The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) is an interdisciplinary investigation to improve understanding of Earth's ocean ecosystem-aerosol-cloud system. Specific overarching science objectives for NAAMES are to (1) characterize plankton ecosystem properties during primary phases of the annual cycle and their dependence on environmental forcings, (2) determine how these phases interact to recreate each year the conditions for an annual plankton bloom, and (3) resolve how remote marine aerosols and boundary layer clouds are influenced by plankton ecosystems. Four NAAMES field campaigns were conducted in the western subarctic Atlantic between November 2015 and April 2018, with each campaign targeting specific Behrenfeld et al. NAAMES Overview seasonal events in the annual plankton cycle. A broad diversity of measurements were collected during each campaign, including ship, aircraft, autonomous float and drifter, and satellite observations. Here, we present an overview of NAAMES science motives, experimental design, and measurements. We then briefly describe conditions and accomplishments during each of the four field campaigns and provide information on how to access NAAMES data. The intent of this manuscript is to familiarize the broad scientific community with NAAMES and to provide a common reference overview of the project for upcoming publications.

The North Atlantic phytoplankton spring bloom is the pinnacle in an annual cycle that is driven by physical, chemical, and biological seasonality. Despite its important contributions to the global carbon cycle, transitions in plankton community composition between the winter and spring have been scarcely examined in the North Atlantic. Phytoplankton composition in early winter was compared with latitudinal transects that captured the subsequent spring bloom climax. Amplicon sequence variants (ASVs), imaging flow cytometry, and flow-cytometry provided a synoptic view of phytoplankton diversity. Phytoplankton communities were not uniform across the sites studied, but rather mapped with apparent fidelity onto subpolar-and subtropical-influenced water masses of the North Atlantic. At most stations, cells < 20µm diameter were the main contributors to phytoplankton biomass. Winter phytoplankton communities were dominated by cyanobacteria and pico-phytoeukaryotes. These transitioned to more diverse and dynamic spring communities in which picoand nano-phytoeukaryotes, including many prasinophyte algae, dominated. Diatoms, which are often assumed to be the dominant phytoplankton in blooms, were contributors but not the major component of biomass. We show that diverse, small phytoplankton taxa are unexpectedly common in the western North Atlantic and that regional influences play a large role in modulating community transitions during the seasonal progression of blooms.

The goal of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign is to develop a predictive understanding of the export, fate, and carbon cycle impacts of global ocean net primary production. To accomplish this goal, observations of export flux pathways, plankton community composition, food web processes, and optical, physical, and biogeochemical (BGC) properties are needed over a range of ecosystem states. Here we introduce the first EXPORTS field deployment to Ocean Station Papa in the Northeast Pacific Ocean during summer of 2018, providing context for other papers in this special collection. The experiment was conducted with two ships: a Process Ship, focused on ecological rates, BGC fluxes, temporal changes in food web, and BGC and optical properties, that followed an instrumented Lagrangian float; and a Survey Ship that sampled BGC and optical properties in spatial patterns around the Process Ship. An array of autonomous underwater assets provided measurements over a range of spatial and temporal scales, and partnering programs and remote sensing observations provided additional observational context. The oceanographic setting was typical of late-summer conditions at Ocean Station Papa: a shallow mixed layer, strong vertical and weak horizontal gradients in hydrographic properties, sluggish sub-inertial currents, elevated macronutrient concentrations and low phytoplankton abundances. Although nutrient concentrations were consistent with previous observations, mixed layer chlorophyll was lower than typically observed, resulting in a deeper euphotic zone. Analyses of surface layer temperature and salinity found three distinct surface water types, allowing for diagnosis of whether observed changes were spatial or temporal. The 2018 EXPORTS field deployment is among the most comprehensive biological pump studies ever conducted. A second deployment to the North Atlantic Ocean occurred in spring 2021, which will be followed by focused work on data synthesis and modeling using the entire EXPORTS data set.

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The dilution‐method has been key in establishing the role of protistan‐grazing in marine foodwebs. Yet its laborious application limits the sampling‐resolution achieved. We assessed the reliability of an abbreviated method known as the 2‐point by analyzing 77 dilution‐experiments performed using 4–5 dilutions in diverse biotic and abiotic conditions. Our aim was to inform practitioners on how experimental design and nonlinear feeding behaviors affect the accuracy of 2‐point rate‐estimates. We found good agreement between rate‐estimates of both phytoplankton growth (μ) and grazer‐induced mortality (g) from either method, even though the comparison included experiments with nonlinear feeding‐responses. The accuracy of 2‐point estimates was similar to the inherent standard deviation of dilution‐series estimates (± ∼ 0.1 d−1). Nonlinear feeding‐responses did not alter overall rate‐estimates, negating the need for more than two dilution‐levels. Decreasing dilution resulting in an increase in biomass in the dilute treatment from 10% to 40% increased the median difference between 2‐point and dilution‐series estimates 3‐fold and increased 2‐point estimates' variance 2‐fold, both for μ and g. Recognition of these biomass vs. accuracy tradeoffs enables practitioners to choose whether to procure more biomass at the expense of constraining estimate variance. Using duplicate bottles at each dilution level doubled average accuracy of 2‐point estimates. The reduction in effort and water‐needs afforded by the 2‐point design facilitates acquisition of higher‐resolution data of predation‐rates across seasons, latitudes, and in response to diverse environmental conditions in the ocean, which is critically needed to decipher abiotic and biotic drivers of protistan‐grazing and to parameterize protistan herbivory in global biogeochemical models.

To identify the effect of microzooplankton grazing on phytoplankton abundance and size structure, we quantified phytoplankton growth and herbivorous grazing rates throughout the euphotic zone and across a light gradient on the North Pacific EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) cruise near Ocean Station Papa. During 30 days of continuous, Lagrangian observation in August and September of 2018, depth integrated chlorophyll a (Chl a) concentrations were stable and averaged 20 AE 2 mg m À2 . Bottleincubation experiments revealed that phytoplankton growth was balanced by microzooplankton grazing even when phytoplankton growth rates varied from 0 to 0.4 d À1 in response to light manipulation. Microzooplankton grazing caused a decline in phytoplankton abundance that was balanced by increased phytoplankton cell size resulting in consistent phytoplankton biomass over time. Microzooplankton grazed phytoplankton at an average rate of 0.11 AE 0.17 d À1 which lead to an intrinsic phytoplankton growth rate of À0.07 AE 0.26 d À1 . Predicted stocks from grazing experiments aligned closely (within 16%) with in situ Chl a dynamics and phytoplankton abundance, suggesting that the dominant loss process of phytoplankton was grazing by microzooplankton rather than physical mixing or sinking of phytoplankton. Consequently, microzooplankton played a critical role in regulating primary producer biomass and in transferring particulate organic carbon through the food web where a fraction could then be exported as byproducts of food web processes.

We measured phytoplankton-growth (l) and herbivorous-protist grazing (g) rates in relation to mixedlayer-depth (MLD) during the March/April 2012 EuroBasin cruise in the subpolar North Atlantic. We performed 15 dilution experiments at two open-ocean ( 1300 m) and one shelf (160 m) station. Of the two open-ocean stations one was deeply mixed (476 m), the other stratified (46 m). At the shelf station, MLD reached the bottom. Initial chlorophyll a (Chl a) varied from 0.2-1.9 lg L 21 and increased up to 2.7 lg L 21 at the shelf station. In 80% of experiments, regardless of MLD, growth-rates exceeded grazing-mortality rates. At the open-ocean stations, the deep ML coincided with l and g that varied over the same range ( 0-0.6 d 21 ), whereas stratification corresponded to l and g that ranged from 0.14-0.41 d 21 to 0.11-0.34 d 21 , respectively. At the stratified station, the balance between l and g explained 98% of in situ variations in Chl a, whereas at the deep-ML station, rate estimates had no explanatory power. The consistent relationship between l and g, which corresponded to a grazing-removal of 64% of primary production, suggests that g might be predictable if l is known, and that a coefficient of 0.64 may be a useful parameter for subarctic carbon models. Composition and persistence of the plankton assemblages differed at the stations and may have been a significant driver of grazing-pressure. Overall, these results showed no association of MLD with grazing-pressure and highlight the need to assess to what extent MLD represents the depth of active-mixing to understand the effects of protistan-grazing on the development of the North Atlantic spring bloom.

Surface‐ocean mixing creates dynamic light environments with predictable effects on phytoplankton growth but unknown consequences for predation. We investigated how variations in average mixed‐layer (ML) irradiance shaped plankton trophic dynamics by incubating a Northwest‐Atlantic plankton community for 4 days at high (H) and low (L) light, followed by exposure to either sustained or reversed light intensities. In deep‐ML (sustained L), phytoplankton biomass declined (μ = −0.2 ± 0.08 d−1) and grazing was absent. In shallow‐ML (sustained H), growth exceeded grazing (μ = 0.46 ± 0.07 d−1; g = 0.32 ± 0.04 d−1). In rapidly changing ML‐conditions simulated by switching light‐availability, growth and grazing responded on different timescales. During rapid ML‐shoaling (L to H), μ immediately increased (0.23 ± 0.01 d−1) with no change in grazing. During rapid ML‐deepening (H to L), μ immediately decreased (0.02 ± 0.09 d−1), whereas grazing remained high (g = 0.38 ± 0.05 d−1). Predictable rate responses of phytoplankton growth (rapid) vs. grazing (delayed) to measurable light variability can provide insights into predator‐prey processes and their effects on spatio‐temporal dynamics of phytoplankton biomass.