Conducting Marine Science in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 218

The most fundamental set of information sought by a physical oceanographer is a ver-
tical profile of the water's temperature and salinity. These two parameters control the dens-
ity of the water and a unique combination of temperature and salinity is characteristic of
water masses formed in specific locations and conditions. Once you have a horizontal pic-
ture of the vertical distribution of temperature and salinity (and hence of density) over a
particular geographical area, you can decide how to organise your chemical, biological and
current meter sampling strategy. One of the seminal technological revolutions taking place
in the 1970s related to the measurement of temperature and salinity. At that time, we still
largely relied on reversing thermometers to measure temperature and the postcruise de-
termination of water conductivity to derive salinity. It worked like this: You would lower a
string of water bottles open at each end until each bottle would eventually be at a preselec-
ted depth. Then, you would send a weight called a messenger down the wire, which would
close the top bottle and release another messenger down to the next bottle. When each
bottle closed, a reversing thermometer attached to the bottle would flip upside down and
the mercury column would break. Once this had happened, the reading on the thermomet-
ers would not change when the bottles were brought back to the surface.
These thermometers were expensive and very temperamental. After reading the tem-
perature, you had to carefully turn the thermometer to its original “upright” position in or-
der to reconnect the mercury column. The thermometers objected to this being done at Arc-
tic air temperature, they did not like to be quickly brought into a warm room, and they did
not appreciate vibration. In other words, they were not happy on our ship. I found that the
ideal spot for this delicate operation was in the doorway between the galley and the mess
and a little forward of the engine room access. Having gone to all this trouble, you still did
not know the salinity until you returned to your home laboratory. You never knew the exact
depth of the sample because you had no idea how the wire angled in response to the ship's
drifting and the currents below.
The path-breaking new technology on our cruise was a CTD (for conductivity, tem-
perature and depth). These instruments started to become generally available in the early
1970s. They were lowered down to whatever depth you wished and they continually meas-