Do Historical "Zero Depth" Hydrographic Data
Contain Useful Information on Climate Trends?
The sea surface temperature observations in the
archives of hydrographic surveys are compared with
comparable observations from ships-of-opportunity as
collected in the familiar COADS data set, with the aim of
quantifying the possible biases in the COADS results.
The focus is on three compact regions of the North
Atlantic. It is found that there is generally a significant
cold bias in the reported hydrographic surface
temperatures and that the magnitude of this bias varies
greatly with location. It is possible that this reflects
extrapolated temperatures from depth being reported as
surface observations. Until the surface hydrographic
data can be sifted to eliminate such suspect values they
are unlikely to be of use in defining climatic trends.