Loess from west Greenland was studied to evaluate Holocene paleoclimate in the Arctic region. Deposits of loess are formed over long time scales through deposition of fine aeolian sediment and they exist in several places in the world. The main aeolian dust source in the study area is glaciofluvial material derived from the Greenland Ice Sheet (GrIS). Studying and understanding paleoclimate can help to make better predictions about the future in this sensitive region. Apart from sea level rise, melting of the GrIS also leads to an increase of aeolian dust as it gets released from the ice, which influences atmospheric and metrological phenomenon as well as the ice sheet’s albedo. This creates negative feedback mechanisms through increasing melting rates of glaciers and warming of the Arctic. Loess samples from two sites in the Kangerlussuaq area were analyzed and the mineral composition was measured with X-Ray Florescence Spectroscopy (XRF). With the measured mineral content, weathering indices were calculated to identify rates of weathering during the Holocene. Increased weathering intensities indicate warmer and more humid climate. The deposits in Greenland are relatively thin. Radiocarbon dating of the sediment suggests that the oldest parts of the profiles are about 4000 cal. yr B.P. (calibrated years before present). Arctic loess has not been studied very extensively. Weathering indices and ratios developed for classical loess, that had not been tested on Arctic loess, was used. The results were plotted by depth and age to visually identify changes over time. By considering the geology, climate and local conditions of the study area, some weathering indices seemed to be suitable, generating matching trends between the two sites. Compared with results from previous studies, the results also seemed credible. / Löss från västra Grönland studerades för att utvärdera holocent paleoklimat i Arktis. Lössjordar bildas över långa tidsskalor genom avsättning av fint vindburet sediment och de finns på flera platser i världen. Den huvudsakliga källan till det vindburna sedimentet i studieområdet är glaciofluvialt material härstammande från Grönlandsisen (GrIS). Att studera och förstå paleoklimat kan underlätta skapandet av bättre prognoser om framtiden i denna känsliga region. Bortsett från höjning av de globala havsnivåerna leder smältningen av GrIS också till en ökning av vindburet sediment då det frigörs från isen, vilket påverkar atmosfäriska och metrologiska fenomen samt isens albedo. Detta skapar negativa återkopplingsmekanismer genom ökande smälthastighet av glaciärer och uppvärmning av Arktis. Lössprover från två ställen i Kangerlussuaq-området analyserades och mineralsammansättningen mättes med röntgenstrålningsspektroskopi (XRF). Med det uppmätta mineralinnehållet beräknades vittringssindex för att identifiera vittringshastigheter under Holocen. Ökad vittringsintesitet indikerar varmare och fuktigare klimat. Avlagringarna på Grönland är relativt tunna. Kol-14-datering av sedimentet antyder att de äldsta delarna är cirka 4000 cal. yr B.P. (kalibrerade år före nutid). Arktisk löss är relativt ostuderad. Vittringsindex som har utvecklats för klassisk löss i tempererade regioner, och tidigare inte testats på arktisk löss, användes. Resultaten ritades i grafer efter djup och ålder för att visuellt identifiera förändringar över tid. Genom att ta hänsyn till geologin, klimatet och lokala förhållanden i studieområdet, verkade några av vittringsindexen ge trovärdiga resultat då matchande trender mellan bägge profiler kunde utläsas. I jämförelse med resultat från tidigare studier verkade resultaten också trovärdiga.

Indiana University-Purdue University Indianapolis (IUPUI) / The frequency and magnitude of flooding events on the Lower Ohio River and their relationship with climate are investigated using a ca. 2000-year-long sediment core collected from Goose Pond, Indiana. Using high-resolution radiocarbon dating (n = 25), late Holocene sedimentation rates were calculated for Goose Pond. Changes in sediment accumulation rates are attributed to variations in the frequency of flooding events on the lower Ohio River. Elevated sedimentation rates immediately following the formation of Goose Pond ca. 2000 years ago persisted until 680 CE, suggesting regular flooding during this interval. Between 680 and 1190 CE, sedimentation rates decreased dramatically and abruptly, indicating a reduction in flood frequencies. Sedimentation rates subsequently increased again at ca. 1190 CE and persisted at a similar level until 1850 CE, suggesting that flooding frequencies increased during a time that overlapped with the Little Ice Age (LIA; 1250-1850 CE). Sedimentation rates increased again at ca. 1850 CE, reaching a 2000-year high (3.33 cm/yr) at 1970 CE and indicating a period characterized by frequent flooding and landscape erosion. The flood record from Goose Pond shows similarities with other Lower Ohio River flood reconstructions from Avery Lake, IL, and Hovey Lake, IN, suggesting the Goose Pond record reflects the regional flooding history for the lower Ohio River. Comparison with paleoclimate records from the Midwest supports the idea that lower Ohio River flood frequencies prior to Euro American occupation in the 1800s increased during times when winter precipitation predominated as a result of atmospheric circulation changes resembling the Pacific North vii American mode (PNA) that appear to have been driven in part by the Pacific Decadal Oscillation (PDO). Following Euro-American land clearance, lower Ohio River flooding increased dramatically despite a decrease in winter precipitation. This likely reflects an increase in runoff and erosion as a result of deforestation and landscape conversion to intensive row crop agriculture. As climate continues to change and the Midwestern United States continues to see an increase in precipitation, both winter and summer, flood frequencies could be expected to increase still further.

The thesis is compilation of four manuscripts discussing the stable isotope analysis modem and archaeological faunal material from Namu, British Columbia. These studies concentrate on the application of stable isotopic analysis of biogenic material for paleonvironmental interpretation over the Holocene. The first study addresses the use of phosphate and carbonate associated oxygen isotopes in bioapatites (Sebastes spp. vertebrae) as a proxy for the isotopic composition of water from approximently 6,000 to 2,000 years before present (BP). The second study evaluates sclerochronological sampling strategies as applicable to the study of bivalves with implications for sampling fragmented material such as that found in archaeological deposits. The third study investigates stable isotopes composition of estuarine bivalve carbonate (Saxidomus gigantea) and the controlling environmental and biological factors. Finally, the fourth study uses a 5,000 year record of archaeological S. gigantea to provide a paleoclimatic record at Namu over the mid-late Holocene. / Thesis / Master of Science (MS)

No description available.

No description available.

Collaborative studies between Quaternary scientists and archaeologists increasingly provide new and informative discussions about the nature and timing of cultural change and links with variation in the natural world (particularly climate). In the Eastern Mediterranean region, connecting the human past with palaeoclimate is an important research theme but the complex interactions between them are still poorly understood and past climate records have often been collected from regions distant from the human record. The thesis aims to derive a record of past climatic and environmental changes from lake sediment cores and synthesise this with archaeological data in order to reconstruct human-climate interactions at the regional scale. Annually laminated sediment data collected from Nar Gölϋ crater-lake and archaeological archives from the same region, Cappadocia (Turkey) allow problems of chronological uncertainty between records of the human past and palaeoclimatic archives, and spatially variable datasets to be addressed. New sediment cores collected from Nar Lake in 2010 cover the last ~14000 years based on varve counting and climate-stratigraphic correlation. The changing chemical composition of these sediments has been obtained using high-resolution Itrax XRF core scanning, mainly at 200μm resolution over 21.6m. Temporal differences in Ca and Sr are interpreted as a record of regional moisture levels, while Ti and Fe are elemental proxies that detail changes in catchment in-wash. These and other sedimentary data (e.g. total carbon analysis) document lake evolution from a predominately stable and moist early Holocene climate dominated by high authigenic Ca precipitation to a drier and less stable IV late Holocene dominated by increased authigenic Sr and Mg (and higher lake salinity levels). The most arid climatic conditions occurred during Bronze and early Iron Age times, but frequent and intense centennial-scale climatic shifts between wet and dry are also evidenced during the last 2600 years from Ca/Sr data. Peaks in Fe and Ti, along with Si, K and Rb indicate two distinct phases of increased sediment influx into Nar Lake, namely ~9200 to ~8000 yr. BP (ceramic Neolithic) and again – more importantly – during the last 2600 years (Iron Age and later). These appear to be related primarily to increased human impact on vegetation and soils in the lake-catchment, but volcanic activity and intense rainfall events and/or water deficits may also have played a role. To determine the degree to which climatic variability and cultural change are interlinked, the geochemical record from Nar Lake is correlated against long-term settlement histories which have been derived from systematic archaeological site survey and excavation data from Cappadocia. One of the key outcomes of the project is an examination of periods of climatic stability and instability which are identified by amplitudinal changes from the mean state using correlation of coefficient statistics on the Nar Lake geochemical record. This information about the predictability of climate has been coupled to data in settlement density and location within the resiliency model framework of Holling and Gunderson (2002). Together these data suggest that a series of four long-term adaptive cycles (Neolithic, Chalcolithic-Bronze Age, Iron Age-Classical, Byzantine-Ottoman) characterise the dynamic inter-play between people, climate and their environment. In each adaptive cycle, environmental change contributed (both positively and negatively) to community resilience, although at no point during the Holocene is climatic variability seen as the sole driver of societal change. There were times such as the post-Roman Dark Age (1300 to 1100 yr. B.P.) when increased climatic variability and environmental degradation may have heightened social vulnerability.

This study contributes to developing terrestrial and marine palynological indicators of winter or summer monsoon signals as well as oceanographic environments of the South China Sea (SCS). The high-resolution reconstructions of Holocene East Asian Monsoon (EAM) climate and oceanographic condition of the northern SCS provide insights into regional climate events in the western low-latitude Pacific Ocean and their impacts on local oceanography and ecology. Sediment trap samples from the southwest Taiwan waters of the SCS in winter monsoon (March-April) and summer monsoon (July-August) seasons identify abundances of Pinus and Ulmus pollen as indicators of the winter monsoon whereas fern spores appeared to be indicators of the summer monsoon. The increased fluxes of dinoflagellate cyst (DC) taxa during summer are correlated with decreased sea-surface salinity (SSS) associated with nutrient-rich river inputs. DC distributions across the SCS show that some taxa are good indicators of changes in sea-surface temperature (SST), SSS, water depth and chlorophyll-a (chl-a) concentrations associated with EAM and oceanographic conditions. In particular, the concenrations of Brigantedinium spp. and cysts of Protoperidinium together with Echinidinium spp. are positively correlatd with SST in January and SST in July, and chl-a concentrations, respectively, which are linked to past monsoon strength and primary productivity. In total, four high cyst concentration regions have been observed off southern Vietnam, Borneo, Hainan, and South China. High-resolution palynological records from a sediment core in the northern SCS reflect several EAM climatic and oceanographic events over the last 12.5 kyr. A short-term Impagidinium decrease implied that the Taiwan Strait opened at ~11.7–11.0 cal kyr BP, with reduced Kuroshio Current influence when the East China Sea waters entered through the strait. Three Holocene relative sea-level stages were identified in the palynomorph records. The highest herb pollen abundances were observed before ~10.4 cal kyr BP, reflecting the shortest distance from the grassland sources on the exposed shelf at the low sea-level stand. High Brigantedinium and cysts of Protoperidinium abundances also indicate a near-shore environment. During ~10.4- ~6.8-6.0 cal kyr BP at the rising sea-level stage, fern spore abundances increased and DC abundances decreased. Consistently low total DC concentrations and high fern spore abundance were observed after ~6.8-6.0 cal kyr BP when the present oceanographic conditions were formed. Increased abundances of Pinus pollen reflected three strengthened winter monsoon intervals at ~5.5, 4.0 and 2.5 cal kyr BP under the present oceanographic conditions. The highest Dapsilidinium pastielsii abundances reflected the warmest interval at ~6.8-5.5 cal kyr BP of the northern SCS. / Graduate / 2019-12-13

No description available.

Three continuous terrestrial high-resolution palaeoenvironmental records for the Late-glacial and the Holocene have been reconstructed for different ecosystems in Fuego-Patagonia on a longitudinal transect at latitude 53°S. The records describe the nature and extent of environmental and climatic changes inferred from palynological evidence supported by lithostratigraphy, tephrochronology and radiocarbon dating. The environmental changes recorded at the three sites displays a significant degree of synchrony in response to similar large-scale climatic changes. Clear stratigraphical evidence alongside the pollen record indicates a shift to warmer interstadial conditions between c. 14,800 Cal yr BP and 14,400 Cal yrs BP. During the period coeval with ACR the vegetation was dominated by cold resistant dry land herbs such as Poaceae, Asteraceae (Suf. Asteroideae) and Acaena, by c. 13,200 Cal yr BP the vegetation changed from the dominance of cold resistant dry land herbs towards more mesic conditions and the expansion of steppe dominated by Poaceae with patches of Nothofagus forest. The establishment of the forest and an eastward shift of the forest-steppe ecotone by c. 12,500 Cal yr BP from which a gradual shift from colder to warmer conditions and the relatively stronger influences of the SSWs is inferred. The sequence of Late-glacial environmental changes places Fuego-Patagonia within the new palaeoecological data provided by this study includes “the earliest” evidence for the establishment of subantarctic Nothofagus forest during the LGIT in Fuego-Patagonia. During the Early-Holocene two major phases of Nothofagus forest expansion were registered between c. 11,700 - 10,500 Cal yr BP and c. 9,500 - 8,200 Cal yr BP. These intervals of expansion of Nothofagus forest are separated by an interval of forest contraction in response to lower effective moisture between c. 10,500 - 9,500 Cal yr BP. An intense arid phase is inferred between c. 8,250 Cal yr BP and 6,800 Cal yr BP and probably leading to an increase in the amount of dry fuel available during the mid-Holocene in Fuego-Patagonia leading to the highest fire activity promoted by very weak SSWs at this time. The later Holocene was characterised by an increase in humidity and an inferred intensification of the SSWs.

L’objectif de ce travail est de reconstituer les changements de la dynamique hydrosédimentaire de la Loire en fonction des variations climatiques globales et régionales depuis l’Holocène Moyen (~7 ka), dans un contexte de ralentissement et de stabilisation de la remontée du niveau marin. Le rôle des aménagements anthropiques de l’estuaire interne depuis le début du XXème siècle, a été également considéré. Dans cet objectif, les séquences sédimentaires étudiées ont été prélevées le long d’un continuum terre-mer entre l’estuaire interne de la Loire et la partie septentrionale du Golfe de Gascogne, en passant par les paléovallées incisées présentes à l’embouchure actuelle.L’emboitement des dimensions temporelle et spatiale fait l’unicité de ce travail de recherche à l’échelle de la Loire mais également sa complexité. Afin de déconvoluer les différents signaux enregistrés, nous avons entrepris une approche analytique combinant des données sédimentologiques, micro-paléontologiques (foraminifères benthiques) et géochimiques, le tout dans un cadre chronologique contraint par des datations 14Cet 210Pb/137Cs. Nos résultats montrent que le ralentissement de la montée des eaux a joué un rôle majeur dans le façonnement du paysage estuarien et par conséquence, dans la chenalisation du flux terrigène vers le large. Ce flux terrigène est également modulé à plus grande échelle par les forçages climatiques internes et externes (e.g., Oscillation Nord Atlantique, forçage solaire) affectant à la fois le bassin versant, l’occurrence des tempêtes au large ainsi que la circulation océanique de surface. Enfin, la partie la plus récente de nos archives sédimentaires estuariennes enregistre l’impact des aménagements humains qui ont profondément modifié la morphologie de l’estuaire interne depuis le début du XXème siècle. / The aim of this work is to reconstruct changes in the hydro-sedimentary dynamics of the Loire River according to global and regional climatic variations since the Middle Holocene (~ 7 ka), in a general context of slowing down of sea-level rise. The impact of the recent human settlements undertaken in the internal Loire estuary since the beginning of the 20th century is also considered. To achieve this objective, the studied sedimentary sequences were collected along a land-sea continuum from the internal estuary, to the incised paleovalleys off the present-day river mouth, until the northern part of the Bay of Biscay (South Brittany). The imbrication of both temporal and spatial dimensions makes the originality of this research on the scale of the Loire River, but also its complexity. In order to deconvolute the various recorded signals, we used a multiproxy approach combining sedimentological, micropaleontological (benthic foraminifera) and geochemical analyses, within a chronological framework constrained by 14C and 210Pb/137Cs dating. Our results show that the Middle to Late Holocene slowing down of sea-level rise plays a major role in shaping the estuarine landscape and in the channelization of the terrigenous flow towards the ocean. At the same time, this terrigenous flow is modulated on a larger scale by internal and external climatic forcing (e.g., North Atlantic Oscillation, solar forcing) controlling humidity over the Loire River catchment area, the occurrence of storms and ocean surface circulation. The most recent parts of our estuarine sedimentary sequences record the impact of human settlements since the beginning of the 20th century modifying significantly the morphology of the inner estuary and the location of the main river channel.