PHOSPHORUS REGENERATION IN CONTINENTAL-MARGIN SEDIMENTS

Benthic incubation chambers have been deployed in a variety of geochem ical environments along the California Continental Margin. These inclu de both high and low oxygen environments and sites where the rate of o rganic matter oxidation on the seafloor (C-ox) ranges from <1 mmol m(- 2) day(-1) to more than 7 mmol m(-2) day(-1) through a depth range of 100-3500 m. This range in the rate of organic matter oxidation along w ith variations in the concentration of bottom water oxygen allow us to elucidate the diagenetic conditions under which P regeneration may be decoupled from organic matter cycling. Under conditions where bottom water oxygen concentration is low (<50 mu M), and the rate of organic matter oxidation is also law (<1 mmol m(-2) day(-1)), P regeneration m ay be less than that expected from the decay of organic debris and, in some cases, there is a flux of phosphate into the sediments. At stati ons where bottom water oxygen is low, and the degradation rate of orga nic material is greater than 1 mmol m(-2) day(-1), phosphate may be re leased at a rate exceeding the production expected from the oxidation of organic matter. At stations having high bottom water oxygen concent rations, rates of organic matter decomposition < similar to 7 mmol m(- 2) day(-1), and where benthic irrigation is not significant, P regener ation is consistent with that expected from the decomposition of organ ic debris. In addition, our data indicate that high benthic iron fluxe s are observed in regions exhibiting a decoupling between organic matt er and phosphate, whereas low to zero iron fluxes are observed in regi ons where P regeneration is either consistent with or less than that e xpected from the decomposition of organic material. These results supp ort previous work suggesting a coupling between iron cycling and phosp hate cycling in suboxic environments. Data presented here show that th is coupling may result in either preferential phosphate burial or rele ase relative to organic material in suboxic environments. Copyright (C ) 1997 Elsevier Science Ltd.