Northwestern Borneo Research Articles

The mountain giant rat of Borneo Sundamys infraluteus (Thomas) and its relations

The genus Sundamys comprises the species Sundamys muelleri, Müller‟s rat, which is widespread in the Sundaic biogeographical subregion, and three other taxa, the mountain giant rats of Borneo S. infraluteus, Java S. maxi and Sumatra S. atchinensis. Nine additional specimens of the Borneo Mountain giant rat are reported, and one field record, adding new locations to the known range of the species in the Crocker Range, notably the vicinity of Gn. Alab, and Gn. Lumaku, Sabah, and at Pa Raye, Kalimantan Utara. Measurements of the specimens, and the first from Gn. Mulu, Sarawak, are tabulated with previously published data. Trapping results indicate that this rat is confined to an altitudinal range, 900 – 2350 m, broadly corresponding with the limits of Lower Montane Forest, especially Oak-Laurel forests, and that it occurs both in pristine habitat and in disturbed forests. The topography of the uplands of northern Borneo provides connections between all locations except Mulu, which is surrounded by lowlands. A review of palaeoecological interpretations indicates that favourable habitat for this rat was more extensive in north-western Borneo in the terminal Pleistocene, but may have been more reduced than at present during warm episodes of the Holocene. Consideration of palaeo-environments in the Sundaic subregion suggests that there may have been no genetic contact between mountain giant rats of Sumatra and Borneo during the Quaternary. Although molecular evidence is lacking, it is reasonable to treat Sundamys infraluteus, S. atchinenesis and Sundamys maxi as distinct species, arising independently by vicariant evolution from a Pliocene ancestry.

A major Miocene deepwater mud canopy system: The North Sabah–Pagasa Wedge, northwestern Borneo

Abstract Three-dimensional seismic reflection data, well data, and analogues from areas with extensive shale tectonics indicate that the enigmatic deepwater “shale nappe or thrust sheet” region of northern offshore Sabah, Malaysia, now referred to as the North Sabah–Pagasa Wedge (NSPW), is actually a region of major mobile shale activity characterized by mini-basins and mud pipes, chambers, and volcanoes. A short burst of extensive mud volcano activity produced a submarine mud canopy complex composed of ~50 mud volcano centers (each probably composed of multiple mud volcanoes) that cover individual areas of between 4 and 80 km2. The total area of dense mud canopy development is ~1900 km2. During the middle Miocene, the post-collisional NSPW was composed predominantly of overpressured shales that were loaded by as much as 4 km thickness of clastics in a series of mini-basins. Following mini-basin development, there was a very important phase of mud volcanism, which built extensive mud canopies (coalesced mud flows) and vent complexes. The mud canopies affected deposition of the overlying and interfingering deposits, including late middle to early late Miocene deepwater turbidite sandstones, which are reservoirs in some fields (e.g., Rotan field). The presence of the extensive mud volcanoes indicates very large volumes of gas had to be generated within the NSPW to drive the mud volcanism. The Sabah example is only the second mud canopy system to be described in the literature and is the largest and most complex.

Diversity and Depth Distribution of Modern Benthic Foraminifera Offshore Brunei Darussalam

ABSTRACT The distribution of modern benthic foraminifera is studied from offshore mixed carbonate-siliciclastic settings of Brunei Darussalam located in northwestern Borneo (South China Sea). The sediments were collected from 17 sites (i.e., shallow reefs, sunken wrecks, and two depth transects). A total of 231 species were identified from 8 to 63 m water depth. We conducted several analyses to understand the patterns of faunal composition, including: (1) Cluster analysis and Principal Component Analysis together with correlation to define relation among the sites; (2) Diversity indices, such as Shannon Index and Fisher's Alpha Index to assess diversity patterns at sites; and (3) Foram Index (FI) to determine whether the water quality indicates conditions that support reef growth. The most abundant foraminiferal groups from the reef and most wreck samples are larger benthic foraminifera (LBF), especially Calcarinidae and Amphisteginidae, whereas in the muddier sites the most abundant are smaller benthic foraminifera (SBF) with the genera Pseudorotalia and Asterorotalia. Certain species from the groups have shown patterns that do or do not correlate with depth and clay content.

Rare homozygous PRKN exon 7 duplication in a Ibanese patient from Northwestern Borneo with young onset Parkinson’s disease

We describe the clinical features of a Sarawakian man of Ibanese ethnicity with young-onset Parkinson’s disease (PD), who carried a very rare homozygous PRKN exon 7 duplication. Truncal dystonia was a prominent feature on presentation, in addition to classical parkinsonian motor features. This report adds to the very limited literature on monogenic causes of PD in Southeast Asia and specifically the indigenous group in the Borneo region.

Rising dissolved organic carbon concentrations in coastal waters of northwestern Borneo related to tropical peatland conversion.

Southeast Asia’s peatlands are considered a globally important source of terrigenous dissolved organic carbon (DOC) to the ocean. Human disturbance has probably increased peatland DOC fluxes, but the lack of monitoring has precluded a robust demonstration of such a regional-scale impact. Here, we use a time series of satellite ocean color data from northwestern Borneo to show that DOC concentrations in coastal waters have increased between 2002 and 2021 by 0.31 μmol liter−1 year−1 (95% confidence interval, 0.18 to 0.44 μmol liter−1 year−1). We show that this was caused by a ≥30% increase in the concentration of terrigenous DOC and coincided with the conversion of 69% of regional peatland area to nonforest land cover, suggesting that peatland conversion has substantially increased DOC fluxes to the sea. This rise in DOC concentration has also increased the underwater light absorption by dissolved organic matter, which may affect marine productivity by altering underwater light availability.

Prevalence of chloramphenicol-resistant gene in Escherichia coli from water sources in aquaculture farms and rivers of Kuching, Northwestern Borneo

Antibiotic resistant Escherichia coli cases are increasing high especially in Southeast Asia. Illegal use of the antibiotic in the aquaculture farming may become the culprit of the outbreak and spread into environmental source. A study was conducted to: 1) detect the chloramphenicol (CAL)-resistant gene in E. coli isolated from three aquaculture farms and six rivers of northwestern Borneo and 2) investigate the correlation between cat gene with five common antibiotics used. Isolation of E. coli was done on Eosin methylene blue agar and characterized using indole, methyl red, Voges-Proskauer, citrate tests. E. coli isolates were subsequently tested for their susceptibility to five antibiotics commonly used in aqua-farming. The CAL-resistant E. coli were further analyzed for the presence of resistant genes (cat I, cat II, cat III, cat IV) using multiplex polymerase chain reaction. 42 bacterial colonies were isolated from a total of 80 individual water samples, 34 of which were identified as E. coli. Result showed 85.3% of the E. coli isolates were resistant to amoxicillin, 35.3% were resistant to tetracycline, 29.4% were resistant to CAL, 17.6% were resistant to nitrofurantoin and 8.8% were resistant to nalidixic acid. All of the 10 CAL resistant E. coli isolateswere detected with cat II genes; five isolates detected with cat IV genes; three isolates detected with cat III genes; and another two detected with cat I genes. Pearson correlation coefficient shows highly significant relationship between resistance pattern of CAL with amoxicillin; and CAL with tetracycline. Our findings provide the supplementary information of the CAL resistance gene distribution, thereby improving our understanding of the potential risk of antibiotic resistance underlying within this microbial ecosystem.

Cretaceous Forearc Sedimentation and Contemporary Basin Tectonics in Northwestern Borneo: New Sedimentological Insights from Pedawan Formation, Kuching Zone, East Malaysia

Sedimentary successions developed at the destructive plate margin settings are extremely important as they bear valuable record of contemporary basin tectonics and consequent sedimentation. Intense deformation and metamorphism often obliterate the primary sedimentary texture and structures of the sedimentary successions formed at destructive plate margins. However, sedimentological analysis of young unmetamorphosed forearc successions provides rare opportunity to infer the interplay between tectonics and sedimentation. Therefore, a process-based sedimentological facies analysis and provenance studies of the Cretaceous Pedawan Formation in the Kuching Zone, Borneo, have been undertaken for the first time. The sandstones are compositionally and texturally immature. They are normally graded with sole marks and have erosional lower contacts with mudstones and generally have gradational upper contacts. The massive sandstones, parallel-laminated sandstones, and the combination of rippled sandstones with thin mudstones are interpreted as turbidites. The lack of wave-generated structures, including hummocky cross stratification, indicates that deposition took place below storm wave base, possibly in a shelf setting. The lower part of the Pedawan Formation is mudstone dominated, and the upper part progressively becomes sandstone dominated. The Pedawan Formation bears several penecontemporaneously deformed horizons sandwiched between laterally persistent undeformed beds. Deformation structures include folds with reclined to recumbent geometry and layer-confined normal and reverse faults. We have interpreted these deformed horizons as seismites. Modal analyses of the sandstones indicate recycled orogenic as well as arc provenance and thus indicate mixing of recycled orogenic sediments with arc-derived volcanic material. The sedimentary facies characteristics of the Pedawan Formation in combination with numerous penecontemporaneous deformation features at selected stratigraphic levels indicate that the turbidites formed in a seismically active deepwater depositional setting as part of a long-lived subduction complex in eastern Sundaland during which several crustal fragments were accreted to Borneo.

New herpetofaunal records from Gunung Mulu National Park and its surrounding areas in Borneo

Gunung Mulu National Park (GMNP) in northwestern Borneo is marked by high species diversity and diverse environments. We present one new amphibian and ten new reptile records from GMNP and its surrounding area. In the records, Asthenodipsas jamilinaisi and Garthius chaseni were newly recorded in the Sarawak State. We also present the first record of Cyrtodactylus muluensis from outside of GMNP and the second record of Opisthotropis typica from the park. Combined with previous information, a total of 108 amphibians and 104 reptiles are known from GMNP, and their preferred habitat types are diverse. Furthermore, observed male-male combat of Dopasia buettikoferi is the first detailed description of the genus. Two color morphs of D. buettikoferi had an identical ND2 haplotype and appeared to be the same species. The present study provides new information about Bornean amphibians and reptiles, and also emphasizes the importance of continuous monitoring.

New tribe, new genera, and new species of the family Issidae (Hemiptera: Fulgoroidea) from Southeastern Asia and New Guinea, with notes on morphology and evolution of the family

Eupilisini trib. nov. is erected for the genera Eupilis Walker, 1857, Gabaloeca Walker, 1870, Syrgis Stål 1870, and Bornepilis gen. nov. (type species: Bornepilis longipennis sp. nov.) in the subfamily Issinae of the family Issidae. Bornepilis longipennis sp. nov. is described from Sabah State of Malaysia in northern Borneo. Two new species of the genus Eupilis are described from northwestern Borneo – E. borneoensis sp. nov. and E. walkeri sp. nov. Eupilis hyalinocosta Melichar, 1914 is redescribed and together with E. rubrovenosa Melichar, 1914 is transferred to Bornepilis gen. nov. Eupilis albilineola Walker, 1857, E. hebes Walker, 1857, and Gabaloeca retifera Walker, 1870 are redescribed. Eupilis nigrinervis Stål, 1870 is redescribed and transferred to the genus Gabaloeca. Three new combinations are formed: Bornepilis hyalinocosta (Melichar, 1914), comb. nov., B. rubrovenosa (Melichar, 1914), comb. nov., and Gabaloeca nigrinervis (Stål, 1870), comb. nov. Paguinella ramosa gen. et sp. nov. is described from the canopies of Madang Province in Papua New Guinea. This new genus is closely related to New Guinean genus Papunega Gnezdilov et Bourgoin, 2015, but well distinguished by ventral aedeagal hooks each with two long branches and wide neck of capitulum of style. Morphology of hind wing and male genitalia of the members of issid tribes Eupilisini trib. nov., Issini, Sarimini, Chimetopini, and Kodaianellini are discussed and illustrated in accordance to evolution and historic distribution of the family Issidae from southeastern Asia to America and tropical Africa. New data on distribution of Bornepilis hyalinocosta and Gabaloeca nigrinervis in the Philippines are given.

Chemical characteristics of rainwater in the tropical rainforest region in northwestern Borneo

A comprehensive study of the chemical composition of rainwater was carried out from October 2016 to September 2017 in the equatorial tropical rainforest region of northwestern Borneo. Monthly cumulative rainwater samples were collected from different locations in the Limbang River Basin (LRB) and were later categorized into seasonal samples representing northeast monsoon (NEM), southwest monsoon (SWM), and inter-monsoon (IM) periods. Physical parameters (pH, EC, TDS, DO, and turbidity), major ions (HCO3-, Cl-, Ca2+, Mg2+, Na+, and K+) and trace metals (Co, Ni, Cd, Fe, Mn, Pb, Zn, and Cu) were analyzed from collected rainwater samples. Rainwater is slightly alkaline with mean pH higher than 5.8. Chloride and bicarbonate are the most abundant ions, and the concentration of major ions in seasonal rainwater has shown slight variation which follows a descending order of HCO3-> Cl-> Na+ > Ca2+ > Mg2+ > K+ in NEM and Cl- > HCO3- > Na+ > Ca2+ > K+ > Mg2+ in SWM and Cl- > HCO3- > Na+ > Ca2+ > Mg2+ > K+ in IM period. Trace metals such as Fe and Ni have shown dominance in seasonal rainwater samples, and all the metals have shown variation in concentration in different seasons. Variation in chemical characteristic of seasonal rainwater samples identified through piper diagram indicates dominance of Ca2+-Mg2+-HCO3- and mixed Ca2+-Mg2+-Cl- facies during NEM, SWM, and IM periods. Statistical analysis of the results through two-way ANOVA and Pearson's correlation also indicates significant variation in physico-chemical characteristics. This suggests a variation in contributing sources during the monsoon seasons. Factor analysis confirmed the source variation by explaining the total variance of 79.80%, 90.72%, and 90.52% with three factor components in NEM, SWM, and IM rainwater samples with different loading of parameters. Enrichment factor analysis revealed a combined contribution of marine and crustal sources except K+ which was solely from crustal sources. Sample analysis of backward air mass trajectory supports all these findings by explaining seasonal variation in the source of pollutants reaching the study area. Overall, the results show that the chemical composition of seasonal rainwater samples in LRB was significantly influenced by natural as well as anthropogenic processes. These include (long-range and local) industrial activities, fossil fuel combustion, forest burning, transportation activities including road transport and shipping activities, and land-derived soil dust along with chemical constituents carried by seasonal wind.

Early life history of yellow puffer, Chonerhinos naritus (Richardson, 1848) from Sarawak, Northwestern Borneo

The growth and morphological development including fins, spine distribution and pigmentation of larval and juvenile of hatchery‐reared yellow puffer, Chonerhinos naritus were described to provide essential information on the early life history of this species. The total length (TL) of newly hatched larvae was 3.42 ± 0.23 (mean ± SD) mm, reaching 5.66 ± 0.38 mm on 5 days after hatched (DAH), 7.80 ± 0.28 mm on 11 DAH, 9.88 ± 0.40 mm on 27 DAH and 10.92 ± 0.58 mm on 30 DAH. The yolk was completely absorbed in preflexion larvae at 4 DAH. The mouth opening started at 3 DAH of yolk sac larvae, while the teeth appeared starting from preflexion larvae at 7 DAH. Overall aggregate fin ray numbers including caudal fin attained full complement in postflexion larvae at 27 DAH. Several melanophores with appearance of small stellate were first appeared dorsally on the head of flexion larvae at 13 DAH, expanded at the dorsal region of the head, above the eye in juveniles at 30 DAH. The spines first appeared in preflexion larvae of C. naritus at 7 DAH, covering the ventral skin region below pectoral fin base and expanded to the ventral part of the body and nearly covered the whole abdomen region before the anus and below the eyes in juveniles. C. naritus remain as larvae for approximately 29 days, during which they metamorphose to the juvenile stage prior to sexual maturation. Observations in larvae development of C. naritus revealed similar characteristics with other Tetraodontidae species.

Assessing tree species diversity and structure of mixed dipterocarp forest remnants in a fragmented landscape of north-western Borneo, Sarawak, Malaysia

Abstract As forest fragmentation continues in many parts of the tropics, the conservation value of forest remnants remains controversial. Our study aimed to assess the structure and tree species diversity of mixed dipterocarp forest remnants from the Planted Forest Zone (PFZ) located in the Bintulu Division, Sarawak, compared with a forest considered relatively undisturbed (i.e. that has experienced no recent logging activities). We also compared three plot methods (50 × 50 m, 20 × 50 m and 10 × 50 m plots) in order to evaluate which could be used for time- and cost-effective inventories of structure and tree species diversity in fragmented forests. No significant differences were found between the fragmented forests and the relatively undisturbed forest for stem density, species richness and diversity indices (Shannon and Simpson). Dissimilarities in species, genus and family composition were observed between fragmented and relatively undisturbed forest, as well as between forest remnants themselves. These dissimilarities were likely to be related to intrinsic variation in these highly diverse tropical forests. However, an unusually high abundance of pioneer species (i.e. Macaranga) was found in plots from forest remnants. The forest remnants also had significantly lower basal areas due to a lack of trees in large diameter classes, which is likely a result of impacts from past logging activities. Otherwise, our results highlight the current high conservation value of the forest remnants—although the studied communities are likely to experience time-delayed shifts in species composition and/or extinctions in the future, with the effect of fragmentation on biodiversity being currently underestimated. Finally, for further studies of fragmented forests we recommend the use of 10 × 50 m plots which are faster and easier to implement in the field while providing estimates of structure and tree species diversity that are consistent with those from larger plots.

Submarine Telegraphy and the Hunt for Gutta Percha: Challenge and Opportunity in a Global Trade by Helen Godfrey

Reviewed by: Submarine Telegraphy and the Hunt for Gutta Percha: Challenge and Opportunity in a Global Trade by Helen Godfrey Bruce J. Hunt (bio) Submarine Telegraphy and the Hunt for Gutta Percha: Challenge and Opportunity in a Global Trade By Helen Godfrey. Leiden: Brill, 2018. Pp. 330. "Gutta percha," as Helen Godfrey notes in her opening line, "is now largely forgotten." A natural plastic derived from the latex of certain trees native to Malaya, Sumatra, and Borneo, it has almost entirely given way to synthetic substitutes; besides a few historians, almost the only people today who have ever heard of it are dentists, who still use it to fill root canals. In the second half of the nineteenth century, however, gutta percha was a significant item of commerce and one of enormous strategic value. As the favored insulating material for submarine telegraph cables, it was the linchpin of the global telecommunications system that powered transoceanic trade and knit together the British Empire. It was also among the most intensively studied materials in the world, its chemical, mechanical, and electrical properties carefully tested and tabulated by British scientists and engineers. For more than fifty years, gutta percha lay at the heart of the leading high-tech industry of its day, yet as Godfrey shows, its availability to cable manufacturers ultimately rested on the skills and labor of axe-wielding forest-dwellers, many of whom, particularly in Borneo, were literally headhunters. Godfrey's book grew out of her 2011 doctoral dissertation in economic history at the University of New England in Australia. It is packed with informative graphs correlating the booms and busts in cable laying between 1850 and 1900 with trends in the trade in gutta percha and associated goods. Drawing on both anthropological literature and economists' analyses of global commodity chains, she illuminates the very different meanings gutta percha acquired as it moved from the forests of Borneo to the cable factories of London before finally being laid to rest at the bottom of the sea. Godfrey devotes her opening chapters to sketching the history of the cable industry and the workings of the gutta percha markets in Singapore, but her real focus is on the forests and peoples of Sarawak. This region in northwestern Borneo supplied only a fraction of total gutta percha production—most came from the Malay Peninsula, Sumatra, and the Dutch portion of Borneo—but it provides a rich ground for Godfrey's analysis of the [End Page 1247] ways indigenous groups responded to the new global demand for this product of their forests. Now a part of Malaysia, Sarawak has an unusual history. In the 1840s, the sultan of Brunei ceded a portion of his territory in Borneo to James Brooke, a British adventurer, as thanks for his help in suppressing a rebellion. Brooke and his successors ruled Sarawak for the next century as its "white rajahs," seeking to extract profit from it with a minimum of capital investment. They found the gutta percha trade suited them very well. Efforts in the nineteenth century to produce gutta percha on plantations or by tapping standing trees proved unworkable; instead, forest trees were felled, their bark slashed, and the latex drawn off, with even large trees only yielding about a pound. Long cables required hundreds of tons of gutta percha, and millions of trees were felled and stripped to build the global cable network. This work of felling and stripping trees was done almost entirely by indigenous people in Sarawak, mainly the Iban, renowned as fearsome headhunters. There was no need to coerce the Iban to gather gutta percha; they were happy to do it. Widely regarded as adventurous and entrepreneurial, their values and traditions seemed tailor made for the gutta percha trade. In particular, young Iban men achieved status by heading off on long and often dangerous journeys, their goal being to earn enough money to buy prestige goods (pusaka), particularly brassware and large Chinese jars. Venturing deep into the forest to gather gutta percha they could trade for pusaka, was thus an attractive prospect. This is perhaps Godfrey's most striking point: the Iban took to the gutta percha trade because it "did not require...

Reply to Discussion: Hennig-Breitfeld, J., H.T. Breitfeld, R. Hall, M. BouDagher-Fadel, and M. Thirlwall. 2019. A new upper Paleogene to Neogene stratigraphy for Sarawak and Labuan in northwestern Borneo: Paleogeography of the eastern Sundaland margin. Earth-Science Reviews 190, 1–32

Reply to Discussion: Hennig-Breitfeld, J., H.T. Breitfeld, R. Hall, M. BouDagher-Fadel, and M. Thirlwall. 2019. A new upper Paleogene to Neogene stratigraphy for Sarawak and Labuan in northwestern Borneo: Paleogeography of the eastern Sundaland margin. Earth-Science Reviews 190, 1–32

Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo

Abstract. Nitrous oxide (N2O) and methane (CH4) are atmospheric trace gases which play important roles in the climate and atmospheric chemistry of the Earth. However, little is known about their emissions from rivers and estuaries, which seem to contribute significantly to the atmospheric budget of both gases. To this end concentrations of N2O and CH4 were measured in the Rajang, Maludam, Sebuyau and Simunjan rivers draining peatland in northwestern (NW) Borneo during two campaigns in March and September 2017. The Rajang River was additionally sampled in August 2016 and the Samunsam and Sematan rivers were additionally sampled in March 2017. The Maludam, Sebuyau, and Simunjan rivers are typical “blackwater” rivers with very low pH (3.7–7.8), very high dissolved organic carbon (DOC) concentrations (235–4387 mmol L−1) and very low O2 concentrations (31–246 µmol L−1; i.e. 13 %–116 % O2 saturation). The spatial and temporal variability of N2O and CH4 concentrations (saturations) in the six rivers or estuaries was large and ranged from 2.0 nmol L−1 (28 %) to 41.4 nmol L−1 (570 %) and from 2.5 nmol L−1 (106 %) to 1372 nmol L−1 (57 459 %), respectively. We found no overall trends of N2O with O2 or NO3-, NO2- or NH4+, and there were no trends of CH4 with O2 or dissolved nutrients or DOC. N2O concentrations showed a positive linear correlation with rainfall. We conclude, therefore, that rainfall is the main factor determining the riverine N2O concentrations since N2O production or consumption in the blackwater rivers themselves seems to be low because of the low pH. CH4 concentrations were highest at salinity = 0 and most probably result from methanogenesis as part of the decomposition of organic matter under anoxic conditions. CH4 in the concentrations in the blackwater rivers showed an inverse relationship with rainfall. We suggest that CH4 oxidation in combination with an enhanced river flow after the rainfall events might be responsible for the decrease in the CH4 concentrations. The rivers and estuaries studied here were an overall net source of N2O and CH4 to the atmosphere. The total annual N2O and CH4 emissions were 1.09 Gg N2O yr−1 (0.7 Gg N yr−1) and 23.8 Gg CH4 yr−1, respectively. This represents about 0.3 %–0.7 % of the global annual riverine and estuarine N2O emissions and about 0.1 %–1 % of the global riverine and estuarine CH4 emissions. Therefore, we conclude that rivers and estuaries in NW Borneo – despite the fact their water area covers only 0.05 % of the global river/estuarine area – contribute significantly to global riverine and estuarine emissions of N2O and CH4.

Discussion on: A new upper Paleogene to Neogene stratigraphy for Sarawak and Labuan in northwestern Borneo: Paleogeography of the eastern Sundaland margin

Important new work is presented by the authors on radiometrically dating the Bukit Piring intrusion and associated Arip Volcanics, as well as confirmation that widespread outcrops of Oligocene and Miocene clastic formations share a common sediment provenance. This valuable contribution is weakened by a poorly researched stratigraphic model that conflicts with much published work. The importance of good micropalaeontology is stressed in this review as without this tool the essential dimension of time is lost, and facies determinations are less reliable. These inputs are two of the three two components, along with space, that make stratigraphy a testable science under Walther’s Law.

Distribution and cycling of terrigenous dissolved organic carbon in peatland-draining rivers and coastal waters of Sarawak, Borneo

Abstract. South-East Asia is home to one of the world's largest stores of tropical peatland and accounts for roughly 10 % of the global land-to-sea dissolved organic carbon (DOC) flux. We present the first ever seasonally resolved measurements of DOC concentration and chromophoric dissolved organic matter (CDOM) spectra for six peatland-draining rivers and coastal waters in Sarawak, north-western Borneo. The rivers differed substantially in DOC concentration, ranging from 120–250 µmol L−1 (Rajang River) to 3100–4400 µmol L−1 (Maludam River). All rivers carried high CDOM concentrations, with a350 in the four blackwater rivers between 70 and 210 m−1 and 4 and 12 m−1 in the other two rivers. DOC and CDOM showed conservative mixing with seawater except in the largest river (the Rajang), where DOC concentrations in the estuary were elevated, most likely due to inputs from the extensive peatlands within the Rajang Delta. Seasonal variation was moderate and inconsistent between rivers. However, during the rainier north-east monsoon, all marine stations in the western part of our study area had higher DOC concentrations and lower CDOM spectral slopes, indicating a greater proportion of terrigenous DOM in coastal waters. Photodegradation experiments revealed that riverine DOC and CDOM in Sarawak are photolabile: up to 25 % of riverine DOC was lost within 5 days of exposure to natural sunlight, and the spectral slopes of photo-bleached CDOM resembled those of our marine samples. We conclude that coastal waters of Sarawak receive large inputs of terrigenous DOC that is only minimally altered during estuarine transport and that any biogeochemical processing must therefore occur mostly at sea. It is likely that photodegradation plays an important role in the degradation of terrigenous DOC in these waters.

New records of guano-associated minerals from caves in northwestern Borneo

Recent studies of ancient bat guano deposits in the caves of Gunung Mulu National Park and Niah National Park, Sarawak, Malaysia, have resulted in noteworthy records of phosphate minerals from these environments, including variscite, nano-particulate silica, fluorapatite, and niter.

Morphology and channel characteristics of an equatorial tropical river in Malaysian Borneo: a detailed evaluation through spatially explicit geomorphometric modelling

Geomorphic and morphodynamic characteristics of Akah River in Sarawak, Malaysia in north-western Borneo were modelled using geographical information system assisted techniques and geomorphometric indices. Stream properties such as longitudinal profile, stream length gradient index (SL), channel slope, hypsometric curve, hypsometric integral, sinuosity index and channel cross profiles were analyzed. Morphological features such as meander and channel bar characteristics were evaluated and compared to classify the river and to identify the processes responsible for its present nature. The longitudinal profile, SL index and channel slope indicate the presence of multiple knick points in the channel, which may be indicative of changes in the base level characteristics of the river or lithological differences. The characteristic convex shape of hypsometric toe indicates late stage of deposition due to diffusive processes and the hypsometric integral identifies the geomorphic evolution as in the advanced stage i.e. erosion is significant. The sinuosity index classifies the entire river as meandering and some segments as tortuously meandering with varied stream valleys. Numerous channel bars of various dimensions are found in different reaches of the stream indicating varying channel bottom characteristics and flow mechanism due to the influence of geological process. The information generated from spatial modelling of different geomorphic indices (different terrain variables) and channel characteristics classifies the Akah subwatershed with slope (diffusive) and fluvial dominated geomorphic process having highly meandering channel and showing anomalous characteristics in some segments. These findings will serve as baseline information, while considering the region for hydrological development activities which include check dams, mini hydroelectric projects.

Interannual Variation of the Summer Rainfall Center in the South China Sea

Abstract A northwest–southeast-oriented summer monsoon trough exists between northern Indochina and northwestern Borneo. Ahead of this the South China Sea (SCS) trough is located at a convergent center west of the Philippines, which provides an environment favorable for rain-producing synoptic systems to produce rainfall over this center and form the SCS summer rainfall center. Revealed from the x–t diagram for rainfall, this rainfall center is developed by multiple-scale processes involved with the SCS trough (TR), tropical depression (TY), interaction of the SCS trough with the easterly wave/tropical depression (EI), and easterly wave (EW). It is found that 56% of this rainfall center is produced by the SCS trough, while 41% is generated by the other three synoptic systems combined. Apparently, the formation of the SCS summer monsoon rainfall center is contributed to by these four rain-producing synoptic systems from the SCS and the Philippines Sea. The Southeast Asian summer monsoon undergoes an interannual variation and exhibits an east–west-oriented cyclonic (anticyclonic) anomalous circulation centered at the western tropical Pacific east of the Luzon Strait. This circulation change is reflected by the deepening (filling) of the SCS summer monsoon trough, when the monsoon westerlies south of 15°N intensify (weaken). This interannual variation of the monsoon westerlies leads to the interannual variation of the SCS summer monsoon rainfall center to follow the Pacific–Japan oscillation of rainfall. The rainfall amount produced over this rainfall center during the weak monsoon season is about two-thirds of that produced during the strong monsoon season. The rain-production ratio between TR and TY + EI + EW is 60:38 during the strong monsoon season and 47:49 during the weak monsoon season.