Global oceanic diazotroph database version 2 and elevated estimate of global oceanic N2 fixation
Authors: Shao Zhibo , Xu Yangchun , Wang Hua , Luo Weicheng , Wang Lice , Huang Yuhong , Agawin Nona Sheila R. , Ahmed Ayaz , Benavides Mar , Bentzon-Tilia Mikkel , Berman-Frank Ilana , Berthelot Hugo , Biegala Isabelle C. , Bif Mariana B. , Bode Antonio , Bonnet Sophie , Bronk Deborah A. , Brown Mark V. , Campbell Lisa , Capone Douglas G. , Carpenter Edward J. , Cassar Nicolas , Chang Bonnie X. , Chappell Dreux , Chen Yuh-ling Lee , Church Matthew J. , Cornejo-Castillo Francisco M. , Detoni Amália Maria Sacilotto , Doney Scott C. , Dupouy Cecile , Estrada Marta , Fernandez Camila , Fernández-Castro Bieito , Fonseca-Batista Debany , Foster Rachel A. , Furuya Ken , Garcia Nicole , Goto Kanji , Gago Jesús , Gradoville Mary R. , Hamersley M. Robert , Henke Britt A. , Hörstmann Cora , Jayakumar Amal , Jiang Zhibing , Kao Shuh-Ji , Karl David M. , Kittu Leila R. , Knapp Angela N. , Kumar Sanjeev , LaRoche Julie , Liu Hongbin , Liu Jiaxing , Lory Caroline , Löscher Carolin R. , Marañón Emilio , Messer Lauren F. , Mills Matthew M. , Mohr Wiebke , Moisander Pia H. , Mahaffey Claire , Moore Robert , Mouriño-Carballido Beatriz , Mulholland Margaret R. , Nakaoka Shin-ichiro , Needoba Joseph A. , Raes Eric J. , Rahav Eyal , Ramírez-Cárdenas Teodoro , Reeder Christian Furbo , Riemann Lasse , Riou Virginie , Robidart Julie C. , Sarma Vedula V. S. S. , Sato Takuya , Saxena Himanshu , Selden Corday , Seymour Justin R. , Shi Dalin , Shiozaki Takuhei , Singh Arvind , Sipler Rachel E. , Sun Jun , Suzuki Koji , Takahashi Kazutaka , Tan Yehui , Tang Weiyi , Tremblay Jean-Éric , Turk-Kubo Kendra , Wen Zuozhu , White Angelicque E. , Wilson Samuel T. , Yoshida Takashi , Zehr Jonathan P. , Zhang Run , Zhang Yao , Luo Ya-Wei 
Published: August 2023

Abstract. Marine diazotrophs convert dinitrogen (N2) gas into
bioavailable nitrogen (N), supporting life in the global ocean. In 2012, the
first version of the global oceanic diazotroph database (version 1) was
published. Here, we present an updated version of the database (version 2),
significantly increasing the number of in situ diazotrophic measurements from
13 565 to 55 286. Data points for N2 fixation rates, diazotrophic cell
abundance, and nifH gene copy abundance have increased by 184 %, 86 %, and
809 %, respectively. Version 2 includes two new data sheets for the nifH gene
copy abundance of non-cyanobacterial diazotrophs and cell-specific N2
fixation rates. The measurements of N2 fixation rates approximately
follow a log-normal distribution in both version 1 and version 2. However,
version 2 considerably extends both the left and right tails of the
distribution. Consequently, when estimating global oceanic N2 fixation
rates using the geometric means of different ocean basins, version 1 and
version 2 yield similar rates (43–57 versus 45–63 Tg N yr−1; ranges
based on one geometric standard error). In contrast, when using arithmetic
means, version 2 suggests a significantly higher rate of 223±30 Tg N yr−1 (mean ± standard error; same hereafter) compared to version 1
(74±7 Tg N yr−1). Specifically, substantial rate increases are
estimated for the South Pacific Ocean (88±23 versus 20±2 Tg N yr−1), primarily driven by measurements in the southwestern subtropics,
and for the North Atlantic Ocean (40±9 versus 10±2 Tg N yr−1). Moreover, version 2 estimates the N2 fixation rate in the
Indian Ocean to be 35±14 Tg N yr−1, which could not be estimated
using version 1 due to limited data availability. Furthermore, a comparison
of N2 fixation rates obtained through different measurement methods at
the same months, locations, and depths reveals that the conventional
15N2 bubble method yields lower rates in 69 % cases compared to
the new 15N2 dissolution method. This updated version of the
database can facilitate 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).