Publications
Here you can discover some scientific articles published by members of the survey teams about the Gomantong Caves and other cave systems in Borneo.
Post-speleogenetic biogenic modification of Gomantong Caves, Sabah, Borneo
The Gomantong cave system of eastern Sabah, Malaysia, is well-known as an important site for harvesting edible bird-nests and, more recently, as a tourist attraction. Although the biology of the Gomantong system has been repeatedly studied, very little attention has been given to the geomorphology. Here, we report on the impact of geobiological modification in the development of the modern aspect of the cave, an important but little recognized feature of tropical caves. Basic modeling of the metabolic outputs from bats and birds (CO2, H2O, heat) reveals that post-speleogenetic biogenic corrosion can erode bedrock by between ~3.0 mm/ka (1 m/~300 ka) and ~4.6 mm/ka (1 m/~200 ka). Modeling at high densities of bats yields rates of corrosion of ~34 mm/ka (or 1 m/~30 ka). Sub-aerial corrosion creates a previously undescribed speleological feature, the apse-flute, which is semicircular in cross-section and ~80 cm wide. It is vertical regardless of rock properties, developing in parallel but apparently completely independently, and often unbroken from roof to floor. They end at a blind hemi-spherical top with no extraneous water source. Half-dome ceiling conch pockets are remnants of previous apse-fluting. Sub cutaneous corrosion creates the floor-level guano notch formed by organic acid dissolution of bedrock in contact with guano. Speleogenetic assessment suggests that as much as 70–95% of the total volume of the modern cave may have been opened by direct subaerial biogenic dissolution and biogenically-induced collapse, and by sub-cutaneous removal of limestone, over a timescale of 1–2 Ma
A note on the occurrence of a crayback stalagmite at Niah Caves
Crayback stalagmites have mainly been reported from New South Wales, Australia. Here we document a small crayback in the entrance of Painted Cave (Kain Hitam), part of the Niah Caves complex in Sarawak, Borneo. Measuring some 65 cm in length and 18 cm in height, this deposit is elongate in the direction of the dominant wind and thus oriented towards the natural tunnel entrance. It shows the classic humpbacked long profile, made up of small transverse segments or plates, in this case the tail extending towards the entrance. The dark blue-green colour down the centre suggests that cyanobacterial growth follows the track of the wind-deflected roof drip. The dry silty cave sediment provides material for accretion onto the biological mat. This is the only example known from Borneo and one of the very few known from outside Australia.
Subaerial freshwater phosphatic stromatolites in Deer Cave, Sarawak - A unique geobiological cave formation
A suite of distinctive freshwater subaerial phosphatic stromatolites is developed close to the northeastern entrance of Deer Cave, Gunung Mulu National Park, Sarawak, Borneo, in conditions of very low light but ample supply of nutrients from guano. These stromatolites are not particulate; they are composed of alternating layers of more porous and more dense amorphous hydroxylapatite. This biomineralization occurs as moulds of coccoid (the majority) and filamentous (less abundant) cyanobacteria. Mineralization occurs at a pH of ~7.0 in the extracellular sheaths and in micro-domains of varying carbonate content in the surrounding mucus of the biofilm. The most recent surfaces that are not yet strongly mineralized show still-living filamentous, coccoid and rod-shaped forms. Trace element composition shows enrichment in metal ions, especially Mn and Zn. The stromatolites are present as horizontal shelves arranged in series on a steep rock face that is vertically under a guano-laden shelf. The rock face undergoes active dissolution from acidic guano drainage water (e.g., pH of 2.43) and from aggressive rainwater from an overhead discharge. However, the rock surface under the stromatolite is protected while the rest of the cliff face is backcut, creating a hoodoo-like effect. The stromatolites are ~15–20 cm deep, ~4–7 cm thick, and of variable width, generally ~50 cm. Eventually, guano and biological detritus in the descending water film lodge in the lee of the stromatolite lip, causing local acidification and erosion of stromatolite and rock on the underside of the ledge. A dynamic equilibrium is established between upward accretion of the fresh surface and destruction at the base such that the base of the stromatolite does not reflect the date of its inception and the stromatolite climbs up the wall.
Lessons learned from a large-scale 3-D mapping project
During a large T-Lidar scanning project of the Gomantong Caves in Sabah, Malaysia we learned that using reference spheres is not really necessary. Not using the references accelerates the pace of scanning, and eliminate the risks associated with placements in hazardous situations. This increase in scanning efficiency does come at a price because scan registration becomes more complex. However, the extended time required for a more complex cloud-to-cloud registration in an office environment is more than compensated for by the increased efficiency and reduced risk of the fieldwork. In this paper we will also review some other “lessons learned” during this project.
Mathematical modelling of the relationship between terrestrial LIDAR scan point density and volumetric assessment of underground cavities.
Terrestrial LIDAR (T-Lidar, or 3-D) scanning is increasingly being used for surveying caves in outstanding detail. These laser systems generate extremely large datasets of dense point clouds, resulting in very detailed and precise 3D models of the scanned caves. These models are commonly used to determine the volume of large chambers, including those recognised as the largest natural underground cavities on Earth. Intuition tells us that the denser the point cloud, the better it will fit the real dimensions of the cave. This concept is used in many discussions about the precision of volume determination by terrestrial LIDAR. Here we prove this is not the case. Using a theoretically constructed structure we show that with a low number of measured points it is already possible to calculate volumes which will match the true volumes of a cavity with high precision.
Estimating colony size of the wrinkle-lipped bat, Chaerephon plicatus (Chiroptera: Molossidae) at Gomantong, Sabah, by quantiative image analysis
The Gomantong cave system, Kinabatangan, Sabah (Malaysia) hosts one of the largest bat colonies known from north Borneo. The nightly exodus of Chaerophon plicatus from this site is an economically valuable tourist attraction, and must impose significant controls on the regional ecology. Monitoring ecosystem health requires monitoring bat population size, but no quantitative assessments for the Gomantong colony are available in the literature. Traditional censusing techniques (based on packing density and roost area or on roost exodus counts) yield notoriously unreliable results. Here we have applied innovative image analysis and counting techniques to videographic, photographic and terrestrial laser scanning data obtained in July 2012. The colony exits in a consistent stream along a narrow exit trajectory. The laser scanning of the large cave entrance allowed precise measurement of bat position. Video data provided 0.02-second time resolution. Average flight speed was calculated (10.38 ± 0.85 m/sec), bat exit rate was estimated at three minute intervals (peaking at 14,000 bats/minute) and then summed over the 40 minutes of bat flight. The resultant colony size estimate of 275,625–276,939 (95% confidence interval) individuals of C. plicatus in Gomantong Caves in 2012 demonstrates that the technique is viable, provides a realistic basis for ecosystem management, and can be repeated to monitor ecosystem change. The estimated insect consumption by the colony of this size is 927 ± 191 metric tons of insects per year over an estimated 270 km2 area, a very important component in maintaining ecosystem stability in the Gomantong Forest Reserve and the Kinabatangan Wildlife Sanctuary, as well as pest control over the large agricultural tracts of the region.
Preliminary Observations on Tropical Bat Caves as Biogeochemical Nitrogen Sinks
A previously unrecognized aspect of nitrogen biogeochemistry in tropical moist forests (TMF) relates to the spatial biogeochemistry of these systems. In general, high levels of herbivory in TMF’s transfer large amounts of fxed nitrogen and other nutrients into the insect community, which itself is harvested by aerial insectivorous vertebrates (bats and birds), or moves directly into the non-volant vertebrate community through leaf eating mammals and frugivorous mammals and birds. In non-karstic TMF’s bats and birds can be expected to redistribute this fxed nitrogen through defecation and urination throughout the TMF, contributing to the efcient recycling of this potentially limiting nutrient. However, in karst environments, TMF’s may support very large (105 – 106 individuals) populations of bats and in Southeast Asia, birds (cave dwelling swiflets), that occupy very spatially localized roosts. A single large cave may support a bat or swiflet population in the hundreds of thousands of individuals that forages for insects over thousands of square kilometers of TMF, but then deposits a substantial fraction of its total excretory nitrogen within that single cave. A large but undetermined fraction of this nitrogen input is retained within the cave, or lost as diatomic nitrogen gas following biological denitrifcation. Such a cave then functions as a point-source sink for TMF fxed nitrogen. Recent work in Deer Cave, Mulu National Park, Sarawak (Malaysia) has mapped the ammonia plume emanating from a large bat guano accumulation. Relating this plume to airfow, frst order estimates of ammonia production are ~ 9 g NH3/m2/day below the main Chaerephon plicata roost. An additional 4 g N/m2, or 45% of the total nitrogen budget, are retained in the guano and eventually lost to the external environment.
Integrated three-dimensional laser scanning and autonomous drone surface-hotogrammetry at Gomantong Caves, Sabah, Malaysia
The famous “bird’s nest caves” of Gomantong Hill, Sabah, are believed to have been extensively modified by zoogenic erosion. We have mapped the caves and the overlying land surface with unprecedented precision, by integrating aerial photogrammetry using an autonomous drone, three-dimensional cave laser scanning at millimeter resolution, differentially-corrected geodetic GPS, and conventional compass-based cave surveying techniques. These data provide exceptional insights into the interplay of biology and geomorphology, with direct benefits for sustainable management planning.
