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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.


72-hour Hysplit back trajectories of air masses that reached positions along 23°W at 1000 m height for October 23 (green), November 8 (red) and November 16 (blue).The inset shows the average satellite rainfall (mm h-1) along 23°W within the longitude range 22°W to 24°W for November 2012. Black lines denote the sampled transects at 23°W and 18°N.
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pone.0131258.g001: 72-hour Hysplit back trajectories of air masses that reached positions along 23°W at 1000 m height for October 23 (green), November 8 (red) and November 16 (blue).The inset shows the average satellite rainfall (mm h-1) along 23°W within the longitude range 22°W to 24°W for November 2012. Black lines denote the sampled transects at 23°W and 18°N.

Mentions: Sampling was conducted along a N-S transect from 15°N to 5°S at 23°W and along an E-W transect from 20 to 27°W at 18°N in the eastern tropical Atlantic (Fig 1) during R/V “Maria S. Merian” cruise MSM 22 (October 24—November 23, 2012). For sampling in the exclusive economic zone of Cape Verde, permission was granted by the Cape Verdean Ministry of Foreign Affairs. Work conducted in international waters did not require a specific permit and did not involve endangered or protected species. Satellite derived rainfall rates (NASA tropical rainfall measuring mission) and back trajectories of air masses for the region and time frame of our observations were downloaded from http://trmm.gsfc.nasa.gov/ and http://ready.arl.noaa.gov/HYSPLIT.php, respectively. Oceanographic observations were conducted using a 24-niskin bottle rosette with a Seabird SBE 11plus CTD equipped with a Dr. Haardt fluorescence probe and an Underwater Vision Profiler 5 (UVP 5, serial number 001). The fluorescence probe was cross-calibrated with regularly conducted chl-a measurements. Chl-a samples were 0.2-mm filtered (25 mm Whatman GF/F), the filters frozen at -80°C for over 5 h, extracted in 90% acetone and measured against a blank in a Turner Trilogy fluorometer calibrated with a chl-a standard dilution series. Trichodesmium distribution and abundance were quantified at 111 stations with the UVP5. This imaging tool allows in situ quantification of particles >60 μm and plankton >500 μm with high vertical resolution [30, 31]. Thumbnails of all objects > 500 μm were extracted using the ZooProcess software [32]. Imaged Trichodesmium were identified by a computer-assisted method [32] and the identification validated by experts. The observed volume of each image was 0.93 L. On average 11.6 (±3.09) images were recorded per m depth and the mean sampling volume for the upper 200 m of the water column was 2.16 m3.


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)

72-hour Hysplit back trajectories of air masses that reached positions along 23°W at 1000 m height for October 23 (green), November 8 (red) and November 16 (blue).The inset shows the average satellite rainfall (mm h-1) along 23°W within the longitude range 22°W to 24°W for November 2012. Black lines denote the sampled transects at 23°W and 18°N.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131258.g001: 72-hour Hysplit back trajectories of air masses that reached positions along 23°W at 1000 m height for October 23 (green), November 8 (red) and November 16 (blue).The inset shows the average satellite rainfall (mm h-1) along 23°W within the longitude range 22°W to 24°W for November 2012. Black lines denote the sampled transects at 23°W and 18°N.
Mentions: Sampling was conducted along a N-S transect from 15°N to 5°S at 23°W and along an E-W transect from 20 to 27°W at 18°N in the eastern tropical Atlantic (Fig 1) during R/V “Maria S. Merian” cruise MSM 22 (October 24—November 23, 2012). For sampling in the exclusive economic zone of Cape Verde, permission was granted by the Cape Verdean Ministry of Foreign Affairs. Work conducted in international waters did not require a specific permit and did not involve endangered or protected species. Satellite derived rainfall rates (NASA tropical rainfall measuring mission) and back trajectories of air masses for the region and time frame of our observations were downloaded from http://trmm.gsfc.nasa.gov/ and http://ready.arl.noaa.gov/HYSPLIT.php, respectively. Oceanographic observations were conducted using a 24-niskin bottle rosette with a Seabird SBE 11plus CTD equipped with a Dr. Haardt fluorescence probe and an Underwater Vision Profiler 5 (UVP 5, serial number 001). The fluorescence probe was cross-calibrated with regularly conducted chl-a measurements. Chl-a samples were 0.2-mm filtered (25 mm Whatman GF/F), the filters frozen at -80°C for over 5 h, extracted in 90% acetone and measured against a blank in a Turner Trilogy fluorometer calibrated with a chl-a standard dilution series. Trichodesmium distribution and abundance were quantified at 111 stations with the UVP5. This imaging tool allows in situ quantification of particles >60 μm and plankton >500 μm with high vertical resolution [30, 31]. Thumbnails of all objects > 500 μm were extracted using the ZooProcess software [32]. Imaged Trichodesmium were identified by a computer-assisted method [32] and the identification validated by experts. The observed volume of each image was 0.93 L. On average 11.6 (±3.09) images were recorded per m depth and the mean sampling volume for the upper 200 m of the water column was 2.16 m3.

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.