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1. Element-Selective Targeting of Nutrient Metabolites in Environmental Samples by Inductively Coupled Plasma Mass Spectrometry and Electrospray Ionization Mass Spectrometry

   https://doi.org/10.3389/fmars.2021.630494  

   Li, Jingxuan ; Boiteau, Rene M. ; Babcock-Adams, Lydia ; Acker, Marianne ; Song, Zhongchang ; McIlvin, Matthew R. ; Repeta, Daniel J. ( May 2021 , Frontiers in Marine Science)

   null (Ed.)

   Metabolites that incorporate elements other than carbon, nitrogen, hydrogen and oxygen can be selectively detected by inductively coupled mass spectrometry (ICPMS). When used in parallel with chromatographic separations and conventional electrospray ionization mass spectrometry (ESIMS), ICPMS allows the analyst to quickly find, characterize and identify target metabolites that carry nutrient elements (P, S, trace metals; “nutrient metabolites”), which are of particular interest to investigations of microbial biogeochemical cycles. This approach has been applied to the study of siderophores and other trace metal organic ligands in the ocean. The original method used mass search algorithms that relied on the ratio of stable isotopologues of iron, copper and nickel to assign mass spectra collected by ESIMS to metabolites carrying these elements detected by ICPMS. However, while isotopologue-based mass assignment algorithms were highly successful in characterizing metabolites that incorporate some trace metals, they do not realize the whole potential of the ICPMS/ESIMS approach as they cannot be used to assign the molecular ions of metabolites with monoisotopic elements or elements for which the ratio of stable isotopes is not known. Here we report a revised ICPMS/ESIMS method that incorporates a number of changes to the configuration of instrument hardware that improves sensitivity of the method by a factor of 4–5, and allows for more accurate quantitation of metabolites. We also describe a new suite of mass search algorithms that can find and characterize metabolites that carry monoisotopic elements. We used the new method to identify siderophores in a laboratory culture of Vibrio cyclitrophicus and a seawater sample collected in the North Pacific Ocean, and to assign molecular ions to monoisotopic cobalt and iodine nutrient metabolites in extracts of a laboratory culture of the marine cyanobacterium Prochorococcus MIT9215. 

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2. Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES‐Era Data

   https://doi.org/10.1029/2020GB006814  

   Horner, T. J. ; Little, S. H. ; Conway, T. M. ; Farmer, J. R. ; Hertzberg, J. E. ; Janssen, D. J. ; Lough, A. J. M. ; McKay, J. L. ; Tessin, A. ; Galer, S. J. G. ; et al ( November 2021 , Global Biogeochemical Cycles)

   Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES‐era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate history.

    

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3. Post-spreading Basalts from the Nanyue Seamount: Implications for the Involvement of Crustal- and Plume-Type Components in the Genesis of the South China Sea Mantle

   https://doi.org/10.3390/min9060378  

   Zheng, Hao ; Zhong, Li-Feng ; Kapsiotis, Argyrios ; Cai, Guan-Qiang ; Wan, Zhi-Feng ; Xia, Bin ( June 2019 , Minerals)

   Fresh samples of basalts were collected by dredging from the Nanyue intraplate seamount in the Southwest sub-basin of the South China Sea (SCS). These are alkali basalts displaying right-sloping, chondrite-normalized rare earth element (REE) profiles. The investigated basalts are characterized by low Os content (60.37–85.13 ppt) and radiogenic 187Os/188Os ratios (~0.19 to 0.21). Furthermore, 40Ar/39Ar dating of the Nanyue basalts showed they formed during the Tortonian (~8.3 Ma) and, thus, are products of (Late Cenozoic) post-spreading volcanism. The Sr–Nd–Pb–Hf isotopic compositions of the Nanyue basalts indicate that their parental melts were derived from an upper mantle reservoir possessing the so-called Dupal isotopic anomaly. Semiquantitative isotopic modeling demonstrates that the isotopic compositions of the Nanyue basalts can be reproduced by mixing three components: the average Pacific midocean ridge basalt (MORB), the lower continental crust (LCC), and the average Hainan ocean island basalt (OIB). Our preferred hypothesis for the genesis of the Nanyue basalts is that their parental magmas were produced from an originally depleted mantle (DM) source that was much affected by the activity of the Hainan plume. Initially, the Hainan diapir caused a thermal perturbation in the upper mantle under the present-day Southwest sub-basin of the SCS that led to erosion of the overlying LCC. Eventually, the resultant suboceanic lithospheric mantle (SOLM) interacted with OIB-type components derived from the nearby Hainan plume. Collectively, these processes contributed crustal- and plume-type components to the upper mantle underlying the Southwest sub-basin of the SCS. This implies that the Dupal isotopic signature in the upper mantle beneath the SCS was an artifact of in situ geological processes rather than a feature inherited from a Southern Hemispheric, upper mantle source. 

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4. Sulfur cycling connects microbiomes and biogeochemistry in deep-sea hydrothermal plumes

   https://doi.org/10.1038/s41396-023-01421-0  

   Zhou, Zhichao ; Tran, Patricia Q. ; Adams, Alyssa M. ; Kieft, Kristopher ; Breier, John A. ; Fortunato, Caroline S. ; Sheik, Cody S. ; Huber, Julie A. ; Li, Meng ; Dick, Gregory J. ; et al ( January 2023 , The ISME Journal)

   Abstract In globally distributed deep-sea hydrothermal vent plumes, microbiomes are shaped by the redox energy landscapes created by reduced hydrothermal vent fluids mixing with oxidized seawater. Plumes can disperse over thousands of kilometers and their characteristics are determined by geochemical sources from vents, e.g., hydrothermal inputs, nutrients, and trace metals. However, the impacts of plume biogeochemistry on the oceans are poorly constrained due to a lack of integrated understanding of microbiomes, population genetics, and geochemistry. Here, we use microbial genomes to understand links between biogeography, evolution, and metabolic connectivity, and elucidate their impacts on biogeochemical cycling in the deep sea. Using data from 36 diverse plume samples from seven ocean basins, we show that sulfur metabolism defines the core microbiome of plumes and drives metabolic connectivity in the microbial community. Sulfur-dominated geochemistry influences energy landscapes and promotes microbial growth, while other energy sources influence local energy landscapes. We further demonstrated the consistency of links among geochemistry, function, and taxonomy. Amongst all microbial metabolisms, sulfur transformations had the highest MW-score, a measure of metabolic connectivity in microbial communities. Additionally, plume microbial populations have low diversity, short migration history, and gene-specific sweep patterns after migrating from background seawater. Selected functions include nutrient uptake, aerobic oxidation, sulfur oxidation for higher energy yields, and stress responses for adaptation. Our findings provide the ecological and evolutionary bases of change in sulfur-driven microbial communities and their population genetics in adaptation to changing geochemical gradients in the oceans. 

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5. Slowly Sinking Particles Underlie Dissolved Iron Transport Across the Pacific Ocean

   https://doi.org/10.1029/2020GB006823  

   Misumi, K. ; Nishioka, J. ; Obata, H. ; Tsumune, D. ; Tsubono, T. ; Long, M. C. ; Lindsay, K. ; Moore, J. K. ( April 2021 , Global Biogeochemical Cycles)

   Continental shelf sediments are an important source of iron (Fe) in the oceans. Observational data suggest that basin‐scale transport of sedimentary sourced Fe accompanies the ventilation of the intermediate layer in the North Pacific. Here we use a marine biogeochemical model to explore the Fe transport mechanism with a focus on the role of sinking particles. The lateral penetration of sedimentary sourced Fe was best simulated when we assumed a short desorption and disaggregation length scale of Fe from sinking particles. The simulation results indicated that Fe is laterally transported mainly through interactions with particles with sinking velocities of 180–460 m yr⁻¹; these velocities are two orders of magnitude slower than typical sinking rates of marine aggregates determined from mass flux measurements. Slowly sinking particles drive the basin‐scale transport of Fe by prolonging its residence time and by injecting sedimentary sourced Fe supplied originally to less dense waters into the intermediate layer water across isopycnal surfaces. A large amount of Fe from shelf sediments of the Okhotsk and Bering Seas is exported to the North Pacific through this particle interaction. These results highlight a biogeochemical linkage between the marginal seas and ocean basins that has been overlooked in global ocean models.

    

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