Oxygen isotope measurement has been carried out on modern and fossil coral cores from Maudulung-North Sumba. The objective of this measurement is to determine oxygen isotope composition due to sea surface temperature change. The method used in preparation was developed by Gagan et al (1994).

Dating on fossil coral yields 3702±42 yr BP, the oxygen isotope ranges of fossil coral and modern coral are respectively -4.60 o/oo - -5.20 o/oo and -5.00 o/oo - -5.80 o/oo. Lower value of oxygen isotope (d18O) is thought to be an indication of temperature decrease which took place about 3.500 yr BP.