Continental Shelf Research 22 (2002) 945–965 Hydrographic and particle distributions over the Palos Verdes Continental Shelf: spatial, seasonal and daily variability Burton H. Jones a, *, Marlene A. Noble b , Tommy D. Dickey c a Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0371, USA b United States Geological Survey, MS 999, 345 Middlefield Road, Menlo Park, CA 94025, USA c Ocean Physics Laboratory, University of California, 6487 Calle Real, Suite A, Santa Barbara, CA 93106-3060, USA Received 23 August 2000; accepted 12 December 2001 Abstract Moorings and towyo mapping were used to study the temporal and spatial variability of physical processes and suspended particulate material over the continental shelf of the Palos Verdes Peninsula in southwestern Los Angeles, California during the late summer of 1992 and winter of 1992–93. Seasonal evolution of the hydrographic structure is related to seasonal atmospheric forcing. During summer, stratification results from heating of the upper layer. Summer insolation coupled with the stratification results in a slight salinity increase nearsurface due to evaporation. Winter cooling removes much of the upper layer stratification, but winter storms can introduce sufficient quantities of freshwater into the shelf water column again adding stratification through the buoyancy input. Vertical mixing of the low salinity surface water deeper into the water column decreases the sharp nearsurface stratification and reduces the overall salinity of the upper water column. Moored conductivity measurements indicate that the decreased salinity persisted for at least 2 months after a major storm with additional freshwater inputs through the period. Four particulate groups contributed to the suspended particulate load in the water column: phytoplankton, resuspended sediments, and particles in treated sewage effluent were observed in every towyo mapping cruise; terrigenous particles are introduced through runoff from winter rainstorms. Terrigenous suspended particulate material sinks from the water column in o9 days and phytoplankton respond to the stormwater input of buoyancy and nutrients within the same period. The suspended particles near the bottom have spatially patchy distributions, but are always present in hydrographic surveys of the shelf. Temporal variations in these particles do not show a significant tidal response, but they may be maintained in suspension by internal wave and tide processes impinging on the shelf. r 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction A variety of natural and anthropogenic sources contributes to particle distributions on the con- tinental shelves of urban regions. Natural sources of particles in the water column include phyto- plankton, resuspended sediments, and surface runoff. In addition to natural sources, most coastal urban centers have major sewage outfalls where treated sewage is released through a diffuser system intended to limit the surfacing of the treated effluent. In addition to the treated human *Corresponding author. Tel.: +1-213-740-5765; fax: +1- 213-740-8123. E-mail address: bjones@earth.usc.edu (B.H. Jones). 0278-4343/02/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0278-4343(01)00114-5