Other
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996gecoa..60.1479f&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 60, Issue 9, p. 1479-1495.
Other
24
Scientific paper
Understanding phosphorus (P) geochemistry and burial in oceanic sediments is important because of the role of P for modulating oceanic productivity on long timescales. We investigated P geochemistry in seven equatorial Pacific sites over the last 53 m.y., using a sequential extraction technique to elucidate sedimentary P composition and P diagenesis within the sediments. The dominant P-bearing component in these sediments is authigenic P (61 86% of total P), followed in order of relative dominance by iron-bound P (7 17%), organic P (3 12%), adsorbed P (2 9%), and detrital P (0 1 %). Clear temporal trends in P component composition exist. Organic P decreases rapidly in younger sediments in the eastern Pacific (the only sites with high sample resolution in the younger intervals), from a mean concentration of 2.3 μmol P/g sediment in the 0 1 Ma interval to 0.4 μmol/g in the 5 6 Ma interval. Over this same time interval, decreases are also observed for iron-bound P (from 2.1 to 1.1 μmol P/g) and adsorbed P (from 1.5 to 0.7 μmol P/g). These decreases are in contrast to increases in authigenic P (from 6.0 9.6 μmol P/g) and no significant changes in detrital P (0.1 μmol P/g) and total P (12 μmol P/g). These temporal trends in P geochemistry suggest that (1) organic matter, the principal shuttle of P to the seafloor, is regenerated in sediments and releases associated P to interstitial waters, (2) P associated with iron-rich oxyhydroxides is released to interstitial waters upon microbial iron reduction, (3) the decrease in adsorbed P with age and depth probably indicates a similar decrease in interstitial water P concentrations, and (4) carbonate fluorapatite (CFA), or another authigenic P-bearing phase, precipitates due to the release of P from organic matter and iron oxyhydroxides and becomes an increasingly significant P sink with age and depth. The reorganization of P between various sedimentary pools, and its eventual incorporation in CFA, has been recognized in a variety of continental margin environments, but this is the first time these processes have been revealed in deep-sea sediments. Phosphorus accumulation rate data from this study and others indicates that the global pre-anthropogenic input rate of P to the ocean (20 × 1010 mol P/yr) is about a factor of four times higher than previously thought, supporting recent suggestions that the residence time of P in the oceans may be as short as 10,000 20,000 years.
Delaney Margaret Lois
Filippelli Gabriel M.
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