CTD casts
Jeremy Wilkinson
Significant and accelerated
change is occurring with respect to
the sea ice in the Arctic Ocean.
Coupled to these changes are
modifications to the ocean structure.
Therefore
as
part
of
the
comprehensive
data
collection
strategy at SEDNA/APLIS the
structure of upper ocean of the
Beaufort Sea was monitored. CTD
casts
were
performed
at
approximately 6 hour intervals. The
CTD used was the battery powered
SEABIRD 19 which logs data to Figure 8.3: Image of the hydro-hole used by
internal memory at 2Hz and carries the CTD to obtain the upper ocean structure
its own internal clock. A pump-fed
conductivity probe within the CTD carries out measurement of conductivity and
temperature.
Once ‘on station’ the CTD was untied and readied for lowering through the
hydro-hole. Before entering the water the logging was initiated by positioning the
switch to ‘on’ position. The lowering of the CTD into the water was generally a 2
person operation with one person operating the hand-winch, and the other
ensuring the unit descended at a constant rate (< 1m/s). As it was not possible
to ‘see’ the data in real time, all data was logged internally within the CTD, we
performed two casts of the CTD at each station; just in case there was a
malfunction in the unit during the first cast.
At the end of a station the CTD was lifted out of the water and stowed
away from the hydro-hole. The standard procedure for pumped SBE19 data
processing, as recommended by SBE, was followed (cf. SBE SEASOFT
manual). The table in appendix 7 lists the position, date, time and depth all CTD
stations made during SEDNA.
An example of the data obtained can be seen in the figure below (up-anddown cast included).
Figure 8.4: Example of up and down cast of one CTD profile