期刊
LIMNOLOGY AND OCEANOGRAPHY-METHODS
卷 9, 期 -, 页码 110-120出版社
WILEY
DOI: 10.4319/lom.2011.9.110
关键词
-
资金
- German Research Foundation (DFG) through MARUM Center for Marine Environmental Sciences
Phosphorus cycling in the ocean is influenced by biological and geochemical processes that are reflected in the oxygen isotope signature of dissolved inorganic phosphate (P-i). Extending the P-i oxygen isotope record from the water column into the seabed is difficult due to low P-i concentrations and small amounts of marine porewaters available for analysis. We obtained porewater profiles of P-i oxygen isotopes using a refined protocol based on the original micro-extraction designed by Colman (2002). This refined and customized method allows the conversion of ultra-low quantities (0.5-1 mu mol) of porewater P-i to silver phosphate (Ag-3 PO4) for routine analysis by mass spectrometry. A combination of magnesium hydroxide co-precipitation with ion exchange resin treatment steps is used to remove dissolved organic matter, anions, and cations from the sample before precipitating Ag-3 PO4. Samples as low as 200 mu g were analyzed in a continuous flow isotope ratio mass spectrometer setup. Tests with external and laboratory internal standards validated the preservation of the original phosphate oxygen isotope signature (delta O-18(P)) during micro extraction. Porewater data on delta O-18(P) has been obtained from two sediment cores of the Moroccan margin. The delta O-18(P) values are in a range of +19.49 to +27.30%. We apply a simple isotope mass balance model to disentangle processes contributing to benthic P cycling and find evidence for P-i regeneration outbalancing microbial demand in the upper sediment layers. This highlights the great potential of using delta O-18(P) to study microbial processes in the subseafloor and at the sediment water interface.
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