A terrestrial reconstruction of Gona, Ethiopia before and during the African Humid Period

The African Humid Period (AHP) resulted in more humid conditions across Northern and Eastern Africa from 15 to 5 thousand years ago (ka). This wetter climate affected flora, fauna and the Homo sapiens living in East Africa. The lack of terrestrial paleoenvironmental reconstructions is a problem in East Africa, especially during the AHP, where most are done utilizing lacustrine or marine proxies. In the case of Gona, Ethiopia, terrestrial proxies are desired due to the rich archaeological and fossil concentrations that occur in the area. Paleosols provide more direct, localized reconstructions that provide context for these finds. This study utilizes paleopedology, geochronology, and geochemistry to reconstruct the environment of Gona during the AHP. We examine paleosols from the Erole and Odele drainages within Gona. The Odele paleosol weathered before the AHP, between the Korina Tuff (\u3c39 \u3eka) and the Kilaitoli Tuff (~25.7 ka). The Erole paleosol is above the Kilaitoli Tuff and immediately above a calibrated 14C age of 12 ka. These paleosols formed in floodplains of tributaries that flowed into the nearby Awash River. Strain calculations show more volumetric collapse at Erole (-39 ± 8 %) than at Odele (-5 ± 4 %). The open-system mass-transfer coefficient, tau, shows average losses of 25 ± 13 % SiO2 and 71 ± 6 % CaO at Erole, which are greater than losses of 8 ± 4 % SiO2 and 7 ± 3 % CaO at Odele. These calculations suggest more weathering and dissolution of minerals during the AHP, as well as more bioturbation. The results of this paleosol comparison are consistent with wetter conditions during the AHP that facilitated the development of grasslands along tributary valleys

First examination of palynolgy across the K-Pg Boundary in the Jackson Purchase region of Kentucky

This study examines the Independence School section of the K-Pg Boundary, which is located in a creek cutbank exposure in Carlisle County, in the Jackson Purchase region of Kentucky. This section has not otherwise been examined since 1980 and has not previously been palynologically studied in detail. Specifically, we are examining the Owl Creek and upper McNairy Formations, deposited as Maastrictian-age sediments and the Clayton Formation, deposited as Danian- age sediments, in a mosaic of onshore, nearshore, and coastal environments (Tschudy, 1970; Olive, 1980). The site was relocated by G. Stinchcomb and students from Murray State University in 2020 and the subject of a presentation on geochemistry and iridium levels at the Geological Society of America in 2021 (Asselta et al., 2021).https://scholarworks.moreheadstate.edu/celebration_posters_2023/1025/thumbnail.jp

Linking Remotely Sensed Carbon and Water Use Efficiencies with In Situ Soil Properties

The capacity of terrestrial ecosystems to sequester carbon dioxide (CO2 ) from the atmosphere is expected to be altered by climate change and CO2 fertilization, but this projection is limited by our understanding of how the soil system interacts with plants. Understanding the soil–vegetation interactions is essential to assess the magnitude and response of terrestrial ecosystems to the changing climate. Here, we used soil profile and satellite data to explore the role that soil properties play in regulating water and carbon use by plants. Data obtained for 19 terrestrial ecosystem sites in a warm temperate and humid climate were used to investigate the relationship between remotely sensed data and soil physical and chemical properties. Classification and regression tree results showed that in situ soil carbon isotope (δ 13C), and soil order were significant predictors (r2 = 0.39, mean absolute error (MAE) = 0 of 0.175 gC/KgH2O) of remotely sensed water use efficiency (WUE) based on the Moderate Resolution Imaging Spectroradiometer (MODIS). Soil extractable calcium (Ca), and land cover type were significant predictors of remotely sensed carbon use efficiency (CUE) based on MODIS and Landsat data-(r2 = 0.64–0.78, MAE = 0.04–0.06). We used gross primary productivity (GPP) derived from solar-induced fluorescence (SIF) data, based on the Orbiting Carbon Observatory-2 (OCO-2), to calculate WUE and CUE (referred to as WUESIF and CUESIF, respectively) for our study sites. The regression tree analysis revealed that soil organic matter and soil extractable magnesium (Mg), δ 13C, and soil silt content were the important predictors of both WUESIF (r2 = 0.19, MAE = 0.64 gC/KgH2O) and CUESIF (r2 = 0.45, MAE = 0.1), respectively. Our results revealed the importance of soil extractable Ca, soil carbon (S13C is a facet of soil carbon content), and soil organic matter predicting CUE and WUE. Insights gained from this study highlighted the importance of biotic and abiotic factors regulating plant and soil interactions. These types of data are timely and critical for accurate predictions of how terrestrial ecosystems respond to climate change

Chromosome Duplication in <i>Saccharomyces cerevisiae</i>

The accurate and complete replication of genomic DNA is essential for all life. In eukaryotic cells, the assembly of the multi-enzyme replisomes that perform replication is divided into stages that occur at distinct phases of the cell cycle. Replicative DNA helicases are loaded around origins of DNA replication exclusively during G 1 phase. The loaded helicases are then activated during S phase and associate with the replicative DNA polymerases and other accessory proteins. The function of the resulting replisomes is monitored by checkpoint proteins that protect arrested replisomes and inhibit new initiation when replication is inhibited. The replisome also coordinates nucleosome disassembly, assembly, and the establishment of sister chromatid cohesion. Finally, when two replisomes converge they are disassembled. Studies in Saccharomyces cerevisiae have led the way in our understanding of these processes. Here, we review our increasingly molecular understanding of these events and their regulation. Keywords: DNA replication; cell cycle; chromatin; chromosome duplication; genome stability; YeastBookNational Institutes of Health (U.S.) (Grant GM-052339

Climatic and human influences on Holocene alluvial history and paleoenvironment of the middle Delaware River Valley, USA.

The potential for future prolonged drought episodes in the Northeastern USA is alarming given that a humid climate currently provides water to +50 million people in the northeast, USA. Hydro-climatic projections are hampered by a lack of regionally-based paleoenvironmental reconstructions. The middle Delaware River Valley provides a unique opportunity to expand the Holocene alluvial history and paleoenvironment for the northeast, USA. Thirty-six soil profile descriptions, 332 grain size analyses, and 82 14C ages from trenches and auger borings show that similar alluvial landforms within the river valley have different formation histories and depict a valley that has experienced middle to late Holocene floodplain and terrace reworking. Despite erosion, secular changes in buried soil and sediment properties are closely associated with climate change and land-use. A Holocene time-series was constructed using 149 δ13Csom values from alluvial terrace profiles. There is good agreement between increasing δ13Csom and Panicoideae phytolith concentrations, suggesting that variations in C4 biomass are a contributor to changes in the soil δ13C. A measurement error deconvolution curve over time reveals two isotope stages (II and I), with nine sub-stages exhibiting variations in average δ13Csom (%C4). Stage II, ~10.7-4.3 ka, shows above average δ13Csom (increase %C4) values with evidence of an early Holocene warm/dry interval (sub-stage IIb, 9.8-8.3 ka) that coincides with rapid warming and cool/dry abrupt climate change. Sub-stage IId, 7.0-4.3 ka, is an above average δ13Csom (increase %C4) interval associated with the mid-Holocene warm/dry Hypsithermal. The Stage II-I shift at 4.3 ka documents a transition toward below average δ13Csom (decrease %C4) values, coinciding with decreasing insolation and moisture budget reorganization. Sub-stages Ib and Id (above average %C4) coincide with the first documented occurrence of maize in northeastern USA and population increase during the Late Woodland. These associations suggest that humans influenced δ13Csom during the late Holocene. The influence of land-use is further corroborated by a regionally extensive anthropogenic sedimentation event documented throughout eastern North America, pre-Colonial sediment (PCS) circa: A.D. 1,100–1,600. These data demonstrate that combined prehistoric land-use and climate change impacted eastern North American floodplains several hundred years prior to the onset of European Settlement.Ph.D

Exploring the impacts of past environments and climates on the initial dispersal of humans out of Africa

Scientists continue to debate the onset and development of hominin migration events throughout the East African Rift System. Recent archaeological discoveries reveal that Homo sapiens initially emerged in north Africa, 300ka. From this initial emergence, sapiens migrated throughout north and sub-Saharan Africa, up the Levantine corridor, and into Eurasia between 50 to 120ka. Variations in climatic and environmental conditions are often inferred to be the catalysts of these migrations, yet the precise context of these dispersals remain unclear. There are two schools of thought on the matter: warm and wet conditions could have facilitated the earliest migration of Homo sapiens approximately 90 to 120ka, or an unusually cold and dry period between 55 to 65ka brought about the initial out-of-Africa event. A lack of land-based records hinders this debate. What were the Late Pleistocene paleoenvironmental and paleoclimatic conditions like on land? How did these conditions cause our ancestors to disperse out of Africa? Answers to these questions may lie in the paleosols (fossilized soils) of Gona, Ethiopia, an area with one of the most established archaeological records in the East African Rift System. This area contains Late Pleistocene paleosol deposits, which are a reservoir of biogeochemical dynamics that can be related to the surrounding environment. Thus, these paleosols are an ideal archive for reconstructing the paleoenvironment associated with Gona’s hominin fossil sites. To answer the questions above, I would like to characterize the bulk and stable isotope geochemistry of these terrestrial paleosols in Gona’s sedimentary record. Establishing a stable isotopic geochemical record of oxygen and carbon isotopes from soil carbonates of the Late Pleistocene in Gona will allow us to reconstruct changes in Late Pleistocene temperature and vegetation over time. The terrestrial isotopic data will then be compared with data from the established archaeological record at Gona to determine when archaeological and hominin fossil sites occur more frequently in the local environmental record - during wetter or drier intervals - and under what type of vegetation. I will characterize the paleosols associated with soil carbonates using bulk geochemical signals of drainage, where mass-balance of geochemical depth trends in paleosols will be used to reconstruct dominant weathering trends and changes throughout the Late Pleistocene. When compared with the terrestrial stable isotopic data, I can see if poorly-drained paleosols/environments at Gona are linked to changes in isotope geochemistry and whether these changes can be correlated to any patterns in local archaeological and hominin fossil records. This project will produce a comprehensive Late Pleistocene record of paleoenvironmental and paleoclimatic change at Gona, which in turn will provide a much-needed baseline of comparison to already established genetic and marine-based records. Land-based records will help us determine to what degree the local/regional environment and climate drove the initial out-of-Africa migration. Furthermore, it will shed light upon the climatic intervals where migration events were likely to occur