Journal Article
Low rates of dinitrogen fixation in the eastern tropical South Pacific
Bonnie X. Chang; Amal Jayakumar; Brittany Widner; Peter Bernhardt; Calvin W. Mordy; Margaret R. Mulholland; Bess B. Ward
Limnology and Oceanography · Vol. 64, Issue 5 · pp. 1913-1923 · 2019
Abstract
Recent work has suggested that the oxygen deficient zone (ODZ) and overlying surface waters of the eastern tropical South Pacific (ETSP) is a potential niche for dinitrogen (N 2 ) fixation. Rates of dinitrogen fixation were measured in the ETSP above and within the ODZ in July 2013 using a modified 15 N 2 bubble addition method, wherein a bubble was added, mixed, and then removed, and the isotopic enrichment of the dissolved N 2 was measured directly for each incubation. N 2 fixation rates in the euphotic zone ranged from below detection to 3.9 nmol L −1 d −1 and were below detection at all depths surveyed within the ODZ. Depth‐integrated rates ranged from below detection to 289.7 μ mol m −2 d −1 . DNA and RNA of diverse nifH genes were detected at both surface waters and in the ODZ. However, the results of this study suggest that N 2 fixation rates were low and contribute little to N cycling in the ETSP.