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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.


Negative linear relationship between individual bulk δ15N and δ13C values of zooplankton functional groups (Trichodesmium-grazer, carnivore, omnivore and euphausiids).
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pone.0131258.g005: Negative linear relationship between individual bulk δ15N and δ13C values of zooplankton functional groups (Trichodesmium-grazer, carnivore, omnivore and euphausiids).

Mentions: Zooplankton δ13C values ranged from a minimum of -23.0‰ in Trichodesmium feeders to -18.7‰ in omnivore species (Fig 5). Spatial differences in zooplankton δ13C were inversely related to δ15N values, with low values in the equatorial region and in the northern part of the 23°W transect that contrasted a peak of high values at about 5°N. At all stations present, δ13C values were lowest in Trichodesmium grazers. Among feeding types, δ15N and δ13C were negatively correlated (Fig 5). The slope of the corresponding linear regression was -0.38(±0.08) in presumable direct consumers of diazotroph biomass (M. gracilis and M. efferata), which was significantly different (ANCOVA, α = 0.05) from that in all other groups, with values of -1.9(±0.1), -1.7(±0.1) and -1.9(±0.2) for carnivores, omnivores and euphausiids, respectively.


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)

Negative linear relationship between individual bulk δ15N and δ13C values of zooplankton functional groups (Trichodesmium-grazer, carnivore, omnivore and euphausiids).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131258.g005: Negative linear relationship between individual bulk δ15N and δ13C values of zooplankton functional groups (Trichodesmium-grazer, carnivore, omnivore and euphausiids).
Mentions: Zooplankton δ13C values ranged from a minimum of -23.0‰ in Trichodesmium feeders to -18.7‰ in omnivore species (Fig 5). Spatial differences in zooplankton δ13C were inversely related to δ15N values, with low values in the equatorial region and in the northern part of the 23°W transect that contrasted a peak of high values at about 5°N. At all stations present, δ13C values were lowest in Trichodesmium grazers. Among feeding types, δ15N and δ13C were negatively correlated (Fig 5). The slope of the corresponding linear regression was -0.38(±0.08) in presumable direct consumers of diazotroph biomass (M. gracilis and M. efferata), which was significantly different (ANCOVA, α = 0.05) from that in all other groups, with values of -1.9(±0.1), -1.7(±0.1) and -1.9(±0.2) for carnivores, omnivores and euphausiids, respectively.

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.