ALBERT

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bundy, R. M., Tagliabue, A., Hawco, N. J., Morton, P. L., Twining, B. S., Hatta, M., Noble, A. E., Cape, M. R., John, S. G., Cullen, J. T., & Saito, M. A. Elevated sources of cobalt in the Arctic Ocean. Biogeosciences, 17(19), (2020): 4745-4767, doi:10.5194/bg-17-4745-2020.

Description: Cobalt (Co) is an important bioactive trace metal that is the metal cofactor in cobalamin (vitamin B12) which can limit or co-limit phytoplankton growth in many regions of the ocean. Total dissolved and labile Co measurements in the Canadian sector of the Arctic Ocean during the U.S. GEOTRACES Arctic expedition (GN01) and the Canadian International Polar Year GEOTRACES expedition (GIPY14) revealed a dynamic biogeochemical cycle for Co in this basin. The major sources of Co in the Arctic were from shelf regions and rivers, with only minimal contributions from other freshwater sources (sea ice, snow) and eolian deposition. The most striking feature was the extremely high concentrations of dissolved Co in the upper 100 m, with concentrations routinely exceeding 800 pmol L−1 over the shelf regions. This plume of high Co persisted throughout the Arctic basin and extended to the North Pole, where sources of Co shifted from primarily shelf-derived to riverine, as freshwater from Arctic rivers was entrained in the Transpolar Drift. Dissolved Co was also strongly organically complexed in the Arctic, ranging from 70 % to 100 % complexed in the surface and deep ocean, respectively. Deep-water concentrations of dissolved Co were remarkably consistent throughout the basin (∼55 pmol L−1), with concentrations reflecting those of deep Atlantic water and deep-ocean scavenging of dissolved Co. A biogeochemical model of Co cycling was used to support the hypothesis that the majority of the high surface Co in the Arctic was emanating from the shelf. The model showed that the high concentrations of Co observed were due to the large shelf area of the Arctic, as well as to dampened scavenging of Co by manganese-oxidizing (Mn-oxidizing) bacteria due to the lower temperatures. The majority of this scavenging appears to have occurred in the upper 200 m, with minimal additional scavenging below this depth. Evidence suggests that both dissolved Co (dCo) and labile Co (LCo) are increasing over time on the Arctic shelf, and these limited temporal results are consistent with other tracers in the Arctic. These elevated surface concentrations of Co likely lead to a net flux of Co out of the Arctic, with implications for downstream biological uptake of Co in the North Atlantic and elevated Co in North Atlantic Deep Water. Understanding the current distributions of Co in the Arctic will be important for constraining changes to Co inputs resulting from regional intensification of freshwater fluxes from ice and permafrost melt in response to ongoing climate change.

Description: This work was supported by National Science Foundation Ocean Sciences (NSF OCE) grants (grant nos. 1435056, 1736599, and 1924554) to Mak A. Saito, as well as by a Woods Hole Oceanographic Institution Postdoctoral Scholar grant to Randelle M. Bundy and Mattias R. Cape. Mariko Hatta was supported by NSF OCE grant no. 1439253. Alessandro Tagliabue was supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (BYONIC, grant no. 724289). Benjamin S. Twining was supported by NSF OCE grant no. 1435862. Peter L. Morton was supported by NSF OCE grant no. 1436019, and a portion of the work was completed at the NHMFL, which is supported by the National Science Foundation through DMR-1644779 and the State of Florida. Jay T. Cullen was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada and an International Polar Year (IPY) Canada grant.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bianchi, T. S., Anand, M., Bauch, C. T., Canfield, D. E., De Meester, L., Fennel, K., Groffman, P. M., Pace, M. L., Saito, M., & Simpson, M. J. Ideas and perspectives: biogeochemistry - some key foci for the future. Biogeosciences, 18(10), (2021): 3005–3013, https://doi.org/10.5194/bg-18-3005-2021.

Description: Biogeochemistry has an important role to play in many environmental issues of current concern related to global change and air, water, and soil quality. However, reliable predictions and tangible implementation of solutions, offered by biogeochemistry, will need further integration of disciplines. Here, we refocus on how further developing and strengthening ties between biology, geology, chemistry, and social sciences will advance biogeochemistry through (1) better incorporation of mechanisms, including contemporary evolutionary adaptation, to predict changing biogeochemical cycles, and (2) implementing new and developing insights from social sciences to better understand how sustainable and equitable responses by society are achieved. The challenges for biogeochemists in the 21st century are formidable and will require both the capacity to respond fast to pressing issues (e.g., catastrophic weather events and pandemics) and intense collaboration with government officials, the public, and internationally funded programs. Keys to success will be the degree to which biogeochemistry can make biogeochemical knowledge more available to policy makers and educators about predicting future changes in the biosphere, on timescales from seasons to centuries, in response to climate change and other anthropogenic impacts. Biogeochemistry also has a place in facilitating sustainable and equitable responses by society.

Description: TSB was supported in part by the Beverly Thompson Endowed Chair in Geological Sciences; MJS acknowledges support from the Natural Sciences and Engineering Research Council via a Tier 1 Canada Research Chair in Integrative Molecular Biogeochemistry.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cohen, N. R., Noble, A. E., Moran, D. M., McIlvin, M. R., Goepfert, T. J., Hawco, N. J., German, C. R., Horner, T. J., Lamborg, C. H., McCrow, J. P., Allen, A. E., & Saito, M. A. Hydrothermal trace metal release and microbial metabolism in the northeastern Lau Basin of the South Pacific Ocean. Biogeosciences, 18(19), (2021): 5397–5422, https://doi.org/10.5194/bg-18-5397-2021.

Description: Bioactive trace metals are critical micronutrients for marine microorganisms due to their role in mediating biological redox reactions, and complex biogeochemical processes control their distributions. Hydrothermal vents may represent an important source of metals to microorganisms, especially those inhabiting low-iron waters, such as in the southwest Pacific Ocean. Previous measurements of primordial 3He indicate a significant hydrothermal source originating in the northeastern (NE) Lau Basin, with the plume advecting into the southwest Pacific Ocean at 1500–2000 m depth (Lupton et al., 2004). Studies investigating the long-range transport of trace metals associated with such dispersing plumes are rare, and the biogeochemical impacts on local microbial physiology have not yet been described. Here we quantified dissolved metals and assessed microbial metaproteomes across a transect spanning the tropical and equatorial Pacific with a focus on the hydrothermally active NE Lau Basin and report elevated iron and manganese concentrations across 441 km of the southwest Pacific. The most intense signal was detected near the Mangatolo Triple Junction (MTJ) and Northeast Lau Spreading Center (NELSC), in close proximity to the previously reported 3He signature. Protein content in distal-plume-influenced seawater, which was high in metals, was overall similar to background locations, though key prokaryotic proteins involved in metal and organic uptake, protein degradation, and chemoautotrophy were abundant compared to deep waters outside of the distal plume. Our results demonstrate that trace metals derived from the NE Lau Basin are transported over appreciable distances into the southwest Pacific Ocean and that bioactive chemical resources released from submarine vent systems are utilized by surrounding deep-sea microbes, influencing both their physiology and their contributions to ocean biogeochemical cycling.

Description: This research has been supported by the National Science Foundation (grant nos. 1031271, 1924554, 1850719, 1736599, and 1851007); the Gordon and Betty Moore Foundation (grant no. 3782); and the Simons Foundation (grant no. 544236).

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chmiel, R., Lanning, N., Laubach, A., Lee, J.-M., Fitzsimmons, J., Hatta, M., Jenkins, W., Lam, P., McIlvin, M., Tagliabue, A., & Saito, M. Major processes of the dissolved cobalt cycle in the north and equatorial Pacific Ocean. Biogeosciences, 19(9), (2022): 2365–2395, https://doi.org/10.5194/bg-19-2365-2022.

Description: Over the past decade, the GEOTRACES and wider trace metal geochemical community has made substantial contributions towards constraining the marine cobalt (Co) cycle and its major biogeochemical processes. However, few Co speciation studies have been conducted in the North and equatorial Pacific Ocean, a vast portion of the world's oceans by volume and an important end-member of deep thermohaline circulation. Dissolved Co (dCo) samples, including total dissolved and labile Co, were measured at-sea during the GEOTRACES Pacific Meridional Transect (GP15) expedition along the 152∘ W longitudinal from 56∘ N to 20∘ S. Along this transect, upper-ocean dCo (σ0〈26) was linearly correlated with dissolved phosphate (slope = 82±3, µmol : mol) due to phytoplankton uptake and remineralization. As depth increased, dCo concentrations became increasingly decoupled from phosphate concentrations due to co-scavenging with manganese oxide particles in the mesopelagic. The transect revealed an organically bound coastal source of dCo to the Alaskan Stream associated with low-salinity waters. An intermediate-depth hydrothermal flux of dCo was observed off the Hawaiian coast at the Loihi Seamount, and the elevated dCo was correlated with potential xs3He at and above the vent site; however, the Loihi Seamount likely did not represent a major source of Co to the Pacific basin. Elevated concentrations of dCo within oxygen minimum zones (OMZs) in the equatorial North and South Pacific were consistent with the suppression of oxidative scavenging, and we estimate that future deoxygenation could increase the OMZ dCo inventory by 18 % to 36 % over the next century. In Pacific Deep Water (PDW), a fraction of elevated ligand-bound dCo appeared protected from scavenging by the high biogenic particle flux in the North Pacific basin. This finding is counter to previous expectations of low dCo concentrations in the deep Pacific due to scavenging over thermohaline circulation. Compared to a Co global biogeochemical model, the observed transect displayed more extreme inventories and fluxes of dCo than predicted by the model, suggesting a highly dynamic Pacific Co cycle.

Description: This research has been supported by the National Science Foundation (grant nos. OCE-1736599, OCE-1756138, OCE-1657781 and OCE-1736601) and the Horizon 2020 research and innovation program (BYONIC; grant no. 724289).

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Held, N. A., Webb, E. A., McIlvin, M. M., Hutchins, D. A., Cohen, N. R., Moran, D. M., Kunde, K., Lohan, M. C., Mahaffey, C., Woodward, E. M. S., & Saito, M. A. Co-occurrence of fe and P stress in natural populations of the marine diazotroph Trichodesmium. Biogeosciences, 17(9), (2020): 2537-2551, doi:10.5194/bg-17-2537-2020.

Description: Trichodesmium is a globally important marine microbe that provides fixed nitrogen (N) to otherwise N-limited ecosystems. In nature, nitrogen fixation is likely regulated by iron or phosphate availability, but the extent and interaction of these controls are unclear. From metaproteomics analyses using established protein biomarkers for nutrient stress, we found that iron–phosphate co-stress is the norm rather than the exception for Trichodesmium colonies in the North Atlantic Ocean. Counterintuitively, the nitrogenase enzyme was more abundant under co-stress as opposed to single nutrient stress. This is consistent with the idea that Trichodesmium has a specific physiological state during nutrient co-stress. Organic nitrogen uptake was observed and occurred simultaneously with nitrogen fixation. The quantification of the phosphate ABC transporter PstA combined with a cellular model of nutrient uptake suggested that Trichodesmium is generally confronted by the biophysical limits of membrane space and diffusion rates for iron and phosphate acquisition in the field. Colony formation may benefit nutrient acquisition from particulate and organic sources, alleviating these pressures. The results highlight that to predict the behavior of Trichodesmium, both Fe and P stress must be evaluated simultaneously.

Description: This research has been supported by the National Science Foundation (Division of Graduate Education (grant nos. 1122274), Division of Ocean Sciences (grant nos. 1657755, 1657757, and 1851222), Directorate for Geosciences (grant no. 1639714)), the Gordon and Betty Moore Foundation (grant no. 3782), and the Natural Environment Research Council (NERC) (grant nos. NE/N001079/1 and NE/N001125/1).