Zenodo repository for: Joh, Y., Yeh, S.-W., Delworth, T. L., Labe, Z. M., Wittenberg, A. T., Cooke, W. F., Lou, J., & Park, Y.-G. (2026):Evolving synchronization of the Gulf Stream and Kuroshio–Oyashio Extension in a changing climate, Science Advances, accepted. This Zenodo repository contains the processed model output and analysis code used to generate all figures and results presented in the manuscript. The study examines seasonal covariability and evolving synchronization between the Gulf Stream and the Kuroshio–Oyashio Extension, using observational reanalysis and large-ensemble simulations from the GFDL SPEAR_HI_25 coupled climate model under control and future forcing scenarios. All model datasets provided here are derived from SPEAR_HI_25 simulations and are organized by experiment type. The accompanying MATLAB code reproduces the full analysis workflow, including preprocessing, diagnostics, and figure generation. Zenodo repository includes: MATLAB code and functions for statistical analysis and figure generation Processed data from SPEAR_HI_25 simulations, including the 1990 control simulation, 1990 control simulation with heat flux adjustment (HFLXADJ), SSP2-4.5, and SSP2-4.5 overshoot scenarios Files in netCDF4 format All model data regridded to a 1° × 1° horizontal resolution for the analysis and presentation of global spatial maps Future projection simulations (SSP2-4.5 and SSP2-4.5 overshoot) consist of 30 ensemble members.