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1. TERMINAL PLEISTOCENE THROUGH MIDDLE HOLOCENE OCCUPATIONS IN SOUTHEASTERN MESOAMERICA: LINKING ECOLOGY AND CULTURE IN THE CONTEXT OF NEOTROPICAL FORAGERS AND EARLY FARMERS

   https://doi.org/10.1017/S0956536121000195  

   Prufer, Keith M. ; Robinson, Mark ; Kennett, Douglas J. ( January 2021 , Ancient Mesoamerica)

   Abstract Data from rock shelters in southern Belize show evidence of tool making, hunting, and aquatic resource exploitation by 10,500 cal b.c. ; the shelters functioned as mortuary sites between 7600 and 2000 cal b.c. Early Holocene contexts contain stemmed and barbed bifaces as part of a tradition found broadly throughout the neotropics. After around 6000 cal b.c. , bifacial tools largely disappear from the record, likely reflecting a shift to increasing reliance on plant foods, around the same time that the earliest domesticates appear in the archaeological record in the neotropics. We suggest that people living in southern Belize maintained close ties with neighbors to the south during the Early Holocene, but lagged behind in innovating new crops and farming technologies during the Middle Holocene. Maize farming in Belize intensified between 2750–2050 cal b.c. as maize became a dietary staple, 1000–1300 years later than in South America. Overall, we argue from multiple lines of data that the Neotropics of Central and South America were an area of shared information and technologies that heavily influenced cultural developments in southeastern Mesoamerica during the Early and Middle Holocene.
2. South-to-north migration preceded the advent of intensive farming in the Maya region

   https://doi.org/10.1038/s41467-022-29158-y  

   Kennett, Douglas J. ; Lipson, Mark ; Prufer, Keith M. ; Mora-Marín, David ; George, Richard J. ; Rohland, Nadin ; Robinson, Mark ; Trask, Willa R. ; Edgar, Heather H. ; Hill, Ethan C. ; et al ( December 2022 , Nature Communications)

   Abstract The genetic prehistory of human populations in Central America is largely unexplored leaving an important gap in our knowledge of the global expansion of humans. We report genome-wide ancient DNA data for a transect of twenty individuals from two Belize rock-shelters dating between 9,600-3,700 calibrated radiocarbon years before present (cal. BP). The oldest individuals (9,600-7,300 cal. BP) descend from an Early Holocene Native American lineage with only distant relatedness to present-day Mesoamericans, including Mayan-speaking populations. After ~5,600 cal. BP a previously unknown human dispersal from the south made a major demographic impact on the region, contributing more than 50% of the ancestry of all later individuals. This new ancestry derived from a source related to present-day Chibchan speakers living from Costa Rica to Colombia. Its arrival corresponds to the first clear evidence for forest clearing and maize horticulture in what later became the Maya region.
3. Evidence, causes, and consequences of declining nitrogen availability in terrestrial ecosystems

   https://doi.org/10.1126/science.abh3767  

   Mason, Rachel E. ; Craine, Joseph M. ; Lany, Nina K. ; Jonard, Mathieu ; Ollinger, Scott V. ; Groffman, Peter M. ; Fulweiler, Robinson W. ; Angerer, Jay ; Read, Quentin D. ; Reich, Peter B. ; et al ( April 2022 , Science)

   BACKGROUND The availability of nitrogen (N) to plants and microbes has a major influence on the structure and function of ecosystems. Because N is an essential component of plant proteins, low N availability constrains the growth of plants and herbivores. To increase N availability, humans apply large amounts of fertilizer to agricultural systems. Losses from these systems, combined with atmospheric deposition of fossil fuel combustion products, introduce copious quantities of reactive N into ecosystems. The negative consequences of these anthropogenic N inputs—such as ecosystem eutrophication and reductions in terrestrial and aquatic biodiversity—are well documented. Yet although N availability is increasing in many locations, reactive N inputs are not evenly distributed globally. Furthermore, experiments and theory also suggest that global change factors such as elevated atmospheric CO 2 , rising temperatures, and altered precipitation and disturbance regimes can reduce the availability of N to plants and microbes in many terrestrial ecosystems. This can occur through increases in biotic demand for N or reductions in its supply to organisms. Reductions in N availability can be observed via several metrics, including lowered nitrogen concentrations ([N]) and isotope ratios (δ 15 N) in plant tissue, reduced rates of N mineralization, and reduced terrestrial Nmore »export to aquatic systems. However, a comprehensive synthesis of N availability metrics, outside of experimental settings and capable of revealing large-scale trends, has not yet been carried out. ADVANCES A growing body of observations confirms that N availability is declining in many nonagricultural ecosystems worldwide. Studies have demonstrated declining wood δ 15 N in forests across the continental US, declining foliar [N] in European forests, declining foliar [N] and δ 15 N in North American grasslands, and declining [N] in pollen from the US and southern Canada. This evidence is consistent with observed global-scale declines in foliar δ 15 N and [N] since 1980. Long-term monitoring of soil-based N availability indicators in unmanipulated systems is rare. However, forest studies in the northeast US have demonstrated decades-long decreases in soil N cycling and N exports to air and water, even in the face of elevated atmospheric N deposition. Collectively, these studies suggest a sustained decline in N availability across a range of terrestrial ecosystems, dating at least as far back as the early 20th century. Elevated atmospheric CO 2 levels are likely a main driver of declines in N availability. Terrestrial plants are now uniformly exposed to ~50% more of this essential resource than they were just 150 years ago, and experimentally exposing plants to elevated CO 2 often reduces foliar [N] as well as plant-available soil N. In addition, globally-rising temperatures may raise soil N supply in some systems but may also increase N losses and lead to lower foliar [N]. Changes in other ecosystem drivers—such as local climate patterns, N deposition rates, and disturbance regimes—individually affect smaller areas but may have important cumulative effects on global N availability. OUTLOOK Given the importance of N to ecosystem functioning, a decline in available N is likely to have far-reaching consequences. Reduced N availability likely constrains the response of plants to elevated CO 2 and the ability of ecosystems to sequester carbon. Because herbivore growth and reproduction scale with protein intake, declining foliar [N] may be contributing to widely reported declines in insect populations and may be negatively affecting the growth of grazing livestock and herbivorous wild mammals. Spatial and temporal patterns in N availability are not yet fully understood, particularly outside of Europe and North America. Developments in remote sensing, accompanied by additional historical reconstructions of N availability from tree rings, herbarium specimens, and sediments, will show how N availability trajectories vary among ecosystems. Such assessment and monitoring efforts need to be complemented by further experimental and theoretical investigations into the causes of declining N availability, its implications for global carbon sequestration, and how its effects propagate through food webs. Responses will need to involve reducing N demand via lowering atmospheric CO 2 concentrations, and/or increasing N supply. Successfully mitigating and adapting to declining N availability will require a broader understanding that this phenomenon is occurring alongside the more widely recognized issue of anthropogenic eutrophication. Intercalibration of isotopic records from leaves, tree rings, and lake sediments suggests that N availability in many terrestrial ecosystems has steadily declined since the beginning of the industrial era. Reductions in N availability may affect many aspects of ecosystem functioning, including carbon sequestration and herbivore nutrition. Shaded areas indicate 80% prediction intervals; marker size is proportional to the number of measurements in each annual mean. Isotope data: (tree ring) K. K. McLauchlan et al. , Sci. Rep. 7 , 7856 (2017); (lake sediment) G. W. Holtgrieve et al. , Science 334 , 1545–1548 (2011); (foliar) J. M. Craine et al. , Nat. Ecol. Evol. 2 , 1735–1744 (2018)« less
4. Stable isotope analysis of vegetation history and land use change at Laguna Santa Elena in southern Pacific Costa Rica

   https://doi.org/10.1007/s00334-019-00755-0  

   Kerr, Matthew T. ; Horn, Sally P. ; Lane, Chad S. ( October 2019 , Vegetation History and Archaeobotany)

   Laguna Santa Elena (8.9290° N, 82.9257° W, 1055 m a.s.l.) is a small lake in the Diquís archaeological sub-region of southern Pacific Costa Rica. Previous analyses of pollen and charcoal in a sediment core from Santa Elena revealed a nearly 2,000 year history of vegetation change, maize cultivation and site occupation that is consistent with the archaeological record from the lake basin and surrounding area. Here we present the results of new loss-on-ignition, geochemical and bulk stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of the Santa Elena sediments that supplement and refine the previous reconstruction. Like many lakes in Central America and the Caribbean, Laguna Santa Elena was a magnet for humans throughout its history. As a result, the lake experienced vegetation modification by humans and maize cultivation at varying intensities over a long duration. The Santa Elena sediments provide a record of palaeoenvironmental change during times of major culture change and increasing cultural complexity in the Diquís region, which occurred during intervals of broader changes driven by external forcing mechanisms, including the Terminal Classic Drought (TCD), the Little Ice Age (LIA) and the Spanish Conquest. Our high resolution lake sediment study from Santa Elena reveals details of thesemore »events at the local scale that are unobtainable by other means, including the timing of the initial intensification of maize cultivation at ca. 1,570 cal BP (AD 380) and two intervals of population decline coinciding with the TCD at ca. 1,085 cal BP (AD 865) and near the start of the LIA at ca. 683 cal BP (AD 1267).« less
5. Discovery of the Youngest Toba Tuff in South Africa; Challenges of Extremely Low Abundance Cryptotephra

   Smith, E ; Johnsen, R ; Ren, M ; Hirniak, J ; Fisher, E ; Campisano, C ; Marean, C. ( July 2021 , Annual VM Goldschmidt Conference)

   The 74 ka Youngest Toba Tuff (YTT) was discovered as cryptotephra in South African archaeological sites at Pinnacle Point (PP) 5-6N, Vleesbaai [1] and Klasies River on the Indian Ocean, and the Diepkloof Rock Shelter on the Atlantic coast nearly 750 km west of PP. The YTT eruption distributed tephra across eastern and southern Africa and provides a widespread isochron useful for dating archaeological deposits, testing age models, and precisely determining the timing of changes in human behavior. At PP, we demonstrated that the MIS 4-5 transition began just before the YTT eruption. Humans thrived both through the YTT event and the changing climate, and important changes in technology occurred just after the Toba eruption [1]. Controversy related to trapped charge age models at the Diepkloof rock shelter [2,3] were resolved by identifying YTT at a location in the stratigraphic section that confirmed the Jacobs et al. [2] model for the site, confirming that technological changes similar to those observed at PP occurred synchronously to those at Diepkloof, not substantially before as suggested by a prior published age model [3]. Processing samples with very low abundance cryptotephra, such as that found in South Africa, is a challenge and requires revisionmore »of standard laboratory techniques. Samples with high organic or clay content benefit by being treated with 10% HCl and 3% hydrogen peroxide (H2O2). This step does not degrade shard integrity or affect chemistry and is useful in separating shards from clay and organic particles allowing better recovery in heavy liquids. We also modified the heavy liquid density range from 1.95 - 2.55 to 2.2 - 2.5 g/cm3 to more effectively remove quartz and feldspar as well as biogenic silica. This density range captures shards ranging from rhyolite to dacite in composition. [1] Smith, E. I. et al. Nature 555, 511, 2018 [2] Jacobs, Z. & Roberts, R. G. Journal of Archaeological Science 63, 175-192, 2015. [3] Tribolo, C. et al. Journal of Archaeological Science 40, 3401-3411 2013.« less