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- Title
Top-down, bottom-up and physical controls on diatom-diazotroph assemblage growth in the Amazon River Plume.
- Authors
Stukel, M. R.; Coles, V. J.; Brooks, M. T.; Hood, R. R.
- Abstract
The nutrient-rich waters of the Amazon River Plume (ARP) support dense blooms of diatom-diazotroph assemblages (DDA) that introduce large quantities of new nitrogen to the planktonic ecosystem and, unlike other nitrogen-fixers, are likely to directly fuel vertical carbon flux. To investigate the factors controlling DDA blooms, we develop a five phytoplankton (cyanobacteria, diatoms, unicellular microbial diazotrophs, DDA, and Trichodesmium), two zooplankton model and embed it within a 1/6° resolution physical model of the tropical and subtropical Atlantic. The model generates realistic DDA blooms in the ARP and also exhibits basin-wide primary production, nitrogen fixation, and grazing rates consistent with observed values. By following ARP water parcels with synthetic Lagrangian drifters released at the river mouth we are able to assess the relative impacts of grazing, nutrient supply, and physical forcing on DDA bloom formation. DDA bloom formation is stimulated in the silica-rich water of the ARP by decreases in grazing pressure when mesozooplankton (which co-occur in high densities with coastal diatom blooms) concentrations decrease. Bloom termination is driven primarily by silica limitation of the DDA. In agreement with in situ data, this net growth niche for DDA exists in a salinity range from ~ 20-34 PSU, although this co-occurrence is coincidental rather than causative. Because net growth rates are relatively modest, bloom formation in ARP water parcels depends critically on the time spent in this ideal habitat, with high DDA biomass only occurring when water parcels spent > 23 days in the optimal habitat niche.
- Subjects
AMAZON River Region; DIATOMS; ALGAL blooms; ECOLOGY of plankton; NITROGEN-fixing microorganisms; ZOOPLANKTON; NITROGEN fixation
- Publication
Biogeosciences Discussions, 2013, Vol 10, Issue 8, p13931
- ISSN
1810-6277
- Publication type
Article
- DOI
10.5194/bgd-10-13931-2013