Budgets of turbulent kinetic energy and scalar variance in the continentalshelf bottom boundary layer

A local turbulent kinetic energy (TKE) budget, in which dissipation balance s production minus buoyancy flux, and a nonlocal turbulent scalar variance (TSV) budget, in which dissipation balances production minus TSV flux diver gence, are tested observationally. The calculations are based on 6 week lon g records of velocity and sound speed measured between 0.7 and 5.4 m above bottom on the New England shelf. Estimates of fluxes and gradients are dire ct, while estimates of dissipation rates are indirectly obtained from inert ial subrange spectra. Within 2 m of the bottom, buoyancy flux is not an imp ortant component of the TI(E budget (flux Richardson number Rf < 0.05, on a verage). At 4.35 m above the bottom, the highest resolved elevation, the di rect effect of stratification is more pronounced (Rf = 0.13, on average). T he local TKE balance is essentially closed by the measurements within 2 m o f the bed (r(2) > 0.8 and regression coefficient = 0.89 x/divided by 1.06 a nd 1.08 x/divided by 1.05 at 1.65 and 0.74 m above the bottom, respectively ). The local TKE budget at 4.35 m above the bed is not closed, however. TSV production and dissipation estimates are strongly correlated at all height s (r(2) > 0.64), but dissipation is systematically greater than production, particularly at 0.74 m above the bed (regression coefficient = 2.42 x/divi ded by 1.28). Including TSV flux divergence in the balance reduces, statist ically significantly, the observed discrepancy. The implications of the res ults for turbulence closure models and microstructure diffusivity estimates are discussed.