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

Daniela Böttjer; John E. Dore; David M. Karl; Ricardo M. Letelier; Claire Mahaffey; Samuel T. Wilson; Jonathan Zehr; Matthew J. Church

doi:10.1002/lno.10386

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

Daniela Böttjer
, John E. Dore
, David M. Karl
, Ricardo M. Letelier
, Claire Mahaffey
, Samuel T. Wilson
, Jonathan Zehr
, Matthew J. Church

Flathead Lake Biological Station

Research output: Contribution to journal › Article › peer-review

114 Scopus citations

Abstract

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.

Original language	English
Pages (from-to)	200-216
Number of pages	17
Journal	Limnology and Oceanography
Volume	62
Issue number	1
DOIs	https://doi.org/10.1002/lno.10386
State	Published - Jan 1 2017

Funding

The authors extend special thanks to the Hawai'i Ocean Time-series scientists and staff for their help and support in facilitating this work. Additionally, we thank S. Ferrón for assistance with running the membrane inlet mass spectrometer and to D. Viviani for support with statistical analyses. We also acknowledge the captains and crews of the research vessels Kilo Moana and Kaimikai-O-Kanaloa. Nitrate isotopic data from Casciotti et al. (2008) were obtained from the Biological and Chemical Oceanography Data Management Office (http://www.bco-dmo.org/dataset/2971/data). This research was supported by grants from the National Science Foundation (OCE09-26766; OCE08-50827; and DBI04-24599). Additional support was derived from the Simons Collaboration on Ocean Processes and Ecology (SCOPE) and the Gordon and Betty Moore Foundation (project #3794). None declared.

Funders	Funder number
OCE08-50827, DBI04-24599, OCE09-26766
3794
Natural Environment Research Council	NE/G018782/1

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title = "Temporal variability of nitrogen fixation and particulate nitrogen export at Station ALOHA",

abstract = "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.",

author = "Daniela B{\"o}ttjer and Dore, \{John E.\} and Karl, \{David M.\} and Letelier, \{Ricardo M.\} and Claire Mahaffey and Wilson, \{Samuel T.\} and Jonathan Zehr and Church, \{Matthew J.\}",

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AU - Mahaffey, Claire

AU - Wilson, Samuel T.

AU - Zehr, Jonathan

AU - Church, Matthew J.

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N2 - 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.

AB - 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.

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

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