Characteristics of the Kinetic Energy Spectra in the Subpolar North Atlantic

Abstract The subpolar North Atlantic is known to have rich mesoscale and submesoscale variations, however, their spectral characteristics have not been documented in observations. This study documents the Kinetic Energy (KE) spectra using Acoustic Doppler Current Profiler measurements that cover both the Iceland Basin and the Irminger Sea. The KE spectrum is partitioned into geostrophically balanced motions and unbalanced motions. The results reveal that balanced motions dominate the KE spectra. The unbalanced motions enhance in spring and fall to flatten the spectra and dominate small scale (<50km) energy, though uncertainty is high due to measurement noise and method assumptions. In addition, the dynamical framework that drives the balanced motions undergoes distinct seasonal shifts. In the spring and summer seasons of the Iceland Basin, as well as the summer season of the Irminger Sea, the wavenumber spectra of balanced motions exhibit a slope of approximately −3, consistent with the internal quasi-geostrophic turbulence theory. Conversely, in the fall season of the Iceland Basin and the spring and fall seasons of the Irminger Sea, the wavenumber spectra of geostrophic balanced motions have a slope close to −2, consistent with surface quasi-geostrophic turbulence theory. Additionally, we have found that the intensity of mesoscale eddies in the spring season can modulate both the slope and intensity of the wavenumber spectra of geostrophic balanced flows.