Akiko Makabe
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View article: Elucidating the isotopic dynamics of nitrate and ammonium in the Fuji River using a Lagrangian approach: stable nitrate and fractionating ammonium
Elucidating the isotopic dynamics of nitrate and ammonium in the Fuji River using a Lagrangian approach: stable nitrate and fractionating ammonium Open
Isotopic signatures ( δ 15 N and δ 18 O) of nitrate (NO 3 − ) have been widely used to trace NO 3 − sources in rivers. These isotopic markers are often treated as “conservative tracers,” reflecting source mixing without significant isotope…
View article: Enhancing role of nitrogen fixation in biogeochemical cycles of the Pacific Arctic
Enhancing role of nitrogen fixation in biogeochemical cycles of the Pacific Arctic Open
The Arctic Ocean is warming rapidly, prompting increased attention to the ecosystem’s response to sea-ice loss and the influx of organisms from lower latitudes. Here we found that nitrogen fixation in the Pacific Arctic region was signific…
View article: Microscopic evidence for nanoparticle-mediated growth of native gold in sulfide deposits at the Higashi–Aogashima Knoll Caldera hydrothermal field
Microscopic evidence for nanoparticle-mediated growth of native gold in sulfide deposits at the Higashi–Aogashima Knoll Caldera hydrothermal field Open
Gold (or electrum) in hydrothermal fluid precipitates directly from gold sulfide complex and/or partly via suspended nanoparticles. The hydrothermal fluid contains “invisible gold” that is atomically dispersed in sulfide minerals or as nan…
View article: Widespread occurrence and relevance of phosphate storage in foraminifera
Widespread occurrence and relevance of phosphate storage in foraminifera Open
Foraminifera are ubiquitous marine protists that intracellularly accumulate phosphate 1 , an important macronutrient in marine ecosystems and in fertilizer potentially leaked into the ocean. Intracellular phosphate concentrations can be 10…
View article: Changes in the Composition of International Association for the Physical Sciences of the Oceans Standard Seawater
Changes in the Composition of International Association for the Physical Sciences of the Oceans Standard Seawater Open
Changes in the composition of International Association for the Physical Sciences of the Oceans Standard Seawater (SSW) for salinity measurements were examined for borosilicate glass bottle-type SSW batches P138 (2000) to P165 (2021) to un…
View article: Oxygen isotope fractionation during anaerobic ammonium oxidation by the marine representative <i>Candidatus</i> Scalindua sp.
Oxygen isotope fractionation during anaerobic ammonium oxidation by the marine representative <i>Candidatus</i> Scalindua sp. Open
Analysing the nitrogen (15ε) and oxygen (18ε) isotope effects of anaerobic ammonium oxidation (anammox) is essential for accurately assessing its potential contribution to fixed-N losses in the ocean, yet the 18ε of anammox remains unexplo…
View article: Elucidating carbon sources of hydrothermal vent animals using natural <sup>14</sup>C abundances and habitat water temperature
Elucidating carbon sources of hydrothermal vent animals using natural <sup>14</sup>C abundances and habitat water temperature Open
Deep‐sea hydrothermal vents host exceptional ecosystems with lush animal communities primarily relying on organic matter (OM) produced by chemoautotrophic microbes. Though energy sources and food webs at vents have been extensively studied…
View article: Nitrogen Isotopes of Sinking Particles Reveal the Seasonal Transition of the Nitrogen Source for Phytoplankton
Nitrogen Isotopes of Sinking Particles Reveal the Seasonal Transition of the Nitrogen Source for Phytoplankton Open
In the high‐productivity subarctic ocean, phytoplankton growth is assumed to rely mainly on nitrate, based on snapshot observations conducted in spring or summer. However, the year‐round utilization of nitrate and ammonium by phytoplankton…
View article: Polysulfide-assisted urea synthesis from carbon monoxide and ammonia in water
Polysulfide-assisted urea synthesis from carbon monoxide and ammonia in water Open
Efficient conversion of carbon monoxide into urea in an aqueous ammonia solution was demonstrated through coupling with the elemental sulfur reduction to polysulfides. This reaction starts with a simple mixture of carbon monoxide, ammonia,…
View article: Nitrogen Sources for Phytoplankton in the Eastern Indian Ocean Determined From δ<sup>15</sup>N of Chlorophyll <i>a</i> and Divinylchlorophyll <i>a</i>
Nitrogen Sources for Phytoplankton in the Eastern Indian Ocean Determined From δ<sup>15</sup>N of Chlorophyll <i>a</i> and Divinylchlorophyll <i>a</i> Open
Nitrogen isotope analysis of chloropigments provides information on the sources of nitrogenous nutrients assimilated by phytoplankton. The abundant, ubiquitous chlorophyll a records nitrogen isotopic compositions (δ 15 N) of eukaryotic phy…
View article: Sulfur-assisted urea synthesis from carbon monoxide and ammonia in water
Sulfur-assisted urea synthesis from carbon monoxide and ammonia in water Open
Efficient conversion of carbon monoxide into urea in an aqueous ammonia solution was demonstrated through coupling with the elemental sulfur reduction to polysulfides. Polysulfides control the overall reaction rate while suppressing the ac…
View article: Hydrogen and carbon isotope fractionation factors of aerobic methane oxidation in deep-sea water
Hydrogen and carbon isotope fractionation factors of aerobic methane oxidation in deep-sea water Open
Isotope fractionation factors associated with various biogeochemical processes are important in ensuring the reliable use of isotope tracers in biogeosciences at large. Methane is a key component of the subsurface biosphere and a notable g…
View article: Hydrogen and carbon isotope fractionation factors of aerobic methane oxidation in deep-sea water
Hydrogen and carbon isotope fractionation factors of aerobic methane oxidation in deep-sea water Open
Isotope fractionation factors associated with various biogeochemical processes are important in ensuring the practicality of isotope tracers in biogeosciences at large. Methane is a key component of the subsurface biosphere and a notable g…
View article: Stable Abiotic Production of Ammonia from Nitrate in Komatiite-Hosted Hydrothermal Systems in the Hadean and Archean Oceans
Stable Abiotic Production of Ammonia from Nitrate in Komatiite-Hosted Hydrothermal Systems in the Hadean and Archean Oceans Open
Abiotic fixation of atmospheric dinitrogen to ammonia is important in prebiotic chemistry and biological evolution in the Hadean and Archean oceans. Though it is widely accepted that nitrate (NO3−) was generated in the early atmospheres, t…
View article: Changes in stable nitrogen isotopes of plants, bulk soil and soil dissolved N during ecosystem retrogression in boreal forest
Changes in stable nitrogen isotopes of plants, bulk soil and soil dissolved N during ecosystem retrogression in boreal forest Open
Stable nitrogen isotope ratios (δ 15 N) of plants and soil have been used to study changes in the N cycle during ecosystem succession and retrogression. However, little is known about how δ 15 N of soil mineral N and dissolved organic N (D…
View article: Nitrogen and Oxygen Isotope Signatures of Nitrogen Compounds during Anammox in the Laboratory and a Wastewater Treatment Plant
Nitrogen and Oxygen Isotope Signatures of Nitrogen Compounds during Anammox in the Laboratory and a Wastewater Treatment Plant Open
Isotopic fractionation factors against 15N and 18O during anammox (anaerobic ammonia oxidization by nitrite) are critical for evaluating the importance of this process in natural environments. We performed batch incubation experiments with…
View article: Microbial community and geochemical analyses of trans-trench sediments for understanding the roles of hadal environments
Microbial community and geochemical analyses of trans-trench sediments for understanding the roles of hadal environments Open
Hadal trench bottom (>6000 m below sea level) sediments harbor higher microbial cell abundance compared with adjacent abyssal plain sediments. This is supported by the accumulation of sedimentary organic matter (OM), facilitated by trench …
View article: Microbial community and geochemical analyses of trans-trench sediments for understanding the roles of hadal environments
Microbial community and geochemical analyses of trans-trench sediments for understanding the roles of hadal environments Open
Hadal trench bottom (>6,000 m below sea level) sediments harbor higher microbial cell abundance compared to adjacent abyssal plain sediments. This is supported by the accumulation of sedimentary organic matter (OM), facilitated by trench t…
View article: Factors Regulating Nitrification in the Arctic Ocean: Potential Impact of Sea Ice Reduction and Ocean Acidification
Factors Regulating Nitrification in the Arctic Ocean: Potential Impact of Sea Ice Reduction and Ocean Acidification Open
Nitrification is susceptible to changes in light and pH and, thus, could be influenced by recent sea ice reductions and acidification in the Arctic Ocean. We investigated the sensitivity of nitrification to light, pH, and substrate availab…
View article: Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria
Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria Open
Natural abundance of stable nitrogen (N) and oxygen (O) isotopes are invaluable biogeochemical tracers for assessing the N transformations in the environment. To fully exploit these tracers, the N and O isotope effects (15ε and 18ε) associ…
View article: Control of the Nitrogen Isotope Composition of the Fungal Biomass: Evidence of Microbial Nitrogen Use Efficiency
Control of the Nitrogen Isotope Composition of the Fungal Biomass: Evidence of Microbial Nitrogen Use Efficiency Open
Changes in 15N/14N in the soil microbial biomass during nitrogen (N) mineralization have been hypothesized to influence 15N/14N in soil organic matter among ecosystem sites. However, a direct experimental test of this mechanism has not yet…
View article: Hadal water biogeochemistry over the Izu–Ogasawara Trench observed with a full-depth CTD-CMS
Hadal water biogeochemistry over the Izu–Ogasawara Trench observed with a full-depth CTD-CMS Open
Full-depth profiles of hydrographic and geochemical properties at the Izu–Ogasawara Trench were observed for the first time using a CTD-CMS (conductivity–temperature–depth profiler with carousel multiple sampling) system. Additionally, com…
View article: Nitrate Isotope Distribution in the Subarctic and Subtropical North Pacific
Nitrate Isotope Distribution in the Subarctic and Subtropical North Pacific Open
Nitrogen and oxygen isotopic compositions of nitrate (δ 15 N Nitrate and δ 18 O Nitrate ) were determined along 47°N in the subarctic North Pacific and 149°E in the western North Pacific. In the western subarctic gyre, known as a high‐nutr…
View article: Hadal water biogeochemistry over the Izu-Ogasawara Trench observed with a full-depth CTD-CMS
Hadal water biogeochemistry over the Izu-Ogasawara Trench observed with a full-depth CTD-CMS Open
Full-depth profiles of hydrographic and geochemical properties at the Izu-Ogasawara Trench were observed for the first time using a CTD-CMS (Conductivity Temperature Depth profiler with Carousel Multiple Sampling) system, supplemented by s…