skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: LA‐ICP‐MS analysis of glass beads from Tié (12th–14th centuries), Kanem, Chad: Evidence of trans‐Sudanic exchanges
Abstract Chemical analysis of glass from African archaeological sites has become a standard research tool over the past decades. Despite the multiplication of studies, the continent still exhibits vast unexplored regions. One of these is the surroundings of Lake Chad. This paper discusses the results of LA‐ICP‐MS analysis of recently excavated glass beads from the late medieval Chadian site of Tié. We demonstrate that the composition of those glass beads largely matches assemblages from along the East African coast. This indicates that most of the beads examined entered the region via a hitherto undocumented east–west Sudanic route linking Northeast Africa with Lake Chad.  more » « less
Award ID(s):
2208558
PAR ID:
10434503
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
Archaeometry
Volume:
66
Issue:
1
ISSN:
0003-813X
Format(s):
Medium: X Size: p. 100-118
Size(s):
p. 100-118
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract Climate models predict Africa will warm by up to 5°C in the coming century, stressing African societies. To provide independent constraints on model predictions, this study compares two notable reconstructions of East African temperatures to those predicted by Paleoclimate Model Intercomparison Project (PMIP3) and transient TraCE (Transient Climate Evolution) simulations, focusing on the Mid‐Holocene (MH, 5–8 kyr B.P.). Reconstructions of tropical African temperature derived from lake sedimentary archives indicate 1–2.5°C of warming during the MH relative to the 20th century, but most climate models do not replicate the warming observed in these paleoclimate data. We investigate this discrepancy using a new lake proxy system model, with attention to the (potentially non‐stationary) relationship between lake temperature and air temperature. We find amplified lake surface temperature changes compared to air temperature during the MH due to heightened seasonality and precessional forcing. Lacustrine processes account for some of the warming, and highlight how the lake heat budget leads to a rectification of the seasonal cycle; however, the simulated lake heating bias is insufficient to reconcile the full discrepancy between the models and the proxy‐derived MH warming. We find further evidence of changes in mixing depth over time, potentially driven by changes in cloud cover and shortwave radiative fluxes penetrating the lake surface. This may confound interpretation for glycerol dialkyl glycerol tetraethers (GDGT) compounds which exist in the mixed layer, and suggests a need for independent constraints on mixed layer depth. This work provides a new interpretive framework for invaluable paleoclimate records of temperature changes over the African continent. 
    more » « less
  2. Abstract While organic photocatalysts provide increasingly versatile chemical pathways under mild conditions, their long‐term stability remains understudied. Here, the photobleaching behavior of xanthene dye photocatalysts is investigated. Rose Bengal, Eosin Y, and fluorescein are studied when in solution, when grafted to glass beads, and when incorporated into polymer brushes that are tethered to glass beads. This provides a comparison between xanthene's stability as a homogeneous and as a heterogeneous photocatalyst. Photobleaching is investigated using UV–vis, diffuse reflectance UV–vis (DR UV–vis), and fluorescence microscopy. Xanthene dyes as homogeneous photocatalysts exhibit the highest photostability, while the grafted systems appeared to fade more rapidly. Notably, heterogenization appears to have different effects based on the photocatalyst system, and further altering the photocatalyst environment with reagents may improve stability. 
    more » « less
  3. Abstract BackgroundAfrican cichlid fishes are well known for their rapid radiations and are a model system for studying evolutionary processes. Here we compare multiple, high-quality, chromosome-scale genome assemblies to elucidate the genetic mechanisms underlying cichlid diversification and study how genome structure evolves in rapidly radiating lineages. ResultsWe re-anchored our recent assembly of the Nile tilapia (Oreochromis niloticus) genome using a new high-density genetic map. We also developed a new de novo genome assembly of the Lake Malawi cichlid, Metriaclima zebra, using high-coverage Pacific Biosciences sequencing, and anchored contigs to linkage groups (LGs) using 4 different genetic maps. These new anchored assemblies allow the first chromosome-scale comparisons of African cichlid genomes. Large intra-chromosomal structural differences (~2–28 megabase pairs) among species are common, while inter-chromosomal differences are rare (<10 megabase pairs total). Placement of the centromeres within the chromosome-scale assemblies identifies large structural differences that explain many of the karyotype differences among species. Structural differences are also associated with unique patterns of recombination on sex chromosomes. Structural differences on LG9, LG11, and LG20 are associated with reduced recombination, indicative of inversions between the rock- and sand-dwelling clades of Lake Malawi cichlids. M. zebra has a larger number of recent transposable element insertions compared with O. niloticus, suggesting that several transposable element families have a higher rate of insertion in the haplochromine cichlid lineage. ConclusionThis study identifies novel structural variation among East African cichlid genomes and provides a new set of genomic resources to support research on the mechanisms driving cichlid adaptation and speciation. 
    more » « less
  4. Tropical mountain ecosystems hold immense ecological and economic importance, yet they face disproportionate risks from shifting tropical climates. For example, present-day montane vegetation of East Africa is characterized by different plant species that grow in and are restricted to certain elevations due to environmental tolerances. As climate changes and temperature/rainfall zones move on mountains, these species must rapidly adjust their ranges or risk extinction. Paleoenvironmental records offer valuable insights into past climate and ecosystem dynamics, aiding predictions for ongoing climate change impacts. In particular, warming and wetting in tropical East Africa during the mid-Holocene resulted in both lowland and highland forest expansion. However, the relative impacts of rainfall and temperature change on montane ecosystems along with the influence of lowland forest expansion on montane communities is not completely understood. We use fossil pollen to study the vegetation changes in two lakes at different altitudes in the Rwenzori Mountains, Uganda: Lake Mahoma (Montane Forest belt) and Upper Kachope Lake (Afroalpine belt). Further, using the newly relaunched African Pollen Database and recent temperature reconstructions, we provide a regional synthesis of vegetation changes in the Rwenzori and then compare this with changes observed from other equatorial East African montane sites (particularly Mt Kenya). In the early to mid-Holocene in the Rwenzori Mountains, trees common today in lowland forests dominated, driven largely by warmer temperatures. After 4000 years ago (4ka), Afromontane forest trees along with grasses progressively replaced lowland trees. Not all sites experienced identical transitions. For instance, at Lake Rutundu on Mt Kenya at the same elevation as Lake Mahoma, bamboo expansion preceded Afromontane forest growth, likely influenced by variations in fire. Variance partitioning indicates that each site responded differently to changes in temperature and rainfall. Therefore, these site-specific ecological responses underscore the importance of considering biogeographic legacies as management strategies are developed, despite similarities in modern ecology. 
    more » « less
  5. The Ogallala Aquifer, a primary irrigation water source in the High Plains region of the United States, is declining, thereby necessitating new water conservation strategies. This paper investigates the impact of mixed wettability on the evaporation dynamics of a 10-µl sessile water droplet placed within simulated soil pores comprised of hydrophobic Teflon beads (CA ∼ 108°) and hydrophilic glass (CA ∼ 41°) beads with 2.38-mm diameters, where homogeneous and heterogenous (i.e., mixed hydrophobicity and hydrophilicity) wettability configurations were investigated. Experiments were performed in an environmental chamber where the relative humidity and temperature were 60% ± 0.1% RH and 20 ± 0.4 °C, respectively. Wettability influenced evaporation times, with homogeneous hydrophobic pores (i.e., three Teflon beads) and heterogenous one glass, two Teflon pores having the longest average evaporation times of 40 and 39 min, respectively. Homogeneous hydrophilic pores (i.e., three glass beads) and heterogenous two glass, one Teflon pores exhibited evaporation times of 34 min. Evaporation times for heterogenous combinations trended based on the predominant wettability. Contact angles and the projected length of contact were analyzed from videos to capture pinning and depinning during evaporation. For many cases including hydrophobicity, contact angles were less than 90°, and in some configurations, water would be pinned on a Teflon bead, whereas depinning (i.e., moving) on a glass bead. Stick-slip evaporation was observed, where the evaporating droplet switched between constant contact radius and constant contact area evaporative modes to minimize droplet surface energy. The results suggest wettability alterations in agricultural settings may reduce evaporation. 
    more » « less