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Abstract Uncertainties in the temporal and spatial patterns of marine primary production and respiration limit our understanding of the ocean carbon (C) cycle and our ability to predict its response to environmental changes. Here we present a comprehensive time‐series analysis of plankton metabolism at the Hawaii Ocean Time‐series program site, Station ALOHA, in the North Pacific Subtropical Gyre. Vertical profiles of gross oxygen production (GOP) and community respiration (CR) were quantified using the¹⁸O‐labeled water method together with net changes in O₂to Ar ratios during dawn to dusk in situ incubations. Rates of¹⁴C‐bicarbonate assimilation (¹⁴C‐based primary production [¹⁴C‐PP]) were also determined concurrently. During the observational period (April 2015 to July 2020), euphotic zone depth‐integrated (0–125 m) GOP and¹⁴C‐PP ranged from 35 to 134 mmol O₂m⁻²d⁻¹and 18 to 75 mmol C m⁻²d⁻¹, respectively, while CR ranged from 37 to 187 mmol O₂m⁻²d⁻¹. All biological rates varied with depth and season, with seasonality most pronounced in the lower portion of the euphotic zone (75–125 m). The mean annual ratio of GOP to¹⁴C‐PP was 1.7 ± 0.1 mol O₂(mol C)⁻¹. While previous studies have reported convergence of GOP and¹⁴C‐PP with depth, we find a less pronounced vertical decline in the GOP to¹⁴C‐PP ratios, with GOP exceeding¹⁴C‐PP by 50% or more in the lower euphotic zone. Variability in CR was higher than for GOP, driving most of the variability in the balance between the two. 

Cross-platform observing systems are requisite to capturing the temporal and spatial dynamics of particles in the ocean. We present simultaneous observations of bulk optical properties, including the particulate beam attenuation ( ${\text{c}}_{\text{p}}$) and backscattering ( $b_{\text{bp}}$) coefficients, and particle size distributions collected in the North Pacific Subtropical Gyre. Clear and coherent diel cycles are observed in all bulk and size-fractionated optical proxies for particle biomass. We show evidence linking diurnal increases in ${\text{c}}_{\text{p}}$and ${\text{b}}_{\text{bp}}$to daytime particle growth and division of cells, with particles $<<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$driving the daily cycle of particle production and loss within the mixed layer. Flow cytometry data reveal the nitrogen-fixing cyanobacteriumCrocosphaera( $\sim <\#comment/>4-<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$) to be an important driver of ${\text{c}}_{\text{p}}$at the time of sampling, whereasProchlorococcusdynamics ( $\sim <\#comment/>0.5\text{µ<\#comment/>}\mathrm{m}$) were essential to reproducing temporal variability in ${\text{b}}_{\text{bp}}$. This study is a step towards improved characterization of the particle size range represented byin situbulk optical properties and a better understanding of the mechanisms that drive variability in particle production in the oligotrophic open ocean. 

Summary In tropical and subtropical oceanic surface waters phosphate scarcity can limit microbial productivity. However, these environments also have bioavailable forms of phosphorus incorporated into dissolved organic matter (DOM) that microbes with the necessary transport and hydrolysis metabolic pathways can access to supplement their phosphorus requirements. In this study we evaluated how the environment shapes the abundance and taxonomic distribution of the bacterial carbon–phosphorus (C–P) lyase pathway, an enzyme complex evolved to extract phosphate from phosphonates. Phosphonates are organophosphorus compounds characterized by a highly stable C–P bond and are enriched in marine DOM. Similar to other known bacterial adaptions to low phosphate environments, C–P lyase was found to become more prevalent as phosphate concentrations decreased. C–P lyase was particularly enriched in the Mediterranean Sea and North Atlantic Ocean, two regions that feature sustained periods of phosphate depletion. In these regions, C–P lyase was prevalent in several lineages ofAlphaproteobacteria(Pelagibacter, SAR116,RoseobacterandRhodospirillales),Gammaproteobacteria,andActinobacteria. The global scope of this analysis supports previous studies that infer phosphonate catabolism via C–P lyase is an important adaptive strategy implemented by bacteria to alleviate phosphate limitation and expands the known geographic extent and taxonomic affiliation of this metabolic pathway in the ocean.