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Title: Activity and distribution of diazotrophic communities across the Cape Verde Frontal Zone in the Northeast Atlantic Ocean
Authors: Hallstrøm, Søren
Benavides Gorostegui,Mar 
Salamon, Ellen R.
Arístegui Ruiz, Javier 
Riemann, Lasse
UNESCO Clasification: 251007 Oceanografía física
251005 Zoología marina
241403 Metabolismo bacteriano
Keywords: Eastern Boundary Upwelling System
N2 Fixation
Northeast Atlantic
Ucyn-A, et al
Issue Date: 2022
Journal: Biogeochemistry 
Abstract: We investigated dinitrogen (N2) fixation activity and diazotroph community composition across the Cape Verde Frontal Zone (CVFZ), from photic epipelagic waters (0-200 m) to aphotic meso- (200–1000 m) and bathypelagic (> 1000 m) waters. The highest N2 fixation rates of 4.1 ± 2.2 nmol N l− 1 day− 1 and 7.8 ± 2.3 nmol N l− 1 day− 1 were in epipelagic waters south of the front. We detected aphotic N2 fixation in 5 out of 32 samples, primarily south of the front, and sporadically down to 3,000 m, with rates ranging from 0.03 ± 0.01 nmol N l− 1 day− 1 to 0.07 ± 0.01 nmol N l− 1 day− 1. Cyanobacteria dominated the diazotroph community and nitrogenase gene (nifH) expression profiles in surface waters and, surprisingly, in aphotic waters. The detection of cyanobacterial nifH genes by DNA sequencing and quantitative PCR in the aphotic zone, together with nifH expression in meso- and bathypelagic waters, indicates a downward flux of metabolically active cyanobacteria, and points to a contribution to the observed aphotic N2 fixation rates. In the photic zone, UCYN-A dominated north of the front, whereas Trichodesmium was mainly found in the southern region. However, our results also show that cross-frontal advection of cyanobacterial diazotrophs can occur via intrusions of surface water. Salinity, temperature, and mixed layer depth were the main determinants of the diazotroph composition and distribution of the key cyanobacteria. Thus, the front appeared to act as a dynamic barrier controlling the distribution of cyanobacterial diazotrophs.
ISSN: 0168-2563
DOI: 10.1007/s10533-022-00940-w
Source: Biogeochemistry [ISSN 0168-2563], (May 2022)
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