Northwestern Borneo Research Articles

Precis hedonia LINNE from Northwestern Borneo, with the description of a new subspecies

Precis hedonia LINNE from Northwestern Borneo, with the description of a new subspecies

Genomic phylogeography of the endemic Mountain Black‐eye of Borneo (Chlorocharis emiliae): montane and lowland populations differ in patterns of Pleistocene diversification

AbstractAimOur understanding of population diversification in the lowlands of Sundaland has improved substantially over the last 20 years through phylogeographical study, but we know almost nothing about population diversification in the mountains of the region. Here, we apply genomic analysis and habitat modelling to the phylogeography of Chlorocharis emiliae, the Mountain Black‐eye, an endemic montane bird of Borneo with a sky‐island distribution, to investigate the structure and interconnectivity of its populations. In the process, we consider factors driving population diversification in the mountains versus lowlands on the island, and how population structure of C. emiliae compares with structure of previously studied lowland species.LocationBorneo.MethodsUsing RAD‐seq, we produced thousands of SNPs in 25 individuals from five sky‐island populations of C. emiliae. These populations represent the species entire range across Borneo. Genetic structure and species tree analyses were applied to measure population relationships and connectivity. Ecological niche modelling was used to estimate habitat distributions during current and LGM time periods.ResultsWe identified slight to moderate genetic distinctiveness among all populations. Based on demographic models, isolation with migration was the main pattern of divergence, and the most admixture occurred among three populations in north‐eastern Borneo: Kinabalu, Trus Madi and Murud. The most divergent population, Pueh, in north‐western Borneo, has low genetic diversity and a small effective population size, is geographically isolated and has diverged in isolation without notable gene flow. These results, based on a large genomic dataset, contradict the evolutionary relationships identified in an earlier mitochondrial DNA study.Main conclusionsGenomic phylogeographical comparisons indicate that diversification among sky‐island populations of C. emiliae was driven largely by distance and historical habitat distribution, resulting in isolation but also some inter‐population gene flow. During Pleistocene glacial events, cooler temperatures would have caused montane forest to descend and spread, thereby increasing connectivity among sky‐island populations. However, despite increased montane habitat, the north‐western population of Pueh remained isolated. This montane pattern contrasts with phylogeographical patterns in the Bornean lowlands, where populations often display evidence of vicariance followed by secondary contact.

Evolutionary and ecological forces influencing population diversification in Bornean montane passerines

The mountains of Borneo are well known for their high endemicity and historical role in preserving Southeast Asian rainforest biodiversity, but the diversification of populations inhabiting these mountains is poorly studied. Here we examine the genetic structure of 12 Bornean montane passerines by comparing complete mtDNA ND2 gene sequences of populations spanning the island. Maximum likelihood and Bayesian phylogenetic trees and haplotype networks are examined for common patterns that might signal important historical events or boundaries to dispersal. Morphological and ecological characteristics of each species are also examined using phylogenetic generalized least-squares (PGLS) for correlation with population structure. Populations in only four of the 12 species are subdivided into distinct clades or haplotype groups. Although this subdivision occurred at about the same time in each species (ca. 0.6–0.7Ma), the spatial positioning of the genetic break differs among the species. In two species, northeastern populations are genetically divergent from populations elsewhere on the island. In the other two species, populations in the main Bornean mountain chain, including the northeast, are distinct from those on two isolated peaks in northwestern Borneo. We suggest different historical forces played a role in shaping these two distributions, despite commonality in timing. PGLS analysis showed that only a single characteristic—hand-wing index—is correlated with population structure. Birds with longer wings, and hence potentially more dispersal power, have less population structure. To understand historical forces influencing montane population structure on Borneo, future studies must compare populations across the entirety of Sundaland.

Analysis of spatial patterns of daily precipitation and wet spell extremes in Southeast Asia

ABSTRACTThe study investigates the spatial distribution of extreme daily rainfall and wet spells in Southeast Asia (SEA) at annual, seasonal, and intraseasonal scales using 16 years of data from the Tropical Rainfall Measurement Mission. A detailed analysis is conducted using various indices that characterize exceedance probabilities and relative contribution of extremes to the total rainfall. The selected indices include the Gini index, which is a measure of overall inequality, and is employed for the first time to examine SEA rainfall characteristics. The favoured regions (hotspots) of rainfall extremes during each season are identified, and their linkages with terrain and seasonal winds discussed. The intraseasonal variability in rainfall extremes is investigated by focusing on different phases of the Madden–Julian Oscillation (MJO). At the annual scale, four main hotspots are observed, which are located off the coast of Myanmar, over eastern Indian Ocean, northwestern Borneo and over Philippines. A majority of indices shows considerable land–sea contrast, with lower values over land. Lower Gini index as obtained for land regions indicate that the rainfall distribution, and the relative contribution of each class to the total rainfall are more uniform over land compared to sea. The land–sea contrast in indices is stronger during boreal summer and winter, and weaker during boreal fall. During boreal spring, the Myanmar coast has high probability of extremes, which further increases during boreal summer. The most evident hotspot regions during boreal fall and winter are along the coast of Vietnam, and the eastern coast of Malay Peninsula, respectively. The wind‐terrain interactions play a crucial role in determining the location of most hotspots. In general, the impact of active (suppressed) MJO phases is to increase (decrease) the probability of extremes in the study domain. However, local scale departures from this general pattern are observed, which are discussed in this work.

An integrated study of geochemistry and mineralogy of the Upper Tukau Formation, Borneo Island (East Malaysia): Sediment provenance, depositional setting and tectonic implications

An integrated study using bulk chemical composition, mineralogy and mineral chemistry of sedimentary rocks from the Tukau Formation of Borneo Island (Sarawak, Malaysia) is presented in order to understand the depositional and tectonic settings during the Neogene. Sedimentary rocks are chemically classified as shale, wacke, arkose, litharenite and quartz arenite and consist of quartz, illite, feldspar, rutile and anatase, zircon, tourmaline, chromite and monazite. All of them are highly matured and were derived from a moderate to intensively weathered source. Bulk and mineral chemistries suggest that these rocks were recycled from sedimentary to metasedimentary source regions with some input from granitoids and mafic-ultramafic rocks. The chondrite normalized REE signature indicates the presence of felsic rocks in the source region. Zircon geochronology shows that the samples were of Cretaceous and Triassic age. Comparable ages of zircon from the Tukau Formation sedimentary rocks, granitoids of the Schwaner Mountains (southern Borneo) and Tin Belt of the Malaysia Peninsular suggest that the principal provenance for the Rajang Group were further uplifted and eroded during the Neogene. Additionally, presence of chromian spinels and their chemistry indicate a minor influence of mafic and ultramafic rocks present in the Rajang Group. From a tectonic standpoint, the Tukau Formation sedimentary rocks were deposited in a passive margin with passive collisional and rift settings. Our key geochemical observation on tectonic setting is comparable to the regional geological setting of northwestern Borneo as described in the literature.

Interannual Variation of the Cold-Season Rainfall Center in the South China Sea

During 15 November–31 December, a cold-season rainfall center appears in the southern part of the South China Sea (SCS) north of northwestern Borneo and juxtaposed along the southwest–northeast direction with rainfall centers for the Malay Peninsula and the Philippines. This SCS rainfall center also coincides geographically with the SCS surface trough. An effort is made to explore the formation mechanism of this rainfall center. It is primarily formed by the second intensification of heavy rainfall/flood cold surge vortex [CSV(HRF)] through its interaction with a cold surge flow over the SCS trough. Both the SCS rainfall center and the SCS surface trough are located at the easterly flow north of the near-equator trough. Modulated by the interannual variation of the cyclonic shear flow along the near-equator trough in concert with the El Niño–Southern Oscillation (ENSO) cycle, the SCS rainfall center undergoes an interannual variation. The impact of this ENSO cycle is accomplished through the regulation of CSV(HRF) trajectories originating from the Philippines vicinity and Borneo and propagating to different destinations. Rain-producing efficiency determined by the interannual variation of the divergent circulation accompanies the cyclonic shear flow around the near-equator trough in response to this ENSO cycle.

Genetic markers provide insight on origins of immature green turtles Chelonia mydas with biased sex ratios at foraging grounds in Sabah, Malaysia

An understanding of population dynamics is needed to assess the viability of migra- tory species. Monitoring of marine turtles at foraging grounds may detect changes in population trends that would take decades to be seen at nesting beaches. Mixed Stock Analysis using molec- ular markers provides a tool for estimating the origin of turtles sampled at foraging grounds. Here, we analysed mitochondrial DNA sequences of 90 immature green turtles at 2 foraging grounds in northwestern Sabah, Malaysia. We used data from 30 Indo-Pacific green turtle rookeries as the baseline for tracing the origin of turtles at the 2 foraging grounds. The inferred origins of turtles at the 2 locations were not different and indicated that the majority originated from 3 major popula- tions in Southeast Asia, the Turtle Islands of Sarawak in northwestern Borneo (29%), the Turtle Islands Heritage Protected Area (TIHPA) (28%) and Peninsular Malaysia (25%). Previous analy- ses indicated a 1:4 female-biased sex ratio at the foraging grounds, and based on our results, this largely reflects the use of unshaded beach hatcheries at some of the source rookeries for decades, which resulted in mostly female hatchlings. This result is supported by differences in the origins of male and female turtles. The result suggests a greater proportion of males originating from Peninsular Malaysia and fewer males originating from Sarawak and possibly the TIHPA com- pared to females. We discuss the implications of hatchery practices that influence sex ratios of hatchlings and recommend future research to improve the management of marine turtles in the region.

The first reported artificial propagation of yellow puffer,Xenopterus naritus(Richardson, 1848) from Sarawak, Northwestern Borneo

Pufferfish from family Tetraodontidae consists of 28 genera and 199 species worldwide, distributed in tropical and subtropical areas of Atlantic, Indian and Pacific Ocean (Nelson 1994). Some pufferfish species has become targeted species for aquaculture industry in various country including Japan, China, South Korea and Mexico. Reproductive biology of these valuable aquaculture species including tawny puffer (Shi, Zhang, Liu & Zang 2011), obscure puffer (Won, Kim & Park 2009; Kim, Dahms & Han 2013), tiger puffer (Wu, Tang, Yuan, Shi, Shakeela & Zhang 2015) and bullseye puffer (Sanchez, Alvarez-Lajonchere, Abdo De La Parra & Garcia 2008; Abdo-de La Parra, Garc�ia- Ortega, Mart�inez-Rodr�iguez, Gonz�alez-Rodr�iguez, Velasco-Blanco, Hern�andez & Duncan 2010) has been studied extensively for optimizing the production in aquaculture. In Sarawak coastal waters, there are 13 species of six genera of marine pufferfish species that has been reported (Vidthayanon 1998). Most of these species are non-target species in capture fisheries and has been considered as trash fish. However, there is one native pufferfish species that is widely consumed by the locals which is yellow puffer, X. naritus. Despite its lethality (Mohd Nor Azman, Samsur & Othman 2014), this species is considered as highly sought after delicacy due to the tenderness of their meat according to the locals.

Nitrous oxide and methane in two tropical estuaries in a peat-dominated region of northwestern Borneo

Abstract. Estuaries are sources of nitrous oxide (N2O) and methane (CH4) to the atmosphere. However, our present knowledge of N2O and CH4 emissions from estuaries in the tropics is very limited because data are scarce. In this study, we present first measurements of dissolved N2O and CH4 from two estuaries in a peat-dominated region of northwestern Borneo. Two campaigns (during the dry season in June 2013 and during the wet season in March 2014) were conducted in the estuaries of the Lupar and Saribas rivers. Median N2O concentrations ranged between 7.2 and 12.3 nmol L−1 and were higher in the marine end-member (13.0 ± 7.0 nmol L−1). CH4 concentrations were low in the coastal ocean (3.6 ± 0.2 nmol L−1) and higher in the estuaries (medians between 10.6 and 64.0 nmol L−1). The respiration of abundant organic matter and presumably anthropogenic input caused slight eutrophication, which did not lead to hypoxia or enhanced N2O concentrations, however. Generally, N2O concentrations were not related to dissolved inorganic nitrogen concentrations. Thus, the use of an emission factor for the calculation of N2O emissions from the inorganic nitrogen load leads to an overestimation of the flux from the Lupar and Saribas estuaries. N2O was negatively correlated with salinity during the dry season, which suggests a riverine source. In contrast, N2O concentrations during the wet season were not correlated with salinity but locally enhanced within the estuaries, implying that there were additional estuarine sources during the wet (i.e., monsoon) season. Estuarine CH4 distributions were not driven by freshwater input but rather by tidal variations. Both N2O and CH4 concentrations were more variable during the wet season. We infer that the wet season dominates the variability of the N2O and CH4 concentrations and subsequent emissions from tropical estuaries. Thus, we speculate that any changes in the Southeast Asian monsoon system will lead to changes in the N2O and CH4 emissions from these systems. We also suggest that the ongoing cultivation of peat soil in Borneo is likely to increase N2O emissions from these estuaries, while the effect on CH4 remains uncertain.

Characterizing forest structure variations across an intact tropical peat dome using field samplings and airborne LiDAR.

Tropical peat swamp forests (PSF) are one of the most carbon dense ecosystems on the globe and are experiencing substantial natural and anthropogenic disturbances. In this study, we combined direct field sampling and airborne LiDAR to empirically quantify forest structure and aboveground live biomass (AGB) across a large, intact tropical peat dome in Northwestern Borneo. Moving up a 4 m elevational gradient, we observed increasing stem density but decreasing canopy height, crown area, and crown roughness. These findings were consistent with hypotheses that nutrient and hydrological dynamics co-influence forest structure and stature of the canopy individuals, leading to reduced productivity towards the dome interior. Gap frequency as a function of gap size followed a power law distribution with a shape factor (λ) of 1.76 ± 0.06. Ground-based and dome-wide estimates of AGB were 217.7 ± 28.3 Mg C/ha and 222.4 ± 24.4 Mg C/ha, respectively, which were higher than previously reported AGB for PSF and tropical forests in general. However, dome-wide AGB estimates were based on height statistics, and we found the coefficient of variation on canopy height was only 0.08, three times less than stem diameter measurements, suggesting LiDAR height metrics may not be a robust predictor of AGB in tall tropical forests with dense canopies. Our structural characterization of this ecosystem advances the understanding of the ecology of intact tropical peat domes and factors that influence biomass density and landscape-scale spatial variation. This ecological understanding is essential to improve estimates of forest carbon density and its spatial distribution in PSF and to effectively model the effects of disturbance and deforestation in these carbon dense ecosystems.

Provenance and tectonic setting of Miocene siliciclastic sediments, Sibuti formation, northwestern Borneo

Provenance and tectonic setting of sandstone and mudstone units of the Miocene Sibuti Formation from northwest Borneo have been studied based on the mineralogy, major and trace element geochemistry data. The X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) data revealed that the sandstones and mudstones were abundant in quartz, pyrite, clay, and heavy minerals such as zircon, rutile, and some detrital cassiterite. Geochemically, the sandstones and mudstones are classified into quartz arenite, litharenite, sublitharenite, arkose, and wacke. Quartz arenites are enriched with SiO2, Zr, and Th and depleted in Al2O3, CaO, and other elements compared to other sandstone types, indicating high maturity and intensive weathering. Chemical index of alteration (CIA: 77–90), plagioclase index of alteration (PIA: 86–100), and A-CN-K diagram suggest intense weathering in the source area. Elemental ratios such as La/Sc, Th/Sc, Cr/Th, La/Co, and Th/Co are similar to sediments derived from the felsic rocks. Also, the provenance discrimination diagrams suggest recycled continental nature of these clastic sediments which are mostly derived from metasedimentary source (Rajang Formation). Discriminant-function diagram for the tectonic discrimination of siliciclastic sediments revealed that the sediments of Sibuti Formation were derived from a collision zone, which is consistent with the geology of the study area.

A new species of Neostethus (Teleostei; Atherinomorpha; Phallostethidae) from Brunei Darussalam, with comments on northwestern Borneo as an area of endemism

A new species of Neostethus (Teleostei; Atherinomorpha; Phallostethidae) from Brunei Darussalam, with comments on northwestern Borneo as an area of endemism

Low energy, low latitude wave-dominated shallow marine depositional systems: examples from northern Borneo

The depositional environments of the wave-dominant successions in the middle to late Miocene Belait and Sandakan Formations in northwestern and northern Borneo, respectively, were determined based on grain size distributions, sedimentary structures and facies successions, as well as trace and microfossil assemblages. Generally, progradational shoreface successions in the Belait Formation were deposited in very low wave energy environments where longshore currents were too weak to generate trough cross-bedding. Shoreface sands are laterally continuous for several km and follow the basin contours, suggesting attached beaches similar to the modern Brunei coastline. In contrast, trough cross-bedding is common in the coarser Sandakan Formation and back-barrier mangrove swamp deposits cap the progradational succession as on the modern northern Dent Peninsula coastline, indicating barrier development and higher wave energy conditions than in the Belait Formation. The Borneo examples indicate that barrier systems that include significant tidal facies form under higher wave energy conditions than attached beaches with virtually no tidal facies. Also, Borneo’s low latitude climate promotes back-barrier mangrove which reduces tidal exchange and reduces tidal influence relative to comparable temperate climate systems. The results of the study indicate that depositional systems on low energy, wave-dominated coasts are highly variable, as are the sand bodies and facies associations they generate.

A 48,000 year record of swiftlets (Aves: Apodidae) in North-western Borneo: Morphometric identifications and palaeoenvironmental implications

This paper reports the results of an analysis of 508 sub-fossil carpometacarpi of swiftlets (Aves: Apodidae) recovered during archaeological excavations of the Great Cave of Niah in Sarawak, North-western Borneo. The bones date from 48kyBP (ky BP: 103 calibrated years before present [1950]) to 0.35kyBP and provide a means to consider populations of birds (of which one species is a significant commercial interest) in the context of environmental and climatic change in the past, and their responses to recent anthropogenic landscape changes in the present.Biometric analyses and comparative data indicate that the collection contained specimens attributable to the three extant species of swiftlet that currently inhabit the Great Cave: the black-nest swiftlet (Aerodramus maximus), mossy-nest swiftlet (Aerodramus salanganus) and the white-bellied swiftlet (Collocalia esculenta). A subset of 267 identified specimens provides a time series that suggests that the Great Cave and environs have sustained populations of these three species throughout last 48,000years. While changes in the wing length of extant species of swiftlet are known as a function of geographical and altitudinal range, statistical testing of a single character (greatest length of the carpometacarpus) did not indicate changes in wing length in any of the identified species.The findings indicate that the local environs maintained a sufficient abundance of aerial arthropods to support populations of these obligate insectivores and are consistent with studies that suggest that the structural diversity of forest habitats was maintained throughout the late Pleistocene (48kyBP to 11.6kyBP) and Holocene (11.6kyBP to 0.35kyBP). The findings also provide context for the recent declines of the commercially-significant black-nest swiftlet and suggest that this species may be ill-equipped to adapt to recent anthropogenic deforestation of the Niah area.

Cypriniformes of Borneo (Actinopterygii, Otophysi): An Extraordinary Fauna for Integrated Studies on Diversity, Systematics, Evolution, Ecology, and Conservation

Borneo Island is governed by the countries of Brunei Darussalam, Malaysia (Sabah and Sarawak) and Indonesia(Kalimantan) and is part of Sundaland. These countries have a high diversity of freshwater fishes, especially describedand undescribed species of Cypriniformes; together these species and other flora and fauna represent an extraordinaryopportunity for worldwide collaboration to investigate the biodiversity, conservation, management and evolution ofBorneo’s wildlife. Much of the fauna and flora of Borneo is under significant threat, warranting an immediate and swiftinternational collaboration to rapidly inventory, describe, and conserve the diversity. The Sunda drainage appears to havebeen an important evolutionary centre for many fish groups, including cypriniforms (Cyprinidae, Balitoridae andGyrinocheilidae); however, Northwestern Borneo (Brunei, Sabah and Sarawak) is not connected to Sundaland, and thisdisjunction likely explains the non-homogeneity of Bornean ichthyofauna. A previous study confirmed that northernBorneo, eastern Borneo and Sarawak shared a similar ichthyofauna, findings that support the general hypothesis forfreshwater connections at one time between western Borneo and central Sumatra, and south Borneo and Java island.Borneo is drained by five major rivers: (1) Rajang and Baram rivers in Sarawak, and (2) Kapuas, Mahakam and Baritorivers in Kalimantan. The Cypriniformes is the most diverse clade in Borneo, and it is represented by at least 285 speciesin 55 genera and eight major clades (Balitoridae, Cobitidae, Cyprinidae, Gyrinocheilidae, Leptobarbidae, rasborines,cultrines and Paedocyprididae); at least 147 (52%) of these species are endemic to the incredibly diverse habitats ofBorneo. Most fish faunal studies in Borneo have involved inventory and discovery; however, none to date have focusedtheir efforts on the great biodiversity and systematics of Cypriniformes. In this paper we briefly discuss the generalbiodiversity of cypriniforms in Borneo, including recent revisions to the classification of the order through theCypriniformes Tree of Life and Planetary Biodiversity Inventory efforts supported by the USA NSF basic scienceinitiatives, in conjunction with researchers in countries of Borneo. It is our hope that this particular summary willgalvanize individuals to increase worldwide collaborative and integrated efforts on the biodiversity of Cypriniformes,and incite lively discussions among a broad array of interested parties, including those involved in the recent and critically important “Heart of Borneo” initiative funded by all these countries and some NGOs.

Decadal variability of chlorophyll a in the South China Sea: a possible mechanism

Four climatologies on a monthly scale (January, April, May and November) of chlorophyll a within the South China Sea (SCS) were calculated using a Coastal Zone Color Scanner (CZCS) (1979-1983) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (1998-2002). We analyzed decadal variability of chlorophyll a by comparing the products of the two observation periods. The relationships of variability in chlorophyll a with sea surface wind speed (SSW), sea surface temperature (SST), wind stress (WS), and mixed layer depth (MLD) were determined. The results indicate that there is obvious chlorophyll a decadal variability in the SCS. The decadal chlorophyll a presents distinct seasonal variability in characteristics, which may be as a result of various different dynamic processes. The negative chlorophyll a concentration anomaly in January was associated with the warming of SST and a shallower MLD. Generally, there were higher chlorophyll a concentrations in spring during the SeaWiFS period compared with the CZCS period. However, the chlorophyll a concentration exhibits some regional differences during this season, leading to an explanation being diffi cult. The deepened MLD may have contributed to the positive chlorophyll a concentration anomalies from the northwestern Luzon Island to the northeastern region of Vietnam during April and May. The increases of chlorophyll a concentration in northwestern Borneo during May may be because the stronger SSW and higher WS produce a deeper mixed layer and convective mixing, leading to high levels of nutrient concentrations. The higher chlorophyll a off southeastern Vietnam may be associated with the advective transport of the colder water extending from the Karimata Strait to southeastern Vietnam.

Phallostethus cuulong, a new species of priapiumfish (Actinopterygii: Atheriniformes: Phallostethidae) from the Vietnamese Mekong

A new species of priapiumfish, Phallostethus cuulong, is described based on nine specimens collected from the Vietnam-ese Mekong. This is the third species of the genus, following the type species P. dunckeri (from Malay peninsula) and P.lehi (from northwestern Borneo), and distinguished from them by having: seven serrae on the second ctenactinium in adultmales (vs. five in P. dunckeri and eight in P. lehi); 25–26 caudal vertebrae (vs. 27 in P. dunckeri and 28 in P. lehi); approx-imately 5–19 teeth on paradentary (vs. 15–20 and 28 or more in P. dunckeri and P. lehi, respectively). All six examinedmales are dextral (vs. one and two known males are sinistral and dextral respectively in P. dunckeri, and all four knowmales are sinistral in P. lehi). Sexual dimorphism is also found in the number of precaudal vertebrae, i.e., 13–14 in males and 11–12 in females (vs. sexual dimorphism is not found in number of precaudal vertebrae of P. dunckeri and P. lehi).

The Paleo-Orientations of Northwestern Borneo and Adjacent South China Sea Basins

DOI: 10.17014/ijog.v7i2.136Limited paleomagnetic data from West Kalimantan and southwestern Sarawak appear to indicate counter-clockwise (CCW) rotation of over 50 degrees during Cenozoic. On the other hand, similar studies from Sabah show conflicting results in terms of paleo-positions. This CCW information and other plate tectonic considerations have formed the base of Southeast Asia’s plate reconstructions that have seen print in a number of updated versions. The existing publications on extensive field and exploration data, including geological stress fields from wellbore breakouts, on northwestern Borneo and basins of South China Sea have not been taken into account. The latter wealth of information already established that the region under discussion consists of a mosaic-like assemblage of diverse tectono-stratigraphic terranes, each with separate tectonic development. Stress fields changed in different ways in the different terranes indicating definitively that regional, progressive CCW rotation of Borneo is not possible.

The Paleo-Orientations of Northwestern Borneo and Adjacent South China Sea Basins

The Paleo-Orientations of Northwestern Borneo and Adjacent South China Sea Basins

Assessment of atmospheric impacts of biomass open burning in Kalimantan, Borneo during 2004

Biomass burning from the combustion of agricultural wastes and forest materials is one of the major sources of air pollution. The objective of the study is to investigate the major contribution of the biomass open burning events in the island of Borneo, Indonesia to the degradation of air quality in equatorial Southeast Asia. A total of 10173 active fire counts were detected by the MODIS Aqua satellite during August 2004, and consequently, elevated the PM10 concentration levels at six air quality stations in the state of Sarawak, in east Malaysia, which is located in northwestern Borneo. The PM10 concentrations measured on a daily basis were above the 50μgm−3 criteria as stipulated by the World Health Organization Air Quality Guidelines for most of the month, and exceeded the 24-h Recommended Malaysian Air Quality Guidelines of 150μgm−3 on three separate periods from the 13th to the 30th August 2004. The average correlation between the ground level PM10 concentrations and the satellite derived aerosol optical depth (AOD) of 0.3 at several ground level air quality stations, implied the moderate relationship between the aerosols over the depth of the entire column of atmosphere and the ground level suspended particulate matter. Multiple regression for meteorological parameters such as rainfall, windspeed, visibility, mean temperature, relative humidity at two stations in Sarawak and active fire counts that were located near the centre of fire activities were only able to explain for 61% of the total variation in the AOD.The trajectory analysis of the low level mesoscale meteorological conditions simulated by the TAPM model illustrated the influence of the sea and land breezes within the lowest part of the planetary boundary layer, embedded within the prevailing monsoonal southwesterlies, in circulating the aged and new air particles within Sarawak.