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Maritime Continent (MC) convection drives zonal and meridional climate modes, including the Australasian monsoon system, but its role in past global climate change remains uncertain. Here we use speleothem oxygen isotope () records from a latitudinal transect across the MC, and a new critically located record for southwest Sulawesi, Indonesia, to reconstruct spatial hydroclimate variability in the Australasian monsoon domain over the last 40,000 yr. Our results show that atmospheric convection in the core MC region was reduced from ∼40,000 to 12,000 yr ago and strengthened rapidly only after the inundation of shallow continental shelves in the region, well after the onset of deglaciation. Interestingly, the millennial-scale climatic impacts of North Atlantic Heinrich events are not evident in Sulawesi. Together with climate model simulations, we demonstrate that changes in deep atmospheric convection dominate glacial–interglacial hydroclimate over the MC, whereas latitudinal shifts in the mean location of the InterTropical Convergence Zone control rainfall patterns during abrupt climate changes. more...

Glacial–interglacial changes in atmospheric CO are generally attributed to changes in seawater carbon chemistry in response to large-scale shifts in the ocean’s biogeochemistry and general circulation. The Southern Ocean currently takes up more CO than any other and it is likely to have played a crucial role in regulating past atmospheric CO. However, the physical, biological and chemical variables that control ocean–atmosphere CO exchange during glacial–interglacial cycles are not completely understood. Here we use boron isotopes and carbon isotopes in planktonic foraminifera and an alkenone-based proxy of temperature to reconstruct seawater pH and CO partial pressure in sub-Antarctic surface waters south of Tasmania over the past 25,000 years, and investigate the mechanisms that regulate seawater CO. The new record shows that surface waters in this region were a sink for atmospheric CO during the Last Glacial Maximum. Our reconstruction suggests changes in the strength of the biological pump and the release of deep-ocean CO to surface waters contributed to the last deglacial rise in atmospheric CO. These findings demonstrate that variations in upwelling intensity and the distribution of Southern Ocean water masses in this sector played a key role in regulating atmospheric CO during the last glacial–interglacial cycle more...

Two thousand years ago, maritime trade flourished in Southeast Asia and archaeological excavations have revealed that Island Southeast Asia played an important role within developing trading networks. The sites of Sembiran and Pacung on the north coast of Bali, Indonesia, have produced a wide range of artifacts that demonstrate links to mainland and island Asia. Here, we examine faunal remains from these sites to assess the role that livestock played in north Bali diet and trade at that time. In addition to abundant pig (Sus cf. scrofa) remains, the sites yielded the earliest securely dated goat (Capra hircus) remains known from Southeast Asia. Moreover carbon, nitrogen, oxygen, and strontium stable isotope analyses of bone collagen and tooth apatite indicate that some of these goats were from a markedly different environment than the pig, human, and dog remains from the sites. It is likely that these goats were imported from a different region—possibly South Asia—where they fed on C4 plants such as millet. This provides evidence that livestock were included in regional exchange networks, and prompts the question as to why goat remains are absent from Mainland Southeast Asia archaeological sites despite their presence in South Asia, East Asia, and Island Southeast Asia. more...

A concerted effort has begun to gather and preserve archives of marine samples and descriptive data, giving scientists ready access to insights on ancient environments.

Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. Here we present a 2,000-year, multiproxy reconstruction of western Pacific hydroclimate from two speleothem records for southeastern Indonesia. The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between ~1000 and 1500 CE Conversely, an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between ~1500 and 1900 CE. Our findings, together with climate model simulations, highlight the likelihood that century-scale variations in tropical Pacific climate modes can significantly modulate radiatively forced shifts in global temperature. more...

Previous studies have analysed the age distributions of stalagmites harvested from multiple caves and inferred important palaeoclimate changes that explain stalagmite growth phases. However, stalagmites may grow over tens of thousands of years; thus, they are irreplaceable. The value of speleothems to science must be weighed against their potential and current aesthetic and cultural value. In this study, we show that some palaeoclimate information can be extracted from a cave system without the removal of stalagmites. Our case study is based on basal U–Th dates for 77 individual stalagmites from thirteen caves located in and around BantimurungBulusaraung National Park, southwest Sulawesi, Indonesia. The stalagmites grew during discrete intervals within the last ~530,000 years, and an analysis of their age distribution shows a first-order exponential decrease in the number of older stalagmites surviving to the present day. Further, this exponential relationship is observed in stalagmite populations around the world and is therefore likely to be a general cave phenomenon. Superimposed on the first-order exponential age distribution in southwest Sulawesi are positive anomalies in stalagmite growth frequency at 425–400, 385–370, 345–335, 330–315, 160–155, 75–70 and 10–5 ka, which are typically coincident with wet periods on Borneo. To explain this distribution, we present a simple model of stalagmite growth and attrition. A first-order trend is controlled by processes intrinsic to karst systems that govern the natural attrition of stalagmites. These processes are nearly constant over time and result in the observed exponential relationship of stalagmite basal ages. Second-order variation is controlled by changes in the rate of stalagmite generation caused by fluctuating climates, which is a well-known concept in the speleothem literature. Removal of the exponential baseline allows for better assessment of relative peak heights and basic palaeoclimate information to be i more...