Description: In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics-namely production, consumption, and net emissions-is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climateactive trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify how these mechanisms affect marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling. Fundamental to these efforts is ensuring that the datasets produced by independent scientists are comparable and interoperable. Equally critical is transparent communication within the research community about the technical improvements required to increase our collective understanding of marine CH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB) was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O. Here, we summarize the outcomes from the workshop to describe the challenges and opportunities for near-future CH4 and N2O research in the marine environment.

Description: Highlights • Submarine basaltic glasses from Pitcairn Island are uniformly high in δ98/95Mo. • Proterozoic pelagic sediments can explain radiogenic EM-1 and heavy Mo signatures. • Enriched “anoxic” signature found in both large low shear velocity provinces (LLSVPs). • Anoxic sediments buffer Precambrian subduction zone fluids to reducing conditions. • Subduction cycling of some redox sensitive metals to the mantle wedge was limited. Abstract Subduction redistributes elements between Earth's principal geochemical reservoirs, modifying the chemical composition of Earth's mantle, crust, atmosphere, and hydrosphere, and consequently having an impact on the evolution of life itself. Subduction of surface material that has been geochemically modified by low-temperature processes leads to mineralogical and chemical heterogeneities in mantle reservoirs over time and is recorded in modern ocean island basalts. One of the principal geochemical end members of the heterogeneous deep mantle, the enriched mantle 1 (EM-1) source of Pitcairn Island, has been attributed to the contribution of crustal material with vastly different chemical compositions and ages. The Mo isotope composition of lavas from Pitcairn Island constrains the nature of this recycled crustal component. Pitcairn lavas have elevated δ98/95Mo relative to the depleted mantle. The high δ98/95Mo is associated with high time-integrated 232Th/238U and 87Rb/86Sr, and low time-integrated 147Sm/144Nd and 238U/204Pb. These characteristics can be attributed to the recycling of nearly pristine pelagic sediments that were deposited in a Proterozoic anoxic deep-ocean into the sources of the Pitcairn Island lavas. The isotope composition of these lavas is similar to that of EM-1 hotspots from the South Atlantic, indicating the addition of reduced sediments in both of Earth's large low shear wave velocity provinces (LLSVPs). Consistent data from both locations imply that the subduction cycling of sedimentary redox-sensitive elements such as Mo, S, Se, and U into arc magmas was in these cases inefficient in the Precambrian and the chemical and isotopic signature of reduced sediments is preserved in the source of ocean island basalts bearing the EM-1 characteristics.

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wilson, S. T., Al-Haj, A. N., Bourbonnais, A., Frey, C., Fulweiler, R. W., Kessler, J. D., Marchant, H. K., Milucka, J., Ray, N. E., Suntharalingam, P., Thornton, B. F., Upstill-Goddard, R. C., Weber, T. S., Arevalo-Martinez, D. L., Bange, H. W., Benway, H. M., Bianchi, D., Borges, A., V., Chang, B. X., Crill, P. M., del Valle, D. A., Farias, L., Joye, S. B., Kock, A., Labidi, J., Manning, C. C., Pohlman, J. W., Rehder, G., Sparrow, K. J., Tortell, P. D., Treude, T., Valentine, D. L., Ward, B. B., Yang, S., & Yurganov, L. N. Ideas and perspectives: a strategic assessment of methane and nitrous oxide measurements in the marine environment. Biogeosciences, 17(22), (2020): 5809-5828, https://doi.org/10.5194/bg-17-5809-2020.

Description: In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics – namely production, consumption, and net emissions – is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climate-active trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify how these mechanisms affect marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling. Fundamental to these efforts is ensuring that the datasets produced by independent scientists are comparable and interoperable. Equally critical is transparent communication within the research community about the technical improvements required to increase our collective understanding of marine CH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB) was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O. Here, we summarize the outcomes from the workshop to describe the challenges and opportunities for near-future CH4 and N2O research in the marine environment.

Description: This article was an outcome of a workshop organized by the Ocean Carbon and Biogeochemistry (OCB) project office, which is supported by the US National Science Foundation (grant no. 1558412) and the National Aeronautics and Space Administration (grant no. NNX17AB17G). The workshop received additional funding from the Scientific Committee on Ocean Research (SCOR) which receives funding from the US National Science Foundation (grant no. 1840868) and contributions by additional national SCOR committees. The Chilean COPAS N2O time-series measurements were supported by Agencia Nacional de Investigación y Desarrollo (grant no. 1200861).