Abstract
An accurate metrological investigation was performed on several units of the two de facto standards for deep-ocean temperature measurements—the SBE35 (the reference thermometer) and the SBE3 (the working thermometer) from SeaBird Scientific. Four SBE35 units were repeatedly calibrated against state-of-the-art fixed-point cells (triple point of water at 0.01 °C and melting point of gallium at 29.7646 °C), with calibration uncertainties of approximately 0.2 mK and 0.5 mK, respectively. Three SBE35 units and one SBE3 unit were calibrated in the temperature range 0 °C to 30 °C, again with sub-millikelvin calibration uncertainties, in a recently-developed water–bath calibration facility. All these calibrations evidenced (1) the deviation of each unit from its original manufacturer’s calibration (up to 1.7 mK), which were found to be inconsistent with the manufacturer’s uncertainty claims and (2) unexplained irreproducibilities, which could not be attributed to the calibration system of up to 1.5 mK. The effect of high pressures (up to 60 MPa) on the response of two SBE35 units was investigated by pressurizing the SBE35 units inside a purpose-built compact pressure enclosure. The results of the pressure investigation confirmed the existence of a small device-dependent pressure effect (approximately 0.3 mK at 60 MPa) and the need for individual temperature–pressure calibration of each SBE35 unit.
Highlights
Global warming is driven by the current imbalance (Earth’s energy imbalance, EEI) at the top of the atmosphere, between the incoming solar energy and the outgoing energy radiated back to space [1]
Continuously added to the Earth system by EEI, is predominantly stored in the oceans, the accuracy in the EEI estimate is related to the accuracy in the total ocean heat content (OHC), which in turn, is directly related to the accuracy of global ocean temperature observations
(Section 2.1) and we report the results of (a) our re-calibration of 4 SBE35 units against (Section 2.1) and we report the results of (a) our re-calibration of 4 SBE35 units against the the Dutch national reference fixed-point cells
Summary
Global warming is driven by the current imbalance (Earth’s energy imbalance, EEI) at the top of the atmosphere, between the incoming solar energy and the outgoing energy radiated back to space [1]. 1 mK·(60 MPa) mK∙(60 MPa)−1 for 2 of the 3 investigated SBE35, and no pressure dependence, within the the measurement uncertainty, for the other SBE35. 5 years, on several units of SBE35 and SBE3 ocean thermometers. MPa) on experiment conducted to investigate the effect of high pressures
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