A 4-6 year time series of monthly measures of primary production (14C uptake) and sediment trap flux was carried out in two fjords of British Columbia, Canada. The fjords, periodically anoxic Saanich Inlet and oxygen-replete Jervis Inlet, were chosen in order to compare organic matter formation and particle flux in these environments with largely differing redox conditions. Hydrographic and nutrient data were collected during portions of the experiment, and 210Pb profiling of bottom sediments allowed comparison of water-column fluxes and sedimentary accumulation rates.

Saanich Inlet was 1.7 times more productive than Jervis Inlet and primary production toward the mouths of both fjords was 1.4 times higher than at the heads of the fjords. The elevated rates of primary production in Saanich Inlet were probably due to exchange with the nutrient-rich surface waters of the passages leading to the Pacific Ocean, and the up-inlet gradients in both fjords reflected the relative nutrient supply. The sediment-trap material was dominated by biogenic silica, especially in the spring and early summer but also in the late summer and fall, while organic carbon fluxes tended to peak in the summer. Winter fluxes were usually dominated by aluminosilicates, but at the mouth of Jervis Inlet organic matter often comprised most of the mass flux to the 50 m sediment traps, as wintertime sources of biogenic silica and aluminosilicates were small. 13C/12C of the trapped material was greater in the summer than in the winter, reflecting a higher ratio of marine to terrestrial organic matter at that time. The relationship between stable carbon isotope ratios and BSi content revealed that 70-80% of the marine OC in these fjords was diatomaceous. This relationship was furthermore used to estimate the 13C/12C endmember of the marine organic matter and the proportion of terrigenous material to the total organic matter flux. At each station, similar proportions of local primary production (approx. 5%) were buried in the sediments below, suggesting that the bulk of the marine organic matter was not preferentially preserved in the intensely anoxic sediments of Saanich Inlet.

A model that estimates rates of water-column decay from sediment-trap data showing increases in flux with depth was used with the time series from Saanich and Jervis Inlets. Model results from Saanich Inlet were not conclusive, possibly because the depth interval between sediment traps was too small to resolve water-column rates of decay. However, the model fit well to the time series from Jervis Inlet, and rate constants for organic carbon and nitrogen agree well with previous estimates made from oceanic settings. The model has also allowed some of the first estimates of depth-dependent dissolution rates of sinking biogenic silica, and translation to time-dependent dissolution using a nominal sinking rate suggests the diatomaceous opal in Jervis Inlet was dissolving rapidly. Changes with depth of rate constants for organic carbon, nitrogen and biogenic silica were well described by the power function, suggesting that organic matter and biogenic silica were composed of a set of multiple components that decay at varying rates. For biogenic silica, this model of decay may be caused by the presence of various diatom species or degrees of frustule fragmentation that result in a number of fractions with different dissolution rates. The model has also allowed a description of the material that causes increases in flux with depth. This sediment was depleted of organic carbon and nitrogen and thus appeared diagenetically altered, and its aluminosilicate and biogenic silica contents were characteristic of hydrodynamically sorted, resuspended material. Additional material was delivered to the deepest sediment traps during deepwater renewals, but a continual process such as tidal resuspension, particle focusing, or increases in trapping efficiency with depth resulted in additional fluxes to the mid-depth sediment traps.