UCLA

Coastal marshes are complex ecogeomorphic feedback systems that require further investigation on the Southern California coast to understand potential responses to sea level rise (SLR). Long-term accretion rates - deposition and erosion of mineral and organic matter - form a basis of understanding processes in the marsh related to SLR responses. From sediment cores, I reconstruct the net accretion rates of three marshes using radiocarbon dating methods and analyze loss on ignition (LOI) data to understand the physical properties of the sedimentary record in the three marshes. Average net accretion rates for Tijuana Estuary are 1.0 ± 0.94 mm yr¬-1, for Upper Newport Bay are 1.0 ± 0.4 mm yr-1, and for Morro Bay are 8.0 ± 8.3 mm yr-1. Over the past 2000 cal YBP, all net accretion rates kept pace or exceed rates of SLR (when compared to historic SLR of 0.6 to 2 mm yr-1); however, only Morro Bay exhibits historic net accretion rates high enough to compare to possible rates of SLR associated with projected sea level gains of 0.3 to 1.6 m on the Pacific coast through 2100. Core stratigraphies indicate marsh conditions change frequently and the current Spartina spp. and Salicornia spp. marsh vegetation communities are geologically recent features in their present locations, existing from 700 to 1000 cal YBP. The future under continued human modification of coastal systems, climate change, and accelerated SLR merit continued research into the dynamics of coastal salt marsh systems on the California coast.