An Ice-Tethered Instrument for Sustained Observation of Arctic Upper-Ocean Freshwater and Heat Content Variability

To address the Arctic gap in the global ocean observing system, we are developing an expendable, ice-tethered instrument capable of making long-term observations of freshwater and heat content variability beneath the ice pack. The system will consist of a small surface package that will support a weighted tether extending down 500 or more meters into the water column along which a variant of the now-operational Moored Profiler instrument will travel. Conductivity-Temperature-Depth data from the Profiler will be transmitted to the surface unit via an inductive modem, be combined with any additional sensor data (such as atmospheric pressure and temperature) and relayed to shore using a satellite data telemetry unit. We envision a loose array of these Ice-Tethered Profilers repeatedly sampling the thermohaline properties of the upper ocean below the perennial ice pack at daily to weekly time scale. Beyond estimating vertically-integrated quantities such as freshwater anomalies, the better-than 1-m-vertical-resolution data will also be valuable for documenting and assessing double-diffusive layering, thermohaline intrusions and mesoscale eddies, all possibly important to the evolution of the Arctic ice-ocean system. Multi-year lifetime and modest cost will permit basin-scale coverage (about 20 or more systems) to be maintained through regular seeding of replacement units as necessary, similar to the surface ice buoys (measuring sea ice drift, sea level atmospheric pressure, and 2-meter air temperature) of the International Arctic Buoy Program (IABP). Operationally, the array will serve as the Arctic analogue of the ARGO float program now being initiated at lower latitudes. Further information on the Ice-Tethered Profiler system is available at http://ioeb.whoi.edu/itp.