Climate has historically been recognized as an influence on sediment flux and deposition. The North American Monsoon is suggested as the forcing mechanism of deltaic progradational events of the Rio Grande River delta. Interpretations of reflection seismic profiles reveal that eustatic rise in sea-level from the Last Glacial Maximum to present is accompanied by several regressional events of the Rio Grande delta 5.5, 9.5, and 11.5 ka BP. Much of the migration of depositional facies within a delta system is forced by hinterland tectonics and base-level rise and fall. However, we suggest that the movement of facies within the Rio Grande delta system represent climate forcing as the most dominant influence on sediment deposition during this short time period. While dominance of climate influence is possible, the sensitivity of an increase in monsoon precipitation and its effect on sediment flux has not yet been tested. We test monsoonal effects using relationships between sediment flux, river discharge, and precipitation. Heavy water management and withdrawal and complexity of precipitation timing and events within the region make the relationship between precipitation and sediment flux difficult to quantify using modern data sources. Therefore, it is necessary to numerically simulate stream discharge to test potential sensitivities of the system to monsoonal precipitation using a stream discharge model. Precipitation input into the stream discharge model is gathered from a suite of climate model simulation outputs. Suspended sediment flux is derived from the outputs of the flow models using empirically derived sediment rating curves. Results of sediment modeling show that increased precipitation during the monsoon months of July-September, 6 ka BP increased monthly suspended sediment flux by 79 percent. The suite of climate models does not include 9 or 11 ka BP, but we suggest the monsoon may have been stronger during this time based on greater received insolation at these times. This study also shows that duration and intensity of monsoonal precipitation events can more greatly affect stream discharge and sediment flux than increased precipitation with constant storm intensity.

Recent research has revealed human settlement on the Pacific coast of Canada extending back nearly 14,000 years, but much of the late Pleistocene record is unknown due to shifting sea levels, poor understanding of Cordilleran ice extent, and limited research on the biota of the coast during this time. This study, undertaken in Quatsino First Nation and ‘Namgis First Nation territories as part of the Northern Vancouver Island Archaeology and Palaeoecology Project, employs modern multi-proxy analysis of lake sediment cores from two sites on northern Vancouver Island to reconstruct palaeoenvironments during and immediately following the Fraser Glaciation in coastal British Columbia. Evidence from radiocarbon samples, pollen, ancient environmental DNA, plant macrofossils, and diatoms indicates that Topknot Lake on the outer coast of Vancouver Island has remained unglaciated through most of the local Last Glacial Maximum since ca. 18,000 cal BP. A non-arboreal herb-shrub tundra assemblage prevailed from ca. 17,500-16,000 cal BP with taxa including willows (Salix), grasses, sedges (Cyperaceae), heathers (Ericaceae), and sagewort (Artemisia). After ca. 16,000 and into the terminal Pleistocene, Topknot Lake was dominated by pine, alder (Alnus), ferns, and aquatic plant species. In the Nimpkish River Valley deep in the Vancouver Island Ranges, Little Woss Lake also demonstrates a record extending to the late Pleistocene (ca. 14,300 cal BP). The environment comprised dry and cool conifer woodland dominated first by fir (Abies) until ca. 14,000 cal BP, then by pine, alder, and ferns from ca. 14,000-12,000 cal BP. eDNA evidence from ca. 14,000 cal BP corroborates these plant taxa as well as indicating brown bear and Chinook salmon in and around the basin at that time. A mixed-conifer assemblage consisting of pine, western hemlock, and alder followed from ca. 12,000-11,100 cal BP into the early Holocene. Collectively, these indicators demonstrate an open environment on the outer coast of northern Vancouver Island since ca. 18,000-17,500 cal BP and well-established biotic communities across the region throughout the late Pleistocene. These results inform future archaeological research for early human habitation in coastal British Columbia and provide key evidence to support the viability of the coastal migration route for the first peopling of the Americas. / Graduate / 2020-12-11

Pendant les transitions glaciaire-interglaciaires,on observe une augmentation en partie abrupte de près de 100 ppm du CO2atmosphérique, indiquant une redistribution majeure entre les réservoirs de carbone des continents, de l'océan et de l'atmosphère.Expliquer les flux de carbone associés à ces transitions est un défi scientifique, qui nécessite une meilleure compréhension du stock de carbone ‘initial’ dans la biosphère terrestre au cours de la période glaciaire. L’objectif de cette thèse est d’améliorer la compréhension du fonctionnement des écosystèmes terrestres et des stocks de carbone au cours du dernier maximum glaciaire (LGM, il y a environ21.000 ans), à travers plusieurs nouveaux développements dans le modèle global de végétation ORCHIDEE-MICT, pour améliorer la représentation de la dynamique de la végétation, la dynamique du carbone dans le sol du pergélisol et les interactions entre les grands herbivores et la végétation dans le modèle de la surface terrestre.Pour la première partie, la représentation de la dynamique de la végétation dans ORCHIDEEMICT pour les régions des moyennes et hautes latitudes, a été calibrée et évaluée avec un ensemble de données spatiales de classes de végétation, production primaire brute, et de biomasse forestière pour la période actuelle.Des améliorations sont obtenues avec la nouvelle version du modèle dans la distribution des groupes fonctionnels de végétation. Ce modèle a ensuite été appliqué pour simuler la distribution de la végétation au cours de laLGM, montrant un accord général avec les reconstructions ponctuelles basées sur des données de pollen et de macro-fossiles de plantes.Une partie du pergélisol (sols gelés en permanence) contient des sédiments épais,riches en glace et en matières organiques appelés Yedoma, qui contiennent de grandes quantités de carbone organique, et sont des reliques des stocks de carbone du Pléistocène.Ces sédiments ont été accumulés sous des climats glaciaires. Afin de simuler l'accumulation du carbone dans les dépôts de Yedoma, j’ai proposé une nouvelle paramétrisation de la sédimentation verticale dans le module de carbone dans le sol de ORCHIDEE-MICT. L'inclusion de ce processus a permis de reproduire la distribution verticale de carbone observée sur des sites de Yedoma. Une première estimation du stock de carbone dans le pergélisol au cours du LGM est obtenue, de l’ordre de ~ 1550 PgC, dont 390 ~446 PgC sous forme de Yedoma encore intacts aujourd’hui (1,3 millions de km2).Potentiellement, une plus grande surface de Yedoma pourrait être présente pendant leLGM, qui a disparue lors de la déglaciation.Pour la troisième partie, à la lumière des impacts écologiques des grands animaux, et le rôle potentiel des méga-herbivores comme une force qui a maintenu les écosystèmes steppiques pendant les périodes glaciaires, j'ai incorporé un modèle de d’herbivores dans ORCHIDEE-MICT, basé sur des équations physiologiques pour l'apport énergétique et les dépenses, le taux de natalité, et le taux de mortalité pour les grands herbivores sauvages.Le modèle a montré des résultats raisonnables de biomasse des grands herbivores en comparaison avec des observations disponibles aujourd’hui sur des réserves naturelles. Nous avons simulé un biome de prairies très étendu pendant le LGM avec une densité importante de grands herbivores. Les effets des grands herbivores sur la végétation et le cycle du carbone du LGM ont été discutés, y compris la réduction de la couverture forestière, et la plus grande productivité des prairies.Enfin, j’ai réalisé une estimation préliminaire du stock total de carbone dans le permafrost pendant le LGM, après avoir tenu compte des effets des grands herbivores et en faisant une extrapolation de l'étendue spatiale des sédiments de type Yedoma basée sur des analogues climatiques et topographiques qui sont similaires à la région de Yedoma actuelle. / During the repeated glacialinterglacialtransitions, there has been aconsistent and partly abrupt increase of nearly100 ppm in atmospheric CO2, indicating majorredistributions among the carbon reservoirs ofland, ocean and atmosphere. A comprehensiveexplanation of the carbon fluxes associatedwith the transitions is still missing, requiring abetter understanding of the potential carbonstock in terrestrial biosphere during the glacialperiod. In this thesis, I aimed to improve theunderstanding of terrestrial carbon stocks andcarbon cycle during the Last Glacial Maximum(LGM, about 21,000 years ago), through aseries of model developments to improve therepresentation of vegetation dynamics,permafrost soil carbon dynamics, andinteractions between large herbivores andvegetation in the ORCHIDEE-MICT landsurface model.For the first part, I improved theparameterization of vegetation dynamics inORCHIDEE-MICT for the northern mid- tohigh-latitude regions, which was evaluatedagainst present-day observation-based datasetsof land cover, gross primary production, andforest biomass. Significant improvements wereshown for the new model version in thedistribution of plant functional types (PFTs),including a more realistic simulation of thenorthern tree limit and of the distribution ofevergreen and deciduous conifers in the borealzone. The revised model was then applied tosimulate vegetation distribution during theLGM, showing a general agreement with thepoint-scale reconstructions based on pollen andplant macrofossil data.Among permafrost (perennially frozen) soils,the thick, ice-rich and organic-rich siltysediments called yedoma deposits hold largequantities of organic carbon, which areremnants of late-Pleistocene carbonaccumulated under glacial climates. In order tosimulate the buildup of the thick frozen carbonin yedoma deposits, I implemented asedimentation parameterization in the soilcarbon module of ORCHIDEE-MICT. Theinclusion of sedimentation allowed the modelto reproduce the vertical distribution of carbonobserved at the yedoma sites, leading toseveral-fold increase in total carbon. Simulatedpermafrost soil carbon stock during the LGMwas ~1550 PgC, among which 390~446 PgCwithin today’s known yedoma region (1.3million km2). This result was still anunderestimation since the potentially largerarea of yedoma during the LGM than todaywas not yet taken into account.For the third part, in light of the growingevidence on the ecological impacts of largeanimals, and the potential role of megaherbivoresas a driving force that maintainedthe steppe ecosystems during the glacialperiods, I incorporated a dynamic grazingmodel in ORCHIDEE-MICT, based onphysiological equations for energy intake andexpenditure, reproduction rate, and mortalityrate for wild large grazers. The model showedreasonable results of today’s grazer biomasscompared to empirical data in protected areas,and was able to produce an extensive biomewith a dominant vegetation of grass and asubstantial distribution of large grazers duringthe LGM. The effects of large grazers onvegetation and carbon cycle were discussed,including reducing tree cover, enhancinggrassland productivity, and increasing theturnover rate of vegetation living biomass.Lastly, I presented a preliminary estimation ofpotential LGM permafrost carbon stock, afteraccounting for the effects of large grazers, aswell as extrapolations for the spatial extent ofyedoma-like thick sediments based on climaticand topographic features that are similar to theknown yedoma region. Since these results werederived under LGM climate and constantsedimentation rate, a more realistic simulationwould need to consider transient climate duringthe last glacial period and sedimentation ratevariations in the next step.

L’acidification des océans provoquée par l’absorption du CO2 atmosphérique par l’eau de merest devenue une préoccupation écologique majeure et menace déjà les organismes calcifiants. Suiteà la révolution industrielle, le pH de l’océan de surface a diminué de 0,1 unité-pH. En revanche, celuides eaux profondes reste peu documenté. Les isotopes du bore (11B) dans les carbonatesbiogéniques se sont révélés être un puissant outil géochimique pour la reconstitution du pH, mais n’apas encore été appliqué aux coraux profonds. Un travail analytique sur MC-ICPMS Neptune et uneanalyse géochimique de ces coraux ont été effectués afin de reconstituer et quantifier l’acidificationdes océans. De même, la valeur 11B de l’eau de mer utilisée pour calculer les paléo-pH a étérevisitée et l’homogénéité des océans vérifiée.L’analyse de deux colonies modernes de Lophelia pertusa et Madrepora oculata a permis dequantifier un taux d’acidification pendant la fin du XXème siècle pour les eaux de sub-surface en mer deNorvège et cela après établissement d’une calibration expérimentale à partir de coraux de culture.L’analyse géochimique des coraux profonds a mis en évidence un effet vital lié à la physiologie quidoit être considéré pour quantifier avec précision la variabilité du pH. Celui-ci peut être en partiecorrigé par une analyse statistique des isotopes stables B, C et O. Cette étude a aussi révélél’influence de l’hydrodynamique régionale. Enfin les variations naturelles du pH pendant l’Holocène etle Dernier Maximum Glaciaire sur des coraux profonds fossiles méditerranéens ont été établies etcelles pendant l’aube de l’explosion de la diversité biologique. / Ocean acidification is caused by the absorption of rising atmospheric CO2 by seawater andrepresents a major environmental issue. Since the beginning of the industrial era, seawater pH hasdecreased by 0.1 pH units and is already threatening calcifying organisms. Boron isotopes (11B) haveproved to be a powerful geochemical tool for the reconstruction of pH variations, but has not yet beenapplied to deep-sea corals (DSC). Accurate and precise measurements of boron isotopes in coralsand seawaters were performed in order to measure small pH variations.The technique of pH reconstruction based on boron isotopes (pH-11B) was used on two specimens of the DSC Madrepora oculata and Lophelia pertusa collected alive in the Norwegian Sea and spanning an age of 40 (3) and 67 (3) years, respectively. Acidification rates were calculated by applying a new pH-11B calibration obtained from the geochemical analysis M. oculata and L. pertusa samples cultured under different pCO2 conditions. The contribution of a biological-related vital effect on d11B was observed at macrometer scale, and a correction was finally suggested based on oxygen and carbon isotopes. Overall, the coral δ 11B-based reconstructions show a pH decrease in the Norwegian Sea since the 1940s, which seems to be related to the local hydrodynamics. The pH-11B technique was also applied to fossil DSC fragments from two “on-mound sediment cores” retrieved in the Siculo-Tunisian Strait with the aim to reconstruct the pH during the Last Glacial Maximum and the Holocene periods. Finally, well-preserved limestone samples from the stratigraphic sequence Nama (551-543 Ma) in Namibia were investigated for 11B to study the pH variations at the beginning of the Cambrian evolutive radiation.

This research is associated to the FAPESP 2011/0095-7 thematic project, \"Interdisciplinary palaeoenviromental studies at Espirito Santo coast\" and to the FAPESP Research Program about Climate Global Change (PFPMCG-FAPESP). The objectives were: (1) to characterize the late Pleistocene connection between Atlantic and Amazon rainforest and possible routes of interaction (coast, continent or both); (2) to identify environmental characteristics that indicates the Northeastern Espírito Santo and Southern Bahia as a stable forest since the late Pleistocene; (3) reconstitute the vegetation dynamics and infer climate fluctuations. Three sedimentary cores were collected: at northern Espirito Santo (ES) state, southern Bahia (BA) and eastern Minas Gerais (MG). Carbon and nitrogen isotope analyses and bioindicators in sediments/ soils, chronologically determined by radiocarbon dating, contributed to the local palaeoenvironmental reconstitution. At ES, from ~33,460 to ~13,740 cal yr BP the vegetation was composed of arboreal/ shrub cold adapted species and the organic matter recorded the dominance of C3 plants (?13C ~-28?), suggesting a cold and humid forest domain. From ~13,740 to ~9500 cal yr BP vegetation changes, with the increase of grasses and decrease of arboreal types. Between ~9500 and to ~4000 cal yr BP herbs were abundant with a probable mixture of C3 and C4 plants (?13C ~-24?) and algae, suggesting a higher seasonality between humid and dry season. From ~7300 cal yr BP until present the peat layer initiates its deposition, and the pollen records represents the current vegetation. At BA, radiocarbon dating in high-resolution, C and N isotopes and palynology each ~150 years from ~6400 to ~3400 cal yr BP showed detailed vegetational dynamics. From ~6400 to ~5620 cal yr BP the pollen record indicates abundance of trees and shrubs (up to 96%). From ~5620 to ~4850 cal yr BP occurred a slightly increase of herbs (28%) but the ?13C of ~-28% indicate C3 plants domain. From 4850 to ~3400 cal yr BP trees and shrubs abundance increases up to 94%, indicating the forest domain. The results confirm the forest stability and high local humidity, allowing to recognize the area as a probable refugee since 6500 cal yr BP. Vegetation, climate and the landscape has changed at MG since ~10,000 cal yr BP. From 10,600 to ~9500 cal yr BP, pollen was not preserved, C/N values (2 to 11) reveal the algal contribution, the ?13C (~-20?) indicate the mixture of C3 and C4 plants and radiocarbon date inversions indicate that the material was reworked. From 9,500 to 7,500 cal yr BP the vegetation was predominantly herbaceous with mixture of C3 and C4 plant sources (?13C ~-17?). From 7,500 to 7,000 cal yr BP C3 plants (?13C ~-30?) as trees/shrubs domains the polen record. From ~7,000 to ~6500 cal yr BP the pollen records the herbaceous abundance, dominated by C4 plants (?13C ~-12 to 18?). Peat deposition starts at ~6500 cal yr BP composed by C3 plants, mainly dominated by trees. Pollen records since at least early Holocene and the floristics of current vegetation did not show any disjunct specie with Amazon / Este projeto está associado ao temático FAPESP 2011/00995-7, \"Estudos paleoambientais interdisciplinares na costa do Espírito Santo\", e ao Programa FAPESP de Pesquisas sobre Mudanças Climáticas Globais (PFPMCG-FAPESP). Os objetivos foram: (1) caracterizar a conexão da Mata Atlântica e Floresta Amazônica e possíveis rotas de interação (litorânea, continental ou ambas); (2) identificar padrões que caracterizem a região da costa norte do Espírito Santo e sul da Bahia como refúgios florestais; (3) reconstituir a dinâmica da vegetação e inferir flutuações climáticas desde o Pleistoceno tardio. Três testemunhos sedimentares foram coletados: ao norte do Espírito Santo (ES), ao sul da Bahia (BA) e ao leste de Minas Gerais (MG). Análises isotópicas de carbono e nitrogênio e bioindicadores em sedimento/solos, cronologicamente determinados por datação 14C, contribuíram para a reconstituição paleoambiental nestas regiões. No ES, de ~33.460 a ~13.740 anos cal AP, a vegetação era composta por espécies de árvores/arbustos típicas de regiões frias com o domínio de plantas C3 (?13C ~-28?), sugerindo a presença de uma floresta fria e úmida. De ~13.740 a ~9500 anos cal AP ocorreu o aumento das herbáceas e diminuição dos tipos arbóreos. Entre ~9500 e ~4000 anos cal AP, as herbáceas tornaram-se abundantes com mistura de plantas C3 e C4 (?13C~-24?) e algas, sugerindo maior sazonalidade entre as estações seca e úmida. De ~7300 anos cal AP até o presente, iniciou-se a deposição da turfa e pólen da vegetação atual. Na BA, a alta resolução de datação C-14, isótopos de C e N e palinologia a cada ~150 anos entre ~6400 e ~3400 anos cal AP revelaram a dinâmica da vegetação. Entre 6400 e 5620 anos cal AP arbóreas/arbustivas (96%) são abundantes. De ~5620 até ~4850 anos cal AP ocorreu um pequeno aumento de herbáceas (28%), e os valores de ?13C ~-28% indicam o domínio de plantas C3. De 4850 a ~3400 anos cal AP, a abundância de arbóreas/arbustivas (94%), indica domínio florestal. Os resultados confirmam a estabilidade florestal e a umidade local, permitindo reconhecer esta área como um possível refúgio florestal desde pelo menos 6500 anos cal AP. Em MG, desde ~10.000 anos cal AP ao presente, a vegetação, o clima e a paisagem modificaram consideravelmente. De 10.600 a ~9500 anos cal AP não houve preservação de pólen, os valores de C/N (~2 e 11) revelam a contribuição algal, o ?13C (~-20?) indica mistura de plantas C3 e C4 e inversões nas datações indicam o retrabalhamento do material. De 9500 a 7500 anos cal AP a vegetação era predominantemente herbácea, com mistura de C3 e C4 (?13C ~-17?). De 7500 a 700 anos cal AP, plantas C3 (?13C ~-30?) arbustivo-arbóreas dominam o registro polínico. De ~7000 a 6500 anos cal AP as herbáceasC4 (?13C ~-12?) são abundantes. A deposição de turfa iniciou em ~6500 anos cal AP, composta por plantas C3 arbóreas. Registros palinológicos desde o Holoceno inferior e a avaliação florística atual não revelaram a presença de espécies de distribuição disjunta com a Amazônia

O objetivo da presente tese é o de documentar, em escala milenar, as variações paleoclimáticas e paleoceanográficas superficiais do Atlântico Sul Ocidental desde o Último Máximo Glacial. Com esta finalidade, foram obtidas estimativas de paleotemperatura, paleossalinidade e paleoprodutividade baseadas na análise de fauna de foraminíferos planctônicos, isótopos estáveis de oxigênio e carbono em Globigerinoides ruber e nove datações de radiocarbono em amostras de um testemunho coletado na Bacia de Santos. Os dados foram complementados com a reanálise de outro testemunho previamente coletado em outro setor da mesma Bacia. Os resultados demonstram que as mudanças paleoceanográficas registradas no período analisado podem ser parcialmente explicadas por variações na exportação de calor e sal para o hemisfério norte relacionadas à atividade da célula de transporte meridional e à configuração das correntes superficiais associadas à circulação atmosférica. Outra parte significativa da variabilidade parece estar relacionada à intensidade do Sistema de Monção da América do Sul resultante de variações na insolação de acordo com o ciclo de precessão. Os principais desvios da tendência de variação da composição isotópica da água do mar esperada em função das mudanças de insolação coincidem com os grandes pulsos de degelo ocorridos em torno de 19, 14 e 8,2 mil anos AP. / The goal of this thesis is to document the paleoclimatic and paleoceanographic changes occurred at the millennial scale since the Last Glacial Maximum at the surface Western South Atlantic. Paleotemperature, paleosalinity and paleoproductivity estimates were obtained for this purpose based on faunal changes of foraminifera assemblages, carbon and oxygen stable isotopes in Globigerinoides ruber and nine radiocarbon datings in a core retrieved at Santos Basin. These data were supplemented by the reanalysis of a second core previously analyzed from a different sector of the same basin. The results demonstrate that paleoceanographic changes recorded in the analyzed period may be partially explained by changes in the heat and salt export to the northern hemisphere related to the meridional overturning cell and the surface currents related to atmospheric circulation. Another significant portion of the observed variability seems to be related to changes in the strength of the South American Monsoon System resulting from insolation changes according to the precessional cycle. The main departures from the expected trend of variation in the isotopic composition of seawater related to insolation changes coincide with great meltwater pulses occurred around 19, 14, and 8.2 kyr BP.

Forests are among the most important repositories of terrestrial biodiversity and provide a broad range of ecosystem services. During millennia, forests have changed, adapted and evolved under changing conditions. However, in the present century, forests are facing environmental changes at rates with no precedents. A major concern is the risk of declining forest genetic diversity, since genetic variation as the raw material underpinning adaptation is key in maintaining the resilience of forest ecosystems against environmental changes. Understanding the different processes responsible for developing and maintaining the genetic diversity of tree species is essential to better predict tree responses under new conditions. Therefore, this thesis aimed to determine how different forces interact to shape and maintain within and among population genetic diversity of Scots pine and what the implications are for conservation and management under forthcoming environmental conditions. From local to continental scales, I followed a multilevel approach, and found that (i) historic climate changes and geographical barriers have played an important role in shaping the extent and spatial distribution of current genetic diversity of Scots pine. Despite contemporary habitat reduction and fragmentation we found that (ii) high levels of neutral genetic diversity remain in the Scottish populations of Scots pine, with gene flow and specifically wind-driven gene flow dominating over genetic drift and preventing differentiation among the Scottish populations. However, (iii) considerable impacts in the spatial distribution of genetic variation have occurred as a consequence of intensive historical forest management practices. Furthermore, we found that (iv) substantial levels of adaptive genetic variation are present in the Scottish populations of Scots pine, likely a result of selective processes resulting from the different environments they live in, with highly heritable traits, although similar capacity for response through phenotypic plasticity to warming. The results of this thesis help to further disentangle the forces maintaining genetic diversity in one of most widespread conifers in the world, and improving predictions of likely range shifts and adaptation of the species in response to contemporary changes. The thesis provides some recommendations to conservation and management practices.

Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are some of the fastest moving portions of the cryosphere and may be the most unstable ice streams in Antarctica. I examined over 133 cores to conduct a detailed sedimentological facies analysis. These data, augmented by new radiocarbon and 210Pb dates, and bathymetric data, are used to reconstruct the post-LGM deglacial history of PIB and gain a better understanding of the causes of ice sheet retreat. My results record a clear retreat stratigraphy in PIB composed of, from top to base; terrigenous sandy silt (plumite), pebbly sandy mud (ice-proximal glacimarine), and till. Initial retreat from the outer-continental shelf began shortly after the LGM and before 16.4 k cal yr BP, in response to rising sea level. Bedforms in outer PIB document episodic retreat in the form of back-stepping grounding zone wedges and are associated with proximal glacimarine sediments. A sub-ice shelf facies is observed in central PIB that spans ∼12.3–10.6 k cal yr BP. Widespread impingement of warm water onto the continental shelf caused an abrupt change from sub-ice shelf sedimentation to distal glacimarine sedimentation dominated by dispersal of terrigenous silt between 7.8 and 7.0 k cal yr BP. The uppermost sediments in Pine Island Bay were hydrodynamically sorted by meltwater plumes. Inner Pine Island Bay contains several large basins that are linked by channels. The most recent release of sediment coincides with rapid retreat of the grounding line, and has an order of magnitude greater flux relative to the entire unit, indicating episodic sedimentation. This is the first identification of a meltwater-derived deposit in Antarctica and demonstrates that punctuated meltwater-intensive glacial retreat occurred at least three times throughout the Holocene in this region. Quartz sand grains were used to conduct an analysis of mode of transport for sediments in the Antarctic Peninsula region from the Eocene to present to record the onset of glaciation. Glacial transport imparts a unique suite of microtextures on quartz grains from high shear-stresses. Eocene samples are free of glacial influence. Late Eocene samples show the inception of glacially derived high-stress microtextures, marking the onset of alpine glaciation. Oligocene grains are similar to the late Eocene samples. Middle Miocene microtextures are characteristic of transport from far-field large ice sheets, originating from ice rafting from the West Antarctic Ice Sheet. The Pliocene and Pleistocene samples indicate the existence of the northern Antarctic Peninsula Ice Sheet at this time, consistent with other proxies.

The Darwin-Hatherton glacial system (DHGS) drains from the East Antarctic Ice Sheet (EAIS) and through the Transantarctic Mountains (TAM) before entering the Ross Embayment. Large ice-free areas covered in glacial sediments surround the DHGS, and at least five glacial drift sheets mark the limits of previous ice extent. The glacier belongs to a group of slow-moving EAIS outlet glaciers which are poorly understood. Despite this, an extrapolation of a glacial drift sheet boundary has been used to determine the thickness of the EAIS and the advanced West Antarctic Ice Sheet (WAIS) during the Last Glacial Maximum (LGM). In order to accurately determine the past and present contributions of the Antarctic ice sheets to sea level changes, these uncertainties should be reduced. This study aims to examine the present and LGM ice dynamics of the DHGS by combining newly acquired field measurements with a 3-D numerical ice sheet-shelf model. The fieldwork included a ground penetrating radar survey of ice thickness and surface velocity measurements by GPS. In addition, an extensive dataset of airborne radar measurements and meteorological recordings from automatic weather stations were made available. The model setup involved nesting a high-resolution (1 km) model of the DHGS within a lower resolution (20 km) all-Antarctic simulation. The nested 3-D modelling procedure enables an examination of the impact of changes of the EAIS and WAIS on the DHGS behaviour, and accounts for a complex glacier morphology and surface mass balance within the glacial system. The findings of this study illustrate the difference in ice dynamics between the Darwin and Hatherton Glaciers. The Darwin Glacier is up to 1500 m thick, partially warm-based, has high driving stresses (~150 kPa), and measured ice velocities increase from 20-30 m yr⁻¹ in the upper parts to ~180 m yr⁻¹ in the lowermost steepest regions, where modelled flow velocities peak at 330 m yr⁻¹. In comparison, the Hatherton Glacier is relatively thin (<900 m), completely cold-based, has low driving stresses (~85 kPa), and is likely to flow with velocities <10 m yr⁻¹ in most regions. It is inferred that the slow velocities with which the DHGS flows are a result of high subglacial mountains restricting ice flow from the EAIS, large regions of frozen basal conditions, low SMB and undulating bedrock topography. The model simulation of LGM ice conditions within the DHGS implies that the ice thickness of the WAIS has been significantly overestimated in previous reconstructions. Results show that the surface of the WAIS and EAIS away from the TAM would have been elevated 600-750 and 0-80 m above present-day levels, respectively, for the DHGS to reach what was inferred to represent the LGM drift sheet limit. Ultimately, this research contributes towards a better understanding of the dynamic behaviour of slow moving TAM outlet glaciers, and provides new insight into past changes of the EAIS and WAIS. This will facilitate more accurate quantifications of contributions of the WAIS and EAIS to changes in global sea level.

Uncertainty about the sensitivity of the climate system to changes in the Earth’s radiative balance constitutes a primary source of uncertainty for climate projections. Given the continuous increase in atmospheric greenhouse gas concentrations, constraining the uncertainty range in such type of sensitivity is of vital importance. A common measure for expressing this key characteristic for climate models is the climate sensitivity, defined as the simulated change in global-mean equilibrium temperature resulting from a doubling of atmospheric CO2 concentration. The broad range of climate sensitivity estimates (1.5-4.5°C as given in the last Assessment Report of the Intergovernmental Panel on Climate Change, 2001), inferred from comprehensive climate models, illustrates that the strength of simulated feedback mechanisms varies strongly among different models. The central goal of this thesis is to constrain uncertainty in climate sensitivity. For this objective we first generate a large ensemble of model simulations, covering different feedback strengths, and then request their consistency with present-day observational data and proxy-data from the Last Glacial Maximum (LGM). Our analyses are based on an ensemble of fully-coupled simulations, that were realized with a climate model of intermediate complexity (CLIMBER-2). These model versions cover a broad range of different climate sensitivities, ranging from 1.3 to 5.5°C, and have been generated by simultaneously perturbing a set of 11 model parameters. The analysis of the simulated model feedbacks reveals that the spread in climate sensitivity results from different realizations of the feedback strengths in water vapour, clouds, lapse rate and albedo. The calculated spread in the sum of all feedbacks spans almost the entire plausible range inferred from a sampling of more complex models. We show that the requirement for consistency between simulated pre-industrial climate and a set of seven global-mean data constraints represents a comparatively weak test for model sensitivity (the data constrain climate sensitivity to 1.3-4.9°C). Analyses of the simulated latitudinal profile and of the seasonal cycle suggest that additional present-day data constraints, based on these characteristics, do not further constrain uncertainty in climate sensitivity. The novel approach presented in this thesis consists in systematically combining a large set of LGM simulations with data information from reconstructed regional glacial cooling. Irrespective of uncertainties in model parameters and feedback strengths, the set of our model versions reveals a close link between the simulated warming due to a doubling of CO2, and the cooling obtained for the LGM. Based on this close relationship between past and future temperature evolution, we define a method (based on linear regression) that allows us to estimate robust 5-95% quantiles for climate sensitivity. We thus constrain the range of climate sensitivity to 1.3-3.5°C using proxy-data from the LGM at low and high latitudes. Uncertainties in glacial radiative forcing enlarge this estimate to 1.2-4.3°C, whereas the assumption of large structural uncertainties may increase the upper limit by an additional degree. Using proxy-based data constraints for tropical and Antarctic cooling we show that very different absolute temperature changes in high and low latitudes all yield very similar estimates of climate sensitivity. On the whole, this thesis highlights that LGM proxy-data information can offer an effective means of constraining the uncertainty range in climate sensitivity and thus underlines the potential of paleo-climatic data to reduce uncertainty in future climate projections. / Eine der entscheidenden Hauptquellen für Unsicherheiten von Klimaprojektionen ist, wie sensitiv das Klimasystem auf Änderungen der Strahlungsbilanz der Erde reagiert. Angesichts des kontinuierlichen Anstiegs der atmosphärischen Treibhausgaskonzentrationen ist die Einschränkung des Unsicherheitsbereichs dieser Sensitivität von entscheidender Bedeutung. Ein häufig verwendetes Maß zur Beschreibung dieser charakteristischen Kenngröße von Klimamodellen ist die sogenannte Klimasensitivität, definiert als die Gleichgewichtsänderung der simulierten globalen Mitteltemperatur, welche sich aus einer Verdoppelung des atmosphärischen CO2-Gehalts ergibt. Die breite Spanne der geschätzten Klimasensitivität (1.5-4.5°C), welche ein Vergleich verschiedener komplexer Klimamodelle nahe legt (IPCC, 2001), verdeutlicht, wie groß die Unsicherheit in der Klimasensitivität ist. Diese Unsicherheit resultiert in erster Linie aus Unterschieden in der Simulation der entscheidenden Rückkopplungs-mechanismen in den verschiedenen Modellen. Das zentrale Ziel dieser Dissertation ist die Einschränkung des breiten Unsicherheitsbereichs der Klimasensitivität. Zunächst wird hierzu ein großes Ensemble an Modellsimulationen erzeugt, in welchem gezielt spezifische Modellparameter variiert, und somit unterschiedliche Rückkopplungsstärken der einzelnen Modellversionen realisiert werden. Diese Simulationen werden dann auf ihre Konsistenz mit sowohl heutigen Beobachtungsdaten, als auch Proxy-Daten des Letzten Glazialen Maximums (LGM) überprüft. Unsere Analysen basieren dabei auf einem Ensemble voll gekoppelter Modellläufe, welche mit einem Klimamodell intermediärer Komplexität (CLIMBER-2) realisiert wurden. Die betrachteten Modellversionen decken eine breite Spanne verschiedener Klimasensitivitäten (1.3-5.5°C) ab und wurden durch gleichzeitiges Variieren von 11 Modellparametern erzeugt. Die Analyse der simulierten Rückkopplungs-mechanismen offenbart, dass unterschiedliche Werte der Klimasensitivität in unserem Modellensemble durch verschiedene Realisierungen der Rückkopplungsstärken von Wasserdampf, Wolken, Temperatur-Vertikalprofil und Albedo zu erklären sind. Die berechneten Gesamt-Rückkopplungsstärken unser Modellversionen decken hierbei fast den gesamten möglichen Bereich von komplexeren Modellen ab. Wir zeigen, dass sich die Forderung nach Konsistenz zwischen simuliertem vorindustriellem Klima und Messdaten, die auf einer Wahl von sieben global gemittelten Datensätzen basieren, als vergleichsweise schwacher Test der Modellsensitivität erweist: Die Daten schränken den plausiblen Bereich der Klimasensitivität lediglich auf 1.3-4.9°C ein. Zieht man neben den genannten global gemittelten Messdaten außerdem klimatische Informationen aus Jahreszeit und geografischer Breite hinzu, lässt sich die Unsicherheit in der Klimasensitivität nicht weiter einschränken. Der neue Ansatz dieser Dissertation besteht darin, in systematischer Weise einen großen Satz an LGM-Simulationen mit Dateninformationen über die rekonstruierte glaziale Abkühlung bestimmter Regionen zu kombinieren. Unabhängig von den Unsicherheiten in Modellparametern und Rückkopplungsstärken offenbaren unsere Modellversionen eine ausgeprägte Beziehung zwischen der simulierten Erwärmung aufgrund der CO2-Verdoppelung und der Abkühlung im LGM. Basierend auf dieser engen Beziehung zwischen vergangener und zukünftiger Temperaturentwicklung definieren wir eine Methode (basierend auf linearer Regression), welche es uns erlaubt, robuste 5-95%-Quantile der Klimasensitivität abzuschätzen. Indem wir Proxy-Daten des LGM von niederen und hohen Breiten heranziehen, können wir die Unsicherheitsspanne der Klimasensitivität auf 1.3-3.5°C beschränken. Unsicherheiten im glazialen Strahlungsantrieb vergrößern diese Abschätzung auf 1.2-4.3°C, wobei die Annahme von großen strukturellen Unsicherheiten die obere Grenze um ein weiteres Grad erhöhen kann. Indem wir Proxy-Daten über tropische und antarktische Abkühlung betrachten, können wir zeigen, dass sehr unterschiedliche absolute Temperatur-Änderungen in hohen und niederen Breiten zu sehr ähnlichen Abschätzungen der Klimasensitivität führen. Vor dem Hintergrund unserer Ergebnisse zeigt diese Dissertation, dass LGM-Proxy-Daten ein effektives Mittel zur Einschränkung des Unsicherheitsbereichs der Klimasensitivität sein können und betont somit das Potenzial von Paläoklimadaten, den großen Unsicherheitsbereich von Klimaprojektionen zu reduzieren.