1. Prospective Tracer Release Experiments In the Arctic Jim Ledwell
Title
Prospective Tracer Release Experiments
In the Arctic
Jim Ledwell
Woods Hole Oceanographic Institution

2. Topics
A proposal submitted to NSF to study gas exchange and mixing
in the upper ocean in the Marginal Ice Zone. 10 to 40-day experiments.
2. Possible large scale studies. Multiyear experiments.

3. IDEAr Interfacial and Diapycnal Exchange in the Arctic
(proposal just submitted to NSF/OPP)
Goals: Study the effect of partial ice cover (30 to 80%) on gas exchange
And mixing in the upper 200 m of the ocean, in order to better understand the
Carbon cycle and other nutrient cycles there.
Investigators:
Brice Loose, URI, Leader, Tracer analysis; Data management
David Ho, U. Hawaii, SF6 for Gas Exchange Tracer Measurements
Peter Schlosser, LDEO, 3He for Gas Exchange
Jim Ledwell, WHOI, Rhd for GX, CF3SF5 for diapycnal mixing, Patch tracking
Sylvia Cole & Rick Krishfield, WHOI, ITP-V for CTD/velocity under ice
Miles McPhee, IOBL fine structure and covariance fluxes, Patch tracking
Bill Asher, APL/UW, Waves, Active IR, Passive IR, Surfactants
Chris Fairall & Byron Blomquist, NOAA/ESRL, ABL fluxes, including CO2, CH4, DMS
Ron Kwok, Remote sensing of the ice
Ilker Fer, U. Bergen, TKE dissipation rates, diffusivity
Taro Takahashi, LDEO, Cooperating: PCO2
Lisa Miller, IOS, Cooperating: Carbonate Chemistry in ice and water

4. Tracer-centric summary of IDEAr
Two Field Efforts in the MIZ:
Ice Retreat Experiment in early summer
Gas exchange, and mixing at the base of the ML
k in the seasonal pycnocline ~ 10 m below base of the ML.
Ice Advance Experiment in early fall
k in the upper permanent pycnocline 60 to 100 m depth.
Multitracer gas exchange experiment in each, with SF6, 3He, Rhodamine.
35-day deeper mixing experiments in each, with CF3SF5.
Plus ABL, IOBL, and water column flux and microstructure measurements,
Wave, surface IR, and surfactant measurements

5. Larger Scale Experiments
Would a multi-year tracer release experiment in the Arctic be useful?
If so, it should be designed and executed together with the modeling
Community

6. Example: DIMES 1st year From Ledwell et al., JPO, 2011
Funded by US NSF and UK NERC, BAS

7. DIMES Pacific Diffusivity
K=1.3x10-5 m/s2
@ 1500 m
Ktracer = 1.3x10-5 m2/s
From Ledwell et al., JPO, 2011

8. Gaussian ‘Fit’
Ly ~ 170 km
Rough measure of along-isopycnal diffusivity (of order 500 m2/s),
But scale-dependence affects the first year result, at least.

9. Residual Circulation in the Arctic?
To what extent is Ekman convergence (e.g.
Proshutinsky et al. JGR 2009) balanced by
a divergence of eddy-mass flow, i.e., thickness flux
e.g. Marshall et al, JPO, 2002:
Use tracer to measure the eddy flux from the center
of the gyre?

10. Or:
Release tracer in a boundary current to study exchange
of mass and heat with the interior, e.g., in the Atlantic
Water?
Note: our long term tracers are volatile; they will escape
to the atmosphere. So surface layer releases are useful
mostly for gas exchange studies.

11. From McLaughlin et al. JGR 2002