Boundary and Abyssal Mixing

enlargeHOME Ridge Dissipation
Long tows across the Hawaiian Ridge system (part of the Hawaiian Ocean Mixing Experiment - HOME) show the tremendous differences in turbulence across a sharp bathymetric feature. Turbulence levels are indicated here by the mixing parameter in the lower panels.
These measurements were made from our towed body, Marlin.
enlargeOR slope
Marlin was originally designed to measure mixing deep off the OR coast. During her maiden science deployment in 1999 (following 2 years of intensive engineering development work), regions of energetic turbulence were indentified near the steep and near-critical Oregon slope. Also observed were Intermediate Nepheloid Layers (INLs), regions of unique T-S and elevated optical backscatter - evidence of offshore transport of boundary-mixed fluid.
enlargeOR tidal modulation
The 1999 Marlin deployment inspired a 2005 internal waves and mixing experiment (with M. Alford and E. Kunze of the universities of Washington and Victoria). Intensive shipboard and moored observations reveal that turbulence is driven by the semidiurnal tide interacting with the steep and rough slope. Moreover, localized hotspots were observed in which turbulence was 100 times more intense than elsewhere. This figure shows the semidiurnal periodicity of Thorpe-scale derived dissipation estimates (lower panel) and its relationship to the near-bottom velocity (middle panels; color), and isopycnals (contrours).

More about our studies of deep ocean mixing:

Hotspots of deep ocean mixing on the Oregon continental slope, Geophys. Res. Lett., 34, L01605, doi:10.1029/2006GL028170, 2007 (Nash, J. D., M. H. Alford, E. Kunze, K. Martini, and S. Kelly) [pdf]

Oceanic isopycnal slope spectra: Part I: Internal waves, J. Phys. Oceanogr., 37(5), 1215-1231, 2007 (J.M. Klymak and J.N. Moum) [pdf]

Oceanic isopycnal slope spectra: Part II: Turbulence, J. Phys. Oceanogr., 37(5), 1232-1245, 2007 (J.M. Klymak and J.N. Moum) [pdf]

An estimate of tidal energy lost to turbulence at the Hawaiian Ridge. J. Phys. Oceanogr., 36, 1148-1164, 2006. (Klymak, J.M., J.N. Moum, J.D. Nash, E. Kunze, J.B. Girton, G.S. Carter, C.M. Lee, T.B. Sanford, and M.C. Gregg) [pdf]

Observations of boundary mixing over the continental slope, J. Phys. Oceanogr., 32, 2113-2130, 2002 (J.N. Moum, D.R. Caldwell, J.D. Nash and G.D. Gunderson) [pdf]