520,000 years of environmental change in West Africa

Global temperatures are predicted to rise by 2-2.5°C by 2065, profoundly affecting the Earth's environment. The response of ecosystems to past climate fluctuations can inform on how systems will respond in the future. This thesis focuses on Quaternary environmental changes in West Africa, a region important because of its high ecological value and role in the global carbon cycle. In 2004, the International Continental Drilling Program recovered c. 291 m of sediments spanning the last c. 1 Myr from Lake Bosumtwi (Ghana). Pollen, charcoal and nitrogen isotopes (ᵟ15N) were analysed from the most recent c. 150m (c. 520 kyr). The latitudinal position and long duration of this core makes it unique for understanding West African monsoon dynamics and vegetation change. To aid characterisation of the Bosumtwi pollen succession, an atlas of present-day pollen was constructed for 364 pollen and spore taxa. The pollen record from Bosumtwi reveals dynamic vegetation change over the last c. 520 kyr, characterized by eleven biome shifts between savannah and forest. Savannah vegetation is dominated by Poaceae (>55%) associated with Cyperaceae, Chenopodiaceae-Amaranthaceae and Caryophyllaceae. Forest vegetation is palynologically diverse, but broadly characterised by Moraceae, Celtis, Uapaca, Macaranga and Trema. Low ᵟ15N values correspond to forest expansion and these are driven by high lake levels. The timescale indicates that the six periods of forest expansion correspond to global interglacial periods. The record indicates that the wettest climate occurred during the Holocene, and the driest during Marine Isotope Stage 7. The vegetation and ᵟ15N records show a strong response to glacial-interglacial variability between 520- 320 kyr and 130- 0 kyr. Between 320- 130 kyr there is a weaker response to glacial-interglacial cycles probably related to high eccentricity during the peak of the 400-kyr component of eccentricity, with high eccentricity resulting in greater seasonality and ultimately drier conditions

Drivers of ecosystem and climate change in tropical West Africa over the past ∼540 000 years

A paucity of empirical non-marine data means that uncertainty surrounds the impact of climate change on terrestrial ecosystems in tropical regions beyond the last glacial period. The sedimentary fill of the Bosumtwi impact crater (Ghana) provides the longest continuous Quaternary terrestrial archive of environmental change in West Africa, spanning the last ∼1.08 million years. Here we explore the drivers of change in ecosystem and climate in tropical West Africa for the past ∼540 000 years using pollen analysis and the nitrogen isotope composition of bulk organic matter preserved in sediments from Lake Bosumtwi. Variations in grass pollen abundance (0−99%) indicate transitions between grassland and forest. Coeval variations in the nitrogen isotopic composition of organic matter indicate that intervals of grassland expansion coincided with minimum lake levels and low regional moisture availability. The observed changes responded to orbitally paced global climate variations on both glacial–interglacial and shorter timescales. Importantly, the magnitude of ecosystem change revealed by our data exceeds that previously determined from marine records, demonstrating for the first time the high sensitivity of tropical lowland ecosystems to Quaternary climate change

Impact of earthquakes on agriculture during the Roman–Byzantine period from pollen records of the Dead Sea laminated sediment

The Dead Sea region holds the archives of a complex relationship between an ever-changing nature and ancient civilisations. Regional pollen diagrams show a Roman–Byzantine period standing out in the recent millennia by its wetter climate that allowed intensive arboriculture. During that period, the Dead Sea formed laminites that display mostly a seasonal character. A multidisciplinary study focused on two earthquakes, 31 BC and AD 363, recorded as seismites in the Ze’elim gully A unit III which has been well dated by radiocarbon in a previous study. The sampling of the sediment was done at an annual resolution starting from a few years before and finishing a decade after each earthquake. A clear drop in agricultural indicators (especially Olea and cereals) is shown. These pollen indicators mostly reflect human activities in the Judean Hills and coastal oases. Agriculture was disturbed in large part of the rift valley where earthquake damage affected irrigation and access to the fields. It took 4 to 5 yr to resume agriculture to previous conditions. Earthquakes must be seen as contributors to factors damaging societies. If combined with other factors such as climatic aridification, disease epidemics and political upheaval, they may lead to civilisation collapse

A statistical sub-sampling tool for extracting vegetation community and diversity information from pollen assemblage data

AbstractPollen assemblages are used extensively across the globe, providing information on various characteristics of the vegetation communities that originally produced them, and how these vary temporally and spatially. However, anticipating a statistically based robust pollen count size, sufficient to characterise a pollen assemblage is difficult; particularly with regard to highly diverse pollen assemblages. To facilitate extraction of ecologically meaningful information from pollen assemblage data, a two part statistical sub-sampling tool has been developed (Models 1 and 2), which determines the pollen count size required to capture major vegetation communities of varying palynological richness and evenness, and the count size required to find the next not yet seen (rare) pollen taxa. The sub-sampling tool presented here facilitates the rapid assessment of individual pollen samples (initial information input of 100 pollen grains) and can, therefore, on a sample by sample basis achieve maximum effectiveness and efficiency. The sub-sampling tool is tested on fossil pollen data from five tropical sites.Results demonstrate that Model 1 predicts count sizes relating to palynological richness and evenness consistently. To characterise major vegetation community components model 1 indicates that, for samples with a lower richness and higher evenness lower count sizes than are considered standard can be used (<300, e.g. 122); however, for samples of high richness and low evenness, higher count sizes are required (>300, e.g. 870). Model 2 calculates the additional number of pollen grains needed to be counted to detect the next not yet seen pollen taxa, outputs were strongly related to input data count size as well as richness and evenness characteristics. We conclude that, given the temporal and spatial variations in vegetation communities and also pollen assemblages, pollen count sizes should be determined for each individual sample to ensure that effective and efficient data are generated and that detection of rare taxa is checked iteratively throughout the counting process

Terrestrial temperature evolution of southern Africa during the late Pleistocene and Holocene:Evidence from the Mfabeni Peatland

The scarcity of suitable high-resolution archives, such as ancient natural lakes, that span beyond the Holocene, hinders long-term late Quaternary temperature reconstructions in southern Africa. Here we target two cores from Mfabeni Peatland, one of the few long continuous terrestrial archives in South Africa that reaches into the Pleistocene, to generate a composite temperature record spanning the last ∼43 kyr. The Mfabeni Peatland has previously been proven suitable for temperature and hydrological reconstructions based on pollen and geochemical proxies. Here we use branched glycerol dialkyl glycerol tetraethers (brGDGTs) preserved in the Mfabeni peatland to derive a new quantitative air temperature record for south-east Africa. Our temperature record generally follows global trends in temperature and atmospheric CO2 concentrations, but is decoupled at times. Annual air temperatures during Marine Isotope Stage (MIS) 3 were moderately high (c. 20.5 °C), but dropped by c. 5 °C during the Last Glacial Maximum, reaching a minimum at c.16–15 ka. Asynchronous with local insolation, this cooling may have resulted from reduced sea surface temperatures linked to a northward shift in the Southern Hemisphere westerly winds. Concurrent with the southward retreat of the westerlies, and increasing sea surface temperatures offshore, warming from minimum temperatures (c. 15.0 °C) to average Holocene temperatures (c. 20.0 °C) occurred across the deglaciation. This warming was briefly but prominently interrupted by a millennial-scale cooling event of c. 3 °C at c. 2.4 ka, concurrent with a sudden change in hydrological conditions. The average Holocene temperatures of c. 20.0 °C were similar to those reconstructed for MIS 3, but after the 2.4 ka cooling period, air temperatures in the Mfabeni peat recovered and steadily increased towards the present. In summary, our record demonstrates that land temperature in eastern South Africa is highly sensitive to global drivers as well as nearby sea surface temperatures

A continental record of the Carnian Pluvial Episode (CPE) from the Mercia Mudstone Group (UK):palynology and climatic implications

The generally arid Late Triassic climate was interrupted by a wet phase during the mid-Carnian termed the Carnian Pluvial Episode (CPE). Quantitative palynological data from the Mercia Mudstone Group in the Wessex Basin (UK) reveal vegetation changes and palaeoclimate trends. Palynostratigraphy and bulk organic carbon isotope data allow correlation to other Carnian successions. The palynostratigraphy indicates that the Dunscombe Mudstone is Julian and the lowest part of the overlying Branscombe Mudstone Formation is Tuvalian. The Aulisporites acme characterizing the CPE in Tethyan successions and the Germanic Basin is missing in the UK. The quantitative palynological record suggests the predominance of xerophyte floral elements with a few horizons of increased hygrophytes. A humidity signal is not seen owing to the dry climate in central Pangea. Also, the signal might be masked by the overrepresentation of xerophyte regional pollen and the predominance of xerophyte hinterland flora. The bias towards regional pollen rain is enhanced by the potential increase in continental runoff related to seasonally humid conditions and differences in pollen production rates and transport mechanisms. The vegetation of British CPE successions suggests a more complex climate history during the Carnian, indicating that the CPE is not recognized by the same changes everywhere

CO\u3csub\u3e2\u3c/sub\u3e and fire influence tropical ecosystem stability in response to climate change

Interactions between climate, fire and CO2 are believed to play a crucial role in controlling the distributions of tropical woodlands and savannas, but our understanding of these processes is limited by the paucity of data from undisturbed tropical ecosystems. Here we use a 28,000-year integrated record of vegetation, climate and fire from West Africa to examine the role of these interactions on tropical ecosystem stability. We find that increased aridity between 28–15 kyr B.P. led to the widespread expansion of tropical grasslands, but that frequent fires and low CO2 played a crucial role in stabilizing these ecosystems, even as humidity changed. This resulted in an unstable ecosystem state, which transitioned abruptly from grassland to woodlands as gradual changes in CO2 and fire shifted the balance in favor of woody plants. Since then, high atmospheric CO2 has stabilized tropical forests by promoting woody plant growth, despite increased aridity. Our results indicate that the interactions between climate, CO2 and fire can make tropical ecosystems more resilient to change, but that these systems are dynamically unstable and potentially susceptible to abrupt shifts between woodland and grassland dominated states in the future

Identifying Dis/Misinformation on Social Media: A Policy Report for the Diplomacy Lab Strategies for Identifying Mis/Disinformation Project

Dis/misinformation was a major concern in the 2016 U.S. presidential election and has only worsened in recent years. Even though domestic actors often spread dis/misinformation, actors abroad can use it to spread confusion and push their agenda to the detriment of American citizens. Even though this report focuses on actors outside the United States, the methods they use are universal and can be adapted to work against domestic agents. A solid understanding of these methods is the first step in combating foreign dis/misinformation campaigns and creating a new information literacy paradigm. This report highlights the primary mechanisms of dis/misinformation: multimedia manipulation, bots, astroturfing, and trolling. These forms of dis/misinformation were selected after thorough research about common pathways dis/misinformation are spread online. Multimedia manipulation details image, video, and audio dis/misinformation in the form of deepfakes, memes, and out-of-context images. Bots are automated social media accounts that are not managed by humans and often contribute to dis/misinformation campaigns. Astroturfing and trolls use deception to sway media users to join false grassroots campaigns and utilize emotionally charged posts to provoke a response from users. This policy report also defines case studies of disinformation in China, Russia, and Iran, outlining common patterns of dis/misinformation specific to these countries. These patterns will allow for more accurate and quick identification of dis/misinformation from the outlined countries by State Department Watch Officers. Recommendations have also been provided for each type of disinformation and include a list of what individuals should look for and how to make sure that the information they receive is accurate and from a reputable source. The addendum at the end of the paper lists all of the recommendations in one place so that individuals do not have to search the paper for the recommendation they are looking for. This report intends to aid State Department Watch Officers as they work to identify foreign developments accurately. Still, researchers may find this information useful in anticipating future developments in foreign dis/misinformation campaigns

Could Public Restrooms Be an Environment for Bacterial Resistomes?

PMCID: PMC3547874This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited