The energy cascade of mesoscale and submesoscale eddies plays a critical role in ocean mixing and climate with implications to oceanic ecosystems. However, its spatiotemporal characteristics and underlying mechanisms remain poorly understood, particularly those associated with available potential energy (APE). To address this challenge, we develop a unified spatial coarse-graining energetics framework to diagnose multiscale kinetic energy (KE) and APE cascades by deriving an explicit cross-scale APE flux \(Π_p\) and KE-APE conversion, and further decomposing the KE transfer \(Π_k\) into three distinct pathways: horizontal normal strain, horizontal shear strain, and vertical shear. We apply this framework to five years of output from a 1/25° Northwest Atlantic simulation, focusing on the Gulf Stream (GS) system across​ three dynamically distinct subregions. The APE cascade remains a robustly forward transfer across regions, depths, seasons, and scales, whereas the KE cascade exhibits pronounced regional, seasonal, and scale dependence. \(Π_k\) decomposition further shows that horizontal strain dominates the overall KE transfer, with normal strain and shear strain exhibiting distinct relative contributions across the subregions. Moreover, the nearshore GS region exhibits a persistent APE-to-KE transfer, whereas the offshore region is characterized by an opposite conversion (KE-to-APE) in the depth-integrated sense. Our study provides the first systematic characterization of both KE and APE cascades at meso- and submesoscales in western boundary current systems, offering new insights into oceanic energy transfers and a valuable framework for application to other oceanic regions.

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