Mixing in the Barents Sea Polar Front near Hopen in spring

284
285
time-averaged conditions at each location, but rather a single realization of the temporal and
spatial variability.
286
287
288
289
290
291
292
It is not trivial to obtain representative average profiles from a site with strong topographic
variability and lateral gradients in hydrography. We therefore present two alternatives:
isopycnal averages and averages in depth coordinate, z, normalized with the total water
depth, H. Isopycnally-averaged variables were obtained in 50 equally spaced bins of the
average profile and are assigned the average isopycnal depth. Each profile was sorted
before calculations. The normalized depth coordinate averaging was done over vertical bins
of z/H = 0.05 thickness.
293
294
295
296
297
298
299
Average dissipation rates were lowest at mid-depth on the AW side, independent of the
averaging method. Isopycnally-averaged profiles showed more than one order of magnitude
increase in dissipation below the upper layer from the AW to PW side of the front. Vertical
gradients of temperature and salinity that appeared in the isopycnally-averaged profiles at the
front were smeared out in z/H coordinates. A clear pattern emerged in z/H-averaged profiles
of : relative to mid-depth the dissipation rate was enhanced by up to two orders of
magnitudes in about z/H = 0.2 unit thick layers in the upper and bottom layers.
300
301
302
303
304
305
306
5.4. Isopycnal mixing
There was significant variability in temperature and salinity properties along isopycnal
surfaces sampled at the station TS. Fluctuations of T and S along the isopycnals relative to the
10-h mean are displayed in Figure 9. Due to the density compensating nature of the
thermohaline BSPF T S, i.e. their contributions to density are similar. The anomalies
appeared to be modulated at a time scale consistent with the tidal frequency suggesting that
the tides were driving along-isopycnal intrusions, whereby allowing the water on either side
14