) are observed at the Fe redox horizon, suggesting a supply from detrital Ge-rich Fe oxides. The precipitation of authigenic phases (most likely aluminosilicate clays) in deeper sediments preferentially incorporates Ge over Si, resulting in low pore water Ge/Si (~0.3μmol/mol). The lack of corresponding δ74Gepw trend indicates negligible Ge isotope fractionation during this process. Ge fluxes measured via core incubations were variable and appeared strongly controlled by Fe redox behavior near the sediment-water interface. In some cases, reductive Fe oxide dissolution appeared to enhance the benthic Ge flux by over 100% and released fractionated low δ74Ge of ~−0.7‰, resulting in overall benthic δ74Geinc between –0.2 and 3.6‰, depending on Fe oxide contribution to Ge flux. We estimate that detrital inputs supply 12–31% of total dissolved Ge to continental margin pore fluids globally, resulting in an average pore water and benthic flux δ74Ge between 2.2 and 2.7‰. Assuming 10-60% of pore water Ge is captured by the authigenic aluminosilicate sink, the dissolved Ge flux to the ocean derived from terrigenous inputs should be roughly 2.5–6.6 Mmol/y, much higher than previously estimated. Our results imply that authigenic Si burial in continental margins should be in the range of 1–8 Tmol/y (best estimate 3.1 Tmol/y), sufficient to close the global marine Si budget

How manganese empowered life with dioxygen (and vice versa)

Throughout the history of life on Earth, abiotic components of the environment have shaped the evolution of life, and in turn life has shaped the environment. The element manganese embodies a special aspect of this collaboration; its history is closely entwined with those of photosynthesis and O_2—two reigning features that characterize the biosphere today. Manganese chemistry was central to the environmental context and evolutionary innovations that enabled the origin of oxygenic photosynthesis and the ensuing rise of O_2. It was also manganese chemistry that provided an early, fortuitous antioxidant system that was instrumental in how life came to cope with oxidative stress and ultimately thrive in an aerobic world. Subsequently, the presence of O2 transformed the biogeochemical dynamics of the manganese cycle, enabling a rich suite of environmental and biological processes involving high-valent manganese and manganese redox cycling. Here, we described insights from chemistry, biology, and geology, to examine manganese dynamics in the environment, and its unique role in the history of life

How manganese empowered life with dioxygen (and vice versa)

Throughout the history of life on Earth, abiotic components of the environment have shaped the evolution of life, and in turn life has shaped the environment. The element manganese embodies a special aspect of this collaboration; its history is closely entwined with those of photosynthesis and O_2—two reigning features that characterize the biosphere today. Manganese chemistry was central to the environmental context and evolutionary innovations that enabled the origin of oxygenic photosynthesis and the ensuing rise of O_2. It was also manganese chemistry that provided an early, fortuitous antioxidant system that was instrumental in how life came to cope with oxidative stress and ultimately thrive in an aerobic world. Subsequently, the presence of O2 transformed the biogeochemical dynamics of the manganese cycle, enabling a rich suite of environmental and biological processes involving high-valent manganese and manganese redox cycling. Here, we described insights from chemistry, biology, and geology, to examine manganese dynamics in the environment, and its unique role in the history of life

Vitamin B1 in marine sediments: pore water concentration gradient drives benthic flux with potential biological implications

Vitamin B1, or thiamin, can limit primary productivity in marine environments, however the major marine environmental sources of this essential coenzyme remain largely unknown. Vitamin B1 can only be produced by organisms that possess its complete synthesis pathway, while other organisms meet their cellular B1 quota by scavenging the coenzyme from exogenous sources. Due to high bacterial cell density and diversity, marine sediments could represent some of the highest concentrations of putative B1 producers, yet these environments have received little attention as a possible source of B1 to the overlying water column. Here we report the first dissolved pore water profiles of B1 measured in cores collected in two consecutive years from Santa Monica Basin, CA. Vitamin B1 concentrations were fairly consistent between the two years ranging from 30 pM up to 770 pM. A consistent maximum at ~5 cm sediment depth covaried with dissolved concentrations of iron. Pore water concentrations were higher than water column levels and represented some of the highest known environmental concentrations of B1 measured to date, (over two times higher than maximum water column concentrations) suggesting increased rates of cellular production and release within the sediments. A one dimensional diffusion-transport model applied to the B1 profile was used to estimate a diffusive benthic flux of ~0.7 nmol m(-2) d(-1). This is an estimated flux across the sediment-water interface in a deep sea basin; if similar magnitude B-vitamin fluxes occur in shallow coastal waters, benthic input could prove to be a significant B1-source to the water column and may play an important role in supplying this organic growth factor to auxotrophic primary producers.Financial support for this research has been provided by the National Science Foundation (OCE 1435666; OCE 0934073; and ANT 1029878).Peer reviewe

Distribution of Extracellular Flavins in a Coastal Marine Basin and Their Relationship to Redox Gradients and Microbial Community Members

The flavins (including flavin mononucleotide (FMN) and riboflavin (RF)) are a class of organic compounds synthesized by organisms to assist in critical redox reactions. While known to be secreted extracellularly by some species in laboratory-based cultures, flavin concentrations are largely unreported in the natural environment. Here, we present pore water and water column profiles of extracellular flavins (FMN and RF) and two degradation products (lumiflavin and lumichrome) from a coastal marine basin in the Southern California Bight alongside ancillary geochemical and 16S rRNA microbial community data. Flavins were detectable at picomolar concentrations in the water column (93–300 pM FMN, 14–40 pM RF) and low nanomolar concentrations in pore waters (250–2070 pM FMN, 11–210 pM RF). Elevated pore water flavin concentrations displayed an increasing trend with sediment depth and were significantly correlated with the total dissolved Fe (negative) and Mn (positive) concentrations. Network analysis revealed a positive relationship between flavins and the relative abundance of Dehalococcoidia and the MSBL9 clade of Planctomycetes, indicating possible secretion by members of these lineages. These results suggest that flavins are a common component of the so-called shared extracellular metabolite pool, especially in anoxic marine sediments where they exist at physiologically relevant concentrations for metal oxide reduction