Solid phase phosphorus species and preservation of fish remains in marine sediments of areas of high primary productivity and oxygen seasonality (36 degrees S, central South Chile)

The main input of phosphorus to the ocean is associated with river runoff, while this element leaves the marine system via burial in the sediments. Solid phase P accumulation is a function of bottom water and surface sediment oxygenation. Theory predicts that suboxic/anoxic sediments act as a source of phosphate, which is released from organic matter and iron oxides, while authigenic precipitation and biogenic apatite preservation are both favored in a phosphate saturated environment. In this paper, we present the results of solid phase phosphorus speciation in sediments collected in central south Chile on the continental shelf off Concepcion. This area is characterized by very high biological productivity and the formation of a strong oxygen minimum zone during summer. We found that total solid phase P was dominated by inorganic phases (60%), mostly comprised by iron-bound P and biogenic apatite P. As expected, biogenic apatite P and iron-bound P were negatively correlated and reflected bottom water oxygen fluctuations during the period analyzed (February September 2009). The biogenic apatite (fish debris) preservation potential was negatively correlated with bottom water dissolved oxygen and its burial averaged 16% of water column's fish production estimated with a trophic dynamic-model that included SeaWIFS-MODIS satellite primary productivity estimations. In spite of intrusions of oxygen in the water column evidenced by the thinning of the oxygen minimum layer in autumn-winter, bottom waters remained suboxic during the studied period and appear to have favored biogenic apatite P (P-fish) preservation. This finding supports the potential of P-fish as a paleotracer for fish abundance in areas previously not considered because of the lack of laminated sediments.