Temporal variability of nitrogen fixation and particulate nitrogen export at Station ALOHA

Bottjer, D, Dore, JE, Karl, DM, Letelier, RM, Mahaffey, C ORCID: 0000-0002-4215-7271, WIlson, ST, Zehr, J and Church, MJ
(2017) Temporal variability of nitrogen fixation and particulate nitrogen export at Station ALOHA. Limnology and Oceanography, 62 (1). 200 - 216.

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We present nearly 9 yrs (June 2005–December 2013) of measurements of upper‐ocean (0 m to 125 m) dinitrogen (N2) fixation rates, coupled with particulate nitrogen (PN) export at 150 m, from Station ALOHA (22° 45′N, 158°W) in the North Pacific Subtropical Gyre. Between June 2005 and June 2012, N2 fixation rates were measured based on adding the 15N2 tracer as a gas bubble. Beginning in August 2012, 15N2 was first dissolved into filtered seawater and the 15N2‐enriched water was subsequently added to N2 fixation incubations. Direct comparisons between methodologies revealed a robust relationship, with the addition of 15N2‐enriched seawater resulting in twofold greater depth‐integrated rates than those derived from adding a 15N2 gas bubble. Based on this relationship, we corrected the initial period of measurements, and the resulting rates of N2 fixation averaged 230 ± 136 μmol N m−2 d−1 for the full time series (n = 71). Analysis of the 15N isotopic composition of sinking PN, together with an isotope mass balance model, revealed that N2 fixation supported 26–47% of PN export during calendar years 2006–2013. The N export derived from these fractional contributions and measured N2 fixation rates ranged between 502 and 919 μmol N m−2 d−1, which are equivalent to rates of net community production (NCP) of 1.5 to 2.7 mol C m−2 yr−1, consistent with previous independent estimates of NCP at this site.

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 12 Jan 2018 11:25
Last Modified: 15 Sep 2022 14:11
DOI: 10.1002/lno.10386
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3012382

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