Vertical convergence of sediment resuspended by internal waves and subducted phytoplankton to a persistent detached layer over the shelf of Monterey Bay, California.

Work by current authors and collaborators from a two-year study on the Central California margin document the importance of internal waves in benthic-interior exchange over the continental shelf (Cheriton et al., 2014, JRG, Cheriton et al., 2014, GRL). Here, primarily using results from deployments in October 2012, we examine in more detail the spatial characteristics of re-suspended sediment and subducted phytoplankton that converge into layers of suspended particulates typically around 16 meters above the sea floor. The long-term average of vertical velocity, a component often overlooked in ADCP data, shows weak but persistent vertical convergence at this location, suggesting vertical convergence as a physical explanation for the particulate layers at that height. An alternative model based on horizontal shear, but over shorter time scales, is also discussed. These layers appear to be a persistent feature with an important role in cross-margin sediment transport, yet their existence has only recently come to light and they have not yet been incorporated into models of continental margin dynamics.