HR: 1340h
AN: PP43B-0672    [Abstracts]
TI: Phosphate oxygen isotope ratio proxy for specific microbial activity in marine sediments (Peru Margin)
AU: * Liang, Y
EM: yuhong.liang@yale.edu
AF: Yale Univesity, P.O. Box 208109, New Haven, CT 06511 United States
AU: Blake, R E
EM: ruth.blake@yale.edu
AF: Yale Univesity, P.O. Box 208109, New Haven, CT 06511 United States
AB: Oxygen (O) isotope ratios of biogenic apatites have been widely used as paleotemperature and environmental geochemical proxies. With improved knowledge of the phosphate O isotope effects of different P cycling pathways, the δ¹⁸O value of inorganic phosphate (δ¹⁸O_P) has been proposed as a useful proxy and tracer of biological reactions and P cycling in natural environments[1,2,3,4]. Being the only way of removing P from oceanic water, sedimentary P burial is one of the most important processes during biogeochemical cycling of P. The high concentrations of organic matter and pronounced microbial activity at ODP Site 1230 along the Peru Margin result in unusually high interstitial water phosphate concentrations, which provides a unique opportunity to use δ¹⁸O_P to investigate inorganic phosphate (P_i) regeneration and P cycling pathways in marine sediments. The isotopic measurements of both dissolved inorganic phosphate (DIP) and bulk sediment P_i show that DIP δ¹⁸O_P values are affected by three different processes, which are all induced by specific microbial activities present in the sediments. In sediments at ~ 65 to 120 mbsf, porewater DIP is derived from dissolved organophosphorus compounds (DOP) through enzymatic degradation pathways, evidenced by both DIP δ¹⁸O_P values and interstitial water chemistry. Measured porewater DIP δ¹⁸O_P values also suggest that 4 to 8% of interstitial water DIP reflects regeneration of P_i from P_org by microbially-synthesized enzymes. Throughout the sediment column and especially at ~ 120 to 150 mbsf, DIP is released from the sediments by microbially-induced reductive dissolution of Fe-oxides, which contributes to the overall high DIP concentrations at Site 1230. The third and dominant process controlling measured DIP δ¹⁸O_P values is microbial turnover of regenerated P_i. The presence of high microbial activities in organic-rich Site 1230 sediments promotes the remobilization of P and affects marine P cycling by potentially enhancing the P flux from sediments to the water column, as well as promoting rapid formation of authigenic apatite. This successful application of DIP and sediment P_i δ¹⁸O_P to natural environments to elucidate specific P_i regeneration pathways, demonstrates that DIP δ¹⁸O_P is a valuable geochemical tool and strongly supports the use of Pi δ¹⁸O as a proxy for tracing biogeochemical cycling of P. [1]Blake et al. Am. Min. 83, 1516-1531 (1998) [2]Blake et al. PNAS, 98, 2148-2153 (2001)[3]Blake et al. AJSin press (2005) [4] Colman, A.S. Ph.D Thesis, Yale University (2002)
DE: 0330 Geochemical cycles (1030)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005