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  1. null (Ed.)
  2. From June to August 2018, the eruption of Kīlauea volcano on the island of Hawai‘i injected millions of cubic meters of molten lava into the nutrient-poor waters of the North Pacific Subtropical Gyre. The lava-impacted seawater was characterized by high concentrations of metals and nutrients that stimulated phytoplankton growth, resulting in an extensive plume of chlorophyll a that was detectable by satellite. Chemical and molecular evidence revealed that this biological response hinged on unexpectedly high concentrations of nitrate, despite the negligible quantities of nitrogen in basaltic lava. We hypothesize that the high nitrate was caused by buoyant plumes of nutrient-rich deep waters created by the substantial input of lava into the ocean. This large-scale ocean fertilization was therefore a unique perturbation event that revealed how marine ecosystems respond to exogenous inputs of nutrients. 
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  3. Summary

    The physical and biological dynamics that influence phytoplankton communities in the oligotrophic ocean are complex, changing across broad temporal and spatial scales. Eukaryotic phytoplankton (e.g., diatoms), despite their relatively low abundance in oligotrophic waters, are responsible for a large component of the organic matter flux to the ocean interior. Mesoscale eddies can impact both microbial community structure and function, enhancing primary production and carbon export, but the mechanisms that underpin these dynamics are still poorly understood. Here, mesoscale eddy influences on the taxonomic diversity and expressed functional profiles of surface communities of microeukaryotes and particle‐associated heterotrophic bacteria from the North Pacific Subtropical Gyre were assessed over 2 years (spring 2016 and summer 2017). The taxonomic diversity of the microeukaryotes significantly differed by eddy polarity (cyclonic versus anticyclonic) and between sampling seasons/years and was significantly correlated with the taxonomic diversity of particle‐associated heterotrophic bacteria. The expressed functional profile of these taxonomically distinct microeukaryotes varied consistently as a function of eddy polarity, with cyclones having a different expression pattern than anticyclones, and between sampling seasons/years. These data suggest that mesoscale forcing, and associated changes in biogeochemistry, could drive specific physiological responses in the resident microeukaryote community, independent of species composition.

     
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  4. Summary

    Emiliania huxleyiis a calcifying haptophyte, contributing to both the organic and inorganic marine carbon cycles. In marine ecosystems, light is a major driver of phytoplankton physiology and ultimately carbon flow through the ecosystem. Here, we analysed a Lagrangian time‐series of metatranscriptomes collected in the North Pacific Subtropical Gyre (NPSG) to examine howin situpopulations ofE.huxleyimodulate gene expression over day–night transitions. ManyE.huxleyicontigs had a diel expression pattern, with 61% of contigs clustering into modules with statistically significant diel periodicity. Contigs involved in processes that build up energy stores, like carbon fixation and lipid synthesis, peaked around dawn. In contrast, contigs involved in processes that released energy stores, like respiration and lipid degradation, peaked mid‐day and towards dusk. These patterns suggest an orchestrated cycle of building, then consuming energy stores inE.huxleyipopulations in the NPSG. Selected contigs related to the cell cycle also exhibited significant diel periodicity consistent with phased modulations of division observed in culture. Overall, these patterns of gene expression suggest a daily metabolic cascade that could contribute to both organic and inorganic carbon flow in this nutrient depleted ecosystem.

     
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