A Lightweight Vertical Rosette for Deployment in Ice Covered Water

In the Arctic Ocean, water samples are difficult to obtain from ships because of the extensive ice cover and thick pressure ridges. However, the ice provides a landing platform for aircraft, which can rapidly cover long distances. Aircraft have been used for sampling the Arctic Ocean for the past half-century using bottles and internally recording CTDs attached to a cable and lowered through leads or holes drilled in the ice. CTD/rosette systems have an advantage over this method in that they provide temperature, salinity and oxygen profiles that can be used to decide on vertical placement of water samples, but these systems are too bulky to use from an aircraft. We have developed a lightweight modular CTD/rosette system that is deployed through a 12-inch diameter hole drilled in the ice. The modules are connected together physically and electrically with the water bottle modules, which contain four 4-liter bottles each, stacked on top of the CTD module. The CTD traces are displayed on a laptop computer and the bottles are tripped using modified Seabird controllers and a melt-lanyard tripping mechanism. We have used this system for several years with Twin Otter fixed wing aircraft as part of the Switchyard Project, sampling a line of stations annually in the heavily ice covered region between Ellesmere Island and the North Pole. Casts are carried out in a tent connected to the airplane using a lightweight winch mounted in the airplane. This prevents freezing of the samples when the rosette is recovered. At the completion of a cast, the water modules are placed in a cooler with bags of snow to provide thermal stability at about 0°C and the end caps clamped shut. The modules are returned to a base camp where a variety of water samples are drawn and processed. We routinely measure samples for salinity, oxygen, nutrients, tritium, helium isotopes, CFCs, SF6, oxygen isotopes, barium and I-129, but the rosette sampler can be used for a wide range of substances. The water temperature of each bottle is measured when the oxygen sample is drawn and the average warming during the 6–10 hour transit time back to the base camp and during the sampling process is 2.5°C. There is no evidence in the gas samples of degassing or contamination with air and all samples are of very high quality. Vertical profiles will be presented to demonstrate data quality.