Oxygen availability restricts groundfish to the oxygenated, shallow margins of Saanich Inlet, an intermittently anoxic fjord in British Columbia, Canada. New and previously reported 210Pb measurements in sediment cores compared with flux data from sediment traps indicate major focusing of sediments from the oxygenated margins to the anoxic basin seafloor. We present environmental and experimental evidence that groundfish activity in the margins is the major contributor to this focusing. Fine particles that are resuspended by the groundfish are advected offshore by weak bottom currents, eventually settling in the anoxic basin. Transmittance and sediment trap data from the water column show that this transport process maintains an intermediate nephloid layer (INL) in the center of the inlet. This INL is unrelated to interfaces of redox or water density changes in the water column. We propose that it is shaped by the distribution of groundfish (as resuspension sources) along the slope and hence by the availability of oxygen to these fish. We support this conclusion with a conceptual model of the resuspension and off-shore transport of sediment. This fish-induced transport mechanism is likely to enhance organic matter decomposition in oxygenated sediments and its sequestration in anoxic seafloors.
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