For an oceanographer, understanding the physical properties of sea water, including salinity and temperature, and depth are parameters that are critical for studying ocean processes. Luckily, oceanographers have an oceanographic instrument that does that very thing, and it’s called a CTD. A CTD is an acronym for sensor that measures conductivity (which can be used to determine salinity), temperature and depth. The instrument can be incorporated into a variety of observing platforms, including gliders, vertical profiling floats, fixed observing buoys, moored pods and vertical profiling rosettes.
The R/V Armstrong is outfitted with a Seabird conductivity, temperature and depth rosette on a hydrographic winch crane on the starboard side of the vessel. This rosette is capable of making vertical profiles to depths exceeding 6000 meters, all the while collecting conductivity, temperature and depth data. In addition to the CTD probes, the rosette has a series of 24 bottles that are open on both ends upon submersion and can be individually triggered to close at a specified depth. This allows scientists to analyze water at specific depths at a particular place and time.
CTD deployments, called casts, are the workhorses of instrument measurements. By knowing the conductivity, temperature and depth of a body of water, many other physical properties of seawater can be inferred. It is for this reason that the CTD is often a staple of oceanographic research cruises.
CTD casts made from the R/V Armstrong require good communication between scientists in the lab and the hydrographic crane operator. Oceanographers in the lab can monitor the CTD measurements real time in the lab, and communicate depth for water capture in the rosette bottles to the crane operator. Once back on board, scientists can retrieve the water samples from the bottles and take them into the lab for analysis.
Over the course of the PEACH research cruise, the Seabird CTD rosette aboard the R/V Armstrong will be making over 70 CTD casts from depths ranging from 17 meters to depths over 3500 meters. In addition, CTDs mounted on gliders, Argo vertical profiling floats, and moored platforms will make over 4,700,000 measurements over the course of their 18 month deployments. All of this data, combined with the other oceanographic data collected, and the numerical models, will assist the oceanographers in better understanding the exchange of shelf water into the deep ocean.
For more information on the PEACH project, please click HERE.