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Nitrogen Fuelling of the Pelagic Food Web of the Tropical Atlantic.

Sandel V, Kiko R, Brandt P, Dengler M, Stemmann L, Vandromme P, Sommer U, Hauss H - PLoS ONE (2015)

Bottom Line: The thickness and depth of the nitracline and phosphocline proved to be significant predictors of zooplankton stable N isotope values.Our approach integrates over large spatial and temporal scales and also quantifies fixed N released as dissolved inorganic and organic N.In a global analysis, it may thus help to close the gap in oceanic N budgets.

View Article: PubMed Central - PubMed

Affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, Kiel, Germany.

ABSTRACT
We estimated the relative contribution of atmosphere (ic Nitrogen (N) input (wet and dry deposition and N fixation) to the epipelagic food web by measuring N isotopes of different functional groups of epipelagic zooplankton along 23°W (17°N-4°S) and 18°N (20-24°W) in the Eastern Tropical Atlantic. Results were related to water column observations of nutrient distribution and vertical diffusive flux as well as colony abundance of Trichodesmium obtained with an Underwater Vision Profiler (UVP5). The thickness and depth of the nitracline and phosphocline proved to be significant predictors of zooplankton stable N isotope values. Atmospheric N input was highest (61% of total N) in the strongly stratified and oligotrophic region between 3 and 7°N, which featured very high depth-integrated Trichodesmium abundance (up to 9.4×10(4) colonies m(-2)), strong thermohaline stratification and low zooplankton δ15N (~2‰). Relative atmospheric N input was lowest south of the equatorial upwelling between 3 and 5°S (27%). Values in the Guinea Dome region and north of Cape Verde ranged between 45 and 50%, respectively. The microstructure-derived estimate of the vertical diffusive N flux in the equatorial region was about one order of magnitude higher than in any other area (approximately 8 mmol m(-2) d(1)). At the same time, this region received considerable atmospheric N input (35% of total). In general, zooplankton δ15N and Trichodesmium abundance were closely correlated, indicating that N fixation is the major source of atmospheric N input. Although Trichodesmium is not the only N fixing organism, its abundance can be used with high confidence to estimate the relative atmospheric N input in the tropical Atlantic (r2 = 0.95). Estimates of absolute N fixation rates are two- to tenfold higher than incubation-derived rates reported for the same regions. Our approach integrates over large spatial and temporal scales and also quantifies fixed N released as dissolved inorganic and organic N. In a global analysis, it may thus help to close the gap in oceanic N budgets.

No MeSH data available.


Contribution of calculated atmospheric N input (%) to zooplankton biomass as a function of integrated Trichodesmium abundance (colonies m-2).The station at 18°N, 19°41’W within the eddy (denoted with an empty circle) was excluded from the analysis. The inset shows UVP5 example images of Trichodesmium puff and tuft, respectively.
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pone.0131258.g006: Contribution of calculated atmospheric N input (%) to zooplankton biomass as a function of integrated Trichodesmium abundance (colonies m-2).The station at 18°N, 19°41’W within the eddy (denoted with an empty circle) was excluded from the analysis. The inset shows UVP5 example images of Trichodesmium puff and tuft, respectively.

Mentions: Relative contribution of atmospheric N input (wet and dry deposition, as well as N fixation) as calculated with δ15N of zooplankton biomass ranged from 23% in the southern part of the 23°W transect to a maximum of 71% around 5°N (Fig 4E). Atmospheric N input estimates for omnivores and carnivores where always closely related. Relative contribution of atmospheric N input was minimal south of the equator, peaked at about 5°N and slightly declined again further towards the north. Along 18°N, the significance of atmospheric N input decreased from west to east for omnivores (Fig 4F). Atmospheric N input to the marine foodweb was described as a nonlinear function of depth-integrated Trichodesmium abundance (r2 = 0.95, Fig 6).


Nitrogen Fuelling of the Pelagic Food Web of the Tropical Atlantic.

Sandel V, Kiko R, Brandt P, Dengler M, Stemmann L, Vandromme P, Sommer U, Hauss H - PLoS ONE (2015)

Contribution of calculated atmospheric N input (%) to zooplankton biomass as a function of integrated Trichodesmium abundance (colonies m-2).The station at 18°N, 19°41’W within the eddy (denoted with an empty circle) was excluded from the analysis. The inset shows UVP5 example images of Trichodesmium puff and tuft, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4476781&req=5

pone.0131258.g006: Contribution of calculated atmospheric N input (%) to zooplankton biomass as a function of integrated Trichodesmium abundance (colonies m-2).The station at 18°N, 19°41’W within the eddy (denoted with an empty circle) was excluded from the analysis. The inset shows UVP5 example images of Trichodesmium puff and tuft, respectively.
Mentions: Relative contribution of atmospheric N input (wet and dry deposition, as well as N fixation) as calculated with δ15N of zooplankton biomass ranged from 23% in the southern part of the 23°W transect to a maximum of 71% around 5°N (Fig 4E). Atmospheric N input estimates for omnivores and carnivores where always closely related. Relative contribution of atmospheric N input was minimal south of the equator, peaked at about 5°N and slightly declined again further towards the north. Along 18°N, the significance of atmospheric N input decreased from west to east for omnivores (Fig 4F). Atmospheric N input to the marine foodweb was described as a nonlinear function of depth-integrated Trichodesmium abundance (r2 = 0.95, Fig 6).

Bottom Line: The thickness and depth of the nitracline and phosphocline proved to be significant predictors of zooplankton stable N isotope values.Our approach integrates over large spatial and temporal scales and also quantifies fixed N released as dissolved inorganic and organic N.In a global analysis, it may thus help to close the gap in oceanic N budgets.

View Article: PubMed Central - PubMed

Affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, Kiel, Germany.

ABSTRACT
We estimated the relative contribution of atmosphere (ic Nitrogen (N) input (wet and dry deposition and N fixation) to the epipelagic food web by measuring N isotopes of different functional groups of epipelagic zooplankton along 23°W (17°N-4°S) and 18°N (20-24°W) in the Eastern Tropical Atlantic. Results were related to water column observations of nutrient distribution and vertical diffusive flux as well as colony abundance of Trichodesmium obtained with an Underwater Vision Profiler (UVP5). The thickness and depth of the nitracline and phosphocline proved to be significant predictors of zooplankton stable N isotope values. Atmospheric N input was highest (61% of total N) in the strongly stratified and oligotrophic region between 3 and 7°N, which featured very high depth-integrated Trichodesmium abundance (up to 9.4×10(4) colonies m(-2)), strong thermohaline stratification and low zooplankton δ15N (~2‰). Relative atmospheric N input was lowest south of the equatorial upwelling between 3 and 5°S (27%). Values in the Guinea Dome region and north of Cape Verde ranged between 45 and 50%, respectively. The microstructure-derived estimate of the vertical diffusive N flux in the equatorial region was about one order of magnitude higher than in any other area (approximately 8 mmol m(-2) d(1)). At the same time, this region received considerable atmospheric N input (35% of total). In general, zooplankton δ15N and Trichodesmium abundance were closely correlated, indicating that N fixation is the major source of atmospheric N input. Although Trichodesmium is not the only N fixing organism, its abundance can be used with high confidence to estimate the relative atmospheric N input in the tropical Atlantic (r2 = 0.95). Estimates of absolute N fixation rates are two- to tenfold higher than incubation-derived rates reported for the same regions. Our approach integrates over large spatial and temporal scales and also quantifies fixed N released as dissolved inorganic and organic N. In a global analysis, it may thus help to close the gap in oceanic N budgets.

No MeSH data available.