A homogeneous, consistent, high-quality in situ temperature data set covering some decades in time is crucial for the detection of climate changes in the ocean.
Systematic errors in the global archive of temperature profiles pose a significant problem for the estimation and monitoring of the global ocean heat content, a most reliable indicator of climate change. During almost four decades between 1940-1970s, the majority of temperature observations in the ocean within the upper 200 meters was obtained by means of mechanical bathythermograph (MBT). Actually MBT contributes to 68% of ocean subsurface data within 1940-1966.
The new study by Viktor Gouretski and CHENG Lijing from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences investigated the quality of MBT data by comparing them with reference profiles obtained by means of Nansen bottle casts and Conductivity-Temperature-Depth (CTD) profilers. The study was published in Journal of Atmospheric and Oceanic Technology.
This comparison revealed significant systematic errors in MBT data. The MBT temperature bias was as large as 0.2°C before 1980 on the global average and reduced to less than 0.1°C after 1980. To eliminate this bias from the original data, a new empirical correction scheme for MBT data was derived, where the MBT correction is country-, depth-, and time-dependent.
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