The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo’s global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities.

In the North Pacific Subtropical Gyre (NPSG), the regular occurrence of summer phytoplankton blooms contributes to marine ecosystem productivity and the annual carbon export. The mechanisms underlying the formation, maintenance, and decay of these blooms remain largely unknown; nitrogen fixation, episodic vertical mixing of nutrients, and meso‐ (<100 km) and submesoscale (<10 km) physical processes are all hypothesized to contribute to bloom dynamics. In addition, zones of convergence in the ocean's surface layers are known to generate downwelling and/or converging currents that affect plankton distributions. It has been difficult to quantify the importance of these convergence zones in the export flux of particulate organic carbon (POC) in the open ocean. Here we use two high‐resolution ocean transects across a pair of mesoscale eddies in the vicinity of Station ALOHA (22° 45′N, 158° 00′W) to show that horizontal turbulent stirring may have been a dominant control on the spatial distribution of the nitrogen fixing cyanobacteriumTrichodesmium spp. Fast repetition rate fluorometry measurements suggested that this distribution stimulated new primary production; this conclusion was not confirmed by ¹⁴C‐based measurements, possibly because of different sampling scales for the two methods. Our observations of particle size distributions along the two transects showed that stretching by the mesoscale eddy field produced submesoscale features that mediated POC export via frontogenetically generated downwelling currents. This study highlights the need to combine high‐resolution biogeochemical and physical data sets to understand the links betweenTrichodesmium spp. surface distribution and POC export in the NPSG at the submesoscale level.

Vertical exchange between deep, nutrient‐rich and nutrient‐depleted surface waters controls the physical supply of nutrients into the euphotic zone in the oligotrophic waters of the subtropical North Pacific Ocean. Sea surface temperature and ocean color satellite images are used in this study to show that submesoscale chlorophyll patches are locally intensified. These patches are associated with surface temperature fronts and regions of strong stretching of the eddying flow. The latter are identified by calculating the finite‐size Lyapunov exponents of the geostrophic flow derived from the sea surface height field from altimetry. Surface frontogenesis and nonlinear Ekman pumping (NLEP) arise as natural candidates for the sporadic generation of large vertical velocities that could favor the formation of these features. A high‐resolution regional numerical model simulation confirms that large vertical velocities are indeed associated with strong density fronts and gradients of relative vorticity. Using the Q vector divergence as a proxy for frontogenetically generated vertical velocities yields good agreement with the model vertical velocities, particularly in regions where they are large. The pattern and magnitude of NLEP suggests that it is also contributing to the strong vertical motions, although NLEP and model vertical velocities are not necessarily in phase. Surface frontogenesis and NLEP provide a possible explanation for the episodic injection of nutrients at the submesoscale, which are then horizontally stirred and modulated by the unstable manifolds of the flow field. Given that these surface‐intensified processes would be biogeochemically more effective when the pycnocline is shallow, they could also serve as one possible explanation for the late summer chlorophyll blooms that are known to occur in the region.

Several hypotheses exist that describe phytoplankton spring blooms in temperate and subpolar oceans: the critical depth, shoaling mixed layer (ML), critical turbulence, onset of stratification and disturbance-recovery hypotheses. These theories appear to be mutually exclusive and none of them describe the annual cycle of phytoplankton biomass. Here, we present a model of the annual cycle in phytoplankton that recognizes that phytoplankton are not always mixed throughout the so-called ML, and that it is important to distinguish between the surface biomass and depth-integrated phytoplankton. Once these important distinctions are made, the annual cycles and blooms in surface and depth-integrated phytoplankton can be described straightforwardly in terms of the physical drivers and biotic responses.