Browsing by Author "Lovejoy, Shaun"

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    Geographic variability in dust and temperature in climate scaling regimes over the Last Glacial Cycle
    (2024) Acuña Reyes Nicolas Martin; van't Wout, Elwin; Lovejoy, Shaun; Lambert Fabrice; NCD Risk Factor Collaboration (NCD-RisC)
    Temperature and mineral dust records serve as valuable palaeoclimatic indicators for studying atmospheric variability across different temporal scales. In this study, we employed Haar fluctuations to analyse global spatiotemporal atmospheric variability over the Last Glacial Cycle, capturing both high- and low-frequency information within the records, regardless of uniform or non-uniform sampling. Furthermore, we utilised Haar fluctuations to compute fluctuation correlations, thereby enhancing our understanding of palaeoclimate dynamics.Our findings reveal a latitudinal dependency in the transition from macroweather to climate regimes (tau c), with polar regions experiencing shorter transitions compared to the tropics and mid-latitudes. These transitions occur at approximately 1/100th of glacial cycle length scales, suggesting a dominant forcing mechanism beyond Milankovitch cycles. Additionally, our analysis shows that polar regions have larger fluctuation amplitudes than lower latitudes as a consequence of the polar amplification effect. Furthermore, fluctuation correlations demonstrate faster synchronisation between the poles themselves compared to lower-latitude sites, achieving high correlation values within 10 kyr.Therefore, our findings suggest a consistent climate signal propagating from the poles to the Equator, representing the first empirical evidence supporting the hypothesis that the poles play a pivotal role as climate change drivers, influencing the variability in climatic transitions worldwide.
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    Geographic variability of dust and temperature in climate scaling regimes over the Last Glacial Cycle
    (2023) Acuña Reyes, Nicolas Martin; Van T Wout, Elwin; Lambert, Fabrice; Lovejoy, Shaun
    Temperature and mineral dust records serve as valuable paleoclimate indicators for studying atmospheric variability across a wide range of temporal scales. Due to the typically lower resolution of older sections within these records, studies investigating the geographical variability of the atmosphere have predominantly focused on periods shorter than one glacial cycle, such as the Holocene or the Last Glacial Maximum. In this study, we utilise a Haar-based algorithm to evaluate the geographic variability of dust and temperature records throughout the last glacial cycle. This algorithm enables us to analyse non-equidistant sampling series, allowing for the utilisation of both high and low-frequency information from the records. Consequently, we can investigate timescales ranging from decades to thousands of years. Notably, our findings indicate that the transition from macroweather to climate regimes occurs at shorter timescales in polar regions compared to the tropics or mid-latitudes. Furthermore, disparities between the dust records of the North and South Poles were observed. Finally, we assess the time-dependent correlation between the polar regions and the lower latitudes. Our analysis reveals high correlations at timescales of approximately 20, 40, and 100 kyr, which aligns with the Milankovitch cycles. Conversely, all sites exhibit a loss of correlation between 40 and 80 kyr, indicating the absence of an identifiable oscillation synchronisation mechanism at these scales. On the one hand, our findings support the use of the Haar-based method as an alternative for analysing nonuniform datasets. On the other hand, they underscore the necessity for additional high-resolution or longer time series data from the tropics or mid-latitudes, as the currently available data fail to adequately represent the glacial-interglacial cycles.
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    Unified scaling framework for Holocene, Quaternary and Phanerozoic geochronology variability
    (2024) Davies, Rhisiart; Lovejoy, Shaun; Hebert, Raphael; Lambert, Fabrice; Spiridonov, Andrej