History of the South Java Current over the past 80 ka

Abstract

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 V12 ka. ß

Past Human Activity and Geomorphological Change in a Guano-Rich Tropical Cave Mouth: Initial Interpretations of the Late Quaternary Succession in the Great Cave of Niah, Sarawak

“…The present limited evidence points to relatively dry conditions, perhaps with the influx of loess, but with no clear indications of episodic local wetness. This provisional reconstruction may again conform with the predictions of greater aridity and marked airflow from the north (Gingele et al 2002;Kershaw et al 2001;Sun et al 2000). There are no clear indications of either greater local wetness or greater moisture stress associated with the relative proximity of the ocean to Niah.…”

“…However, Sun et al (2000) and Kershaw et al (2001) have suggested that northeast Borneo, which would include Niah, might have been notably and consistently wetter than much of the rest of Sundaland during the LGM because of the relative proximity of the ocean and the inferred strengthening of the winter monsoon (Gingele et al 2002). Increased seasonality of climate around Niah during the last glaciation would have resulted.…”

“…Increased seasonality of climate around Niah during the last glaciation would have resulted. Farther to the northwest, more open vegetation and aridity dominated the extensive coastal plain, perhaps associated with the input of abundant Artemisia pollen and loess from central Asia (Gingele et al 2002;Sun et al 2000). Such regional climatological and oceanographic concepts underpin arguments that the "coastal" lands of north and northwest Borneo, including Niah, may have remained sufficiently humid to have been a refugium for lowland rainforest during the late Pleistocene (Brandon-Jones 1998; Gathorne-Hardy et al 2002;Kershaw et al 2001).…”

Southern Hemisphere control on Australian monsoon variability during the late deglaciation and Holocene

“…2). Biogenic and terrigenous proxy records in a core from the northwestern Timor Sea (off South Java), located below the present South Java Current initially indicated that dry conditions with weak monsoonal rainfall and intensified SE trades persisted until B12 ka at that location 21 . However, recent investigations in the same area revealed a more complex pattern with an earlier onset of wet monsoon conditions during the B-A (B15-13 ka), interrupted by a brief period of intensified trade winds and dry conditions during the YD (B13-12 ka) before a second sustained increase from B12 ka onwards 14 (Fig.…”

A Biogeographic Synthesis of the Amphibians and Reptiles of Indochina

“…At the Last Glacial Maximum (LGM; 18,000 years ago) the winter monsoon strengthened and the summer monsoon weakened; as a result rainfall over the Sunda Shelf may have been 30%-50% lower than present levels. Temperatures were reduced by as much as 6-7uC, and sea levels withdrew to a maximum of 120 m below current levels Kershaw et al, 2001;Gingele et al, 2002;Bird et al, 2005); however, there is evidence that despite being cooler the climate was not significantly less humid .…”