Carbon and phosphorus cycling in anoxic sediments of the Saanich Inlet, British Columbia

Uncertainty currently exists about the removal of carbon (C) and phosphorus (P) from the oceanic reservoir, especially in low oxygen settings. In this paper, the cycling of C and P is examined in sediments from the anoxic Saa nich Inlet, cored by Ocean Drilling Program (ODP) Leg 169S in 1996 at two s ites. Although C-org/P-org ratios are high and increase with depth in the S aanich Inlet, this effect is due largely to a remobilization of P from an o rganic matter sink to an authigenic sink. Reducible sedimentary components act as temporary shuttles in this process even in this anoxic setting, with the ultimate burial sink for the remobilized P being carbonate fluorapatit e. The effective C-org/P-reactive molar ratio appears to be about 150-200, indicating some preferential loss of P compared to C during organic matter degradation, but not approaching previously reported values of over 3000 in black shales, Reactive P accumulation rates in this basin range from 10,00 0-60,000 mu mol/cm(2)/kyr, greatly exceeding the range of 500-8000 mu mol/c m(2)/kyr found in most continental-margin settings, including regions of mo dern phosphogenesis. The initiation of marine sedimentation in the Saanich Inlet occurred after deglaciation, and the high rates of P burial seen here may provide an end-member example of the effects of sea level and margin s edimentation on the distribution of P within the marine P cycle. (C) 2001 E lsevier Science B.V. All rights reserved.