Erroneously Old Radiocarbon Ages From Terrestrial Pollen Concentrates in Yellowstone Lake, Wyoming, Usa

Schiller, Christoph; Whitlock, Cathy; Elder, Kathryn; Iverson, Nels; Abbott, Mark B.

doi:10.1017/rdc.2020.118

Cited by 12 publications

(12 citation statements)

References 63 publications

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“…Radiocarbon dating of pollen concentrates is a method developed for use in lacustrine and freshwater bog sediments (Howarth et al, 2013; Kasai et al, 2021; Neulieb et al, 2013; Newnham et al, 2007; Vandergoes and Prior, 2003), but has yet to be applied to mangrove sediments. Some studies reported pollen reworking from surrounding terrestrial and marine environments, and therefore ages that are too old (Howarth et al, 2013; Kilian et al, 2002; Li et al, 2014; Neulieb et al, 2013; Schiller et al, 2021). Isolating mangrove pollen (an above-ground source that likely formed in situ in the mangrove stand) for radiocarbon dating may reduce the potential of sampling and dating organics that are not representative of the depositional age.…”

Section: Radiocarbon Dating Of Mangrove Sedimentsmentioning

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: Radiocarbon Dating Of Mangrove Sedimentsmentioning

confidence: 99%

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

et al. 2022

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“…While some lakes may present relatively simple results (e.g., Tennant et al, 2013 and the FLL results in Figure 6), in other lakes complications may arise that are specific to the dynamics in that particular basin. Basins where regression has exposed old lake sediments (Zimmerman et al, 2018), where deep soils develop and are periodically eroded into the lake (Howarth et al, 2013); and where the potential for unusual carbon dynamics exists (Schiller et al, 2021) demonstrate the need to understand each lake basin as an individual, until enough lakes have been characterized to understand the variety of locations where pollen dating is likely to be successful.…”

Section: Outlook For the Futurementioning

confidence: 99%

An Improved Method for Extracting, Sorting, and AMS Dating of Pollen Concentrates From Lake Sediment

et al. 2021

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High-resolution chronologies are crucial for paleoenvironmental reconstructions, and are particularly challenging for lacustrine records of terrestrial paleoclimate. Accelerator Mass Spectrometry (AMS) radiocarbon measurement of terrestrial macrofossils is the most common technique for building age models for lake sediment cores, but relies on the presence of terrestrial macrofossils in sediments. In the absence of sufficient macrofossils, pollen concentrates represent a valuable source of dates for building high-resolution chronologies. However, pollen isolation and dating may present several challenges, as has been reported by different authors in previous work over the last few decades. Here we present an improved method for extracting, purifying and radiocarbon-dating pollen concentrates using flow cytometry to improve the extraction efficiency and the purity of the pollen concentrates. Overall, the nature of the sediments and the abundance of the pollen represent major considerations in obtaining enough pollen grains and, consequently, enough carbon to be dated. Further, the complete separation of pollen from other forms of organic matter is required to ensure the accuracy of the dates. We apply the method to surface samples and sediment cores recovered from two contrasting lake basins on the eastern side of the Sierra Nevada (California), and describe the variations that may be used to optimize pollen preparation from a variety of sediments.

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“…All but sample OS-144561 were interpreted as erroneously old. The cause of these erroneously old ages is not clear, but old carbon contamination has been documented within the Yellowstone caldera in lake sediments (Schiller et al, 2021) and in organic material entombed in silica sinter (Churchill et al, 2020). It is likely that Goose Lake samples contained old carbon sourced from either reworked sediment, volcanic CO 2 incorporated into plants during photosynthesis (Evans et al, 2010), or volcanic CO 2 in the water column and surficial sediments (Schiller et al, 2021).…”

Section: Chronologymentioning

confidence: 99%

Holocene geo-ecological evolution of Lower Geyser Basin, Yellowstone National Park (USA)

2021

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Changes in climate and fire regime have long been recognized as drivers of the postglacial vegetation history of Yellowstone National Park, but the effects of locally dramatic hydrothermal activity are poorly known. Multi-proxy records from Goose Lake have been used to describe the history of Lower Geyser Basin where modern hydrothermal activity is widespread. From 10,300 cal yr BP to 3800 cal yr BP, thermal waters discharged into the lake, as evidenced by the deposition of arsenic-rich sediment, fluorite mud, and relatively high δ13Csediment values. Partially thermal conditions affected the limnobiotic composition, but prevailing climate, fire regime, and rhyolitic substrate maintained Pinus contorta forest in the basin, as found throughout the region. At 3800 cal yr BP, thermal water discharge into Goose Lake ceased, as evidenced by a shift in sediment geochemistry and limnobiota. Pollen and charcoal data indicate concurrent grassland development with limited fuel biomass and less fire activity, despite late Holocene climate conditions that were conducive to expanded forest cover. The shift in hydrothermal activity at Goose Lake and establishment of the treeless geyser basin may have been the result of a tectonic event or change in hydroclimate. This record illustrates the complex interactions of geology and climate that govern the development of an active hydrothermal geo-ecosystem.

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Erroneously Old Radiocarbon Ages From Terrestrial Pollen Concentrates in Yellowstone Lake, Wyoming, Usa

Cited by 12 publications

References 63 publications

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

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

An Improved Method for Extracting, Sorting, and AMS Dating of Pollen Concentrates From Lake Sediment

Holocene geo-ecological evolution of Lower Geyser Basin, Yellowstone National Park (USA)

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