| 1. |
- Baker, Andrea, et al.
(author)
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Biomarker records of palaeoenvironmental variations in subtropical Southern Africa since the late Pleistocene : Evidences from a coastal peatland
- 2016
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In: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 451:1, s. 1-12
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Journal article (peer-reviewed)abstract
- Southern Africa's unique global position has given rise to a dynamic climate influenced by large sea surface temperature gradients and seasonal fluctuations in the Inter Tropical Convergence Zone. Due to the semi-arid climate of the region, terrestrial palaeorecords are rare and our understanding of the long-term sensitivity of Southern African terrestrial ecosystems to climatic drivers is ambiguous. A 810 cm continuous peat core was extracted from the Mfabeni peatland with a 14C basal age of c. 47 thousand years calibrated before present (kcal yr BP), positioning it as one of the oldest known sub-tropical coastal peatlands in Southern Africa. This peat core provides an opportunity to investigate palaeoenvironmental changes in subtropical Southern Africa since the late Pleistocene. Biomarker (n-alkane, n-alkanoic acid and n-alkanol) analysis, in conjunction with previously published bulk geochemical data, was employed to reconstruct organic matter (OM) sources, rates of OM remineralisation and peatland hydrology. Our results showed that the principal OM source into the peatland was emergent and terrestrial plants with exception of shallow lake conditions when submerged macrophytes dominated (c. 44.5–42.6, 29.7, 26.1–23.1, 16.7–7.1 and 2.2 kcal yr BP). n-Alkane proxies suggest that local plant assemblages were predominantly influenced by peatland hydrology. By incorporating temperature sensitive n-alkanoic acid and n-alkanol proxies, it was possible to disentangle the local temperature and precipitation changes. We report large variations in precipitation intensities, but subdued temperature fluctuations during the late Pleistocene. The Holocene period was characterised by overall elevated temperatures and precipitation compared to the preceding glacial period, interspersed with a millennial scale cooling event. A close link between the Mfabeni archive and adjacent Indian Ocean marine core records was observed, suggesting the regional ocean surface temperatures to be the dominant climate driver in this region since the late Pleistocene.
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| 2. |
- Baker, Andrea, et al.
(author)
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Climatic variability in Mfabeni peatlands (South Africa) since the late Pleistocene
- 2017
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In: Quaternary Science Reviews. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0277-3791 .- 1873-457X. ; 160, s. 57-66
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Journal article (peer-reviewed)abstract
- It has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the Northern and Southern hemisphere climates since the late Pleistocene. A key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions. Southern Africas contemporary C-3 and C-4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones; however, the region is generally archive poor due to its overall semi-arid climate and high relief topography. The Mfabeni peatland, with a basal age of c. 47 k yrs calibrated before present (kcal yr BP), is one of the oldest continuous coastal peat deposits in Southern Africa. Molecular leaf wax isotopes (delta C-13(wax)) were generated for a 810 cm long core, and combined with previously published bulk geochemical (delta C-13(bulk), %TOC), palynological, and stratigraphic data, to reconstruct the late Pleistocene and Holocene palaeoenvironments. We interpreted environmental shifts associated with the Heinrich 4, Last Glacial Maximum, deglacial and Holocene periods, which are consistent with adjacent Indian Ocean sea surface temperature records. However, the other shorter climate perturbations during the Heinrich 5, 3, 2, 1, Antarctic cold reversal and Younger Dryas, were muted, most likely due to local hydrological overprinting on the Mfabeni record. A general anti-phase sequence was observed between the Mfabeni record and better established Northern Hemisphere events, underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the Late Pleistocene. (C) 2017 Elsevier Ltd. All rights reserved.
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| 3. |
- Baker, A., et al.
(author)
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Geochemical records of palaeoenvironmental controls on peat forming processes in the Mfabeni peatland, Kwazulu Natal, South Africa since the Late Pleistocene
- 2014
-
In: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 395, s. 95-106
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Journal article (peer-reviewed)abstract
- The Mfabeni peatland is the only known sub-tropical coastal fen that transcends the Last Glacial Maximum (LGM). This ca. 10 m thick peat sequence provides a continuous sedimentation record spanning from the late Pleistocene to present (basal age c. 47 kcal yr BP). We investigated the paleaeoenvironmental controls on peat formation and organic matter source input at the Mfabeni fen by: 1) exploring geochemical records (mass accumulation rate, total organic carbon, carbon accumulation rate, delta C-13, delta N-15 and C/N ratio) to delineate primary production, organic matter source input, preservation and diagenetic processes, and 2) employ these geochemical signatures to reconstruct the palaeoenvironmental conditions and prevailing climate that drove carbon accumulation in the peatland. We established that the Mfabeni peat sediments have undergone minimal diagenetic alteration. The peat sequence was divided into 5 linear sedimentation rate (LSR) stages indicating distinct changes in climate and hydrological conditions: ISR stage 1 (c. 47 to c. 32.2 kcal yr BP): predominantly cool and wet climate with C4 plant assemblages, interrupted by two short warming events. LSR stage 2 (c. 32.2 to c. 27.6 kcal yr BP): dry and windy climate followed by a brief warm and wet period with increased C4 sedge swamp vegetation. LSR stage 3 (c. 27.6 to c. 20.3 kcal yr BP): initial cool and wet period with prevailing C4 sedge plant assemblage until c. 23 kcal yr BP; then an abrupt change to dry and cool glacial conditions and steady increases in C3 grasses. LSR stage 4 (c. 203 to c. 10.4 kcal yr BP): continuation of cool and dry conditions and strong 0 grassland signature until c. 15 kcal yr BP, after which precipitation increases. LSR stage 5 (c. 10.4 kcal yr BP to present): characterised by extreme fluctuations between pervasive wet and warm to cool interglacial conditions with intermittent abrupt millennial-scale cooling/drying events and oscillations between C3 and C4 plant assemblages. In this study we reconstructed a high-resolution record of local hydrology, bulk plant assemblage and inferred climate since the Late Pleistocene, which suggest an anti-phase link between Southern African and the Northern Hemisphere, most notably during Heinrich (5 to 2) and Younger Dryas events.
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| 4. |
- Baker, Andrea, et al.
(author)
-
n-Alkan-2-one biomarkers as a proxy for palaeoclimate reconstruction in the Mfabeni fen, South Africa
- 2018
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In: Organic Geochemistry. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0146-6380 .- 1873-5290. ; 120, s. 75-85
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Journal article (peer-reviewed)abstract
- The sub-tropical Mfabeni fen is the only continuous coastal peat deposit that documents glacial and interglacial palaeoenvironmental conditions since the late Pleistocene (ca. 47 cal kyr BP) in southern Africa. Published bulk geochemical, biomarker and leaf wax delta C-13 data, along with palynology and stratigraphic studies of the Mfabeni peat sequence, render it an ideal record for testing new palaeoreconstruction proxies. In this study, we aimed to establish the proxy potential of n-alkan-2-one (n-ket) compounds by tracing their source/origin and post-depositional diagenetic change, and if they preserve or not a robust palaeoenvironment signal that complements our understanding of palaeoclimatic variations. In the Mfabeni archive the most likely source for n-kets is via microbial decarboxylation of n + 1-alkanoic acids (n-FAs) and, to a lesser degree, oxidation of same chain length n-alkanes (n-alks). The n-ket average chain length (ACL(ket)) and n-C-23 and C(25)ket/precursor ratios displayed a statistical significant negative relationship with the n-alk aquatic plant proxy (P-aq), suggesting the source of n-kets to be submerged aquatic plants during waterlogged conditions that suppressed microbial activity during the ensuing anoxic conditions. Both the mid-chain and long chain n-ket/precursor ratios displayed predominant water level fluctuation controls, with temperature as a secondary regulator. By comparing the n-ket data with published environmental and climate reconstructions from the same core, and with geomorphology and palynological studies of the Mfabeni basin, we conclude that the n-kets show promise as a palaeoclimate proxy and can be used in conjunction with other biomarker proxies to reconstruct ancient hydrological changes in sub-tropical peatlands. (C) 2018 Elsevier Ltd. All rights reserved.
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| 5. |
- Baskar, Sushmitha, et al.
(author)
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Biogenic evidences of moonmilk deposition in the Mawmluh cave, Meghalaya, India
- 2011
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In: Geomicrobiology Journal. - : Taylor & Francis. - 0149-0451 .- 1521-0529. ; 28:3, s. 252-265
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Journal article (peer-reviewed)abstract
- Moonmilk, a microcrystalline secondary cave deposit, actively forms on the floor of Krem Mawmluh - a limestone cave in Meghalaya, Northeastern India. Due to the abundance of micrite and calcified microbial filaments, we hypothesize that these deposits form as a result of ongoing microbial interactions. Consistent with this idea, we report electron microscopic and microbiological evidences for the biological origin of moonmilk in Krem Mawmluh. Scanning electron microscopy indicated abundant calcified microbial filaments, needle calcite, fibre calcites (micro-fibre and nano-fibre calcite crystals), biofilm and microbial filaments in the moonmilk. The total viable culturable microbes showed high population densities for microbes in the moonmilk and moonmilk pool waters. In vitro culture experiments, confirmed the capability of many of the isolated strains to precipitate calcite and some of the identified isolates belonged to the Bacillus sp. and Actinomycetes. These results clearly support the biogenic nature of the deposits.
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| 6. |
- Baskar, Sushmitha, et al.
(author)
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Evidences for Microbial Precipitation of Calcite in Speleothems from Krem Syndai in Jaintia Hills, Meghalaya, India
- 2016
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In: Geomicrobiology Journal. - : TAYLOR & FRANCIS INC. - 0149-0451 .- 1521-0529. ; 33:10, s. 906-933
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Research review (peer-reviewed)abstract
- Speleothems from Krem Syndai, Meghalaya in Northeast India were studied for their microbial diversity using 16S rDNA-based phylogenetic approach and conventional microbiological techniques along with geochemistry, mineralogy and in vitro experiments to understand participation of microorganisms in CaCO3 precipitation. Speleothems imaged by scanning electron microscopy showed round coccoid-like, sporangia-like and spinose calcified structures, numerous broken cocci shells with spotted interiors inside a calcite crystal, honeycomb long reticulate, smooth, flat, twisted, ribbon-like, tubular, beaded, microbe-mineralized filaments and extracellular polymeric substances (EPS). Fourier spectroscopy indicated the presence of various organic compounds. C-13 and O-18 isotopic ratios of speleothems ranged from -4.65 to -7.34 parts per thousand and -3.06 to -6.80 parts per thousand, respectively. Total number of microbial cells using SYBR Gold was high. Fluorescence in situ hybridization (FISH) indicated approximately 3x 10(5) to 5x 10(5) cells g sed(-1) in the speleothems out of which the number of microbes belonging to Eubacteria ranged from 1.8x 10(5) to 3.6x 10(5) cells, g sed(-1). FISH showed approximate to 45% active microbial cells of the total cell number in samples. DNA-based high-throughput amplicon sequencing revealed 19 bacterial phyla in the speleothem. Approximately 42% of the sequences were similar to Proteobacteria (Alphaproteobacteria: 22.4%, Betaproteobacteria: 8.9%, Gammaproteobacteria: 8.6%). Sequences similar to Nitrospiraceae (22.8%) had the highest proportion of sequences belonging to a single family. Bacterial strains isolated from the speleothems raised alkalinity and precipitated calcite in the laboratory cultures which was confirmed by X-ray diffraction (XRD) analyses. These isolates belonged to Bacillus spp., Actinomycetes spp., Streptomyces spp., Pseudomonas spp., Micrococcus spp., Staphylococcus spp., Xanthobacter spp. and Arthrobacter spp. Overall, the results showed unequivocal evidence of bacterial fingerprints during CaCO3 precipitation in the cave.
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| 7. |
- Baskar, Sushmitha, et al.
(author)
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Speleothems from Sahastradhara Caves in Siwalik Himalaya, India: Possible Biogenic Inputs
- 2014
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In: Geomicrobiology Journal. - : Taylor andamp; Francis: STM, Behavioural Science and Public Health Titles. - 0149-0451 .- 1521-0529. ; 31:8, s. 664-681
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Journal article (peer-reviewed)abstract
- Stalactites and moonmilk from Sahastradhara caves in Siwalik Himalayas were studied to understand the role of microbes in their genesis. Fourier spectroscopy in the moonmilk indicates a complex milieu of organic compounds that is unusual for inorganic formations. Stable C and O isotopes show trends in the moonmilk and stalactite, which suggest biogenic input; the geochemical inference is consistent with evidence from microscopy and laboratory-based microbial cultures. Light microscopy of moonmilk samples show the presence of a number of microbial forms similar to Cyanobacteria, and scanning electron microscope (SEM) images show microbial structures similar to Spirulina. The total number of microbial cells using SYBR Gold is 6.5 x 10(5) cells, g sed(-1) in moonmilk and 3.2 x 10(5) cells, g sed(-1) in stalactites. FISH indicates approximately 3.5 x 10(5) cells, g sed(-1) in moonmilk and 2 x 10(5) cells, g sed(-1) in stalactites. SEM images of the moonmilk indicate a large network of microbial filaments along with minerals, which are identified as calcite based on their x-ray diffraction pattern. In vitro laboratory cultures with pure monogenic strains isolated from the moonmilk and stalactites raise pH in the medium, which facilitate calcite precipitation. The mineral precipitating isolates were identified as: Bacillus pumilis, B. cereus, B. anthracis, B. lentus, B. sphaericus, B. circulans and Actinomycetes. The Sahastradhara moonmilk and statactites are colonized by a diverse microbial community and the isolated bacterial strains induce biomineralization on different nutrient media, supporting their biogenic origin.
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| 8. |
- Bhandari, Rajendra, et al.
(author)
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Bulk carbon and lignin fingerprinting of catchment sediments transported by mountain rivers in Nepal Himalayas
- 2022
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In: Catena (Cremlingen. Print). - : Elsevier. - 0341-8162 .- 1872-6887. ; 216
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Journal article (peer-reviewed)abstract
- The Himalayan rivers yield the most significant flux of continental sediments into the ocean. Organic matter (OM) transported by these rivers provides a peek at the influence of diverse geological terrains, soil types, vegetation, and climate on carbon cycling within a narrow boundary. We analyzed suspended and bedload sediments from four Himalayan rivers to trace their sources, elucidate their fate during fluvial transport, and estimate the organic carbon (OC) flux. Hence, total OC (TOC), dissolved organic carbon (DOC), C:N ratios, and lignin phenols were measured. Consistent with the erosional intensity in the rivers, suspended sediment load input followed the order: Kaligandaki > Myagdikhola > Aadhikhola > Tinahukhola. C:N values in rivers from the Lesser Himalayas and Siwalik indicate sediments from mixed biogenic sources. In contrast, high TOC and C/N values in the trans-Himalaya rivers flowing through barren landscapes reflect the erosion of catchment sediments yielding petrogenic carbon. The suspended matter in rivers from the Lesser Himalayas and Siwalik has higher lignin phenol concentrations than the trans-Himalaya and Higher Himalaya rivers. The lignin phenol ratios indicate higher degradation in rivers from the trans and Higher Himalaya sections. This implies that only a small fraction of the terrestrial OM transported by these rivers deposits in the ocean sink. In contrast, rivers from the Lesser Himalayas and Siwaliks sequester a significant amount of OM bound to their bedload. As a result, these rivers transferred lower particulate OC (POC) but higher DOC than similar rivers worldwide. Rivers from Lesser Himalayas and Siwaliks transfer > 90 % of annual POC flux during monsoons. Finally, although Himalayan rivers transport less OC than other global rivers traversing densely vegetated landscapes, the sheer number of these rivers has significant implications on the fate and transport of total OC from catchments sediments.
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| 9. |
- Bhandari, Rajendra, et al.
(author)
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Contrasting lipid biomarkers in mountain rivers in the Nepal Himalayas : Organic matter characteristics and contribution to the fluvial carbon pool
- 2021
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In: Geoscience Frontiers. - Beijing : China University of Geosciences. - 1674-9871. ; 12:6
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Journal article (peer-reviewed)abstract
- The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain. There is an increasing recognition of small mountain rivers (SMRs) to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux. We analyzed fluvial sediments from two SMRs and compared the results with two large mountain rivers (LMRs) in Nepal. We investigated the organic matter (OM), its compositional variability, and seasonal export using a suite of lipid biomarkers, namely n-alkanes, n-alkanoic acids, n-alkanols, and sterols. The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability. The LMRs showed a distinct contrast in the distribution of lipids in suspended sediments. Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the suspended load. Functional lipids (n-alkanoic acids and n-alkanols) were the major constituents in SMR sediments, indicating better preservation. In contrast, n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs. The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs. A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs. Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems. Topsoil colonized by fungal species under moist acidic conditions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs. In LMRs, the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of nalkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool. The differences in lipid concentrations, their distribution, seasonality, and the size of rivers suggest differential preservation/degradation of the organic matter pool and their importance in contributing to the carbon budget. (c) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
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| 10. |
- Bhandari, Rajendra, 1986-
(author)
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Provenance, transport, and the fate of organic matter and sediments drained through Himalayan Rivers in Nepal
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Despite its small area (ca. 595,000 km2), the Himalayan region transfers disproportionally high amounts of sediments and organic matter (OM) through a network of rivers into the oceanic sink. Such a high contribution is due to the synergistic effects of active tectonics, variable precipitation, and steep slopes aided by human perturbations on exhumed and young mountain terrains. Seasonality in the mobilization and transport of fresh biogenic OM and petrogenic carbon, including paleosols, is dominant in this unique landscape with implications for climate change and the global carbon budget. However, a comprehensive assessment of sources and the fate of organic carbon (OC) in Himalayan rivers remains elusive, driving considerable uncertainty in estimates of the fluvial transport of carbon, its budget, and its impacts on the global carbon cycle. Four rivers from diverse physiographic zones with specific rock types were selected from the Nepal Himalayas to characterize the OM sources and their fate using C:N ratios, lipid biomarkers, and lignin phenols. The seasonal OC fluxes were estimated, and strontium (Sr) and neodymium (Nd) isotope data were utilized to elucidate the provenance. Finally, monitoring of runoff plots and RUSLE modeling was conducted to estimate soil erosion from different land-use practices. The suspended sediment load in these rivers was proportional to the erosional intensity. Unlike suspended sediments, OM in bedload samples was derived from multiple sources with weak terrigenous dominance. The influence of seasonality on OM and elemental concentrations was evident in the new data. The abundance of sedimentary lipids in these small rivers represents high OM sequestration and corroborates the inference derived from diagnostic lignin ratios. These rivers transport > 90% POC and ca. 75% DOC during the short monsoon season, highlighting rapid transport/mobilization of OC from the Nepal Himalayas. The high strontium isotope (87Sr/86Sr) ratio in silicates drives the high radiogenic Sr input, which exceeds the global average. The clusters in Sr and Nd isotope data represent specific physiographic zones and rock types that can help infer OM provenance and trace the fate of carbon from source to sink. Data from the runoff plots suggest that irrigated croplands drive topsoil erosion. The soil erosion rate in the watersheds is high (> 24 tons ha-1 yr-1). This is attributed to anthropogenic disturbance associated with cropping patterns, soil disturbance, and waterlogging. The contrasting features in the Himalayan region and new data on the role of mountain rivers invite global attention to infer ongoing and future changes in OM flux.
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