biological n2 fixation in the galician upwelling system ... · biological n 2 fixation in the...
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Biological N2 fixation in the Galician upwelling system: magnitude, relevance and main players
Víctor Moreira-Coello*, Beatriz Mouriño-Carballido, Emilio Marañón, Ana Fernández, Paloma Chouciño, Eva Sintes, Marta M. Varela & Antonio Bode
18 November 201614:45
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Modified from Sohm et al., 2011
What is Biological Nitrogen Fixation?
Biological conversionN2 NH4
+
NH4+
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Luo et al., 2012
Background
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Tropical and subtropical regions
From TRYNITROP Project and www.whoi.edu
Trichodesmium sp.
Background
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Background:evidences of N2 fixation in N-rich temperate regions
Upwelling region off NW Iberia, July 2009 (Benavides et al., 2011; Agawin et al., 2014)
Tropical and subtropical regions
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1) To describe the seasonal variability of N2 fixation andquantify its biogeochemical relevance.
2) To characterize the diazotrophic community.
Our goals
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Study area & Methods
MSS profiler
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Hydrography
Hydrographic conditions
U: Upwelling (↑ Chl a, Bloom)
D: Downwelling (↑ Mixing)
R: Relaxation (↑ Stratification)
Mixed layer depth
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Our goals
1) To describe the seasonal variability of N2 fixation andquantify its biogeochemical relevance.
2) To characterize the diazotrophic community.
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N2 fixation similar to the lower-end of rates described for NASE
Downwelling Upwelling Relaxation
Depth
-Inte
gra
ted N
2fixation r
ate
s
(µm
ol m
-2d
-1)
Seasonal variability of N2 fixation
2.5
2
1.5
1
0.5
0
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Depth
-Inte
gra
ted N
2fixation r
ate
s
(µm
ol m
-2d
-1)
2.5
2
1.5
1
0.5
0
Seasonal variability of N2 fixation and biogeochemical role
Downwelling Upwelling Relaxation
14
16
Contr
ibution
tonew
N
(%)
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Our goals
1) To describe the seasonal variability of N2 fixation andquantify its biogeochemical relevance.
2) To characterize the diazotrophic community.
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Principal Coordinate Analysis
Diazotrophic community composition
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Principal Coordinate Analysis
Relaxation
Diazotrophic community composition: clusters
Bray-Curtis similarity
50%
Downwelling
Upwelling
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Diazotrophic community composition
Relaxation
Downwelling
Upwelling
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UCYN-A1 and UCYN-A2 abundance (nifH copies L -1)
Upwelling
Downwelling
(14%)
(14%)38
Relaxation
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1) N2 fixation slightly higher during relaxation (0.1–2.5 µmol N m-2 d-1 ).
2) Minor biogeochemical role (< 14%).
3) Seasonal variability in diazotrophic community:
‒ UCYN-A2: Relaxation-Stratification.
‒ Heterotrophic bacteria: Downwelling-Mixing.
‒ Similar contribution of both groups: Upwelling-Bloom.
Conclusions
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Acknowledgments:
FPU fellowship to V.M. from Spanish Ministry of Education,
Culture and Sports (FPU13/01674).
Study supported by projects NICANOR from Xunta de Galicia
(EM2013/021, Galician Government) and RADIALES (IEO).
Thank you for your attention!
Contact the author Víctor Moreira: [email protected]