The Arctic is climatically sensitive to global change and therefore climate records from this region are of key importance. Little, however, is known of the state of the Arctic in the traditionally “greenhouse” period of the Cretaceous. Climate conditions are often assumed to have been warm-temperate as evidenced by the presence of conifers and dinosaur trackways on Svalbard and other Arctic localities. However, isotopic evidence for cooling episodes, sequence stratigraphic evidence for interpreted glacio-eustatic sea-level falls, and the presence of more enigmatic deposits such as dropstones and glendonites has led to a re-evaluation of the question of climatic dynamism during the Cretaceous. This project evaluates the climatic and environmental character of Arctic Svalbard during the Early Cretaceous (palaeo-latitude of c. 65 °N), via a multiproxy sedimentological, geochemical, sequence- and chemo- stratigraphic study of Berriasian–Albian strata from the Central Basin of Svalbard. The “outsized clasts” recorded on Spitsbergen do not show evidence that they were rafted by glacial ice (e.g. surface striations), although could have been rafted by seasonal sea-ice. The results show that regionally widespread cold water conditions were the most likely control on ikaite formation and glendonite preservation. This counters recent studies that suggest a methane-seep driver for Mesozoic glendonites, and supports the global extent of Valanginian to Hauterivian and Late Aptian global cooling. Surface temperatures during cool episodes of < 14 °C, as implied by the presence of glendonites at the seafloor, are consistent with Polar (90 °N) temperatures being below freezing (even given reduced pole-to-equator temperature gradients). This study therefore supports the hypothesis that small polar ice-caps developed during the Valanginian – Hauterivian and Late Aptian cooling events.

This thesis presents research that improves our understanding of the relationship between climate and tree-ring stable isotopes in New Zealand kauri (Agathis australis (D. Don) Lindl.) and cedar (Libocedrus bidwillii Hook. F). As a whole, this research creates a framework from which future investigations of stable isotope dendroclimatology can pursued at high temporal resolution across longer term temporal intervals. Such a framework is required to realize the full potential of New Zealand tree-ring records as archives of palaeoclimatic information. In the Southern Hemisphere, mid-to-high latitude terrestrial climate proxy records are sparse; the long-lived endemic conifers of New Zealand present a rare opportunity to gain valuable insight into Late-Quaternary and Holocene climatic change. A major barrier to long stable isotope dendroclimatic proxy records has been the time-and-resource intensive nature of associated sample preparation and analytical processes. Through experimental assessment of the SBrendel α-cellulose extraction method, this research demonstrates that this simple processing method can, with some caveats, be successfully applied to resinous conifers, facilitating rapid chemical preparation of samples. Further efficiency gains are documented in through use of dual element low temperature pyrolysis of cellulose, providing carbon and oxygen stable isotope determinations on a single sample, rather than the traditionally separate analyses. These preliminary investigations into methodological efficiency enabled the ~3000 stable isotope determinations on kauri and cedar, on which the following investigations into isotopic variability, chronology quality and climate-isotope relationships are based. Both kauri and cedar exhibit substantial intra and inter-tree isotopic variability, resulting in greater than normal sample numbers being required to isolate the common variance in composite time-series. Despite sampling 7 trees (18 cores) at one site and 8 trees (21 cores) at another, only oxygen isotope time-series reach an Expressed Population Signal score of 0.85, a common benchmark of chronology quality. Further investigations using high-resolution sequential sampling of single rings show that this variability extends to a sub-annual scale. Within single rings there are large ranges in δ13C and δ18O, generally corresponding with regular annual cycles of up to 4.6‰ for δ13C and 8.1‰ for δ18O. These data show high frequency (sub weekly) changes in δ18O, demonstrating sufficiently fine resolution for event-to-seasonal scale climate/weather reconstruction. However, that potential is complicated by the lack of strong climatic correlations with isotopic cycles. Due to their stronger common signal, δ18O time series are investigated for inter-annual stable isotope dendroclimatic reconstruction from kauri and cedar. Bootstrapped correlation and multiple regression models show strong relationships between kauri and cedar δ18O and relative humidity, accumulated rainfall and soil moisture deficit. The correlations are strongest for all variables during the period from Autumn prior to growth to the current growth summer. Tree-ring δ18O in kauri and cedar is identified as an effective recorder of regional hydroclimate leading up to and during the Austral growth season. While it is demonstrated that tree-ring δ18O holds significant promise for inter-annual palaeoclimate reconstruction, it is equally apparent from this research that stable isotope dendroclimatology in New Zealand faces significant challenges. Foremost is gaining an improved understanding of seasonal dendrochemical cycles and their relationship with tree-physiology. Increasing the spatial and temporal coverage of tree-ring isotope records is vital to realising New Zealand’s vast potential for stable isotope dendroclimatic reconstruction.

Correlations between societal development and climate changes have been investigated for a long period of time. At the archaeological site of Beidha, southern Jordan, most studies have focussed on the Late Pleistocene/Holocene, however, the importance of the Beidha region may even reach further back in time. The presence of water in a generally very dry landscape would have been crucial to early modern humans en route from Africa to all other continents. Through sedimentological observations and OSL dating, this study aims to contribute to solving the puzzle of the local landscape development at Beidha during a longer time scale. It is suggested that a long period of calm floodplain conditions took place, approximately during periods of high lake levels in Lake Lisan ~70-21 ka. After that, a period of soil development has been identified between two phases of aeolian deposition. More recently, during the Holocene, phases of mass flow events may have affected the area.

Large Igneous Provinces (LIPs) represent geologically rapid emplacements of vast quantities of igneous material into/onto Earth's crust. There is a marked correlation in the known ages of LIPs and Mesozoic extinctions and other environmental perturbations, suggesting a possible causal link between these events. However, uncertainties in matching LIP basalt ages to the stratigraphic record of Mesozoic events mean that a sedimentary tracer of volcanism would better indicate a precise coincidence between the two phenomena. Mercury (Hg) has shown potential as such a proxy. Volcanism is a major source of Hg to the natural environment, and its relatively long atmospheric residence time (0.5–2 years) allows global distribution of the element before it is deposited to sediments. However, questions remain about how the manner of LIP emplacement might influence its impact on the Hg cycle, as well as how sedimentary processes may locally overprint any global signal. Here, the Hg records of three Mesozoic events are investigated: the end-Triassic extinction (TJ: ~201.5 Ma), Cretaceous Oceanic Anoxic Event 2 (OAE 2: ~94 Ma), and the latest Cretaceous (K–Pg: ~67–66 Ma). These events coincided with markedly different LIPs: OAE 2 with multiple submarine LIPs; the K–Pg and TJ with subaerial LIPs; with the TJ also featuring release of additional thermogenic volatiles from intrusion of organic-rich lithologies by LIP sills. Additionally, mercury is used with osmium and carbon isotopes to study the temporal relationships between volcanism, weathering, and the carbon cycle during the Toarcian Oceanic Anoxic Event (~183 Ma). This work highlights the links between LIP volcanism and other surface processes, and shows that subaerial LIPs featuring thermogenic emissions are most likely to perturb the global Hg cycle, with the record of such perturbations dependent on the nature of the sedimentary archive.

The relationship between leaf physiognomy and precipitation has been explored worldwide in regions under different climate conditions. Unlike the linear relationship established between the percentage of woody dicot species with entire margins and mean annual temperature, precipitation has been reported to correlate to different leaf physiognomic characters depending on the region where the correlation is studied. To investigate if precipitation can be calculated from leaf physiognomic characters on the basis of regional sample sites, data from 50 mesic to humid forests in China were analyzed in this study. With data from Chinese forests, the leaf-area analysis based on linear regression between natural logarithms of leaf size and mean annual precipitation (MAP) shows no significant correlation. Both single and multiple linear regression analyses fail to confirm the correlation between leaf physiognomy and precipitation, which may result from the similarity of modern spatial distribution of temperature and precipitation in China. Our results show that, due to variations in climatic conditions among sampling regions, leaf physiognomic characters that correlate to precipitation are not consistent worldwide, and applications of models without considering regional constraints could mislead our understanding of palaeoclimate. Therefore, when choosing a leaf physiognomic model for palaeoclimate reconstructions, it is important to determine if the leaf physiognomy of the palaeoflora lies within the leaf physiognomic spectrum of the model used.

The relationship between leaf physiognomy and precipitation has been explored worldwide in regions under different climate conditions. Unlike the linear relationship established between the percentage of woody dicot species with entire margins and mean annual temperature, precipitation has been reported to correlate to different leaf physiognomic characters depending on the region where the correlation is studied. To investigate if precipitation can be calculated from leaf physiognomic characters on the basis of regional sample sites, data from 50 mesic to humid forests in China were analyzed in this study. With data from Chinese forests, the leaf-area analysis based on linear regression between natural logarithms of leaf size and mean annual precipitation (MAP) shows no significant correlation. Both single and multiple linear regression analyses fail to confirm the correlation between leaf physiognomy and precipitation, which may result from the similarity of modern spatial distribution of temperature and precipitation in China. Our results show that, due to variations in climatic conditions among sampling regions, leaf physiognomic characters that correlate to precipitation are not consistent worldwide, and applications of models without considering regional constraints could mislead our understanding of palaeoclimate. Therefore, when choosing a leaf physiognomic model for palaeoclimate reconstructions, it is important to determine if the leaf physiognomy of the palaeoflora lies within the leaf physiognomic spectrum of the model used.

The Coexistence Approach was established by Mosbrugger and Utescher (1997) as a plant-based method to reconstruct palaeoclimate by considering recent climatic distribution ranges of the nearest living relatives of each fossil taxon. During its existence for over more than 15. years, its basics have been tested and reviewed in comparison with other terrestrial and marine climate reconstruction techniques and climate modelling data. However, some controversies remain about its underlying data or its applicability in general.In view of these controversies this paper discusses the power and limitations of the Coexistence Approach by summarising past results and new developments. We give insights into the details and problems of each step of the application from the assignment of the fossil plant to the most suitable nearest living relative, the crucial consideration of the usefulness of specific taxa towards their climatic values and the correct interpretation of the software-based suggested palaeoclimatic intervals. Furthermore, we reflect on the fundamental data integrated in the Coexistence Approach by explaining different concepts and usages of plant distribution information and the advantages and disadvantages of modern climatic maps. Additionally, we elaborate on the importance of continually updating the information incorporated in the database due to new findings in e.g., (palaeo-)botany, meteorology and computer technology.Finally, for a transparent and appropriate use, we give certain guidelines for future applications and emphasize to users how to carefully consider and discuss their results. We show the Coexistence Approach to be an adaptive method capable of yielding palaeoclimatic and palaeoenvironmental information through time and space.

The Miocene Lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern Yunnan (SW China) and the evolution of monsoon intensity. Three quantitative methods were chosen for this reconstruction, i.e. Leaf Margin Analysis (LMA), Climate Leaf Analysis Multivariate Program (CLAMP), and the Coexistence Approach (CA). These methods, however, yield inconsistent results, particularly for the precipitation, as also shown in European and other East Asian Cenozoic floras. The wide range of the reconstructed climatic parameters includes the Mean Annual Temperature (MAT) of 18.5-24.7°C and the Mean Annual Precipitation (MAP) of 1213-3711. mm. Compared with the modern Lincang climate (MAT, 17.3°C; MAP, 1178.7. mm), the Miocene climate is slightly warmer, wetter and has a higher temperature seasonality. A detailed comparison on the palaeoclimatic variables with the coeval Late Miocene Xiaolongtan flora from the eastern part of Yunnan allows us to investigate the development and interactions of both South Asian and East Asian monsoons during the Late Miocene in southwest China, now under strong influence of these monsoon systems. Our results suggest that the monsoon climate has already been established in southwest Yunnan during the Late Miocene. Furthermore, our results support that both Southeast Asian and East Asian monsoons co-occurred in Yunnan during the Late Miocene.

‘Tipping points’ in the climate system are characterised by a nonlinear response to gradual forcing, and may have severe and wide-ranging impacts. One of the best ways to identify and potentially predict threshold behaviour in the climate system is through analysis of palaeoclimate records. It has been suggested that early warning signals occur on the approach to a tipping point, generated from characteristic fluctuations in a time series as a system loses stability. Although early warning signals have been found in climate models and high-resolution marine and ice core palaeodata, studies from terrestrial records are lacking. In this study, a number of Pleistocene terrestrial records were selected to represent a range of regions strongly influenced by different climate modes which are thought to be capable of displaying threshold behaviour. These records included lake sediments from the North Atlantic, tree-rings from the South Pacific, a Chinese speleothem and were complemented by a new Greenland ice core chronology. Recently developed methods to detect signals of ‘critical slowing down’, ‘flickering’, and stability changes on the approach to a tipping point were utilised. Specific methodological issues arising from analysing palaeoclimate data were also investigated using a simple bifurcation model. A number of key criteria were found to be necessary for the reliable identification of early warning signals in palaeoclimate records, most crucially, the need for a low-noise record of sufficient data length, resolution and accuracy. Analysis of a Chinese speleothem identified the East Asian Summer Monsoon as an important climate ‘tipping element’, which may display a cascade of impacts. However, in some cases where early warning signals may fail, a deeper understanding of the underlying system dynamics is required to inform the development of more robust system-specific indicators. This was exemplified by the analysis of an abrupt, centennial-duration shutdown recorded during the Younger Dryas Chronozone in New Zealand, which demonstrated no slowing down, consistent with a freshwater pulse into the Southern Ocean. This study demonstrates that time series precursors from palaeoclimate archives provide a means of useful forewarning of many potential climate tipping points.

This study examined samples part of a larger project exploring environmental changes at Lake Hawdon, mid Canterbury, involving Queen’s University Belfast and the University of Canterbury. The author was responsible for the analysis of 85 fossil diatom samples from Lake Hawdon to create a high resolution study to assess their use as a biological proxy of past environmental changes through the Late Glacial Inter-Glacial Transition. Qualitative interpretations suggest three main phases of environmental change in Lake Hawdon during ~17,000 to 10,000 cal. BP. The first is a cool stage where taxa such as Cocconeis placentula and fragilarioid complex taxa Staurosirella pinnata and Pseudostaurosira brevistriata suggest a cool shallow lake with increasing macrophyte growth. The second phase suggests cold deepening water from at 13,928 +/- 142 to 12,686 +/- 166 cal. BP, dominated by Pseudostaurosira brevistriata, which coincides with the Antarctic Cold Reversal. The third phase represents a warm deep water phase after 12,686 +/- 166 cal. BP, dominated by planktonic taxon Cyclotella stelligera and epiphytic taxon Epithemia sorex, suggesting that Lake Hawdon does not exhibit the Younger Dryas event. Pollen and chironomid data from Lake Hawdon, generated by other project members, are included in the quantitative analyses to further inform palaeoenvironmental inferences generated from diatom data. Chironomid temperature reconstructions complement diatom interpretations for all three phases of change in the lake however diatom resolution allows changes to be detected earlier than other proxies suggest. Stabilisation of the landscape ~12, 686 +/- 166 cal. BP is suggested by tree pollen appearing near the end of the diatom cold phase, confirming with the diatoms and chironomid data that there was a warming out of the cold phase. Interpretations from Lake Hawdon add to other proxy studies in New Zealand that suggest an Antarctic Cold Reversal type event, but fail to highlight the Younger Dryas event. The generation of a transfer function was attempted with the diatom data based on Northern Hemisphere datasets, but a Principal Component Analysis plot highlighted major dissimilarities between the New Zealand fossil data and modern European data. This raised the issue of having morphologically similar but genetically separate taxa, potentially displaying convergent environmental adaptation, a crucial area for further research globally, and particularly in isolated areas like New Zealand.