The mid-Pleistocene transition in the subtropical southwest Pacific

Reconstructions of subtropical southwest Pacific climate variability over the Pleistocene were derived from coupled planktic foraminiferal δ¹⁸O-Mg/Ca measurements taken from a southern Coral Sea sediment core. A clear shift from ∼40 kyr to ∼100 kyr modes of reconstructed glacial-interglacial sea surface temperature (SST) variability is seen over the mid-Pleistocene transition, and these fluctuations are shown to have remained coherent with the orbital obliquity cycle across the transition. The likely origin of this strong obliquity signal in subtropical southwest Pacific SST is shown to be the southern high latitudes, and comparison with existing SST reconstructions from the equatorial Pacific is consistent with the communication of the signal occurring principally by greenhouse gas forcing. In contrast to the SST reconstruction, regional hydrological cycle variability (based on the calculated local component of δ¹⁸O_sw change) does not show significant coherence with obliquity after ∼1000 ka. The decoupling of the SST and hydrological cycle responses over the mid-Pleistocene transition allows constraints to be placed on the evolution and extent of orbitally paced fluctuations within the coupled low-latitude ocean-atmosphere system.