Hydroclimate Variability in the Western Pacific Warm Pool Over the Last 15 kyr

Abstract

The Western Pacific Warm Pool (WPWP) is the heat engine of the global climate system and has a major impact on the tropical hydroclimate, yet rainfall reconstructions from this core region remain scarce. Here, we present multi‐proxy hydroclimate reconstructions from marine sediment core GeoB17429‐2, recovered off the coast of northern Papua New Guinea (PNG). We integrate compound‐specific plant‐wax‐derived hydrogen and carbon isotopes with sediment element ratios over the past 15 ka together with isotope‐enabled Community Earth System Model 1.2 simulations. All our rainfall proxy records consistently document a distinct Middle Holocene (MH) dry interval (∼7–4 ka BP), expressed by enriched plant‐wax isotope values indicative of reduced rainfall, and low terrigenous input reflecting less riverine discharge. We suggest that the decrease in rainfall over northern PNG is related to more La Niña‐like conditions or alternatively a reduced frequency of El Niño during the MH time interval ∼7–4 ka BP. Principal component (PC1) analysis of precipitation‐sensitive proxy records across the Maritime Continent (MC) identifies a dominant hydroclimate mode characterized by contrasting rainfall pattern with dry conditions over northern PNG and southwestern regions concurrent with wetter conditions in Borneo and Sulawesi. This mode is strongly correlated with equatorial September insolation, demonstrating that insolation‐driven modulation of El Niño Southern Oscillation (ENSO)‐like variability could have controlled the Holocene rainfall patterns in the WPWP. Our results demonstrate the sensitivity of PNG rainfall to orbitally forced changes in ENSO‐like activity and Walker Circulation strength during the MH.