Solar modulation of the western tropical Pacific hydroclimate over the last ∼1200 years

Abstract

The western tropical Pacific hydroclimate variability of the last millennium has long been investigated but its forcing(s) are still disputed, e.g., solar activity and/or volcanic eruptions. To provide additional insight into the respective roles of the two drivers, we analyzed biomarkers of a sediment core at the Cattle Pond, Xisha Islands, South China Sea, to illuminate decadally-resolved changes of hydrological conditions over the last ∼1200 years. Multiple glycerol dialkyl glycerol tetraether (GDGT)-based records, including relative abundance of crenarchaeol to total isoprenoid GDGTs, branched and isoprenoid tetraether, ratio of archaeol to caldarchaeol and methane index, and n-alkanes collectively reveal a remarkable increase of water depth, exclusively resulting from local rainfall, during the Little Ice Age (ca. 1400–1850 CE). Furthermore, multidecadal-to centennial-scale variations of inferred rainfall appear to resemble the temporal features of solar irradiance changes, with increased rainfall at solar minima such as the Oort, Spörer and Dalton events, which, together with published paleorecords nearby, indicate solar control on the western tropical Pacific hydroclimate, although model simulations are still needed to further decipher its physical dynamics.