『Abstract
Sediments underlying the major coastal upwelling systems of the
world oceans are hot-spots of modern formation of hydroxyapatites,
often associated with benthic communities of large, nitrate-accumulating
sulfur bacteria. We studied the association between phosphate
release, organic phosphorus mineralization, and occurrence of
dense communities of the filamentous sulfur bacteria, Thioploca
spp., on the continental shelf off central Chile during the austral
summer when high phytoplankton productivity and anoxic bottom
water prevailed. Freshly deposited phytodetritus stimulated extremely
high sulfate reduction rates, which supported a large Thioploca
community of up to 100 g biomass per m2. Effective
bacterial sulfide uptake kept the sulfide concentration low, which
enabled the accumulation of free iron, thus demonstrating intensive
iron reduction concurrent with sulfate reduction. Phosphate released
to the pore water reached 100-300 μM peak concentrations within
the uppermost 0-5 cm and phosphate was lost to the overlying anoxic
water column. The large phosphate release was not directly related
to the presence of Thioploca but was rather the result
of a high deposition and mineralization rate of fresh organic
detritus. Although the pore water was super-saturated with respect
to hydroxyapatite, this mineral was only a minor P-component in
the sediment. Most solid-phase phosphate was bound to iron.
Keywords: Chile; Thioploca; Phosphorus; Hydroxyapatite;
Phosphate release』
1. Introduction
2. Materials and methods
2.1. Sampling
2.2. Pore water extraction and solid phase sampling
2.3. Pore water analysis
2.4. Solid phase iron and sulfur extraction
2.5. Sequential solid phase phosphate extraction
2.6. Sulfate reduction rates
2.7. Sediment characteristics and Thioploca biovolume
determination
2.8. Polyphosphate in Thioploca cells
2.9. Modeling of pore water data
3. Results
3.1. Description of sediment
3.2. Thioploca
3.3. Sulfate reduction
3.4. Sulfur and iron in pore water and sediment
3.5. Ammonium in pore water
3.6. Phosphate in pore water and sediment
3.7. Calcium in pore water
4. Discussion
4.1. Thioploca populations
4.2. Mineralization of organic matter
4.3. Thioploca and phosphate
4.4. Remobilization of phosphate to the pore water
5. Conclusion
Acknowledgements
References