Glacial conditions in the northern Molucca Sea region (Indonesia)

Abstract

Palynological, planktonic foraminiferal and stable isotope data from a sediment core in the northern Mollucca Sea have been used to evaluate regional glacial climatic and hydrographic conditions. The palynological record shows that in glacial time the climate was drier than today, indicating a weakened influence of the northwesterly winds at that time. The drier climatic conditions at glacial time were associated with a higher lapse rate, which, together with a lower sea level, resulted in a large expansion of the Lower Montane oak forests on the nearby island of Halmahera. Glacial Mollucca Sea surface water salinities were probably higher than today, while glacial surface water temperatures might have been close to present-day values. The Deep Chlorophyll Maximum (DCM) layer in the northern Molucca Sea at glacial time was more productive and cooler than today, probably the result of the inflow of cooler and nutrient-enriched Subtropical Lower Water from the Pacific. The less asymmetrical high-latitude ice coverage at glacial time and the particularly strong increase in the pole to equator thermal gradient on the Northern Hemisphere, provides theoretical evidence that the Intertropical Convergence Zone (ITCZ) shifted equatorwards and oscillated over a more narrow latitudinal range than today. This inferred configuration of the ITCZ at glacial time, however, fails to explain the observed increased aridity in the study area at that time. We propose, therefore, that the drier glacial climatic conditions are related to a possible disturbance in the El Niño Southern Oscillation (ENSO) system.