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Organic carbon export and burial in coastal upwelling regions is an important mechanism for oceanic uptake of atmospheric CO 2. In order to understand how these complex systems will respond to future climate forcing, further studies of nutrient input, biological production and export are needed. Using a 7 Be-based approach, we produced an 18-month record of upwelling velocity estimates at the San Pedro Ocean Time-series (SPOT), Southern California Bight. These upwelling rates and vertical nutrient distributions have been combined to make estimates of potential new production (PNP), which are compared to estimates of net community oxygen production (NOP) made using a one-dimensional, two-box non-steady state model of euphotic zone biological oxygen supersaturation. NOP agrees within uncertainty with PNP, suggesting that upwelling is the dominant mechanism for supplying the ecosystem with new nutrients in the spring season, but negligible in the fall and winter. Combining this data set with estimates of sinking particulate organic carbon (POC) flux from water column 234 Th: 238 U disequilibrium and sediment trap deployments, and an estimate of the ratio of dissolved organic carbon (DOC):POC consumption rates, we construct a simple box model of organic carbon in the upper 200m of our study site. This box model (with uncertainties of ± 50%) suggests that in spring, ~28% of net production leaves the euphotic zone as DOC, of this, ~12% as horizontal export and ~16% via downward mixing. The remaining ~72% of net organic carbon export exits as sinking POC, with only ~10% of euphotic zone export reaching 200m. We find the metabolic requirement for the local heterotrophic community below the euphotic zone, but above 200m, is ~105 ± 50 mmol C m-2 d-1 , or ~80% of net euphotic zone production in spring.

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Carbon export out of the surface ocean via the biological pump is a critical sink for atmospheric carbon dioxide. This process transports organic carbon to the deep ocean through sinking particulate organic carbon (POC) and the downward transport of suspended POC and dissolved organic carbon (DOC). Changes in the relative contribution of each pathway can significantly affect the magnitude and efficiency of carbon export to depth. Net community production (NCP), an analog of carbon export under steady state assumptions, is typically estimated using budgets of biologically important chemical tracers in the upper ocean constrained by ship-board or autonomous platform observations. In this study, we use measurements from biogeochemical profiling floats, the Ocean Station Papa mooring, and recently developed algorithms for carbonate system parameters to constrain budgets for three tracers (nitrate, dissolved inorganic carbon, and total alkalinity) and estimate NCP in the Northeast Pacific from 2009 to 2017. Using our multiple-tracer approach, and constraining end-member nutrient ratios of the POC and DOC produced, we not only calculate regional NCP throughout the annual cycle and across multiple depth horizons, but also partition this quantity into particulate and dissolved portions. We also use a particle backscatter-based approach to estimate POC attenuation with depth and present a new method to constrain particle export across deeper horizons and estimate in situ export efficiency. Our results agree well with previously published estimates of regional carbon export annually and suggest that the approaches presented here could be used to assess the magnitude and efficiency of carbon export in other regions of the world's oceans. Plain Language Summary "Carbon export" refers to the amount of carbon dioxide that is removed from the atmosphere by organisms in the surface ocean and subsequently transported into the deep sea, either through sinking particles (more efficient process) or downward mixing (less efficient process), making the ocean a natural sink for atmospheric carbon dioxide and significantly influencing ocean chemistry. The relative proportion of export through each pathway significantly affects the overall efficiency of this process and has implications for the pattern of carbon export globally. Measuring carbon export throughout the year traditionally requires persistent ship-based observations, which can be costly and perilous for researchers. Instead, carbon export is often estimated by budgeting nutrient distributions and changes through time, as they are also controlled by the same processes. These measurements can now be made remotely using autonomous biogeochemical profiling floats. Here, we present a new approach utilizing multiple chemical budgets to estimate carbon export over a decade in the Northeast Pacific, which can be combined to partition export occurring through sinking particles and downward mixing. Our results are supported by previously published estimates of carbon export and sugges...

Mixed layer (ML) gross (GOP) and net (NOP) oxygen production rates based on in situ mass balances of triple oxygen isotopes (TOI) and O2/Ar are influenced by vertical transport from below, a term traditionally difficult to constrain. Here we present a new approach to estimate vertical eddy diffusivity (Kz) based on density gradients in the upper thermocline and wind speed‐based rates of turbulent shear at the ML depth. As an example, we use this Kz, verified by an independent 7Be‐based estimate, in an O2/TOI budget at a site in the oligotrophic South Pacific Gyre. NOP equaled 0.31 ± 0.16 mmol m−2 d−1 in the ML (~55–65 m depth) and 1.2 ± 0.4 mmol m−2 d−1 (80%) beneath the ML, while GOP equaled 74 ± 27 mmol m−2 d−1 (86%) in the ML and 12 ± 4 mmol m−2 d−1 (14%) below, revealing a vertical gradient in production rates unquantifiable without the Kz estimate.

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The balance of marine autotrophy and heterotrophy regulates the ocean's ability to serve as a CO2 sink, as organic material produced by autotrophs sinks into the ocean interior to drive the biological pump. Marine ecosystems over the continental margins, especially coastal upwelling regions, account for a disproportionate amount of carbon export; thus, even small fluctuations in export in these regions can have a large impact on the global carbon cycle. In this study, we estimated the rate of gross oxygen production (GOP), stoichiometrically related to gross primary production, by combining measurements of the triple isotope composition of dissolved oxygen with estimates of vertical advection, eddy diffusion, and air‐sea gas exchange in a one‐dimensional two‐box nonsteady state model of the euphotic zone. Net oxygen production (NOP) estimates based on O2/Ar were then combined with GOP to estimate the NOP/GOP ratio, or potential export efficiency, out of the euphotic zone at the San Pedro Ocean Time‐series during an 18 month period between January 2013 and June 2014. GOP estimates ranged from 161 ± 44 to 477 ± 155 mmol m−2 d−1 during this period, peaking in May each year, and NOP/GOP ratios ranged from 0.05 ± 0.10 to 0.65 ± 0.28. The highest export efficiency occurred in late February/early March, following the onset of spring upwelling, declining as the upwelling season continued. This study demonstrates that export efficiency changes through time in this temperate coastal upwelling region on a repeated annual cycle, and the magnitude of export efficiency suggests efficient photosynthetic energy conversion by phytoplankton in spring.

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