Deep-Sea Research II 53 (2006) 77–95 Scaling turbulent dissipation in an Arctic fjord Ilker Fer à Bjerknes Centre for Climate Research & Geophysical Institute, University of Bergen, Allegaten 70, N-5007, Bergen, Norway Accepted 6 December 2005 Abstract In September 2003, microstructure and fine-scale shear (vertical derivative of horizontal current) and strain (vertical derivative of isopycnal displacements) profiles were collected in Storfjorden, Svalbard Archipelago. Storfjorden is a sill- fjord of significant dense water production and the period of observations corresponds to weak overflow conditions of the dense water. The data set comprises fine-scale measurements combined with simultaneous dissipation and buoyancy frequency profiles and allows for evaluation of various turbulence scalings and internal wave–wave interaction models. Microstructure profiles identified high levels of background vertical diffusivity, K r , O(10 4 )m 2 s 1 , which increased by one order within the overflow. Fine-scale shear and strain spectral levels were found to be elevated above those of Garrett–Munk, consistent with the observed enhanced mixing, whereas their average ratio was comparable to that of Garrett–Munk. Among the internal wave–wave interaction models, a shear–strain model agreed with the observations (between the surface and bottom mixed layers) within a factor of 2, on the average. A scaling of the dissipation, e, in the form of total-energy  N suggests that approximately 0.5% of the energy is dissipated per buoyancy period, 2p/N. The best-fit power-law scaling between diffusivity and N is K r pN 1.4 (70.2) . For this environment, a parameterization of the form of Pacanowski–Philander is suggested with background levels of eddy viscosity and diffusivity elevated by an order of magnitude. r 2006 Elsevier Ltd. All rights reserved. Keywords: Turbulence; Mixing; Dissipation; Internal waves; Storfjorden 1. Introduction With an aim to better quantify the marine climate processes in the polar marginal seas, a multi- investigator project ‘‘Polar Ocean Climate Pro- cesses’’ (ProClim) was initiated with geographical emphasis on the western Barents Sea, Svalbard region, and Greenland Sea. In one of the four work packages, microstructure measurements in Storfjorden in Svalbard Archipelago (Fig. 1) were foreseen in order to evaluate and attempt to parameterize the background mixing rate and that associated with the dense overflow plume dynamics. Storfjorden is a sill-fjord 1 of significant dense water production in winter. The dense water is of ARTICLE IN PRESS www.elsevier.com/locate/dsr2 0967-0645/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr2.2006.01.003 à Tel.: +47 55 58 25 80; fax: +47 55 58 98 83. E-mail address: ilker.fer@gfi.uib.no. 1 Two narrow and shallow (o50 m deep) straits in the North connect the basin with the northwestern Barents Sea. The basin is therefore not strictly a fjord by definition; however, the straits are not significant for the dynamics of the basin, especially when they are ice covered in winter.