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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.


Spatial distribution of nitracline depth, nitracline thickness, phosphocline depth and phosphocline thickness (A, B), mean (±SD) zooplankton δ15N (C, D), and mean (±SD) relative contribution (%) of atmospheric input to zooplankton biomass (E, F) along 23°W and 18°N, respectively.
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pone.0131258.g004: Spatial distribution of nitracline depth, nitracline thickness, phosphocline depth and phosphocline thickness (A, B), mean (±SD) zooplankton δ15N (C, D), and mean (±SD) relative contribution (%) of atmospheric input to zooplankton biomass (E, F) along 23°W and 18°N, respectively.

Mentions: The spatial distribution of macronutrients was closely related to pycnocline depth (Figs 2 and 3). Mean near-surface (10m) concentrations of dissolved inorganic N (combined NO2-/NO3-) often reached the detection limit of 0.004 μmol L-1. North of about 7°N along the 23°W transect, a shallow nitracline with minimum depth of about 20 m was observed. Between 3 and 7°N, the nitracline was generally deeper and characterized by steep vertical gradients. At the equator, the vertical gradient was less sharp compared to off-equatorial locations and nutrient depletion reached deep into the water column. Along the 18°N transect, the nitracline ascended from west to east and its vertical extension decreased concomitantly (Figs 3 and 4). Mean near-surface values of dissolved inorganic phosphate (DIP) were 0.18 ±0.045 μmol L-1 and 0.14 ±0.021 μmol L-1 for the 23°W and 18°N transect, respectively (Figs 3 and 4). Along both transects, nitracline and phosphocline depths were highly correlated (0.96 cor, p<0.0001, Pearson`s test), with the nitracline being below the phosphocline with the exception of two stations.


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)

Spatial distribution of nitracline depth, nitracline thickness, phosphocline depth and phosphocline thickness (A, B), mean (±SD) zooplankton δ15N (C, D), and mean (±SD) relative contribution (%) of atmospheric input to zooplankton biomass (E, F) along 23°W and 18°N, respectively.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131258.g004: Spatial distribution of nitracline depth, nitracline thickness, phosphocline depth and phosphocline thickness (A, B), mean (±SD) zooplankton δ15N (C, D), and mean (±SD) relative contribution (%) of atmospheric input to zooplankton biomass (E, F) along 23°W and 18°N, respectively.
Mentions: The spatial distribution of macronutrients was closely related to pycnocline depth (Figs 2 and 3). Mean near-surface (10m) concentrations of dissolved inorganic N (combined NO2-/NO3-) often reached the detection limit of 0.004 μmol L-1. North of about 7°N along the 23°W transect, a shallow nitracline with minimum depth of about 20 m was observed. Between 3 and 7°N, the nitracline was generally deeper and characterized by steep vertical gradients. At the equator, the vertical gradient was less sharp compared to off-equatorial locations and nutrient depletion reached deep into the water column. Along the 18°N transect, the nitracline ascended from west to east and its vertical extension decreased concomitantly (Figs 3 and 4). Mean near-surface values of dissolved inorganic phosphate (DIP) were 0.18 ±0.045 μmol L-1 and 0.14 ±0.021 μmol L-1 for the 23°W and 18°N transect, respectively (Figs 3 and 4). Along both transects, nitracline and phosphocline depths were highly correlated (0.96 cor, p<0.0001, Pearson`s test), with the nitracline being below the phosphocline with the exception of two stations.

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.