Statistically homogenous concatenation of Kaplan et al [1998] OS SST and Reynolds and Smith [1994] NCEP OI analyses; the latter gets degraded to the resolution of the former.
Kaplan, A., M. Cane, Y. Kushnir, A. Clement, M. Blumenthal, and B. Rajagopalan, Analyses of global sea surface temperature 1856-1991, Journal of Geophysical Research, 103, 18,567-18,589, 1998
R. W. Reynolds, T. M. Smith. Improved global sea surface temperature analyses.. J. Climate 7, 1994