Precession Control of Temperature Seasonality Changes in the West Pacific Warm Pool since the Last Glacial Maximum

The Holocene temperature history and its forcing mechanisms remain elusive due to the conflict between proxy reconstructions and model simulations. Recently, this model-data inconsistency has been partly attributed to the seasonal bias in the proxy indicators. This study attempts to assess changes in the seasonal variability of sea surface temperature in the low-latitude western Pacific since the Last Glacial Maximum (LGM), based on the standard deviation of oxygen isotope (δ¹⁸O) measured from individual planktonic foraminifera at four sites. The reconstructed temperature seasonality shows interhemispheric trends since the LGM, increasing in the Northern Hemisphere and decreasing in the Southern Hemisphere from the LGM to the early Holocene, then reversing towards the late Holocene. And we find that the meridional gradient in the amplitudes of temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Combining with the model outputs from transient simulations (Trace-21ka), we suggest that temperature seasonality of the west Pacific warm pool appears to be controlled solely by precession, and shows no evident response to changes in global ice volume and atmospheric CO₂ levels. According to our reconstruction, if proxies from tropical-subtropical oceans tended to record warm season temperature changes as proposed by previous studies, they would cause the ‘Thermal Maximum’ phenomenon during the early-mid Holocene.