High-resolution age-depth chronology from tropical montane minerotrophic peat in the Sandynallah valley, Western Ghats, southern India: Analytical issues and implications

Bala, Prabhakaran Ramya; Nakamura, Toshio; Sajeev, K.

doi:10.1016/j.quageo.2016.03.003

Cited by 8 publications

(4 citation statements)

References 43 publications

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“…The potassium hydroxide digestion was repeated until the supernatant became translucent and less opaque. We limited potassium hydroxide digestion to ~500 ml per sample because even after this amount the supernatant did not become clear (Ramya Bala et al, 2016). Samples were washed to neutral pH with deionised water and then digested again with 1M HCl at 60°C for 10 min, and then washed again to neutral pH with deionised water.…”

Section: Methodsmentioning

confidence: 99%

Reliability of mangrove radiocarbon chronologies: A case study from Mahé, Seychelles

et al. 2022

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Mangrove sediments are valuable archives of paleoenvironmental and relative sea-level changes. The most widely applied method to obtaining chronologies of past changes in mangrove sediments is radiocarbon dating, because mangroves produce large amounts of organic matter in situ. However, there are many challenges to obtaining reliable radiocarbon chronologies because bioturbation processes from roots and crabs can rework mangrove sediments, resulting in ages that are not in stratigraphic order. Previous studies have suggested that methods that isolate specific sediment size fractions may yield ages closer to the age of the paleo depositional surface by removing younger carbon contamination from fine roots. This study examines which sample types are more likely to yield reliable radiocarbon ages using shallow cores from a mangrove environment on Mahé, Seychelles, in the Indian Ocean. We compare radiocarbon ages from bulk sediment, sieved organic concentrates and above-ground macrofossils collected from the same stratigraphic depths. Bulk sediment and organic concentrate ages are comparable, which suggests that methods that separate out different size fractions do not sample different carbon sources in Seychelles mangrove cores. Identifiable above-ground macrofossils are rare in Seychelles mangrove cores, but yield older radiocarbon ages than comparable bulk sediment or organic concentrate ages. We suggest that in Seychelles, limited accommodation space over the late-Holocene, determined by relatively stable relative sea levels, has resulted in poor preservation of above-ground macrofossils for radiocarbon dating due to low rates of burial and sediment accretion. Low accretion rates have likely resulted in a mangrove sediment sequence that is highly bioturbated and degraded, meaning both bulk sediment and organic concentrate samples are impacted by contamination from younger roots. We argue that the availability of accommodation space and sediment composition controls the reliability of mangrove radiocarbon chronologies, which has implications for sample choice and site selection.

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Section: Methodsmentioning

confidence: 99%

Reliability of mangrove radiocarbon chronologies: A case study from Mahé, Seychelles

et al. 2022

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“…Although the site is located in the tropical belt, peat is preserved in valleys in this mountain range due to cool temperatures (annual average 13.5 °C) and moderately high precipitation leading to water logging (annual average precipitation of about 1400 mm) (von Lengerke 1977). These tropical mountain ranges feature peat deposits dating back to >40,000 radiocarbon yr BP which have been studied extensively to reconstruct Late Quaternary vegetation and climate (Vasanthy 1988; Sukumar et al 1993; Sutra, Bonnefille, and Fontugne 1997; Rajagopalan et al, 1997; Ramya Bala 2015; Ramya Bala et al 2016).…”

Section: Methodsmentioning

confidence: 99%

“…A pit of ~1.8 m depth was dug close to a location from which a core (labelled as Core 1) had been previously taken and radiocarbon dated (Ramya Bala et al 2016), and peat samples collected as monoliths at regular intervals in a stainless-steel box of dimensions 15.6 cm x 9.3 cm x 3.0 cm. Thirteen samples were collected in zip lock bags, adjacent samples starting from the surface separated by ~2 cm, down to a depth of ~1.6 m. Sub-samples were freeze dried (Labconco bulk drier) and crushed into fine powder and stored.…”

Section: Methodsmentioning

confidence: 99%

Climate change and the migration of a pastoralist people c.3500 cal. years BP inferred from palaeofire and lipid biomarker records in the montane Western Ghats, India

Kavil¹,

Bala²,

Kumar

et al. 2020

Preprint

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Human migration in response to climate change during the Holocene has been recorded in many regions of the world. The Todas are a pastoralist people who are believed to have colonized the higher elevations (>2000 m asl) of the Nilgiris in the Western Ghats, India, not earlier than about 2000 cal. yr BP. Vegetation shifts in response to changing climate in tropical montane forest-grassland mosaic of the Ghats have been well documented using stable carbon isotopes and pollen profiles; however, there have been no corresponding investigations of human presence and activity at the highest elevations. We used a number of other proxies to infer the human ecology of this montane region. Radiocarbon dated (~22,000 cal. BP to the present) peat samples from the Sandynallah basin (2200m asl, Nilgiri hills, Tamil Nadu State) were used to reconstruct fire history, animal abundance, and human presence since the Last Glacial Maximum (LGM). While the macro-charcoal record indicates fires at the LGM, macro- and micro-charcoal counts indicate intense fire at ~3500 cal. yr BP, coprophilous fungal spores indicate a large population of herbivorous mammals, and steroid biomarkers indicate human faecal remains for the first time. This period is also characterized by dry arid conditions and dominant grassy vegetation as inferred from n-alkane signatures. We thus infer that a pastoralist people, most likely the Todas, migrated to the highest elevations of the Western Ghats along with their buffalo herds in response to prolonged or abrupt climate change in peninsular India, about 3500 cal. yr BP or at least 1500 years prior to what historical accounts assume.

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“…Each study site establishes its own age-depth model independently by obtaining separate radiocarbon dates for independently selected layers. Owing to "internal uncertainties" intrinsic in the radionuclide activity measurements using Accelerator Mass Spectrometry (AMS) and "external uncertainties" introduced by sample handling and age-depth modeling (Ramya Bala et al, 2016), the chronology-based proxy comparison of different studies might be subject to the influence of chronological uncertainties, which might eventually lead to incorrect "Cause-Consequence" evaluations.…”

Section: Introductionmentioning

confidence: 99%

A humification-based method toward refining Holocene radiocarbon chronologies: Wetland records from southeastern China

Chambers

et al. 2023

The Holocene

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Holocene paleoclimate reconstructions and comparisons largely rely on accurate age-depth modeling. However, uncertainties in chronology, such as those caused by sparse radiocarbon dates, will hamper inter-core comparisons and correlations, and might result in misleading “cause and consequence” conclusions. This study aimed to find a solution to increase the comparability and minimize the uncertainty of wetland chronology as much as possible. Sediment cores were recovered and radiocarbon dated from the Lianhuachi wetland located in Southeastern China. Humification degree and loss-on-ignition (LOI) were determined using colorimetric and combustion methods respectively. Our data were compared with previously published datasets obtained in the same wetland. The results show that independent humification profiles from the Lianhuachi wetland displayed high similarities. This high similarity between the humification profiles allowed us to transfer radiocarbon ages from one core to another using sequence slotting correlation. Applying the humification-based chronology refinement method to all sediment cores resulted in an improvement in the correlation coefficients between the same but independently measured proxy sequences from the wetland, which suggests both the inter- and intra-core comparability was improved. Because determining peat humification degree is easy, inexpensive, and time-saving, we suggest that humification can serve as a tool that can be used to correlate different cores and to transfer published radiocarbon ages within the same wetland (peatland) or in a comparable geological setting, to establish a more robust chronology of these comparable cores. The degree of peat humification can thus serve as a relative dating technique to refine the chronology of wetland (including peatland) records.

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High-resolution age-depth chronology from tropical montane minerotrophic peat in the Sandynallah valley, Western Ghats, southern India: Analytical issues and implications

Cited by 8 publications

References 43 publications

Reliability of mangrove radiocarbon chronologies: A case study from Mahé, Seychelles

Reliability of mangrove radiocarbon chronologies: A case study from Mahé, Seychelles

Climate change and the migration of a pastoralist people c.3500 cal. years BP inferred from palaeofire and lipid biomarker records in the montane Western Ghats, India

A humification-based method toward refining Holocene radiocarbon chronologies: Wetland records from southeastern China

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