Factors Influencing Suspended Sediment Flux in the Upper Gulf of California

Few studies exist of sediment dynamics in inverse estuaries, which are characterized by hypersaline water bodies and associated gravity currents and arise in arid regions where little precipitation and runoff combine with a high evaporation. Observations of velocity, density and suspended sediment concentration profiles have been made using an acoustic Doppler current profiler, CTD, optical backscatter sensors and water sampling at a shallow water site in the Upper Gulf of California over a spring to neap tidal cycle. These revealed contrasting dynamic conditions in which gravity current events produced significant net near-bed suspended sediment fluxes of 2•5 g m−2 s−1 out of the Gulf during neap tides. Instantaneous suspended sediment fluxes exceeded 30 g m−2 s−1during spring tides due to tidal resuspension, but net fluxes were near zero. The baroclinic gravity current is shown to be the dominant mechanism for net flux of suspended sediment toward deeper waters, at least during quiescent summer conditions. This flux is proposed to be confined within a wide, western along-Gulf channel. This is consistent with evidence that the Colorado River delta system is exporting sediments to deeper water after becoming unstable due to switching off of river discharge since 1930.