Particle Export during the Southern Ocean Iron Experiment (SOFeX)

• Published in: Limnology and oceanography Vol. 50; no. 1; pp. 311 - 327
• Main Authors: Buesseler, K. O., Andrews, J. E., Pike, S. M., Charette, M. A., Goldson, L. E., Brzezinski, M. A., Lance, V. P.
• Format: Journal Article
• Language: English
• Published: Waco, TX The American Society of Limnology and Oceanography 01-01-2005; American Society of Limnology and Oceanography
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Carbon; Diatoms; Earth sciences; Earth, ocean, space; Exact sciences and technology; Exports; Fundamental and applied biological sciences. Psychology; Geochemistry; Isotope geochemistry; Isotope geochemistry. Geochronology; Marine; Mineralogy; Oceans; Particulate matter; Phytoplankton; Ratios; Sea water; Sea water ecosystems; Silicates; Surface water; Synecology; Time series; Water geochemistry; sea water; experimental studies; particulate matters; models; silica; latitude; climate; nitrates; enrichment; biogenic origin; primary production; depth; hydrochemistry; marine environment; ecosystems; Antarctic Ocean; iron; silicates; particles; export; organic carbon; Th-234
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2005.50.1.0311

We studied the effect of iron addition on particle export in the Southern Ocean by measuring changes in the distribution of thorium-234 during a 4-week iron (Fe) enrichment experiment conducted in the high-silicate high-nitrate waters just south of the Southern Antarctic Circumpolar Current Front at 172.5°W. Decreases in ^{234}\text{Th}$ activity with time in the fertilized mixed layer (0-50 m) exceeded those in unfertilized waters, indicating enhanced export of ^{234}\text{Th}$ on sinking particles after Fe enrichment. The addition of Fe also affected export below the fertilized patch by increasing the efficiency of particle export through the 100-m depth horizon. Extensive temporal and vertical Lagrangian sampling allowed us to make a detailed examination of the ^{234}\text{Th}$ flux model, which was used to quantify the fluxes of particulate organic carbon (POC) and biogenic silica ($\text{bSiO}_{2}$). Iron addition increased the flux of both POC and $\text{bSiO}_{2}$ out of the mixed layer by about 300%. The flux at 100 m increased by more than 700% and 600% for POC and $\text{bSiO}_{2}$, respectively. The absolute magnitude of the POC and $\text{bSiO}_{2}$ fluxes were not large relative to natural blooms at these latitudes or to those found in association with the termination of blooms in other ocean regions. Our results support the hypothesis that Fe addition leads directly to significant particle export and sequestration of C in the deep ocean. This is a key link between ocean Fe inputs and past changes in atmospheric CO2 and climate.