143
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
J. P. Zehr, D. G. Capone, Marine Nitrogen Fixation,
https://doi.org/10.1007/978-3-030-67746-6_8
Chapter 8
N 2 Fixation in Ocean Basins
With the accelerating research of the last few decades enabled by improved
methodologies (see Chaps. 3 and 5), estimates of the global inputs of N by N 2 fixation to the oceans have steadily evolved and improved. One early extrapolation
(Soderlund and Svensson 1976) provided a wide estimate of water column N 2 fixation, primarily by Trichodesmium and Richelia, ranging from 20 to 120 Tg N y
−1
based on extrapolation from 2 research cruises in the tropical North Atlantic
(Goering et al. 1966), another in the North Pacific near Hawaii (Gruber 2004;
Gundersen 1974), and additional benthic N 2 fixation of 10 Tg y
−1
derived from a
range of benthic habitats. The database for N 2 fixation field observations has
expanded greatly (Deutsch et al. 2007; Luo et al. 2012; Tang and Cassar 2019) and
estimates have risen considerably (Table 8.1; discussed below). For context, current
approximations of N 2 fixation inputs in natural terrestrial environments are thought
to be about 100 Tg N y
−1
(Davies-Barnard and Friedlingstein 2020; Großkopf et al.
2012) with managed agricultural systems contributing about 60 Tg N y
−1
and industrial produced fertilizers by the Haber-Bosch process now exceeding 120 Tg y
−1
(Fowler et al. 2013; Sipler et al. 2017) (Fig. 8.1).
Oceanic N losses (now known to be through anaerobic ammonia oxidation as
well as canonical denitrification) primarily occur in shelf and coastal sediments and
in the major oxygen deficient zones (ODZs), which include the Eastern Tropical
North (ETNP) and South (ETSP) Pacific and the Arabian Sea (AS) (Gruber 2008).
ODZs have been long recognized as major oceanographic features with unique biogeochemistry, particularly with respect to the N cycle (Helly and Levin 2004).
Integrated rates of removal of combined N in these environments along with that
occurring in coastal shelf sediments appeared to considerably exceed many of the
concurrent estimates of global N 2 fixation rates estimated from field observations
(Codispoti et al. 2001; Codispoti 2007). Indeed, by some reports, integrated estimates (Codispoti et al. 2001) suggested almost twice as much removal (~ 482 Tg or
10
12
g) of N per year compared to total inputs of 294 Tg y
−1
(Codispoti et al. 2001;
Codispoti 2007).
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
J. P. Zehr, D. G. Capone, Marine Nitrogen Fixation,
https://doi.org/10.1007/978-3-030-67746-6_8
Chapter 8
N 2 Fixation in Ocean Basins
With the accelerating research of the last few decades enabled by improved
methodologies (see Chaps. 3 and 5), estimates of the global inputs of N by N 2 fixation to the oceans have steadily evolved and improved. One early extrapolation
(Soderlund and Svensson 1976) provided a wide estimate of water column N 2 fixation, primarily by Trichodesmium and Richelia, ranging from 20 to 120 Tg N y
−1
based on extrapolation from 2 research cruises in the tropical North Atlantic
(Goering et al. 1966), another in the North Pacific near Hawaii (Gruber 2004;
Gundersen 1974), and additional benthic N 2 fixation of 10 Tg y
−1
derived from a
range of benthic habitats. The database for N 2 fixation field observations has
expanded greatly (Deutsch et al. 2007; Luo et al. 2012; Tang and Cassar 2019) and
estimates have risen considerably (Table 8.1; discussed below). For context, current
approximations of N 2 fixation inputs in natural terrestrial environments are thought
to be about 100 Tg N y
−1
(Davies-Barnard and Friedlingstein 2020; Großkopf et al.
2012) with managed agricultural systems contributing about 60 Tg N y
−1
and industrial produced fertilizers by the Haber-Bosch process now exceeding 120 Tg y
−1
(Fowler et al. 2013; Sipler et al. 2017) (Fig. 8.1).
Oceanic N losses (now known to be through anaerobic ammonia oxidation as
well as canonical denitrification) primarily occur in shelf and coastal sediments and
in the major oxygen deficient zones (ODZs), which include the Eastern Tropical
North (ETNP) and South (ETSP) Pacific and the Arabian Sea (AS) (Gruber 2008).
ODZs have been long recognized as major oceanographic features with unique biogeochemistry, particularly with respect to the N cycle (Helly and Levin 2004).
Integrated rates of removal of combined N in these environments along with that
occurring in coastal shelf sediments appeared to considerably exceed many of the
concurrent estimates of global N 2 fixation rates estimated from field observations
(Codispoti et al. 2001; Codispoti 2007). Indeed, by some reports, integrated estimates (Codispoti et al. 2001) suggested almost twice as much removal (~ 482 Tg or
10
12
g) of N per year compared to total inputs of 294 Tg y
−1
(Codispoti et al. 2001;
Codispoti 2007).