South Pacific Convergence Zone in Mid‐Holocene, Last Glacial Maximum and Last Glacial Cycle Climate Model Simulations

Abstract The South Pacific Convergence Zone (SPCZ) is a dominant feature of South Pacific climate variability. Sensitivity of the SPCZ to changes in mean climate is investigated for a set of past climate simulations of Last Glacial Maximum (LGM, 21,000 years before present) and mid‐Holocene (6,000 years before present) from the Paleoclimate Modeling Intercomparison Project (PMIP). The PMIP time‐slice simulations are compared with a set of simulations from the HadCM3 model spanning the last glacial cycle (120,000 years to present). Changes in surface temperature and precipitation are examined, showing a northward shift of the multi‐model mean SPCZ in the LGM and southward shift of the SPCZ in the mid‐Holocene. In both cases, the SPCZ shifts are highly correlated with changes in the strength of zonal and meridional sea surface temperature (SST) gradients in the South Pacific. The HadCM3 simulations show strong shifts in SPCZ mean latitude and slope over the glacial cycle, predominantly on precession timescales. The SPCZ position in HadCM3 varies over the glacial cycle with zonal and meridional SST gradients, in qualitative agreement with the PMIP simulations, while SPCZ precipitation amount varies with global mean temperature. These past climate simulations suggest that patterns of SST change in the South Pacific are the main driver of shifts in the SPCZ position, consistent with previous work. The model changes in LGM and mid‐Holocene SPCZ position appear to disagree with proxy‐based reconstructions of SPCZ precipitation shifts, implying that further paleoclimate archives and model simulations are required to confidently reconstruct past SPCZ changes.