Version 2 of the global oceanic diazotroph database

Abstract

Abstract. Marine diazotrophs convert dinitrogen (N2) in seawater into bioavailable nitrogen (N), contributing approximately half of the external input of bioavailable N to the global ocean. A global oceanic diazotroph database was previously published in 2012. Here, we compiled version 2 of the database by adding 23,095 in situ measurements of marine diazotrophic abundance and N2 fixation rates published in the past decade, increasing the number of N2 fixation rates and microscopic and qPCR-based diazotrophic abundance data by 140 %, 26 % and 443 %, respectively. Although the updated database expanded spatial coverage considerably, particularly in the Indian Ocean, the data distribution was still not uniform and most data were sampled in the surface Pacific and Atlantic Oceans. By summing the arithmetic means of the N2 fixation rates in each ocean basin, the updated database substantially increased the estimate of global oceanic N2 fixation from 137 ± 9 Tg N yr-1 using the old database to 260 ± 20 Tg N yr-1 (mean ± standard error). However, using geometric means instead, the updated database gave an estimate of global oceanic N2 fixation (60 Tg N yr-1) similar to that estimated from the old database (62 Tg N yr-1), while the new estimate had a larger uncertainty (confidence intervals based on one standard error: 47 – 107 Tg N yr-1 versus 52 – 73 Tg N yr-1), mostly attributable to elevated uncertainties in the Pacific Ocean. An analysis comparing N2 fixation rates measured at the same months and location (1° × 1° grids) showed that the new 15N2 dissolution method obtained N2 fixation rates higher than the conventional 15N2 bubble method in 65 % of cases, with this percentage increasing when the N2 fixation rates were high (> approximately 3 μmol N m-3 d-1 using the 15N2 dissolution method). With greatly increased data points, this version 2 of the global oceanic diazotrophic database can support future studies in marine ecology and biogeochemistry. The database is stored at the Figshare repository (https://doi.org/10.6084/m9.figshare.21677687) (Shao et al., 2022).

Continuous Zonal Gradients Characterize Epipelagic Plankton Assemblages and Hydrography in the Subtropical North Atlantic

“…Even when converted to their corresponding biovolume NBSS [56], our values varied between −1.89 and −1.00, extending the range of NBSS for phytoplankton [21,55], but also the values reported in studies also including zooplankton [8,56]. Steeper slopes imply larger energy losses in the transfer from the small and more abundant phytoplankton cells to the larger and less abundant mesozooplankton, and therefore a reduced number of trophic levels [34,57]. Thus, the linear decrease in NBSS (and the corresponding increase in NBSI) from east to west indicates a gradual transition from a food web based on relatively large phytoplankton and mesozooplankton near the Canary Current (flatter slopes) to a food web where small cells and microzooplankton dominate (steeper slopes).…”

“…Scientific names were assigned following the World Register of Marine Species (WoRMS) [33]. Trichodesmium abundance data can be found in Version 2 of the Global Oceanic Diazotroph Database [34].…”

Upper Ocean Biogeochemistry of the Oligotrophic North Pacific Subtropical Gyre: From Nutrient Sources to Carbon Export

“… N 2 fixation rates in the North Pacific Subtropical Gyre (NPSG). (a) In situ N 2 fixation measurements (gridded on 1° × 1°) in the upper 50 m (μmol m −3 d −1 ) and (b) integrated through the water column (μmol m −2 d −1 ) (Shao et al., 2023). (c–f) Latitudinal and meridional averages of measured N 2 fixation in the NPSG for (a, b) using the samples inside a climatological surface chlorophyll‐ a concentration of 0.1 mg m −3 (marked by the black contours).…”