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Planktonic calcifying organisms play a key role in regulating ocean carbonate chemistry and atmospheric CO₂. Surprisingly, references to the absolute and relative contribution of these organisms to calcium carbonate production are lacking. Here we report quantification of pelagic calcium carbonate production in the North Pacific, providing new insights on the contribution of the three main planktonic calcifying groups. Our results show that coccolithophores dominate the living calcium carbonate (CaCO₃) standing stock, with coccolithophore calcite comprising ~90% of total CaCO₃production, and pteropods and foraminifera playing a secondary role. We show that pelagic CaCO₃production is higher than the sinking flux of CaCO₃at 150 and 200 m at ocean stations ALOHA and PAPA, implying that a large portion of pelagic calcium carbonate is remineralised within the photic zone; this extensive shallow dissolution explains the apparent discrepancy between previous estimates of CaCO₃production derived from satellite observations/biogeochemical modeling versus estimates from shallow sediment traps. We suggest future changes in the CaCO₃cycle and its impact on atmospheric CO₂will largely depend on how the poorly-understood processes that determine whether CaCO₃is remineralised in the photic zone or exported to depth respond to anthropogenic warming and acidification.

Persistent nitrogen depletion in sunlit open ocean waters provides a favorable ecological niche for nitrogen-fixing (diazotrophic) cyanobacteria, some of which associate symbiotically with eukaryotic algae. All known marine examples of these symbioses have involved either centric diatom or haptophyte hosts. We report here the discovery and characterization of two distinct marine pennate diatom-diazotroph symbioses, which until now had only been observed in freshwater environments. Rhopalodiaceae diatomsEpithemia pelagicasp. nov. andEpithemia catenatasp. nov. were isolated repeatedly from the subtropical North Pacific Ocean, and analysis of sequence libraries reveals a global distribution. These symbioses likely escaped attention because the endosymbionts lack fluorescent photopigments, havenifHgene sequences similar to those of free-living unicellular cyanobacteria, and are lost in nitrogen-replete medium. Marine Rhopalodiaceae-diazotroph symbioses are a previously overlooked but widespread source of bioavailable nitrogen in marine habitats and provide new, easily cultured model organisms for the study of organelle evolution.

A flow cytometry method for enumerating marine heterotrophic bacteria and phytoplankton in a living or preserved sample using a low power solid state near‐ultraviolet laser is described. The method uses Hoechst 34580 to stain DNA in microbial cells in seawater samples. This stain is optimally excited at 375 nm unlike the similar Hoechst 33342, which requires ~ 350 nm excitation only available on more expensive lasers. Phytoplankton abundances from the Hoechst 34580 method are comparable to those of unstained samples and when analyzed by the Hoechst 33342 staining method. With this new method, nonpigmented marine bacteria and phytoplankton abundances are obtained simultaneously in a single sample as the Hoechst emission wavelength (~ 450 nm) is well separated from the emission wavelengths of chlorophyll and phycoerythrin fluorescence. Bacteria abundances are similar between this new method and those obtained with established Hoechst 33342 and SybrGreen I methods. Precision estimates (coefficient of variation) on populations with abundances near ~ 10⁵cells mL⁻¹are 1–3%, increasing to 3–9% at lower cell concentrations of 10³cells mL⁻¹. The Hoechst 34580 method is simple, requiring no heating or pretreatment with RNAse, can be used on unpreserved and formaldehyde‐preserved cells, and is amenable to at‐sea use with portable, compact, low power‐requiring flow cytometers.

Systematic regional variations in the ratio of nutrient depth gradients of dissolved inorganic carbon (ΔDIC):nitrate (ΔNO₃):phosphate (ΔPO₄) in the upper layer (300 m) of the Pacific Ocean are observed. Regional variations in the ΔDIC/ΔNO₃/ΔPO₄are primarily the result of three processes, that is, the C/N/P of organic matter (OM) being exported and subsequently degraded, nitrogen fixation, and air‐sea CO₂gas exchange. The link between the observed dissolved ΔDIC/ΔNO₃/ΔPO₄and the C/N/P of exported OM is established using surface layer dissolved DIC, NO₃, and PO₄budgets. These budgets, in turn, provide a means to indirectly estimate the C/N/P of OM being exported from the surface layer of the ocean. The indirectly estimated C/N/P of exported OM reach maxima in the subtropical gyres at 177/22/1, that is, significantly greater than the Redfield ratio and a minimum in the equatorial ocean at 109/16/1 with both results agreeing with available observed particle C/N/P and ocean biogeochemical models. The budget approach was applied to a bioactive trace element (TE) using the measured dissolved Cadmium (Cd) to PO₄gradients to estimate the Cd/P of exported OM in the Pacific Ocean. Combining the budget method with the availability of high‐quality dissolved nutrient and TE data collected during the GOSHIP and GEOTRACES programs could potentially provide estimates of the C/N/P/TE of exported OM on global ocean scales which would significantly improve our understanding of the link between the ocean's biological pump and dissolved nutrient distributions in the upper ocean.

We examined variability in the euphotic zone (0–175 m) picoeukaryotic community based on time‐series observations (2011–2013) at Station ALOHA in the North Pacific Subtropical Gyre. By sampling over scales ranging from daily to approximately monthly over 2.25 years, we evaluated the resilience of the picoeukaryotic community to seasonal‐ to episodic‐scale physical disturbances, such as convective mixing and mesoscale processes, respectively. We quantified the frequency and intensity of disturbances that altered upper ocean light and nutrients in the context of the Hawaii Ocean Time‐series program climatology, and evaluated picoeukaryotic community resilience based on shifts in dissimilarity in community structure at different depths in the euphotic zone. Our results suggest that in this stratified habitat, picoeukaryote communities are resilient on timescales of days to weeks in response to these physical disturbances, and that the juxtaposition of mesoscale and submesoscale disturbances on more predictable seasonality requires spatially and temporally resolved assessment of community response and resilience. We highlight the value of examining recent (days to weeks) physical forcing of the upper ocean for insight into the influences of physical habitat alterations that structure the contemporaneous plankton community.

Are the oceans turning into deserts? Rising temperature, increasing surface stratification, and decreasing vertical inputs of nutrients are expected to cause an expansion of warm, nutrient deplete ecosystems. Such an expansion is predicted to negatively affect a trio of key ocean biogeochemical features: phytoplankton biomass, primary productivity, and carbon export. However, phytoplankton communities are complex adaptive systems with immense diversity that could render them at least partially resilient to global changes. This can be illustrated by the biology of theProchlorococcus“collective.” Adaptations to counter stress, use of alternative nutrient sources, and frugal resource allocation can allowProchlorococcusto buffer climate‐driven changes in nutrient availability. In contrast, cell physiology is more sensitive to temperature changes. Here, we argue that biogeochemical models need to consider the adaptive potential of diverse phytoplankton communities. However, a full understanding of phytoplankton resilience to future ocean changes is hampered by a lack of global biogeographic observations to test theories. We propose that the resilience may in fact be greater in oligotrophic waters than currently considered with implications for future predictions of phytoplankton biomass, primary productivity, and carbon export.

Carbon is not only the foundation of all life on our planet, but also an element that persists in detrital material long after living organisms die. Quantifying the relative amount of living and nonliving carbon in suspended particles in the ocean is challenging and rarely done; yet it is key to understanding the fate of organic matter and informing food web models. Here, we use particulate adenosine‐5′‐triphosphate (ATP) and particulate carbon (PC) data collected as a component of the Hawaii Ocean Time‐series program to show that living particles comprise only ~ 26–42% of the total PC pool in the surface waters of the North Pacific Subtropical Gyre, regardless of time of year. Diel‐resolving particulate beam attenuation data are then used in conjunction with PC and ATP data to constrain living particle net growth rates for this system, yielding rates of ~ 0.5–0.7 d⁻¹year‐round. These estimates are realistic and consistent with previous microscopy and incubation‐based work in the region.

Mesoscale eddies may enhance nutrient injection into the photic zone and ultimately the magnitude and composition of particle export to depth. Using satellite altimetry, we identified 38 cyclonic eddies that passed in close proximity to the Hawaii Ocean Time‐series (HOT) Station ALOHA, located in the North Pacific Subtropical Gyre, from 1993 to 2018. Particulate carbon (C), nitrogen (N), and biogenic silica (Si) export rates, measured using free floating sediment traps deployed at 150 m as part of HOT, were then associated with either the eddy core or edge based on distance to the eddy center and time of eddy evolution. Elemental fluxes varied significantly within and among individual eddies depending on season and eddy age. Spatially, biogenic Si fluxes were enhanced relative to particulate C and N fluxes at both the cores and edges, with temporally highest particulate C, N and biogenic Si fluxes occurring during the mature stage (3–8 weeks). On average, biogenic Si fluxes were 200 ± 80% (30–270% increase) higher relative to non‐eddy and during non‐bloom periods, with modest enhanced particulate C (10–30% increase) and N (10–20% increase) fluxes. In contrast, during the bloom season (July and August), elemental fluxes were all reduced by 20% relative to non‐eddy references, suggesting that cyclonic eddies depress export during the bloom period. Our results indicate that cyclonic eddies not only increase, but differentially impact the sinking export of critical biological elements, thereby contributing to long term ecological changes in foodwebs that rely on silica as well as carbon for growth.

In the oligotrophic ocean where inorganic phosphate (P_i) concentrations are low, microorganisms supplement their nutrient requirements with phosphorus (P) extracted from dissolved organic matter (DOM). Most P in DOM is bound as phosphate esters, which are hydrolyzed by phosphoesterases to P_i. However, a large fraction of DOM‐P occurs as phosphonates, reduced organophosphorus compounds with a CP bond that do not yield P_ithrough simple ester hydrolysis alone. Phosphonates require an additional step that cleaves the CP bond and oxidizes P(III) to P(V) to yield P_i. Most phosphonates are metabolized by the C‐P lyase pathway, which cleaves CP bonds and oxidizes phosphonates to P_i, enabling microbial assimilation. While the activity of common phosphoesterases such as alkaline phosphatase and phosphodiesterase can be measured by a fluorescent assay, a comparable method to assess C‐P lyase activity (CLA) in natural water samples does not exist. To address this, we synthesized a dansyl‐labeled phosphonate compound, and measured its hydrolysis by C‐P lyase using high performance liquid chromatography. We found that laboratory cultures of marine bacteria expressing the C‐P lyase pathway are able to hydrolyze the dansyl phosphonate, while bacteria expressing other phosphonate degradation pathways do not. Finally, we performed several field tests of the assay to measure water column profiles of CLA at Sta. ALOHA in the North Pacific Subtropical Gyre. Activity was elevated near the deep chlorophyll maximum suggesting high levels of phosphonate degradation in that region.

Ammonia-oxidizing archaea (AOA) are among the most abundant and ubiquitous microorganisms in the ocean, exerting primary control on nitrification and nitrogen oxides emission. Although united by a common physiology of chemoautotrophic growth on ammonia, a corresponding high genomic and habitat variability suggests tremendous adaptive capacity. Here, we compared 44 diverse AOA genomes, 37 from species cultivated from samples collected across diverse geographic locations and seven assembled from metagenomic sequences from the mesopelagic to hadopelagic zones of the deep ocean. Comparative analysis identified seven major marine AOA genotypic groups having gene content correlated with their distinctive biogeographies. Phosphorus and ammonia availabilities as well as hydrostatic pressure were identified as selective forces driving marine AOA genotypic and gene content variability in different oceanic regions. Notably, AOA methylphosphonate biosynthetic genes span diverse oceanic provinces, reinforcing their importance for methane production in the ocean. Together, our combined comparative physiological, genomic, and metagenomic analyses provide a comprehensive view of the biogeography of globally abundant AOA and their adaptive radiation into a vast range of marine and terrestrial habitats.