Dissipation of Turbulent Kinetic Energy Inferred from Seagliders: An Application to the Eastern Nordic Seas Overflows NICHOLAS BEAIRD School of Oceanography, University of Washington, Seattle, Washington ILKER FER Geophysical Institute, University of Bergen, Bergen, Norway PETER RHINES AND CHARLES ERIKSEN School of Oceanography, University of Washington, Seattle, Washington (Manuscript received 31 May 2012, in final form 16 August 2012) ABSTRACT Turbulent mixing is an important process controlling the descent rate, water mass modification, and volume transport augmentation due to entrainment in the dense overflows across the Greenland–Scotland Ridge. These overflows, along with entrained Atlantic waters, form a major portion of the North Atlantic Deep Water, which pervades the abyssal ocean. Three years of Seaglider observations of the overflows across the eastern Greenland–Scotland Ridge are leveraged to map the distribution of dissipation of turbulent kinetic energy on the Iceland–Faroe Ridge. A method has been applied using the finescale vertical velocity and density measurements from the glider to infer dissipation. The method, termed the large-eddy method (LEM), is compared with a microstructure survey of the Faroe Bank Channel (FBC). The LEM reproduces the patterns of dissipation observed in the microstructure survey, which vary over several orders of magni- tude. Agreement between the inferred LEM and more direct microstructure measurements is within a factor of 2. Application to the 9432 dives that encountered overflow waters on the Iceland–Faroe Ridge reveals three regions of enhanced dissipation: one downstream of the primary FBC sill, another downstream of the sec- ondary FBC sill, and a final region in a narrow jet of overflow along the Iceland shelf break. 1. Introduction The Faroe Bank Channel (FBC) and its smaller neighboring overflow across the Iceland–Faroe Ridge (IFR) account for one-third of total Nordic Seas outflow into the North Atlantic (Hansen and Østerhus 2000). Considerable effort has been focused on the region in general and on the FBC in particular. Along with en- trained Atlantic waters, which double the initial overflow volume transport, these overflows make up a large part of the North Atlantic Deep Water (NADW). NADW has global extent in the deep ocean and its circulation forms the lower limb of the Atlantic meridional overturning circulation. The location and intensity of turbulent mixing and entrainment in these overflows has an im- portant impact on ventilation of the deep ocean and the oceanic meridional heat transport. Entrainment of overlaying waters is particularly interesting in this re- gion where wintertime mixed layers can sometimes reach the depth of the overflow plume interface. A comprehensive review of North Atlantic–Nordic Seas exchanges is given by Hansen and Østerhus (2000) and of the FBC overflow by Hansen and Østerhus (2007). At the sill thresholds, approximately 3 Sv (Sv [ 10 6 m 3 s 21 ) of Nordic origin waters form energetic bottom-intensified gravity currents flowing into the Iceland Basin. Of the total 3 Sv, 1.9 Sv exits through the FBC, and the remainder crosses the IFR. The Faroe Bank Channel overflow is swift [O(1 m s 21 )] and uni- directional, with a bottom mixed layer of cold (;08C) water capped by a thick [O(100 m)] interfacial layer below the ambient Atlantic waters. Dissipation levels Corresponding author address: Nicholas Beaird, University of Washington, 1492 NE Boat St., Seattle, WA 98195. E-mail: nlbeaird@uw.edu 2268 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 42 DOI: 10.1175/JPO-D-12-094.1 Ó 2012 American Meteorological Society