Oxygen and carbon stable-isotope compositions of modern benthic foraminifera in the Kara and Pechora estuarine regions of the Arctic continental shelf were compared with water δ18O, δ13CDIC, temperature, and salinity. The foraminiferal δ18O distribution is mostly similar to that of equilibrium calcite, primarily controlled by mixing of runoff and seawater in near-estuarine areas (depth < 15--20 m), with additional temperature control seaward. The δ13C composition is controlled by remineralization of organic matter, mostly imported by rivers, and by water mixing. Most analyses used the common Arctic foraminifer Elphidium excavatum forma clavata, which yields depleted δ13C, as expected for an infaunal species. Isotope records for sediment cores off the Pechora and Yenisey rivers show a decelerating rise in isotope values, of up to 10? in δ18O, over the last 10 kyr in a pattern similar to that of rising sea level and concomitant retreat of river mouths, with local complexities probably resulting from glacio-isostatic rebound and changes in sedimentation.