Radiocarbon in coastal waters off the eastern United State

An important aspect of the physical and chemical oceanography of a coastal water body is the identification of the water masses which contribute to its nutrient and energy balances. In this study, the radiocarbon activity ($Deltasp{14}$C) of dissolved inorganic carbon and the oxygen isotopic ratio ($deltasp{18}$O) of coastal water samples are used to identify the water types which make up the Middle Atlantic Bight (MAB) and South Atlantic Bight (SAB) coastal waters.;Radiocarbon is an excellent tracer of seawater masses in coastal ocean regions where it behaves conservatively. Surface waters taken from the MAB for this study show significant temporal and spatial variability in $Deltasp{14}$C (from +7 to +150 for the period 1983-1988). This range can be explained by relative mixing between three seawater end members; Labrador Sea water (LSW, $Deltasp{14}$C = +50), Sargasso Sea surface water (SSW, $Deltasp{14}$C = +160), and Antarctic Intermediate water (AAIW, $Deltasp{14}$C = $-$90).;In the northern MAB $Deltasp{14}$C values of coastal waters are coherent spatially and have a higher mean $Deltasp{14}$C value (+86) than LSW. Some southern MAB surface water have $Deltasp{14}$C (+7 to +39) which is lower than LSW suggesting an increased contribution of AAIW caused by upwelling as the Gulf Stream diverges from the shelf break near Cape Hatteras. AAIW upwelling in the SAB associated with Gulf Stream meanders also lowers $Deltasp{14}$C of surface shelf waters off South Carolina.;Both salinity and $deltasp{18}$O are conservative tracers of fresh water inputs to the coastal ocean. These two properties can be used in combination to pinpoint the source of fresh water off the Eastern US coast because the $deltasp{18}$O in runoff becomes progressively lower with increasing latitude. Salinity vs. $deltasp{18}$O was plotted for shelf water, slope water and cold pool samples in order to evaluate the sources of fresh water to the MAB circulation. Local MAB river runoff with a $deltasp{18}$O composition of $-$9.2 ($pm$1.0) was identified as the dominant source of fresh water to the shelf. Runoff to the Labrador Sea ($deltasp{18}$O = $-$18.7) was the main source of fresh water to both the slope water and the cold pool.