Palynomorph evidence for tropical climate stability in the Gulf of Papua, Papua New Guinea, over the latest marine transgression and highstand (14,500 years BP to today)

Abstract

Three sediment cores (MV-41, MV-46, and MD-50) from the Gulf of Papua (GoP), Papua New Guinea, were analyzed to assess changes in climatic, oceanographic, and sedimentological conditions over the last 14.5 kyr. Palynomorphs, which were isolated from sediment core samples, were collected at approximately 0.5-m intervals using a strong acid and oxidant (MD-50)/non-oxidant (MV-41, MV-46) procedure. Radiocarbon (14C) stable isotope geochronology, magnetic susceptibility, stable isotope analysis (MD-50 only; Oxygen-18 [18O] and Carbon-13 [13C]), and clay mineral maturity analysis were also completed for each core. Palynological data indicate that climatic conditions at sea level have remained warm, wet, and stable for the past 14.5 kyr with sea surface temperatures in the GoP above 14 °C. Potential decreases in vegetative cover marked the Younger Dryas interval (12.5–11.5 kyr BP), as indicated by reduced pollen and spore recovery. The end of the latest marine transgression (and the subsequent return to eustatic sea level highstand) is clearly delineated by increases in marine palynomorph recovery and decreases in mangrove pollen at approximately 5 kyr BP. An increase in seasonality and potential El Niño Southern Oscillation variability is observed in MD-50's oxygen isotope results at ∼5 kyr BP. This is not supported by the palynomorph record, likely because of the sampling interval and dilution by tropical pollen flora, which indicates stable climatic conditions throughout the last 14.5 kyr. Sediment transport pathways in the GoP remained fairly constant throughout the time interval, which is supported by the lack of major changes in palynomorph assemblage composition.