| Summary: | North Pole Environmental Observatory - Arctic Ocean Internal Wave and Mixing Data Archive Website at http://psc.apl.washington.edu/northpole/Mixing.html NSF Grants ARC-0909408 Sensitivity of Arctic Ocean Change to Background Mixing and ARC-0856330, OPP-9910305, OPP-0352754 North Pole Environmental Observatory Recent findings demonstrate the sensitivity of Arctic Ocean circulation to background, deep-ocean mixing. Results with a large-scale coupled ice-ocean model [Zhang and Steele, 2007] suggest the appropriate model background mixing for the Arctic Ocean is an order of magnitude lower than for ice-free oceans. Background mixing in the deep ocean is related to internal wave energy, which in ice-covered seas has been observed to be lower than in ice-free oceans, and to change with time and bathymetric conditions [Levine et al., 1985 and 1987; Halle and Pinkel, 2003; Pinkel, 2005]. Present thinking is that internal wave energies and background mixing are reduced in ice-covered seas by, among other things, dissipation of internal wave energy in the surface boundary layer immediately below the ice. Consequently, if the ice cover is reduced due to global warming, we may see a climate feedback that has not been considered before. If the ice cover is reduced, we may see increased internal wave energy, mixing, and heat flux in the deep ocean because less internal wave energy would be lost in the under-ice boundary layer. This would tend to result in increased heat flux to the ice, a positive climate feedback that would melt more ice. The effect could arguably be greatest near the continental slopes and submarine ridges, which are the likely areas of greatest internal wave increase and the paths of warm Atlantic water through the Arctic Basin. The sensitivity ocean circulation and energy balance to background mixing and the criticality of ocean heat and freshwater fluxes, suggest that as the Arctic Ocean changes, we should be tracking background mixing the way we track temperature and salinity. Direct measurements of mixing are difficult, but decades of research show that deep background mixing is a consequence of dissipation of internal wave energy. The exact nature of this relationship is an ongoing question, but it makes it possible to infer mixing from relatively simple observations of internal wave energy [e.g., Gregg, 1989; D'Asaro and Morison, 1992; Kunze et al., 2006]. In our new NSF-OPP project, Sensitivity of Arctic Ocean Change to Background Mixing (ARC- 0909408), we will be gathering together and analyzing existing Arctic Ocean data for internal waves and mixing using new methods, which in many cases have not been applied to the Arctic environment. As part of our renewed North Pole Environmental Observatory Grant (ARC-0856330) we are now dropping eXpendable Current Profilers (XCP) as a standard part of our NPEO airborne hydrographic surveys. The velocity shear measured by these probes, along with the CTD data, gives us a simple estimate of background internal wave energy from which background mixing can be inferred. We are collaborating with Ilker Fer of the University of Bergen in deploying and analyzing both his and our NPEO XCPs. We analyze the XCP data under our "Mixing" grant, and with other data, we will use them to track changes in internal wave energy and related mixing. We will also be performing a simple studies of the energetics of internal waves that combine existing ideas about the forcing of internal waves with new ice model results [Heil and Hibler, 2002; Hibler et al., 2006]. As part of the Mixing Project we are offering here data suitable for use by anyone doing Arctic Ocean model predictions (e.g., the Arctic Ocean Model Intercomparison Project, AOMIP). We are starting by assembling and analyzing XCP data from field projects associated with the North Pole Environmental Observatory beginning in 2007, plus older data from the first SCICEX cruise in 1993. CTD profile profile data pertient to the analysis are either included or directly referenced in other archives. New data will be added as it becomes available. References: - D'Asaro, Eric A. and J.H. Morison, 1992, Internal waves and mixing in the Arctic Ocean, Deep Sea Research, Vol. 39, Suppl. 2, pp. S459-S484. - Fer, I., 2009, Weak vertical diffusion allows maintenance of cold halocline in the central Arctic, Atmos. and Oceanic Sci. Lett., 2 (3), 148-152. - Gregg, M. C., 1989, Scaling turbulent dissipation in the thermocline, J. Geophys. Res., 94, (C7), 9686-9698. - Halle, C., and R. Pinkel, 2003, Internal wave variability in the Beaufort Sea during the winter of 1993/94, J. Geophys. Res., 108, 3210, doi:10.1029/2000JC000703. - Heil, P. and W. D. Hibler III, 2002, Modeling the high-frequency component of Arctic sea ice drift and deformation, J. Phys. Ocean., 32, 11; p. 3039-57. - Hibler, W. D. III, A. Roberts, P. Heil, A. Y. Proshutinsky, H. L. Simmons, and J. Lovick, 2006, Modeling M2 tidal variability in Arctic sea-ice drift and deformation, Annals of Glaciology, 44, 418-428. - Kunze E., E. Firing, J. M. Hummon, T. K. Chereskin, and A. M. Thurnherr, 2006, Global abyssal mixing inferred from lowered ADCP shear and CTD strain profiles, J. Phys Ocean., 36 (12), 2350-2352, correction from vol. 36, pg 1553, 2006. - Levine, M.D., C.A. Paulson and J.H. Morison, 1985: Internal waves in the Arctic Ocean: Observations and comparison with lower latitude climatology. J. Phys. Oceanogr., 15, 800-809. - Levine, M.D., C.A. Paulson and J.H. Morison, 1987. Observations of internal gravity waves under the arctic ice pack. J. Geophys. Res., 92 (C1), 779-782. - Pinkel, R., 2005, Near-inertial wave propagation in the Western Arctic, J. Phys. Oceanog., 35,645-665. - Zhang, J., and M. Steele, 2007, Effect of vertical mixing on the Atlantic Water layer circulation in the Arctic Ocean, J. Geophys. Res., 112, C04S04, doi:10.1029/2006JC003732. Acknowledgements: We would like to express our gratitude to: - Ilker Fer of the University of Bergen for providing expertise, mixing comparisons, and XCP probes for the NPEO drops starting in 2007. - Andrey Proshutinsky, Sarah Zimmermann, Tim Kane, and Luc Rainville of the 2007 Beaufort Gyre Exploration Project cruise on the Louis St. Laurent for dropping XCPs in the Beaufort Sea. - Mike Steele, Wendy Ermold, Roger Andersen, and Dale Chayes for supplying probes and doing drops during the Switchyard experiments. For further information, please contact Dr. James Morison morison@apl.washington.edu (206) 543-1394 Roger Andersen roger@apl.washington.edu (206) 543-1258 Departmental mailing address for both Dr. James Morison and Roger Andersen: Polar Science Center Applied Physics Lab, University of Washington 1013 NE 40th Seattle, WA 98105-6698 FAX (206) 616-3142
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