Thermistor string corrections in data from very weakly stratified deep-ocean waters

An important parameter for observational studies on dynamical variations of the ocean is temperature (T) which determines density together with salinity. While achievement high absolute accuracy T-sensors a formidable task, even maintaining precision difficult any long-term deep-ocean observations. This because deep very weakly stably stratified in density, all dynamics covered by range about 0.001 °C. One requires high-resolution low noise levels and precisely calibrated. However, common Negative Temperature Coefficient (NTC) thermistor have electronic drift causing bias time. The rate varies (change) time (age) between 0.0002 °C wk−1 used here. A string such moored open-ocean more than month after calibration drift-correction. When deep-ocean, secondary correction necessary immediately calibration. Secondary uses reference layers that are homogeneous to within 0.00005 over 100 m vertically plus an additional polynomial remove remaining prior or date. may also involve pressure information surface tides mooring deflection. In this paper, corrections described two cases data. For one case from West-Mediterranean varying temperature-density relationship near-homogeneous conditions exist. other hadal-deep instruments long line Challenger Deep, Mariana Trench, affected tidal flow. Nearby shipborne CTD-data always needed establish background vertical slope T-sensor data referenced. stability compared sensors CTD.