Geoscience Reference
In-Depth Information
Fig. 2.6
Timeseries of temperature and salinitymeasured atthelevels shown during March 1998.
On day 78, the two lower clusters were enveloped in the upwelled pycnocline for several hours.
During this time, turbulent heat flux at 9.7m reached nearly 400W m
−
2
(3-h average). During the
timebetweenthearrows,theautomatedprofilersystemwaswithoutpower(AdaptedfromMcPhee
et al. 2005. Withpermission American Geophysical Union)
icedeformation,whichplayedhavocwithouroceanographicdatagathering,mainly
by severing the powerline from the ship when a lead formedoff the starboardside
late on day 75.
3
Without ship power, the SHEBA automatedprofiling CTD system
ceasedoperationearlyonday76,anddidnotresumeprofilinguntilearlyonday79.
In the meantime, the turbulence mast was rigged to run on portable generator with
sporadiccoverageuntil it resumed full operation early on day 78 (UT). Recordsof
temperature and salinity at constant levels in the upper ocean (Fig. 2.6) show well
mixed conditions in the upper 18m of the water column before and after day 78,
but during that day there were large excursionsindicating upwelling of pycnocline
water. Figure 2.7 shows that the potential density measured at noon (UT) by the
TICat17.7mwasabout0
5kgm
−
3
largerthanatthebeginningandendoftheday.
Also shown are profiles of
.
σ
0
from the automated profiler system at times 76.25
and 79.0, taken as representative of the ambient conditions surrounding the event.
Themaximumdensityobservedat 17.7m correspondsto thedensity at about30m
in the surroundingundisturbedocean.This broughtwater thatwas usuallywell be-
lowtheactiveturbulencezonecloseenoughtothesurfacethatmixingwas intense.
3
The SHEBA experience in March 1998, accentuates an annoying, and to some extent unavoid-
able, aspect of ice camp measurements: that itis often difficult tokeep theinstrumentation operat-
ing ina rapidly changing environment, just when things get really interesting.
