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  1. One pathway of the biological pump that remains largely unquantified in many export models is the active transport of carbon from the surface ocean to the mesopelagic by zooplankton diel vertical migration (DVM). Here, we develop a simple representation of zooplankton DVM and implement it in a global export model as a thought experiment to illustrate the effects of DVM on carbon export and mesopelagic biogeochemistry. The model is driven by diagnostic satellite measurements of net primary production, algal biomass, and phytoplankton size structure. Due to constraints on available satellite data, the results are restricted to the latitude range from 60°N to 60°S. The modeled global export flux from the base of the euphotic zone was 6.5 PgC/year, which represents a 14% increase over the export flux in model runs without DVM. The mean (± standard deviation, SD) proportional contribution of the DVM‐mediated export flux to total carbon export, averaged over the global domain and the climatological seasonal cycle, was 0.16 ± 0.04 and the proportional contribution of DVM activity to total respiration within the twilight zone was 0.16 ± 0.06. Adding DVM activity to the model also resulted in a deep local maximum in the oxygen utilization profile. The model results were most sensitive to the assumptions for the fraction of individuals participating in DVM, the fraction of fecal pellets produced in the euphotic zone, and the fraction of grazed carbon that is metabolized.

     
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  2. Abstract. Tritium and helium isotope data provide key information on oceancirculation, ventilation, and mixing, as well as the rates of biogeochemicalprocesses and deep-ocean hydrothermal processes. We present here globaloceanic datasets of tritium and helium isotope measurements made by numerousresearchers and laboratories over a period exceeding 60 years. The dataset'sDOI is https://doi.org/10.25921/c1sn-9631, and the data are available athttps://www.nodc.noaa.gov/ocads/data/0176626.xml (last access: 15 March2019) or alternatelyhttp://odv.awi.de/data/ocean/jenkins-tritium-helium-data-compilation/(last access: 13 March 2019) and includes approximately 60 000 valid tritiummeasurements, 63 000 valid helium isotope determinations, 57 000 dissolvedhelium concentrations, and 34 000 dissolved neon concentrations. Somequality control has been applied in that questionable data have been flaggedand clearly compromised data excluded entirely. Appropriate metadata havebeen included, including geographic location, date, and sample depth. Whenavailable, we include water temperature, salinity, and dissolved oxygen. Dataquality flags and data originator information (including methodology) arealso included. This paper provides an introduction to the dataset along withsome discussion of its broader qualities and graphics. 
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  3. Abstract. Significant rates of primary production occur in the oligotrophic ocean, without any measurable nutrients present in the mixed layer, fueling a scientific paradox that has lasted for decades. Here, we provide a new determination of the annual mean physical supply of nitrate to the euphotic zone in the western subtropical North Atlantic. We combine a 3-year time series of measurements of tritiugenic 3He from 2003 to 2006 in the surface ocean at the Bermuda Atlantic Time-series Study (BATS) site with a sophisticated noble gas calibrated air–sea gas exchange model to constrain the 3He flux across the sea–air interface, which must closely mirror the upward 3He flux into the euphotic zone. The product of the 3He flux and the observed subsurface nitrate–3He relationship provides an estimate of the minimum rate of new production in the BATS region. We also apply the gas model to an earlier time series of 3He measurements at BATS in order to recalculate new production fluxes for the 1985 to 1988 time period. The observations, despite an almost 3-fold difference in the nitrate–3He relationship, yield a roughly consistent estimate of nitrate flux. In particular, the nitrate flux from 2003 to 2006 is estimated to be 0.65 ± 0.14 mol m−2 yr−1, which is ~40 % smaller than the calculated flux for the period from 1985 to 1988. The difference in nitrate flux between the time periods may be signifying a real difference in new production resulting from changes in subtropical mode water formation. Overall, the nitrate flux is larger than most estimates of export fluxes or net community production fluxes made locally for the BATS site, which is likely a reflection of the larger spatial scale covered by the 3He technique and potentially also by the decoupling of 3He and nitrate during the obduction of water masses from the main thermocline into the upper ocean. The upward nitrate flux is certainly large enough to support observed rates of primary production at BATS and more generally in the oligotrophic subtropical ocean. 
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