Abstract
AbstractDinitrogen (N2) fixation is the source of all biologically available nitrogen on earth, and its presence or absence impacts net primary production and global biogeochemical cycles. Here, we report rates of 3.5–17.2 nmol N L−1 d−1 in the ice‐free coastal Alaskan Arctic to show that N2 fixation in the Arctic Ocean may be an important source of nitrogen to a seasonally nitrogen‐limited system. If widespread in surface waters over ice‐free shelves throughout the Arctic, N2 fixation could contribute up to 3.5 Tg N yr−1 to the Arctic nitrogen budget. At these rates, N2 fixation occurring in ice‐free summer waters would offset up to 27.1% of the Arctic denitrification deficit and contribute an additional 2.7% to N2 fixation globally, making it an important consideration in the current debate of whether nitrogen in the global ocean is in steady state. Additional investigations of high‐latitude marine diazotrophic physiology are required to refine these N2 fixation estimates.
Highlights
These objectives were achieved using 15N tracer techniques to measure rates of N2 fixation during the summer under ice-free conditions at marine and estuarine sites in the Chukchi Sea, near Barrow, Alaska
For each of the three domains that we described above, the total amount of nitrogen fixed each year was calculated by integrating, in space and time, the measured N2 fixation rates over the water column depth down to a maximum depth of 50 m for ice-free days from 01 June to 30 September
Active N2 fixation was found in the coastal Chukchi Sea near Barrow, Alaska with average rates of 7.7 6 1.8 nmol N L21 d21 and 5.3 6 0.2 nmol N L21 d21 at marine and estuarine sites, respectively (Table 2)
Summary
These objectives were achieved using 15N tracer techniques to measure rates of N2 fixation during the summer under ice-free conditions at marine and estuarine sites in the Chukchi Sea, near Barrow, Alaska. The data presented here, and reported in Blais et al (2012), were extrapolated to provide rough estimates of the potential range of fixed nitrogen contributed by Arctic marine N2 fixation.
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