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Pollen analysis has been conducted on a 90 cm gravity core taken from the Karimata Strait to reveal pollen facies in marine sediment and Late Holocene environmental changes in the central Sunda Shelf region. The core site is at 32 m water depth and located about 170 km northwest of Bangka Island. Indonesia. Ten samples were collected at 10 cm intervals through the core. The total number of pollen grains counted in the samples varies between very low (<50 grains) to abundant (>200 grains). High frequencies (50 - 70%) of mangrove pollen are found at 90 to 40 cm indicating that pollen facies in offshore marine sediment may be comparable with those in mangrove forest floor sediment. The core site has been in a neritic environment since its early deposition ca. 1.800 yr B.P. (~150 A.D.) when mangroves vastly grew on the tidal flats of the surrounding islands and they persisted to ca. 700 yr B.P. (~1,250 A.D.). In the middle of this period, a catastrophic event speculatively due to the 535 A.D. Krakatau eruption might have responsible for the decrease of mangroves and the disappearance of benthic foraminifers. The deposition of silicious materials (tephra) due to tins eruption might have provided an opportunity for benthic foraminifers to increase their population subsequently. From ca. 700 yr B.P. (~ 1.250 A.D.) mangroves declined, as indicated by lower frequencies of pollen grain in samples from 30 cm deep upward. It occurred simultaneously with the deposition of coarser sediment and the increase of benthic foraminifer abundance. Interplay of anthropogenic activities, strengthening ENSO cycle, and lowering erosion base level might have been responsible for these environmental changes. [ABSTRACT FROM AUTHOR]

Abstract: We present a precisely dated, multi-proxy stalagmite record from Liang Luar Cave, Flores (southeast Indonesia) that reveals a rapid increase in Indonesian monsoon rainfall at ∼9.5 ka. A “ramp-fitting” method for detecting statistically significant inflections in a time-series was applied to the stalagmite δ18O, Mg/Ca, and Sr/Ca profiles to quantify the precise timing and magnitude of an abrupt increase in monsoon strength over a period of ∼350 years. Previously published lake-level records from the monsoon-affected Australian interior show a sudden intensification of the Australian monsoon at ∼14 ka. However, our records indicate that monsoon intensification in Flores occured ∼4–5 kyr later. The timing of the monsoon shift in Flores is synchronous with the rapid expansion of rainforest in northeast Australia and regional freshening of the southern Makassar Strait which, under present-day conditions, is sensitive to monsoon variability. The freshening of southern Makassar was coeval with an abrupt ∼1.5 °C cooling in the upper thermocline of the Timor Sea ∼9.5 ka, indicative of reduced surface heat transport by the Indonesian Throughflow (ITF) when the Java Sea opened during postglacial sea-level rise. This suggests that the abrupt increase in monsoon rainfall on Flores was not due to a change in the ITF – because a decrease in rainfall would be expected to accompany cooler local sea surface temperatures (SSTs) – but rather by the sudden increase in ocean surface area and/or temperature in the monsoon source region as the Sunda Shelf flooded during deglaciation. We propose that it was the abrupt intensification of the monsoon through the late deglaciation that maintained the subsequent structure of the ITF following the flooding of the Sunda Shelf at ∼9.5 ka. [Copyright &y& Elsevier]

Aim The four Mentawai islands, south-west of Sumatra, have long been isolated from the remainder of Sundaland, resulting in a high level of endemism. We examined the distribution of 151 species of the Mentawai Islands in Sundaland and assessed various processes that may have resulted in the various biogeographical patterns. Location Southeast Asia, particularly the Mentawai Islands and nearby large landmasses (Sumatra, Java, Borneo and Peninsular Malaysia). Methods We compared the faunal composition of the Mentawai Islands for selected taxa (43 mammals, 92 reptiles and 16 amphibians) with that of the four nearby large landmasses of Sundaland using morphological comparisons and the most recent molecular phylogenetic analyses available in the literature. These comparisons yielded sister taxa, which were used to simulate species absence data for the four Sundaland landmasses under several scenarios to investigate how patterns of species absence could have arisen. Results In contrast to our expectations, several Mentawai species did not have their closest relatives on neighbouring Sumatra, but rather on the more distant Borneo, Java or Peninsular Malaysia. For mammals, the similarity between species from Mentawai and Borneo was greater than that observed between species from Mentawai and Sumatra. We conclude that the relationships represent traces of species historically distributed throughout Sundaland that became extinct in Sumatra during the Pleistocene. For reptiles and amphibians the observed pattern of species absences generally resembled the simulated pattern expected under the scenario of absence rates increasing with landmass isolation, whereas for mammals we observed more species than expected missing from Java and Sumatra, and fewer than expected from Borneo. Main conclusions The potential extinctions on Sumatra probably had two causes: changes of climate and vegetation during the Pleistocene and environmental impacts from the Toba supervolcanic eruption. [ABSTRACT FROM AUTHOR]

A high-precision relative sea level (RSL) record over the past 6400 years, reconstructed from fossil coral microatoll colonies, is reported for Natuna Island, Indonesia. The timing of 11 fossil microatolls from four sites on Natuna Island is constrained by replicate 14C and 230Th dates. We investigate the local marine reservoir correction (∆R) using the replicate dates. The two sets of dates become aligned if a Marine20 ∆R of −143 ± 176 yr, 1σ (Marine13 ∆R of 15 ± 63 yr) is assigned to the 14C dates. The distribution of microatoll ages and elevations indicates that RSL was relatively stable from 6400 to 1400 yr BP at 0.2–0.7 ± 0.4 m (2σ) higher than present, before a fall to current levels. A comparison with the predictions of a suite of glacial isostatic adjustment (GIA) models for Southeast Asia suggests refinements are needed in ice-history models to fully capture our RSL data. These new constraints on past RSL of the Sunda Shelf contribute to further calibration of GIA models in the tropics, where RSL data are presently insufficient. • High-resolution Holocene RSL proxy record developed for Natuna Island • Porites fossil microatoll elevations used as sea-level index points • Stable RSL from 6400 to 1400 yr BP at 0.2–0.7 ± 0.4 m (2σ) relative to present • Radiocarbon marine reservoir correction ∆R = −143 ± 176 yr (Marine20) for Natuna • No obvious time-dependency in ∆R over the period 6400 to 1400 yr BP [ABSTRACT FROM AUTHOR]

Due to its position between the highly distinct Oriental and Australasian biogeographical realms, much effort has been spent demarcating associated separations and transitions in the faunal assemblages of the Indo-Australian Archipelago. Initially, sharp boundary lines were proposed, with the earliest dating from the mid-1800s. Notably, the one published by Alfred R. Wallace in 1863, based upon land-mammal and land-bird distributions, has since achieved iconic status and today its significance is recognized well beyond the confines of the biogeography community. Over the next four decades many such divides were engraved onto plates and inked onto charts of SE Asia using additional information, different organisms or other criteria. However, it became apparent that, as Wallace had noted, all such lines were to some degree permeable, and by the 1880s transition zones were being put forward instead; the label 'Wallacea' was introduced in 1924. Interestingly, the last decade has seen new divides and sub-regions being proposed, some departing markedly from earlier offerings. Although currently there is general agreement regarding much of the terminology associated with both the lines and the areas, the record of publication indicates that this consensus has emerged obliquely, and in some cases is weakly founded. This review does not present new data nor new analyses; rather it summarizes the development of ideas and reflects upon attendant issues that have emerged. After reviewing the key proposals, recommendations are presented that should in future alleviate perceived difficulties or inadequacies. Reference to specific divides must be true to their original definitions; there are many instances where the secondary literature has portrayed them incorrectly and with some this has rippled through into later publications. Moreover, Wallace's 1863 line is not the one that he finally settled upon (in 1910); its path around Sulawesi was transferred from the west to the east of the Island. Ideally, Huxley's divide (1868) should carry his name rather than Wallace's; the latter never accepted the proposition. Lydekker's Line (1896) ought to be labelled the Heilprin-Lydekker Line in recognition of Angelo Heilprin's 1887 contribution. Concerning transition zones, ideally Wallacea should correspond to its original 1924 description, which incorporated the Philippine islands bar the Palawan group. Notably, though, a smaller form (introduced by Darlington in 1957, used frequently from 1998 onwards) in which all of the Philippine islands are excluded is entrenched within the recent literature, but this is often without evident justification. It should also be recognized that the 'reduced' (=southern) Wallacea area was effectively defined by Heilprin in 1887, but was then labelled the 'Austro-Malaysian Transition Zone'. Finally, the application in recent years of modern analytical techniques has not led to a consensus view on where the lines/areas should run/be placed; with such a large, diverse set of organisms, each with differing histories, this is perhaps not surprising., (© 2021 Cambridge Philosophical Society.)

Catastrophic events, such as volcanic eruptions, can have profound impacts on the demographic histories of resident taxa. Due to its presumed effect on biodiversity, the Pleistocene eruption of super-volcano Toba has received abundant attention. We test the effects of the Toba eruption on the diversification, genetic diversity, and demography of three co-distributed species of parachuting frogs (Genus Rhacophorus) on Sumatra. We generate target-capture data (~950 loci and ~440,000 bp) for three species of parachuting frogs and use these data paired with previously generated double digest restriction-site associated DNA (ddRADseq) data to estimate population structure and genetic diversity, to test for population size changes using demographic modelling, and to estimate the temporal clustering of size change events using a full-likelihood Bayesian method. We find that populations around Toba exhibit reduced genetic diversity compared with southern populations, and that northern populations exhibit a shift in effective population size around the time of the eruption (~80 kya). However, we infer a stronger signal of expansion in southern populations around ~400 kya, and at least two of the northern populations may have also expanded at this time. Taken together, these findings suggest that the Toba eruption precipitated population declines in northern populations, but that the demographic history of these three species was also strongly impacted by mid-Pleistocene forest expansion during glacial periods. We propose local rather than regional effects of the Toba eruption, and emphasize the dynamic nature of diversification on the Sunda Shelf., (© 2020 John Wiley & Sons Ltd.)