A MID-HOLOCENE RECORD OF SEDIMENT DYNAMICS AND HIGH RESOLUTION ACCRETION RATES IN COASTAL SALT MARSHES FROM SOUTHERN CALIFORNIA

Sediment accretion rates in coastal salt marshes are the critical determining factor in terms of ecosystem stability in the face of accelerated sea level rise (SLR), projected to rise by up to 1.4 m by 2100 in Southern California (National Research Council, 2012). However, high resolution studies of accretion rates in coastal salt marshes over the past several millennia have not yet been conducted for most of the US west coast. We collected multiple sediment records, ranging from 2 to 6 m depth, from four coastal salt marshes in Southern California (Tijuana River Estuary, Upper Newport Bay, Point Mugu Lagoon, Morro Bay) in the low, mid, and high marsh zones (Zedler, 1977). We analyzed all cores for magnetic susceptibility, % organic matter, and select cores for particle size. High resolution, millennial and centennial scale, radiocarbon dating for these sediment records reveals a detailed history of marsh accretion rates extending up to 5663 ± 600 calendar years before present. In conjunction with modern accretion data, this study investigates the millennial-scale history of physical ecosystem dynamics in coastal salt marshes. The work aims to answer questions concerning the timing of salt marsh initiation, evidence of agriculture and ranching, and the recent effects of intensive urbanization to inform efforts to preserve and restore salt marshes in a future of accelerated SLR.