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1. Late Pleistocene shrub expansion preceded megafauna turnover and extinctions in eastern Beringia

   https://doi.org/10.1073/pnas.2107977118  

   Monteath, Alistair J.; Gaglioti, Benjamin V.; Edwards, Mary E.; Froese, Duane (December 2021, Proceedings of the National Academy of Sciences)

   The collapse of the steppe-tundra biome (mammoth steppe) at the end of the Pleistocene is used as an important example of top-down ecosystem cascades, where human hunting of keystone species led to profound changes in vegetation across high latitudes in the Northern Hemisphere. Alternatively, it is argued that this biome transformation occurred through a bottom-up process, where climate-driven expansion of shrub tundra ( Betula , Salix spp.) replaced the steppe-tundra vegetation that grazing megafauna taxa relied on. In eastern Beringia, these differing hypotheses remain largely untested, in part because the precise timing and spatial pattern of Late Pleistocene shrub expansion remains poorly resolved. This uncertainty is caused by chronological ambiguity in many lake sediment records, which typically rely on radiocarbon ( 14 C) dates from bulk sediment or aquatic macrofossils—materials that are known to overestimate the age of sediment layers. Here, we reexamine Late Pleistocene pollen records for which 14 C dating of terrestrial macrofossils is available and augment these data with 14 C dates from arctic ground-squirrel middens and plant macrofossils. Comparing these paleovegetation data with a database of published 14 C dates from megafauna remains, we find the postglacial expansion of shrub tundra preceded the regional extinctions of horse ( Equus spp.) and mammoth ( Mammuthus primigenius ) and began during a period when the frequency of 14 C dates indicates large grazers were abundant. These results are not consistent with a model of top-down ecosystem cascades and support the hypothesis that climate-driven habitat loss preceded and contributed to turnover in mammal communities. 

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2. Human–environment interactions at Ta'ab Nuk Na, a submerged Maya salt works site in Belize

   https://doi.org/10.1017/S0956536123000196  

   Foster, Cheryl M; McKillop, Heather; Sills, E Cory (August 2023, Ancient Mesoamerica)

   Abstract Sea-level rise and settlement are investigated at Ta'ab Nuk Na, an ancient Maya salt works in Belize, by examining samples from wooden posts and marine sediment. The samples included Post 145 of Building B and the Nunavut beam, along with marine sediment columns cut from beside both wooden posts. The sediment columns were sampled at 2 cm intervals. Loss-on ignition confirmed the presence of organic material. Identifying the organic content involved removing nonorganic material from the sediment and sorting the organic material under magnification. This procedure established that most of the organic material was red mangrove (Rhizophora mangle). Red mangroves tolerate salt water, but under conditions of sea-level rise, the plants grow vertically to keep their leaves above water. Sediment, leaves, and detritus trapped in the prop roots form mangrove peat, which serves as a proxy for sea-level rise. AMS dating of fine red mangrove roots determined that the local sea levels rose at Ta'ab Nuk Na throughout the Late Classic period and continued into the Postclassic period. Radiocarbon dates obtained from the wood-post samples yielded Late Classic–period dates. Comparing the radiocarbon dates from the wooden posts and the sediment core samples determined that the site was abandoned before the rising seas flooded the area. Evidently, sea-level rise did not play a role in site abandonment. 

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3. Human-environment interactions at Ta’ab Nuk Na, a submerged Maya salt works site in Belize

   Foster, Cheryl M; McKillop, Heather; Sills, E Cory (August 2023, Ancient Mesoamerica)

   Sea-level rise and settlement are investigated at Ta'ab Nuk Na, an ancient Maya salt works in Belize, by examining samples from wooden posts and marine sediment. The samples included Post 145 of Building B and the Nunavut beam, along with marine sediment columns cut from beside both wooden posts. The sediment columns were sampled at 2 cm intervals. Loss-on ignition confirmed the presence of organic material. Identifying the organic content involved removing nonorganic material from the sediment and sorting the organic material under magnification. This procedure established that most of the organic material was red mangrove (Rhizophora mangle). Red mangroves tolerate salt water, but under conditions of sea-level rise, the plants grow vertically to keep their leaves above water. Sediment, leaves, and detritus trapped in the prop roots form mangrove peat, which serves as a proxy for sea-level rise. AMS dating of fine red mangrove roots determined that the local sea levels rose at Ta'ab Nuk Na throughout the Late Classic period and continued into the Postclassic period. Radiocarbon dates obtained from the wood-post samples yielded Late Classic–period dates. Comparing the radiocarbon dates from the wooden posts and the sediment core samples determined that the site was abandoned before the rising seas flooded the area. Evidently, sea-level rise did not play a role in site abandonment. 

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4. Sea-level rise and settlement at Ek Way Nal: Coring the past

   Foster, Cher; McKillop, Heather; Sills, E Cory (July 2023, Research reports in Belizean archaeology)

   Excavations in the spring and summer of 2022 were carried out at the underwater ancient Maya salt work of Ek Way Nal in Punta Ycacos Lagoon, Paynes Creek National Park, Belize. Ek Way Nal provided salt to the ancient Maya during the Late and Terminal Classic periods (600-900 C.E.). In additional to excavations in buildings at the site, a 1 X 2 m unit was excavated to extract a sediment column for examining the relationship between the ancient Maya settlement at Ek Way Nal and sea-level rise. In this article, the excavations, extraction of the sediment column, and processing it for laboratory analyses are described. Field observations are discussed. Fine red mangrove root (Rhizophora mangle) and charcoal samples were extracted from the sediment column for radiocarbon dating. The results from the datum core excavation indicate that sea-level rise occurred before, during, and after the ancient Maya occupation at Ek Way Nal. 

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5. Pollen Geochronology from the Atlantic Coast of the United States during the Last 500 Years

   https://doi.org/10.3390/w13030362  

   Christie, Margaret; Bernhardt, Christopher; Parnell, Andrew; Shaw, Timothy; Khan, Nicole; Corbett, D.; García-Artola, Ane; Clear, Jennifer; Walker, Jennifer; Donnelly, Jeffrey; et al (February 2021, Water)

   Building robust age–depth models to understand climatic and geologic histories from coastal sedimentary archives often requires composite chronologies consisting of multi-proxy age markers. Pollen chronohorizons derived from a known change in vegetation are important for age–depth models, especially those with other sparse or imprecise age markers. However, the accuracy of pollen chronohorizons compared to other age markers and the impact of pollen chronohorizons on the precision of age–depth models, particularly in salt marsh environments, is poorly understood. Here, we combine new and published pollen data from eight coastal wetlands (salt marshes and mangroves) along the Atlantic Coast of the United States (U.S.) from Florida to Connecticut to define the age and uncertainty of 17 pollen chronohorizons. We found that 13 out of 17 pollen chronohorizons were consistent when compared to other age markers (radiocarbon, radionuclide 137Cs and pollution markers). Inconsistencies were likely related to the hyperlocality of pollen chronohorizons, mixing of salt marsh sediment, reworking of pollen from nearby tidal flats, misidentification of pollen signals, and inaccuracies in or misinterpretation of other age markers. Additionally, in a total of 24 models, including one or more pollen chronohorizons, increased precision (up to 41 years) or no change was found in 18 models. 

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