| This dissertation explores two recently recognized pathways of organic matter supply to marine sediments and their impact on sedimentary biogeochemistry: The entrapment and decomposition of particulate organic matter in permeable sediments and the resulting nutrient dynamics were investigated with a specially designed experimental laboratory microcosm that allows permeable sediment incubation under controlled physical forcing. Microcosm generated enhanced solute transport rates were roughly proportional to sediment column permeability. Comparison with field observations revealed that the enhanced transport rates induced by the experimental conditions were lower than those observed in the field, and this was also reflected in the enhanced buildup of pore water nutrients relative to concentrations in field sediments. Particulate organic matter and nutrient enrichment experiments, conducted with the microcosm, demonstrated the rapid uptake of both particles and solutes by the permeable sediment column under physical forcing, the rapid decomposition of the removed particles, and the lack of regenerated nutrient build-up. Nutrient enrichment experiments with sediment plug chambers demonstrated the rapid uptake and retention of nutrients by surface permeable sediments, as well as the loss of nitrogen though benthic denitrification in sediment grain microzones. The processing of large organic matter packages on the deepsea floor by deep-sea communities was investigated using natural and experimental whale, kelp and wood falls in the California Borderland Basins region, focusing on their quality and its impact on sedimentary organic enrichment and redox shifts. Labile organic material generated by the processing of whale falls and kelp falls generated substantial pore water sulfide levels in impacted sediment, despite a small organic enrichment signal. In contrast, wood derived material input did not result in sulfidic conditions, despite generating very high organic enrichment in impacted sediments, due to its refractory nature. A constructed model incorporating metazoan processing and dispersal of fragmented material revealed that whale fall processing is characterized by higher rates of tissue removal, organic carbon release, and carbon sedimentation rates than wood fall processing. However, organic carbon release rates, when normalized to fall weight, are similar between the two types of falls, due to differences in their carbon content and in absorption rates during metazoan ingestion. |
