ORCID Profile
0000-0001-6089-6097
Current Organisation
Nanyang Technological University
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Publisher: Cambridge University Press (CUP)
Date: 2004
DOI: 10.1017/S0033822200039734
Abstract: This study estimates the maximum and minimum degrees of autocompaction for radiocarbon-dated Holocene mangrove sediments in Singapore, in order to correct apparent sediment accretion rates for the effects of sediment compression due to autocompaction. Relationships developed for a suite of modern (surface) sediment s les between bulk density, particle-size distribution, and organic matter content were used to estimate the initial (uncompacted) bulk density of buried and variably compressed Holocene sediments, based on the grain-size distribution and organic matter content of the sediment. The difference between measured (compacted) and initial (uncompacted) bulk density of each buried sediment interval can be interpreted as the amount of length shortening experienced by each interval since burial. This allows the elevation of s les selected for 14 C dating to be corrected for the effects of autocompaction of the underlying sediment sequence, so that accurate estimates of vertical sediment accretion rates can be calculated. The 3 Holocene mangrove sequences analyzed and dated for this study ranged in age from 2000 to 8500 cal BP. The effects of autocompaction are significant, even in comparatively thin sequences, with subsidence of up to 56 cm calculated for carbon-dated s les presently 2 m above incompressible basement. The vertical sediment accretion rates for these mangrove sequences ranged from 0.99 to 6.84 mm/yr and carbon sequestration rates ranged from 0.9 to 1.7 t/ha/yr, all within the range observed for comparable Holocene and modern mangrove sediments elsewhere.
Publisher: Springer Science and Business Media LLC
Date: 08-06-2023
DOI: 10.1038/S43247-023-00868-5
Abstract: Low elevation equatorial and tropical coastal regions are highly vulnerable to sea level rise. Here we provide probability perspectives of future sea level for Singapore using regional geological reconstructions and instrumental records since the last glacial maximum ~21.5 thousand years ago. We quantify magnitudes and rates of sea-level change showing deglacial sea level rose from ~121 m below present level and increased at averaged rates up to ~15 mm/yr, which reduced the paleogeographic landscape by ~2.3 million km 2 . Projections under a moderate emissions scenario show sea level rising 0.95 m at a rate of 7.3 mm/yr by 2150 which has only been exceeded (at least 99% probability) during rapid ice mass loss events ~14.5 and ~9 thousand years ago. Projections under a high emissions scenario incorporating low confidence ice-sheet processes, however, have no precedent during the last deglaciation.
Publisher: Research Square Platform LLC
Date: 18-11-2022
DOI: 10.21203/RS.3.RS-2157980/V1
Abstract: Low-lying equatorial islands are susceptible to relative sea level (RSL) rise. Here, we quantify magnitudes and rates of RSL change since the last glacial maximum (LGM) to provide probability perspectives of future sea level. Geological reconstructions and instrumental records from the Sunda Shelf and Singapore show RSL rose ~ 121 m at rates up to ~ 15 mm/yr since the LGM, which reduced the paleogeographic landscape by ~ 2.3 million km 2 . In the 20th century, RSL began to rise, increasing at a rate of ~ 1.7 mm/yr to ~ 2.2 mm/yr between 1915 and 2020 CE. Future projections under a moderate emissions scenario show RSL rising 0.95 m at a rate of 7.3 mm/yr by 2150 which has only been exceeded (at least 99% probability) during rapid ice melting events ~ 14.5 and ~ 9 thousand years ago. Future projections under a high emissions scenario incorporating low confidence ice-sheet processes, however, have no precedent since the LGM.
Publisher: Research Square Platform LLC
Date: 12-05-2022
DOI: 10.21203/RS.3.RS-1611443/V1
Abstract: The most prominent abrupt climate event during the Holocene, the ‘8.2 ka event’, was characterized by severe cooling at high northern latitudes causing erse hydroclimate shifts globally. To date, a precise understanding of the hydroclimate response of the Indo-Pacific Warm Pool (IPWP) region to abrupt climate changes in the North Atlantic around 8.2 ka remains elusive. Here we present a high-resolution stable carbon isotope record on foraminifera species Asterorotalia pulchella and sediment characteristics of a marine sediment core from the Kallang River Basin, Singapore. Foraminifer stable isotope data in concert with sedimentological proxies provide coherent evidence of weakened rainfall for ~ 180 years in the western tropical Indo-Pacific region from ~ 8.14 ka to 7.96 ka BP. A robust age model suggests that the timing of the onset of reduced convective activity in the western IPWP region lags the cooling in the North Atlantic and the synchronous droughts in the Asian and Indian monsoon regions, by ~ 100years possibly implying a north-south signal propagation via oceanic route that operates on centennial scales. The termination of the ‘8.2 ka event’, however may have occurred near synchronously between high and low tropical regions at ~ 7.96ka BP possibly linked via both atmospheric and oceanic processes.
Publisher: Elsevier BV
Date: 07-2004
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-11157
Abstract: In the context of warming climate and rising sea level, records from the early-to-mid Holocene provide important analogues to investigate how the environment responds to such changes. The Sunda shelf provides favourable conditions to reconstruct past environmental change as the presence of numerous large paleo-valley systems and high sedimentation rates allow transgressive deposits from the early-mid Holocene sea-level rise to accumulate continuously in topographic depressions.& To this end, we analysed the sedimentological, geochemical and micropaleontological characteristics of a sediment core (GRBH03) to investigate early-to-mid Holocene environmental changes in southern Singapore. We constrained the chronology with ten radiocarbon dates that were placed in Bchron age-depth model. Using a multi-proxy approach (e.g., grain size distribution, loss on ignition and XRF core-scanning), supported by benthic foraminifera, three sedimentary units were identified in GRBH03. Sedimentary unit I was found at the base of the core. This unit was characterised by a dark grey sandy silt unit deposited from about 9.0 to 8.9 cal ka BP. Few or no foraminifera were found in this unit, likely due to degradation of organic material. Sedimentary unit II was a blue-grey marine mud that was deposited between 8.8 and 5.8 cal ka BP. Within the marine mud unit, foraminiferal assemblages show a transition to shallow marine environment from about 8.8 to 6.4 cal ka BP as open marine species (e.g., Murrayinella murrayi and Bulimina sp. cf. B. marginata) become more abundant up-core. Subsequently, brackish species such as Muyrrayinella globosa and Ammonia veneta started to dominate mud unit assemblages, reflecting a transition from shallow marine to brackish environments, likely associated with decelerating sea level rise. The marine unit is then overlain by the sedimentary unit III, which is a shelly-silt unit deposited after 5.9 cal ka BP. This unit was mostly barren of foraminifera, which may be attributed to a high-energy marginal marine environment where conditions were unfavourable for foraminiferal preservation. Our study show that changes in sedimentary units and foraminiferal assemblages present in GRBH03 are linked to varying rate of relative sea-level rise during the early-to-mid Holocene.&
Publisher: Elsevier BV
Date: 09-2020
No related grants have been discovered for Stephen Chua.