History of the South Java Current over the past 80 ka

A sediment core located below the present South Java Current (SJC) was used to reconstruct paleoclimate and paleoceanography on the basis of biogenic and terrigenic proxy-records. The core spans the past 80 ka of environmental change and shows considerable contrasts from the glacial to the Holocene. Presently, the core site is situated beneath a seasonally varying low-salinity tongue which is advected from the Java Sea via the Sunda Strait. It carries terrigenous matter of a characteristic signature. During the last glacial period (stage 4-2), when sea level was lower than during the Holocene, the Sunda Strait was closed and the terrigenous supply from that source ceased. As the core site is close to the equator, our results indicate that atmospheric and oceanographic circulation was alternatively dominated by the Northern Hemisphere East Asian Monsoon system and the Southern Hemisphere Australian Monsoon system. Between 20 and 12 ka, the (Australian) SE Winter Monsoon reached its maximum and intensified the westward flowing SJC. Increased mixing of the surface waters led to a slight rise in paleoproductivity. A similar but much weaker situation prevailed from 74 to 70 ka. During most of the glacial period, from 70 to 20 ka, strong northeasterly winds associated with the East Asian Winter Monsoon intensified the Indian Monsoon Current and the eastward flowing SJC, and may have also carried dust across the equator to our core site. During this glacial phase, populations of the giant diatom Ethmodiscus rex were thriving and may indicate a reduced deep and intermediate thermohaline circulation at the site. The monsoonal system as we know it today, with distinct dry and wet seasons, may not have been active before ∼ 12 ka.