Submesoscale (SMS) processes are increasingly recognised as a ubiquitous component of stratified marine environments. As a transitional regime between quasi-geostrophic flow and fully three-dimensional turbulence, they enhance vertical and lateral exchange and actively restructure tracer fields. In shallow, strongly forced coastal systems such as the Baltic Sea, their relative influence may be amplified by spatial scales that are compressed compared to the open ocean, together with strong seasonal stratification and rapidly varying wind forcing. Using repeated glider observations in the Gulf of Finland, complemented with realistic numerical simulations that resolve the associated dynamical fields, we demonstrate that SMS activity leaves dynamically consistent signatures in thermohaline tracer variability (spice). Along-isopycnal wavenumber spectra of temperature exhibit a −2 slope over horizontal scales of 1–10 km within a mesoscale frontal system, both in the surface layer and in the thermocline, consistent with active SMS stirring. A late-summer upwelling event illustrates how mesoscale forcing generates fine-scale tracer structure. Period-mean Rossby numbers of order one coincide with strongly tilted density surfaces, indicating an energetically active frontal regime. The period-mean rate at which vertical motions redistribute spice reveals persistent zones of tracer restructuring: a near-surface maximum co-occurs with elevated Rossby number, while a deeper hotspot follows sloping isopycnals. We suggest that processes such as SMS subduction can displace tracers vertically and laterally, producing subsurface variability offset from surface dynamical indicators (e.g. maxima in surface Rossby number).