Results of extensive site reconnaissance on the Isles of Tiree, Coll and north-west Mull, Inner Hebrides are presented. Pollen-stratigraphic records were compiled from a profile from Glen Aros, north-west Mull and from two profiles on Coll located at Loch an t-Sagairt and Caolas an Eilean. Quantification of microscopic charcoal provided records that were used to facilitate a preliminary evaluation of the causal driving mechanisms of vegetation change. Bayesian modelling of radiocarbon dates was used to construct preliminary chronological frameworks for these records. Basal sedimentary deposits at Glen Aros contain pollen records that correspond with vegetation succession typical of the early Holocene dating to c. 11,370 cal BP. Woodland development is a key feature of the pollen records dating to the early Holocene, while records from Loch an t-Sagairt show that blanket mire communities were widespread in north-west Coll by c. 9800 cal BP. The Corylus-rise is dated to c. 10,710 cal BP at Glen Aros and c. 9905 cal BP at Loch an t-Sagairt, with records indicating extensive cover of hazel woodland with birch. All of the major arboreal taxa were recorded, though Quercus and Ulmus were nowhere widespread. Analysis of wood charcoal remains from a Mesolithic site at Fiskary Bay, Coll indicate that Salix and Populus are likely to be under-represented in the pollen records. Reconstructed isopoll maps appear to underplay the importance of alder in western Scotland during the mid-Holocene. Alder-rise expansions in microscopic charcoal dating to c. 7300 cal BP at Glen Aros and c. 6510 to 5830 cal BP on Coll provide records of significance to the issue of human-induced burning related to the expansion of alder in Britain. Increasing frequencies in microscopic charcoal are correlated with mid-Holocene records of increasing aridity in western Scotland after c. 7490 cal BP at Glen Aros, 6760 cal BP at Loch an t-Sagairt and 6590 cal BP at Caolas an Eilean, while several phases of increasing bog surface wetness were detected in the Loch an t-Sagairt archive during the Holocene. At least five phases of small-scale woodland disturbance during the Mesolithic period were identified in the Glen Aros profile dating to c. 11,650 cal BP, 9300 cal BP, 7840 cal BP, 7040 cal BP and 6100 cal BP. The timing of the third phase is coincident with evidence of Mesolithic settlement at Creit Dhu, north-west Mull. Three phases of small-scale woodland disturbance were detected at Loch an t-Sagairt dating to c. 9270 cal BP, 8770 cal BP and 8270 cal BP, all of which overlap chronologically with evidence of Mesolithic activity at Fiskary Bay, Coll. A number of these episodes are aligned chronologically with phases of Holocene climate variability such as the 8.2 K event.

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No description available.

This thesis presents the late Miocene/early Pliocene climate transition (7-5 Ma) as recorded in marine sediments from Ocean Drilling Programme (ODP) Site 959 in the equatorial Atlantic off tropical West Africa, and a reconstruction of changing Holocene environments of the Eastern Tropical Atlantic (CHEETA) based on surface and core sediments from a transect along the Portuguese and NW African margin. The late Miocene to early Pliocene climate transition had irreversible consequences for atmospheric and ocean circulation leading to global cooling, northern hemisphere glaciations and modern climate conditions. In this study, continental climate, vegetation change and surface ocean dynamics at millennial time scale resolution is investigated from UK37’ alkenone derived SST, leaf wax lipids and organic carbon records (TOC). Despite low TOC (<1%) which was highly variable at cm-scale (~2.5-5 kyr) resolution, ubiquitous evidence from alkenones (C37:2 and C37:3) and leaf wax lipids indicate that the primary climate signal was preserved. The UK37’ based SST estimates (24.8-29°C) showed pronounced warm and cool cycles in the magnitude of 4°C. Elevated leaf wax lipids n–alkanes (C27, C29, and C31) correspond with cool SSTs and indicate a coupled relationship between upwelling and atmospheric ocean circulation patterns which intensified around 5.6 Ma arguing for wind driven deposition from terrestrial sources related to the position and strength of the ITCZ. The high amplitude cyclic patterns in the ODP Site 959 records were investigated by time frequency analyses. The common 41 kyr in all records supports a response to high latitude climate forcing. The 75 kyr variations and lead/lag observed in the leaf waxes and SST records during the late Miocene to early Pliocene are probably related to continental ice volume variations. The study on surface sediments from the Portuguese and NW African margins, confirm the presence of two soil-specific biomarkers, branched GDGTs (expressed as the BIT index) and bacteriohopanepolyols (BHPs), in this region of almost exclusive aeolian export. TOC exceeding 2% and δ13Corg gradients from -22.5‰ off Portugal to -19‰ off W Africa identify areas of upwelling off Cape Blanc and the transition from C3 to C4 vegetation habitats in Northern Africa, respectively. Despite low signals of the molecular records, slightly stronger response of soil-marker BHPs in the sediments is attributed to preferential erosion of the upper, (oxic) part of the soil column in central African source areas, the proposed source for soil BHPs. An alternative explanation is that in situ production of the branched GDGTs may be responsible for the low BIT index. As yet there is no evidence of the soil BHPs, adenosylhopane produced in situ in marine systems and aeolian transport of GDGTs is yet to been proven. More studies on dust samples from continental margins needs to be carried out to validate this transport mechanism of branched GDGTs and BHPs. A compilation of first bulk geochemical and molecular results from a selection of cores from the Portuguese and NW African margin within an integrated chronological framework document the variations in marine sedimentation and constrain regional variations in continental climate and terrigenous supply since the last glacial period. TOC accumulation records document millennial scale variability in response to the African Humid Period. Carbon isotope trends pronounced during the last glacial maximum support organic matter input from C4 type vegetation during colder glacial periods. Preliminary molecular isotopic records of n-alkanes identify gaps in this study that will need further investigation to assess and confirm vegetation sources and continental climatic conditions over Northwest Africa.

In the semi-arid environment of the Eastern Mediterranean, water can be a limiting resource and its availability is influenced by different climate factors. Knowledge of late Holocene water balance is limited for this region. Lake systems and organisms respond to environmental variability and can be used as a proxy for palaeoclimate. The aims of this research project were to reconstruct late Holocene palaeoclimate using diatom frustules preserved within crater lake sediments in central Turkey. Two lakes (Nar Gölü and Kratergöl), located in the same climate region, were selected for this purpose. Modem lake samples and sediment cores collected between 1999-2006 were subsampled at high resolution for diatom analysis, Nar G610 provided an uninterrupted annually-laminated late Holocene sequence covering the last 1720 years. The varied lake sedimentation rate of Kratergöl was evident in sediment core coarse sandy sections and the sequence was thought to represent the mid-late 20`h century. A diatom-salinity transfer function was employed using existing training sets from the European Diatom Database to infer past water balance. The reconstruction was calibrated with instrumental meteorological data. Reconstructed salinity was limited by poor analogue matching between the palaeo-diatom assemblage and the modem training set. This was partly associated with the presence of a previously undescribed diatom genus (newly named Clipeoparvus anatolicus), which was highly abundant in the Nar modern environment and sediment record. Additional methods to extract palaeoenvironmental information from the diatom record were explored. This included calibrating diatom DCA axes with instrumental temperature in order to reconstruct palaeo-temperature, identifying mono-specific diatom bloom events in situ on core thin section slides, calculating diatom biovolume, concentration, diversity and grouping species according to their habitat preferences. Comparison of the Nar and Kratergöl records highlighted the advantages of annually laminated lake sediments for palaeoenvironmental research and the limitations of sediment sequences from lakes with a varied sedimentation rate and poor chronological control. The primary meteorological control on the Nar diatom population was identified as summer temperature, via the link with lake water salinity. The Nar diatom sequence was compared with an oxygen isotope (palaeo-evaporation) and pollen record (human land use) from the same sediment cores and palaeoclimate reconstructions from other sites and regions. Nar diatoms and oxygen isotopes revealed that Cappadocia experienced high aridity prior to AD 540 and mono-specific diatom bloom events have become increasingly common during the most recent -400 years. A diatom assemblage shift at AD 2001 also indicated a recent change in the system. Human land use evident in the pollen sequence may have influenced the diatom relationship with climatic variability in the later part of the record. The Kratergöl diatom record indicated environmental variability throughout the mid-late 20`h century; however, interpretations were limited due to chronological discrepancies. The annually laminated Nar diatom record has provided a detailed account of palaeoenvironmental variability in central Anatolia throughout the late Holocene and contributes towards our understanding of Eastern Mediterranean palaeoclimate.

Pescadero Marsh is a back-barrier wetland environment located on the central coast of California. In an attempt to reconstruct sub-annual trends in back-barrier environmental change over the late Holocene, driven by the presence and integrity of a coastal barrier system, carefully targeted sections of the sediment record from this site were analysed at high resolution (2mm) for their grain size and geochemical characteristics. Where possible, diatom analysis supplemented these data. The sediment record, and the methodology employed, proved to be sufficiently sensitive for this purpose by distinguishing between a series of barrier estuarine and lagoonal sedimentary environments. Grain size data were the primary basis for environmental interpretation. At this resolution, the grain size distribution curves of individual samples revealed sensitive environmental information regarding deposition through different transport processes, i.e. saltation vs suspension loads. Distinctions between samples were driven by the interaction of the lagoonal pool, tidal ingress, river flow and the integrity of the barrier system. Geochemical data indicated sediment provenance, distinguishing between samples primarily sourced by marine and terrestrial waters, and grain size related controls on many geochemical characteristics. Diatom assemblages reflected high energy inputs from the ocean and the feeding creeks whilst recording limited change in the salinity of the back-barrier environment. A confident chronology was constructed for Euro-American era sediments, with a sedimentation rate of 144.2 days per 2mm sample established above a 1963 'weapons testing' peak in 137Cs. A similar rate was demonstrated to continue to at least 1900 through the presence of geochemical markers of anthropogenic activity (pollution, catchment destabilisation and development of infrastructure). This represented a marked increase above the prehistoric rate (~0.8mm per year). During the late-Holocene period of relative sea-level stability, the environmental trends established are characteristic of a morphologically resilient coastal system. A barrier estuarine environment persisted, despite changing boundary conditions and a perturbation of very high magnitude/Iow frequency, and was observed to shift though a series of 'static equilibrium' operational states. From wavelet analysis, the ENSO phenomenon emerged as the likely principal driver of variability in the most recent of these static equilibra. The research presented greatly improves understanding of the sites prehistoric functioning and suggests significant anthropogenic impacts on the system during the Euro-American era. Such information can inform management of this and other analogous sites.

The Permian/Triassic (P/Tr) boundary is widely assumed to have been a time of extreme environmental upheaval and change. In the terrestrial realm, a negative anomaly in 813C isotope values has been reported from organic carbon in Antarctica, Australia, India and Madagascar, and from marine carbonate in the Karoo Basin. However, these sections are all from southern palaeolatitudes. Analysis from the Permian-Triassic terrestrial sedimentary record of the South Urals, in Russia, comprising of many Aridisol and Vertisol horizons has revealed that, like the Southern Hemisphere, there is a dramatic change in paleosol morphology across the P/Tr boundary linked to a shift from meandering rivers to conglomeratic alluvial fans. Most of the paleosols include pedogenic carbonates at different stages of development, both above and below the P/Tr boundary. By the Triassic there is evidence of depressed water tables and increased seasonality. Analyses of the S13Qarba nd S18Ocarbsi gnatures of these pedogenic carbonates have revealed a number of negative excursions in 813Ccarabn d 5180carbin the Late Permian, including a negative excursion in the mid-Changhsingian, the first time such an event has been recorded in a terrestrial environment. Associated with this excursion are indicators of increasing extremes of climate, including pedogenic dolomite, which suggest a dramatic change in climate up to the P/Tr boundary. Equally, there is an increase in the range of precipitation, suggesting that what caused this mid-Changhsingian event also had a profound effect on the atmosphere. There is also evidence, in the form of the 818Ocaeßx, cursion, of a rise in temperaturej ust prior to the onset of the conglomeratic alluvial fan deposits, which mark the P/Tr boundary in Russia. Although in the Russian paleosols this excursion could be explained by a rise in the effect of seasonal rain or atmospheric temperature, estimates from unaltered brachiopods from the Italian Dolomites confirm that there is a rise in temperature and suggests that this is in the region of 7-8°C. These paleosols also record a dramatic rise in pCO2 in the Earliest Triassic similar to what has been recorded in stomatal records across this period suggesting a dramatic input of CO2 in to the atmosphere.

Diatoms represent between 25% and 45% of all marine primary productivity. As yet, however, the potential of using diatom isotopes, in particular oxygen (518Odiatom), in palaeoceanographic reconstructions has yet to be fully assessed. Work here within this thesis demonstrates a method for extracting pure, mono or near mono species specific, diatom samples from marine sediments. Over two time intervals, the potential of using 8l8Odiatom in palaeoceanographic reconstructions is then shown at ODP site 882 in the North West Pacific Ocean over the onset of major Northern Hemisphere Glaciation (2.73 Ma) and over the last 200 kyr BP. During both periods, major changes in the halocline/stratification of the water column, relating to significant freshwater input to the region, are reconstructed. These results indicate a significant role for the region in initiating glacier growth across the North American continent and in causing changes in atmospheric pC02. Strong evidence exists, however, that both an inter- and intra-species vital/species effect of up to 3.5l%o may be present in 518Odiatom. As such, this may limit future applications of 518Odiatom to samples which are dominated by only one taxa. Section two of the thesis investigates the potential for wet-alkaline measurements of BSi to provide insights into the global silicon cycle. A sequential Si/Al technique, which directly accounts for levels of clay/aluminosilicate digestion, is demonstrated to produce lower and more accurate measurement of BSi in samples for which a rapid non-BSi digestion phase occurs. However, comparisons between wet-alkaline BSi measurements and diatom biovolume measurements, which more accurately reflect the true amount of BSi within a sample, show a poor relationship between the two variables. This is particularly true in samples where diatom dissolution is high. Consequently, diatom biovolume measurements may be better suited for making quantitative palaeoenvironmental reconstructions.

This thesis examines the interplay between the palaeoenvironment and human population during the late Pleistocene in the Maghreb region (North Africa). Currently there is a lack of published palaeoenvironmental studies that cover the last 20-30,000 years and this prompted the work carried out in this thesis. Using a multi- proxy approach it is possible to improve our understanding of broad palaeoenvironmental changes throughout this period and their effects on humans in the area. The study site, Grotte des Pigeons (N 34° 48' 83.9" W 2° 24' 24.4"), is situated in northeast Morocco and is one of the most important archaeological sites in the Maghreb. The depositional sequences at the site show that humans were present throughout most of the Late Glacial Maximum (LGM) and the following phase which coincided with Heinrich Event 1 (c. 22-15 ka BP). This does not mean that the occupation was continuous, however the site was not abandoned for a very long time. Another matter that has become clearer during the course of this work is the contrast between the rapidity and the scale of climatic change in Europe and North Africa. In Northern Europe, for example, the LGM is typified by a major decline in temperature that had marked effects on the natural vegetation. In Northwest Africa, or at least in the Maghreb, the impact of the glacial advance seems to have been less marked. The sedimentological data from Taforalt show that the palaeoenvironment became increasingly variable from the LGM onwards, but there is no verification of a dramatic change of the kind seen in Europe.