In spite of the important role played by the Southern Ocean in global climate, the few existing paleoceanographic records in the east Pacific sector do not extend beyond one glacial‐interglacial cycle, hindering circumpolar comparison of past sea surface temperature (SST) evolution in the Southern Ocean. Here we present three alkenone‐based Pleistocene SST records from the subantarctic and subtropical Pacific. We use a regional core top calibration data set to constrain the choice of calibrations for paleo SST estimation. Our core top data confirm that the alkenone‐based UK37 and UK′37values correlate linearly with the SST, in a similar fashion as the most commonly used laboratory culture‐based calibrations even at low temperatures (down to ∼1°C), rendering these calibrations appropriate for application in the subantarctic Pacific. However, these alkenone indices yield diverging temporal trends in the Pleistocene SST records. On the basis of the better agreement withδ18O records and other SST records in the subantarctic Southern Ocean, we propose that the UK37 is a better index for SST reconstruction in this region than the more commonly used UK′37 index. The UK37‐derived SST records suggest glacial cooling of ∼8°C and ∼4°C in the subantarctic and subtropical Pacific, respectively. Such extent of subantarctic glacial cooling is comparable to that in other sectors of the Southern Ocean, indicating a uniform circumpolar cooling during the Pleistocene. Furthermore, our SST records also imply massive equatorward migrations of the Antarctic Circumpolar Current (ACC) frontal systems and an enhanced transport of ACC water to lower latitudes during glacials by the Peru‐Chile Current.

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The Humboldt Current System (HCS) is the world's most productive eastern boundary upwelling system (Montecino & Lange, 2009). It stretches along the west coast of South America, from southern Chile (40°S-45°S) to northern Peru (4°S) (Figure 1a). Historical data show that the HCS's marine productivity changes in response to inter-annual climatic modes, such as the El Niño-Southern Oscillation (Montecino & Lange, 2009). However, our knowledge about the response of the HCS to climate change on longer time scales, especially beyond the last glacial, is still largely fragmentary.Paleoproductivity studies in the southern part of the HCS have so far been confined to the coastal area between 36°S and 41°S, and their findings suggest either lower glacial productivity (