The ocean surface boundary layer (OSBL) is a critical interface across which momentum, heat, and trace gases are exchanged between the oceans and atmosphere. Surface processes (winds, waves, and buoyancy forcing) are known to contribute significantly to fluxes within this layer. Recently, studies have suggested that submesoscale processes, which occur at small scales (0.1-10 km, hours-to-days) and therefore are not yet represented in most ocean models, may play critical roles in these turbulent exchanges. While observational support for such phenomena has been demonstrated in the vicinity of strong current systems and littoral regions, relatively few observations exist in the open-ocean environment to warrant representation in Earth system models.
We use observations and simulations to quantify the contributions of surface and
submesoscale processes to turbulent kinetic energy (TKE) dissipation in the open-OSBL. Our observations are derived from moorings in the North Atlantic, December 2012-April 2013, and are complemented by atmospheric reanalysis. We develop a conceptual frame work for dissipation rates due to surface and submesoscale processes. Using this framework and comparing with observed dissipation rates, we find that surface processes dominate TKE dissipation. A parameterization for symmetric instability (SI) is consistent with this result. We next employ simulations from an ocean front-resolving model to establish, again, that dissipation due to surface processes exceeds that of submesoscale processes by one-to-two orders of magnitude. Together, these results suggest submesoscale processes do not dramatically modify vertical TKE budgets, though we note that submesoscale dynamics may be climatically important owing to their effect on ocean circulation.