The Hawaii Ocean Time‐series (HOT) at Station ALOHA (22.75°N, 158°W) in the North Pacific Subtropical Gyre (NPSG) serves as a critical vantage point for observing plankton biomass production and its ecological implications. However, the HOT program's near‐monthly sampling frequency does not capture shorter time scale variability in phytoplankton populations. To address this gap, we deployed the SeaFlow flow cytometer for conti...

The combination of taxa and size classes of phytoplankton that coexist at any location affects the structure of the marine food web and the magnitude of carbon fluxes to the deep ocean. But what controls the patterns of this community structure across environmental gradients remains unclear. Here, we focus on the North East Pacific Transition Zone, a ~ 10° region of latitude straddling warm, nutrient‐poor subtropical and cold,...

Photosynthesis acts as a fundamental control in the cycling of biologically reactive elements in the ocean. Modeling photosynthesis requires an understanding of its response to light, specifically the maximum rate of photosynthesis per photon absorbed and the irradiance level at which it becomes light‐saturated ( E k ), though field measurements of these parameters are both time and labor intensive. As absorbed light either dr...

In the North Pacific Subtropical Gyre, the daily pulse of photosynthetic carbon (C) fixation is closely balanced by losses. This concert of growth and loss is driven by a diverse assemblage of plankton, including the diazotroph Crocosphaera sp. While primary production is relatively well characterized in this ecosystem, the extent of C transfer to secondary producers is poorly constrained. Here, we use automated imaging flow c...

The number of marine environments known to harbor dinitrogen (N 2 )‐fixing (diazotrophic) microorganisms is increasing, prompting a reassessment of the biogeography of marine diazotrophs and N 2 fixation rates (NFRs). Here, we investigate the diversity, abundance, and activity of diazotrophic microorganisms in the North Pacific Subtropical Gyre (NPSG), a diazotrophic habitat, and the North Pacific Transition Zone (NPTZ), a reg...

The carbon, nitrogen, and phosphorus (C, N, and P, respectively) composition and elemental ratios were measured in the 20–200 μ m size fraction during July 2015 in the surface waters of an anticyclonic eddy encountered north of Hawaii in the oligotrophic North Pacific Subtropical Gyre. The observed particulate N : P ratio fluctuated by approximately a factor of two over the diel cycle. We present a simple mathematical argument...

Recent observations of N 2 fixation rates (NFR) and the presence of nitrogenase ( nifH ) genes from heterotrophic N 2 ‐fixing (diazotrophic) prokaryotes in unusual habitats challenge the paradigm that pelagic marine N 2 fixation is constrained to cyanobacteria in warm, oligotrophic, surface waters. Here, we compare NFR and diazotrophic diversity (assessed via high‐throughput nifH sequencing) from a region known to be dominated...

To constrain the energy fueling photosynthesis in the North Pacific Subtropical Gyre (NPSG) we characterize the variability of phytoplankton absorption spectra in conjunction with that of the light field at Station ALOHA (22 ° 45′N, 158 ° 00′W). Furthermore, we decompose the phytoplankton absorption into photosynthetic and photoprotective components based on high‐performance liquid chromatography pigment analysis. Between Janu...

We conducted 11 independent short‐term carbon dioxide (CO 2 ) manipulation experiments using colonies of the filamentous cyanobacteria Trichodesmium isolated on three cruises in the North Pacific Subtropical Gyre (NPSG). Dinitrogen (N 2 ) and carbon (C) fixation rates of these colonies were compared over CO 2 conditions ranging from ∼ 18 Pa (equivalent to last glacial maximum atmospheric ) to ∼ 160 Pa (predicted for ∼ year 220...

We conducted laboratory experiments to assess the bioelemental plasticity of cultures of Trichodesmium IMS101 under phosphorus (P)‐replete, P‐restricted, and light‐limited conditions. The results reveal a high degree of stoichiometric flexibility. Specifically, Trichodesmium IMS101 is capable of growth with carbon (C) : nitrogen (N) : P ratios of C 585±56 : N 90±10 : P 1 , approximately six times higher than would be predicted...