Observing turbulent fluxes in the upper Arctic Ocean

Principal Investigator: 
Proposal Abstract: 

Intellectual Merit:
Accurate measurements and ultimately predictions of turbulent salt and heat fluxes in the upper Arctic
Ocean are essential to make sense of a changing climate. The Beaufort Gyre (BG) is historically home to some
of the oldest and thickest ice in the Arctic, but is now remarkably ice free in summer. Large areas of ocean are
now exposed to direct wind forcing. Turbulence directly forced by surface wind stress is confined to a shallow
mixed layer. However, wind stress also generates near-inertial internal waves (NIW) that can propagate
downwards into stratified water and break hundreds of meters or more below the surface. Crucially, mixing in
this depth range can tap into the large heat reservoir of Atlantic-origin water. Increased turbulent heat fluxes
up from this water mass could significantly warm the upper ocean and accelerate ice loss. Understanding of
this process has been hampered in large part by a lack of detailed measurements of turbulent mixing rates
below the surface mixed layer, especially in open water where NIW are expected to be strong.
Here we propose 1) direct microstructure measurements to accurately constrain the turbulent heat and salt
fluxes in the upper ocean and 2) a combination of moored and towed-body measurements to develop a dynamical
understanding that relates those fluxes to local internal wave and mesoscale features. The cruise will be
bracketed at both ends by  400 kilometer horizontal sections across the Beaufort Gyre with our towed body,
SWIMS. This will provide an unprecedented 0.5 km horizontal resolution snapshot of T,S, velocity, and scalar
microstructure across the ice free Arctic. Time series at select locations with our tethered microstructure profiler
will provide detailed and high frequency estimates of the turbulent mixing rate in relation to unfolding
wave breaking events. Finally, a mooring placed in the center of the BG will provide temporal context to
interpret other measurements. Analysis will focus on 1) quantifying mixing rates, 2) understanding how NIW
propagation and breaking respond to variable forcing rates and refraction by mesoscale vorticity, and 3) evaluating
several candidate dynamical relationships and between the two with an eye towards parameterization.


Broader Impacts:
Our proposed work contributes to an outstanding question in physical oceanography - understanding
the ocean’s role in rapid Arctic Ice loss. The insight gained here will not only give a significantly better
appreciation for the role of turbulent heat fluxes for accelerating ice loss, but will help develop appropriate
parameterizations of the process for use in regional or global numerical models. MacKinnon and Alford are
both active members in a NSF and NOAA funded Climate Process team tasked with improving representations
of diapycnal mixing in global climate models. To date that project has been focusing on diapycnal mixing
due to the breaking of internal tides and wind-generated near-inertial internal waves at lower latitudes. The
resultant geography of elevated mixing being implemented in GCMs so far resembles maps of tidal and
wind generation, and GCMs have been shown to be very sensitive to those mixing patterns. The experiment
proposed here will allow similar work to be done for the Arctic Ocean.
All three PI’s actively engage in public outreach via volunteering in K-12 programs and through our
websites (e.g. http://wavechasers.uw.edu). For this project, we will also contribute to the the Birch Aquarium
at Scripps Perspectives on Ocean Science (POS) speaker series. Perspectives on Ocean Science is a monthly,
ocean sciences speaker series hosted by BAS that provides the public with direct access to up-to-date science
in a presentation that is specifically designed for a lay audience. Finally, the proposal will train a graduate
student.
 

External Principal Investigator: 
John Mickett, University of Washington
Start and End Date: 
July 2014 to October 2017