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Measurements of particulate organic carbon (POC) are critical for understanding the ocean carbon cycle, including biogenic particle formation and removal processes, and for constraining models of carbon cycling at local, regional, and global scales. Despite the importance and ubiquity of POC measurements, discrepancies in methods across platforms and users, necessary to accommodate a multitude of needs and logistical constraints, commonly result in disparate results. Considerations of filter type and pore size, sample volume, collection method, and contamination sources underscore the potential for dissimilar measurements of the same variable assessed using similar and different approaches. During the NASA EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) 2018 field campaign in the North Pacific Ocean, multiple methodologies and sampling approaches for determining POC were applied, including surface inline flow-through systems and depth profiles using Niskin bottles, in situ pumps, and Marine Snow Catchers. A comparison of results from each approach and platform often resulted in significant differences. Supporting measurements, however, provided the means to normalize results across datasets. Using knowledge of contrasting protocols and synchronous or near-synchronous measurements of associated environmental variables, we were able to reconcile dataset differences to account for undersampling of some particle types and sizes, possible sample contamination and blank corrections. These efforts resulted in measurement agreement between initially contrasting datasets and insights on long-acknowledged but rarely resolved discrepancies among contrasting methods for assessing POC concentrations in the ocean. 

Abstract Each spring, the North Atlantic experiences one of the largest open‐ocean phytoplankton blooms in the global ocean. Diatoms often dominate the initial phase of the bloom with succession driven by exhaustion of silicic acid. The North Atlantic was sampled over 3.5 weeks in spring 2021 following the demise of the main diatom bloom, allowing mechanisms that sustain continued diatom contributions to be examined. Diatom biomass was initially relatively high with biogenic silica concentrations up to 2.25 μmol Si L⁻¹. A low initial silicic acid concentration of 0.1–0.3 μM imposed severe Si limitation of silica production and likely limited the diatom growth rate. Four storms over the next 3.5 weeks entrained silicic acid into the mixed layer, relieving growth limitation, but uptake limitation persisted. Silica production was modest and dominated by the >5.0 μm size fraction although specific rates were highest in the 0.6–5.0 μm size fraction over most of the cruise. Silica dissolution averaged 68% of silica production. The resupply of silicic acid via storm entrainment and silica dissolution supported a cumulative post‐bloom silica production that was 32% of that estimated during the main bloom event. Diatoms contributed significantly to new and to primary production after the initial bloom, possibly dominating both. Diatom contribution to organic‐carbon export was also significant at 40%–70%. Thus, diatoms can significantly contribute to regional biogeochemistry following initial silicic acid depletion, but that contribution relies on physical processes that resupply the nutrient to surface waters.