Publications

Peer-Reviewed     |    Conference Abstracts

Summary:  

Undergraduate: I received a B.Sc. in Physics and Math honors from the University of British Columbia in 1979, after working in a plasma physics lab with Frank Curzon one summer and a solidstate lab with John Berlinsky on a microwave resonant cavity 2 subsequent summers.

Near-Inertial Waves in Geostrophic Shear: I received a Masters in Oceanography in 1981 and a Ph.D. in 1985 from the University of Washington. Tom Sanford was my advisor. My Mastersthesis research involved analyzing survey data from his eXpendable Current Profiler (XCP), an electromagnetic means of measuring horizontal velocity. Analysis of data collected by Dr. Sanford in the North Pacific Subtropical Front revealed elevated downgoing near-inertial internal gravity waves on the warm (negative vorticity) side of the front (Kunze and Sanford 1984 JPO). This motivated developing a ray-tracing theory for near-inertial wave propagation in geostrophic shear for my Ph.D. thesis that predicted trapping and amplification of these waves at critical layers in regions of negative vorticity (Kunze 1985 JPO). Analysis of subsequent data collected by myself (Kunze 1986 JPO), Tom Sanford (Kunze and Sanford 1986 JPO) and Rolf Lueck (Kunze and Lueck 1986 JPO) supported this conclusion. Later, data collected in a Gulf Stream warm-core ring with XCPs and a microstructure profiler demonstrated that near-inertial energy trapped at a critical layer was lost to turbulent dissipation and mixing (Kunze et al. 1995 JPO). Vortex-trapping also appeared to explain the diurnal internal wave found in the vortex cap above Fieberling Seamount just poleward of the diurnal turning latitude (Kunze et al. 1997; Kunze and Boss 1998 JPO). While a graduate student, I took part in 4 cruises, on 3 of which I collected data. I also attended the WHOI GFD summer program in 1983 where I studied internal wave/wave interactions under the supervision of Francis Bretherton.

Salt-Fingering:    I obtained a WHOI postdoctoral fellowship in 1985, working first with Ray Schmitt and Sandy Williams on salt fingering. I developed an ad hoc theory to explain salt-finger signals in the thermohaline staircase east of Barbados (Kunze 1987 JMR). While this was little more than dotting the i’s and crossing the t’s of seminal work by Melvin Stern, it made the theory more accessible to the observationalist community. A major conclusion was that staircase interfaces in the ocean are too thick for laboratory ΔS^4/3 flux laws to apply. It predicted weaker fluxes in the ocean than thought, consistent with the observations. I also analyzed shadowgraph data collected by Sandy Williams, concluding that salt fingers were tilted over by shear (Kunze et al. 1987 DSR). I was later to develop a theory for the evolution of salt-fingers in near-inertial shear (Kunze 1990 JMR), and propose alternative flux laws in the presence of shear (Kunze 1994 JMR) which have since proven incorrect (Inoue et al. 2008 JMR). I wrote a review of salt-fingering theory as part of a special volume on double diffusion (Kunze 2003 Prog. Oceanogr.) while on the SCOR committee on double diffusion.

Shear Instability and Interpreting Finestructure    In my second year at WHOI, I began a collaboration with Melbourne Briscoe and Sandy Williams to measure finecale (1-5 m) shear, stratification and instability from a neutrally buoyant float. These data were used to construct a parameterization for turbulence production based on the available kinetic energy in unstable shear and to characterize the dynamics on these scales as mostly near-inertial waves rather than potential-vorticity-carrying finestructure (vortical mode) (Kunze et al. 1990 JGR). Subsequent measurements I have participated in have found potential-vorticity-carrying structures in the wake of a seamount (Kunze and Sanford 1993; Kunze 1993 JPO). On the basis of the changing shear/strain ratio with wavelength, Polzin et al. (2003 JPO) suggested that vertical wavelengths of 1-10 m contain a significant contribution from vertical mode arising from turbulence patches. A later deployment of the float was used to directly estimate turbulent heat-fluxes (Sun et al. 1994 JPO).

Parameterizing Turbulence Production:    In 1987, I joined the research faculty at U of Washington at around the time that Michael Gregg was developing a parameterization of internal-wave-driven turbulence using internal wave shear following internal wave/wave interaction theories developed by Hank McComas, Peter Müller and Frank Henyey. I realized the same might be done with internal wave strain (Gregg and Kunze 1991 JGR) and also used this method for shear profiles collected over a seamount in the California coastal margin (Kunze et al. 1992 JPO), finding elevated inferred turbulence above the summit. Applying this parameterization to full-depth shear profiles collected during MODE helped establish that abyssal mixing is weak over gently sloping topography (Kunze and Sanford 1996 JPO). Predictions that the cascade of energy through the internal wave field from large to small vertical scales should be sensitive to the aspect ratio of the internal wave field and so to its frequency spectra and shear/strain ratio were tested with numerical ray-tracing simulations (Sun and Kunze 1999 JPO). After development of corrections for lowered ADCP velocity data (Polzin et al. 2002 JTech), a shear-and-strain form of the parameterization was applied to 3500 full-depth lowered ADCP profiles collected by Eric Firing, Jules Hummon and Teri Chereskin worldwide along hydrographic sections (Kunze et al. 2006 JPO). These revealed generally weak vertical mixing (diffusivity K ~ 0.1 × 10^–4 m² s^–1) in most of the ocean, even weaker near the equator, but elevated over rough topography. Diffusivity increased poleward and with depth for latitudes below 30º. The parameterization has been found to fall short of direct microstructure measurements in a submarine canyon (Kunze et al. 2002 JPO) and on continental shelves but appears to work well on continental slopes (Nash et al. 2004 JPO; Nash et al. 2007 GRL) away from direct generation or interaction of internal waves with the bottom.

Flow/Topography Interactions at Seamounts, Ridges and Canyons:    The inferred enhancement of mixing over Pioneer Seamount (Kunze et al. 1992 JPO) and flow structures near Caryn Seamount (Kunze and Sanford 1986 JPO) and Ampere Seamount (Kunze and Sanford 1993 JPO) got me interested in flow/topography interactions, particularly with internal waves. As well as this work leading to my participation in several observational programs, I co-authored 2 reviews of internal wave generation by flow/topography interactions (Kunze and Llewellyn Smith 2004 Oceanography; Garrett and Kunze 2007 Ann. Rev. Fluid Mech.). An intense vortex-trapped diurnal near-inertial wave was found in the anticyclonic vortex cap straddling the summit of Fieberling Guyot. Elevated turbulence was found both over the summit and flanks of the seamount (Kunze et al. 1997 JPO; Toole et al. 1997 JGR). Measurements in Monterey Submarine Canyon found elevated internal tides and turbulence (Kunze et al. 2002 JPO) that has been verified by subsequent measurements in Monterey and other canyons.

Internal Wave Energy-Fluxes:    The Monterey Canyon measurements also motivated development of a technique to quantify internal wave energy-fluxes from the velocity-pressure correlation (Kunze et al. 2002 JPO; Nash et al. 2005 JTech) that has found wide application to studies internal tide generation at ridges (Althaus et al. 2003 JPO; Rudnick et al. 2005 Science; Lee et al. 2006 JPO; Nash et al. 2006 JPO) and on continental slopes (Nash et al. 2004 JPO; Nash et al. 2007 GRL) where the signal can be difficult to interpret because superposition of incident and reflected waves (Martini et al. 2007 GRL). Generation theories and models correctly predict the transfer of energy from barotropic to baroclinic tide. Most of this transfer is into low modes which radiate away rather than being dissipated locally (Klymak et al. 2006 JPO). Where the radiated energy dissipates remains unknown with possibilities including an internal wave/wave interaction mechanism known as parametric subharmonic instability that transfers energy to high wavenumber at half frequency equatorward of 30 (Frajka Williams et al. in prep) and critical reflection and scattering on continental slopes (Nash et al. 2004 JPO; McPhee-Shaw and Kunze 2002 JGR) where enhanced mixing is extremely heterogeneous (Nash et al. 2007 GRL) and its products appear to rapidly exchange with the stratified interior.

Equatorial Deep Jets:    I inherited my first student Joanna Muench from Lew Rothstein. She was already trying to understand the dynamics of equatorial deep jets in a remarkable set of sections collected by Eric Firing. She found that there was a potential vorticity anomaly associated with these features, suggesting that they might be equatorial Rossby waves rather than Kelvin waves (Muench et al. 1994 JPO). Her Ph.D. research on internal wave interactions with the jets suggested that they might be at least partially maintained by critical-layer deposition of internal wave momentum-fluxes (Muench and Kunze 1999-2000 JPO). Subsequent work using historical CTD data has found evidence for zonal propagation on timescales of years for these persistent features (Johnson et al. 2002 JPO).

Biologically-Generated Turbulence:    Since becoming a Canada Research Chair at U of Victoria, I have continued to study flow/topography interactions in canyons and other topographic features, now using microstructure instruments built by Rockland Scientific as well as standard shipboard ADCPs. During the first instrument test of a vertical microstructure profiler in local waters, we examined the notion that swimming marine organisms could generate turbulence. While energetics considerations suggest that significant turbulence could be generated, this idea was previously unverified. Collecting data through the upward migration of a dense krill swarm after dusk revealed a 15-minute burst of intense turbulent mixing (Kunze et al. 2006 Science). If this was to occur every dawn and dusk, it would swamp all other sources of mixing in Saanich Inlet. But subsequent measurements have found that the generation of turbulence is intermittent. Research is ongoing to determine under what conditions migrating krill swarms produce turbulence and whether this mechanism is important for mixing.

Future Research:    Future plans also include dye-release experiments to study how waters move and spread vertical and horizontally, particularly near topography, and deployment of an electromagnetic profiling float to measure horizontal velocity as well as temperature and salinity.