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Martin, Patrick; Rutgers van der Loeff, Michiel M; Cassar, Nicolas; Vandromme, Pieter; d'Ovidio, Francesco; Stemmann, Lars; Rengarajan, Ramabadran; Soares, Melena; González, Humberto E; Ebersbach, Friederike; Lampitt, Richard Stephen; Sanders, Richard J; Barnett, Bruce A; Smetacek, Victor; Naqvi, Syed Wajih Ahmad (2013): Net community production, Thorium-234 activity and particle flux during the Southern Ocean iron fertilization experiment LOHAFEX [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.832525, Supplement to: Martin, P et al. (2013): Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX. Global Biogeochemical Cycles, 27(3), 871-881, https://doi.org/10.1002/gbc.20077

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Abstract:
A closed eddy core in the Subantarctic Atlantic Ocean was fertilized twice with two tons of iron (as FeSO4), and the 300 km**2 fertilized patch was studied for 39 days to test whether fertilization enhances downward particle flux into the deep ocean. Chlorophyll a and primary productivity doubled after fertilization, and photosynthetic quantum yield (FV/FM) increased from 0.33 to >0.40. Silicic acid (<2 µmol/L) limited diatoms, which contributed <10% of phytoplankton biomass. Copepods exerted high grazing pressure. This is the first study of particle flux out of an artificially fertilized bloom with very low diatom biomass. Net community production (NCP) inside the patch, estimated from O2:Ar ratios, averaged 21 mmol POC/m**2/d, probably ±20%. 234Th profiles implied constant export of ~6.3 mmol POC/m**2/d in the patch, similar to unfertilized waters. The difference between NCP and 234Th-derived export partly accumulated in the mixed layer and was partly remineralized between the mixed layer and 100 m. Neutrally buoyant sediment traps at 200 and 450 m inside and outside the patch caught mostly <1.1 mmol POC/m**2/d, predominantly of fecal origin; flux did not increase upon fertilization. Our data thus indicate intense flux attenuation between 100 and 200 m, and probably between the mixed layer and 100 m. We attribute the lack of fertilization-induced export to silicon limitation of diatoms and reprocessing of sinking particles by detritus feeders. Our data are consistent with the view that nitrate-rich but silicate-deficient waters are not poised for enhanced particle export upon iron addition.
Project(s):
Marine Geochemistry @ AWI (AWI_MarGeoChem)
Coverage:
Median Latitude: -47.972615 * Median Longitude: -15.137787 * South-bound Latitude: -49.037300 * West-bound Longitude: -16.097930 * North-bound Latitude: -44.509310 * East-bound Longitude: -12.881320
Date/Time Start: 2009-01-26T13:04:00 * Date/Time End: 2009-03-06T12:31:00
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
7 datasets

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Datasets listed in this publication series

  1. Martin, P; Rutgers van der Loeff, MM; Cassar, N et al. (2013): Vertical profiles of Thorium-234 relative to Uranium-238 activity measured during POLARSTERN cruise ANT-XXV/3 (LOHAFEX). https://doi.org/10.1594/PANGAEA.832519
  2. Martin, P; Rutgers van der Loeff, MM; Cassar, N et al. (2013): Calculated downward export flux based on surface thorium depletion and assuming steady-state export during POLARSTERN cruise ANT-XXV/3 (LOHAFEX). https://doi.org/10.1594/PANGAEA.832520
  3. Martin, P; Rutgers van der Loeff, MM; Cassar, N et al. (2013): Downward particle fluxes measured in neutrally buoyant PELAGRA sediment traps during POLARSTERN cruise ANT-XXV/3 (LOHAFEX). https://doi.org/10.1594/PANGAEA.832524
  4. Martin, P; Rutgers van der Loeff, MM; Cassar, N et al. (2013): Carbon/Thorium ratios from in situ pumps during POLARSTERN cruise ANT-XXV/3 (LOHAFEX). https://doi.org/10.1594/PANGAEA.832521
  5. Martin, P; Rutgers van der Loeff, MM; Cassar, N et al. (2013): Carbon/Thorium ratios from sediment traps during POLARSTERN cruise ANT-XXV/3 (LOHAFEX). https://doi.org/10.1594/PANGAEA.832522
  6. Martin, P; Rutgers van der Loeff, MM; Cassar, N et al. (2013): Underway Thorium-234 measurements during POLARSTERN cruise ANT-XXV/3 (LOHAFEX) using automated sampler Nick. https://doi.org/10.1594/PANGAEA.832523
  7. Martin, P; Rutgers van der Loeff, MM; Cassar, N et al. (2013): Net community production estimates from underway O2:Ar measurement during POLARSTERN cruise ANT-XXV/3 (LOHAFEX). https://doi.org/10.1594/PANGAEA.832518