Ion current rectification (ICR) is a transport phenomenon inwhich an electrolyte conducts unequal currents at equal and opposite voltages.Here, we show that nanoscalefluid vortices and nonlinear electroosmoticflow(EOF) drive ICR in the presence of concentration gradients. The same EOFcan yield negative differential resistance (NDR), in which current decreaseswith increasing voltage. Afinite element model quantitatively reproducesexperimental ICR and NDR recorded across glass nanopipettes underconcentration gradients. The model demonstrates that spatial variations ofelectrical double layer properties induce the nanoscale vortices and nonlinearEOF. Experiments are performed in conditions directly related to scanningprobe imaging and show that quantitative understanding of nanoscale transport under concentration gradients requiresaccounting for EOF. This characterization of nanopipette transport physics will benefit diverse experimentation, pushing theresolution limits of chemical and biophysical recordings.