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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.


Related in: MedlinePlus

Sections of temperature (°C), salinity (PSU), potential density anomaly σθ (kg m-3) and chlorophyll-a (mg m-3) in the upper 300 m of the 23°W transect (A, C, E, G) and the 18°N transect (B, D, F, G), respectively.
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pone.0131258.g002: Sections of temperature (°C), salinity (PSU), potential density anomaly σθ (kg m-3) and chlorophyll-a (mg m-3) in the upper 300 m of the 23°W transect (A, C, E, G) and the 18°N transect (B, D, F, G), respectively.

Mentions: Stations were grouped according to the following oceanographic areas: 3–5°S—oligotrophic South Atlantic (OSA), 3°S-3°N—equatorial upwelling region influenced by strong diapycnal mixing (EU), 3–7°N—oligotrophic North Atlantic (ONA), 7–15°N—Guinea Dome (GD), along 18°N—north of Cape Verde (NCV; Fig 2). South of approximately 3°S, the water column was highly stratified, but lacked superficial fresher water. Around the equator (3°S-3°N), a comparatively shallow and intense chl-a maximum and elevated vertical shear of horizontal velocity were observed due to the presence of the eastward Equatorial Undercurrent and westward South Equatorial Current (not shown). Between 3°N and 7°N, the water column was highly stratified, featuring a superficial “lens” of very low salinity and a deep chl-a maximum. In the GD region, the pycnocline was considerably shallower than in the southern portion of the transect, and the chl-a maximum was approximately as shallow and intense as in the EU. Along the 18°N transect (Fig 2, right panels), the deep chl-a maximum was generally shallower than at the 23°W transect and shoaling towards the eastern margin (Fig 2H). Within an anticyclonic mode water eddy at 19°40'W identified from shipboard ADCP data (not shown) the chl-a maximum extended to the surface.


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)

Sections of temperature (°C), salinity (PSU), potential density anomaly σθ (kg m-3) and chlorophyll-a (mg m-3) in the upper 300 m of the 23°W transect (A, C, E, G) and the 18°N transect (B, D, F, G), respectively.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131258.g002: Sections of temperature (°C), salinity (PSU), potential density anomaly σθ (kg m-3) and chlorophyll-a (mg m-3) in the upper 300 m of the 23°W transect (A, C, E, G) and the 18°N transect (B, D, F, G), respectively.
Mentions: Stations were grouped according to the following oceanographic areas: 3–5°S—oligotrophic South Atlantic (OSA), 3°S-3°N—equatorial upwelling region influenced by strong diapycnal mixing (EU), 3–7°N—oligotrophic North Atlantic (ONA), 7–15°N—Guinea Dome (GD), along 18°N—north of Cape Verde (NCV; Fig 2). South of approximately 3°S, the water column was highly stratified, but lacked superficial fresher water. Around the equator (3°S-3°N), a comparatively shallow and intense chl-a maximum and elevated vertical shear of horizontal velocity were observed due to the presence of the eastward Equatorial Undercurrent and westward South Equatorial Current (not shown). Between 3°N and 7°N, the water column was highly stratified, featuring a superficial “lens” of very low salinity and a deep chl-a maximum. In the GD region, the pycnocline was considerably shallower than in the southern portion of the transect, and the chl-a maximum was approximately as shallow and intense as in the EU. Along the 18°N transect (Fig 2, right panels), the deep chl-a maximum was generally shallower than at the 23°W transect and shoaling towards the eastern margin (Fig 2H). Within an anticyclonic mode water eddy at 19°40'W identified from shipboard ADCP data (not shown) the chl-a maximum extended to the surface.

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.


Related in: MedlinePlus