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We leverage observations from chemical and bio‐optical sensors mounted on a biogeochemical profiling float in the Northeast Pacific Ocean to quantify the cycling and export potential of distinct biogenic carbon pools, including particulate inorganic carbon (PIC), particulate organic carbon (POC), and dissolved organic carbon (DOC). Year‐round observations reveal complex carbon cycle dynamics among these carbon pools. Net DOC production peaked during bloom initiation, about 3 months prior to the summer peak in POC production. We validate the float estimates of DOC cycling with seasonal accumulation and removal rates derived from ship‐board DOC observations over the same period. By combining chemical and bio‐optical tracers of POC cycling, we estimate the instantaneous POC sinking flux (FPOCsinking ${\mathrm{F}}_{{\text{POC}}_{\text{sinking}}}$). The cooccurrence of DOC consumption and POC production and sinking during fall and winter resolves the regional conundrum of a persistent particle sinking flux observed by sediment traps during a season that is known to be heterotrophic. PIC production is small, and uncertainties are large. By combining float‐based estimates of instantaneous net primary production (NPP) and FPOCsinking ${\mathrm{F}}_{{\text{POC}}_{\text{sinking}}}$, we quantify a real‐time carbon export ratio ([FPOCsinking ${\mathrm{F}}_{{\text{POC}}_{\text{sinking}}}$/NPP] × 100%) for the euphotic zone. Elevated export ratios during summer are associated with an increase in the fraction of particles larger than 100 μm in size. Elevated export ratios during winter are associated with the physical redistribution of particles through seasonal deep mixing. Our study demonstrates how the combined use of multiple sensors on biogeochemical profiling floats can provide more nuanced information about upper ocean carbon cycle dynamics. Key Points: The export potential of distinct biogenic carbon pools is determined from multiple chemical and bio‐optical sensors on a profiling floatContinuous observations confirm the mechanism sustaining simultaneous particle export and heterotrophy in the Northeast PacificReal‐time export ratios are calculated from float‐based estimates of net primary production and sinking particulate organic carbon [ABSTRACT FROM AUTHOR]

The California Current System is thought to be particularly vulnerable to ocean acidification, yet pH remains chronically undersampled along this coast, limiting our ability to assess the impacts of ocean acidification. To address this observational gap, we integrated the Deep-Sea-DuraFET, a solid-state pH sensor, onto a Spray underwater glider. Over the course of a year starting in April 2019, we conducted seven missions in central California that spanned 161 glider days and >1600 dives to a maximum depth of 1000 m. The sensor accuracy was estimated to be ± 0.01 based on comparisons to discrete samples taken alongside the glider (n = 105), and the precision was ± 0.0016. CO2 partial pressure, dissolved inorganic carbon, and aragonite saturation state could be estimated from the pH data with uncertainty better than ± 2.5%, ± 8 μmol kg-1, and ± 2%, respectively. The sensor was stable to ± 0.01 for the first 9 months but exhibited a drift of 0.015 during the last mission. The drift was correctable using a piecewise linear regression based on a reference pH field at 450 m estimated from published global empirical algorithms. These algorithms require accurate O2 as inputs; thus, protocols for a simple predeployment air calibration that achieved accuracy of better than 1% were implemented. The glider observations revealed upwelling of undersaturated waters with respect to aragonite to within 5 m below the surface near Monterey Bay. These observations highlight the importance of persistent observations through autonomous platforms in highly dynamic coastal environments. [ABSTRACT FROM AUTHOR]

Here we used data from six BGC-floats deployed in the southeast Pacific and southwest Atlantic Oceans, within the Southern Ocean's Subtropical Zone, to assess the seasonality of particulate organic carbon production from phytoplankton (POC phyto) and estimate POC transfer efficiencies at 100 m below the euphotic zone (T_100). While small particles <100 μM dominated the mixed layer, large particles >100 μM comprised a significant fraction of POC phyto below the mixed layer in both areas, possibly due to a "shade flora" composed by large diatoms. POC phyto was highly seasonal with highest biomass accumulation in the Atlantic side for both small and large particles. In the Pacific, the seasonal change in small particle production ΔPOC phyto was ∼66 mg m−2 versus ∼54 mg m−2 from large particles. In the Atlantic, ΔPOC phyto was ∼852 mg m−2 for small particles versus ΔPOC phyto ∼ 262 mg m−2 for large particles. Monthly T_100s in the Pacific ranged from 76% to 92% with maximum efficiencies during the deepening of the mixed layer depth. In the Atlantic, T_100s ranged from 43% to 76% with two periods of high T_100s: the first coinciding with the decline of large particles from the "shade flora", and the second coinciding with the deepening of the mixed layer during elevated small particle production. • Large phytoplankton particles accumulated below the mixed layer at mid-latitudes • The Atlantic Subtropical Zone produced more particulate organic carbon than the Pacific • Particle transfer efficiency in the Pacific was 85%, with a monthly amplitude of 76–92% • Particle transfer efficiency in the Atlantic was 60%, with a monthly amplitude of 43–76% [ABSTRACT FROM AUTHOR]