Submesoscale Frontal Dynamics Drive Local Formation of Gulf Common Water-Type Waters in the Yucatan Channel

We report the recurrent formation of waters with thermohaline properties similar to Gulf Common Water (GCW) in the western Yucatan Channel, absent upstream in the Caribbean. Mooring observations and a submesoscale-permitting model show that these Yucatan GCW-type (YGCW) waters form locally when the Yucatan Current separates from the slope, intensifying a frontal zone with isopycnal uplift, cyclonic vorticity, and sharp lateral gradients. These conditions favor interleaving and mixing among Caribbean inflow waters within a vertically compressed isopycnal layer. Lagrangian backtracking confirms their local origin, while forward tracking reveals export within cyclonic frontal eddies along the Loop Current periphery. Our findings uncover a previously unrecognized frontal transformation pathway in a western boundary current choke point and underscore the role of submesoscale fronts in localized water mass transformation, with potential implications for Loop Current variability.