Argo Trajectories Reveal Changing Core-Peripheral Partitioning of Gulf Stream Transport

Abstract. Long-term Gulf Stream transport estimates diverge, partly because existing observing systems sample different locations and cross-stream extents. Most studies assess transport at fixed sections, leaving changes in the core and surrounding flow unresolved. Here, we develop a Core-Peripheral Transport Decomposition Method using Argo float trajectories from 2003 to 2024. We identify the mean core band from velocity gradients and quantify core-band and peripheral transport from annual mean time series. Core-band transport shows no significant trend, while peripheral transport declines at −4.99 Sv yr^-1 before 2017 and recovers at +20.01 Sv yr^-1 afterward. The core fraction of the fixed-latitude total rises from approximately 33 % to more than 100 % in 2015 and 2019, before decreasing to 26 % at the end of the record. Validation against shipboard ADCP observations yields significant interannual correlation (R = 0.667). These results reveal changing cross-stream transport partitioning and provide an observational basis for interpreting divergent Gulf Stream transport estimates across observing systems.