Environmental Engineering Reference
In-Depth Information
ured temperature and conductivity as they descended. Conductivity of seawater primarily
depends on salinity, which makes the conversion fairly simple. The early versions of CTDs
recorded internally on magnetic tape you could read later if you had the necessary equip-
ment. We had one of these and a more advanced model that somewhat resembled those
used today. The sensors on this later version sent their measurements up an electrical cable,
and in theory, you could access the vertical profile of conductivity and temperature while
still on station. It was a tremendous advance because the profile was continuous (not just a
setofpointsdeterminedbywhereyouhaddecidedtoplacethebottles).Furthermore(again
in theory), there was the potential to almost instantly have the data. You could change your
sampling strategy as you went along. Note that I said “in theory”. These were early days
and the electronics were designed for use on purpose-built oceanographic ships with care-
fully regulated electrical systems. The voltage on board our trusted vessel varied dramatic-
ally by the minute. It was so unpredictable that it sometimes fried the portable voltage reg-
ulators that we had brought to protect the entire CTD system! We suffered so many break-
downs that we still relied heavily on water samples analysed months later in the laboratory.
Of course, we were not just interested in salinity and temperature. The measurement
of other parameters was approached by collecting samples, such as dissolved oxygen, plant
nutrients, chlorophyll (as an indicator of phytoplankton biomass), benthic biota and plank-
ton, that were then “fixed” for analysis ashore. As a result, you had very limited notions of
the significance of the cruise until weeks or months after return. It was only then that you
knew what you should have done and where you should have done it. Enlightenment dur-
ing the cruise could have enabled changes to activities, which would have greatly increased
the value of the whole exercise.
In the winter, all the northern Canadian Coast Guard operations shut down and we had
to rely on Greenland stations for radio communications. The only radio channel we could
get often was on the Greenland emergency frequency. Consequently, we were generally out
of communication with the rest of the world for six or seven days. One characteristic of the
ship was that obsolete equipment seemed to have never been removed. It was a veritable
maritime museum. Behind the bridge was the radio room, which years earlier would have
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