Time series sediment trap samples were used to examine the rates and mechanisms of particulate organic carbon (POC) flux at three continental margin locations, Santa Barbara Basin, Cariaco Basin, and Guaymas Basin, marked by seasonal upwelling and high primary production. The mean POC flux in Santa Barbara Basin (0.096 g m-2 d-1) is nearly twice that of Cariaco Basin and 4 times higher than that in Guaymas Basin, with all three sites having POC fluxes significantly higher than the open ocean average (0.007 g m-2 d-1). In Cariaco Basin, the only site with available primary production numbers, there is no significant relationship between POC flux and monthly primary production. Rather, POC fluxes in all three areas strongly correlate with mineral (carbonate, opal, and lithogenic material) fluxes. This supports the "mineral ballast" hypothesis, where it has been suggested that higher-density minerals enhance the flux of organic matter to the deep ocean. On the basis of multiple regression analysis, the three mineral components explain 72% of the total variance in POC fluxes at the three study sites, with biogenic carbonate particles being the most effective transport mineral.