Understanding past changes in sea surface temperatures (SSTs) is crucial; however, existing proxies for reconstructing past SSTs are hindered by unknown ancient seawater composition (foraminiferal Mg/Ca and d 18 O) or reflect subsurface temperatures (TEX 86 ) or have a limited applicable temperature range (U k' 37 ). We examine clumped isotope (D 47 ) thermometry to fossil coccolith-rich material as an SST proxy, as clumped isotopes are independent of original seawater composition and applicable to a wide temperature range and coccolithophores are widespread and dissolution resistant. The D 47 -derived temperatures from <63, <20, <10, and 2-5 lm size fractions of two equatorial Pacific late Miocene-early Pliocene sediment samples (c1; c2) range between $18 and 298C, with c1 temperatures consistently above c2. Removing the >63 lm fraction removes most nonmixed layer components; however, the D 47 -derived temperatures display an unexpected slight decreasing trend with decreasing size fraction. This unexpected trend could partly arise because larger coccoliths (5-12 lm) are removed during the size fraction separation process. The c1 and <63 lm c2 D 47 -derived temperatures are comparable to concurrent U k' 37 SSTs. The <20, <10, and 2-5 lm c2 D 47 -derived temperatures are consistently cooler than expected. The D 47 -U k' 37 temperature offset is probably caused by abiotic/diagenetic calcite present in the c2 2-5 lm fraction ($53% by area), which potentially precipitated at bottom water temperatures of $68C. Our results indicate that clumped isotopes on coccolith-rich sediment fractions have potential as an SST proxy, particularly in tropical regions, providing that careful investigation of the appropriate size fraction for the region and time scale is undertaken.