Il mio lavoro di tesi è stato svolto presso il gruppo di Cosmogeofisica dell'Università di Torino, che si occupa di studi climatici basati sull'analisi di sedimenti marini del Mediterraneo centrale e, in particolare, su misure di isotopi stabili. I sedimenti depositati nei mari e negli oceani sono archivi ricchi di informazioni sull'evoluzione climatica. In questa tesi mi sono focalizzata sullo studio di due core estratti nel Mediterraneo, accuratamente datati con tecniche radiometriche e di tefroanalisi. In entrambi la misura del delta-O18 ha permesso di studiare variazioni climatiche negli ultimi 2,700 anni (core GT 90-3) e negli ultimi 60,000 anni (core CT 85-5). La serie temporale ricavata dal core GT 90-3, caratterizzata da un'alta risoluzione temporale di 3.87 anni, è stata studiata con varie tecniche classiche ed avanzate di analisi spettrale (per esempio la Singular Spectrum Analysis e la Continuous Wavelet Transform) che hanno rivelato variazioni climatiche di alta e bassa frequenza. In particolare è stata rivelata una componente di periodo decennale, legata alle variazioni di portata del fiume Po. Grazie alla lunghezza della serie temporale di delta-O18, la componente decennale ci ha permesso di ricostruire le portate del Po relative agli ultimi 2,700 anni, periodo per il quale abbiamo informazioni molto scarse. Proprio sulla serie di portate del Po, misurata negli ultimi 200 anni, mi sono focalizzata durante il mio lavoro di tesi e, in particolare, mi sono occupata di prevedere l'andamento di tale serie utilizzando reti neurali feed-forward e modelli autoregressivi. Nonostante l'alto livello di rumore di questa serie e la sua brevità, sono riuscita ad ottenere una previsione affidabile per i prossimi 15 anni. La serie di delta-O18 ricavata dal core di mare profondo CT 85-5 è stata utile per lo studio delle variazioni climatiche legate all'ultima deglaciazione. La cronologia della serie è stata ricostruita con il metodo del radiocarbonio in collaborazione con l'ETH di Zurigo. Questa serie mostra diverse fasi climatiche durante la deglaciazione e, durante il periodo freddo dello Younger Dryas, rivela un minimo locale di delta-O18 sul quale ho focalizzato la mia attenzione. Le cause di tale evento potrebbero essere legate ad un breve ed improvviso aumento di temperatura o ad una variazione di composizione isotopica dell'acqua. Per indagare su questi aspetti, ho paragonato la nostra serie a misure di altri proxy ricavati sia dall'area Mediterranea, sia dal Nord Atlantico e dalla Groenlandia.
My thesis work was carried out at the Cosmogeophysics Group at the University of Turin, that studies climatic variations in the past, on the basis of the analysis of marine sediments from Central Mediterranean and in particular of the measurement of stable isotopes. Records deposited in sea and oceans are rich archives of information about climate evolution. In this thesis work I focused on the study of two Mediterranean cores, dated with high accuracy by radiometric methods and tephroanalysis. In both cores, delta-O18 measurement allowed to study climatic variations for the last 2,700 years (core GT 90-3) and for the last 60,000 years (core CT 85-5). The time series measured from GT 90-3 core, characterized by a high temporal resolution of 3,87 years, has been studied with various spectral methods (e.g., Singular Spectrum Analysis and Continuous Wavelet Transform), that allowed detecting high- and low-frequency climatic variations. In particular, a decennial component was detected, which is linked to the variations of Po River discharge. Thanks to the length of delta-O18 time series, the decennial component allowed to reconstruct the Po river discharge relative to the last 2,700 years, a period for which information is scarce. During my thesis work, I focused on the Po River discharge series measured during the last 200 years. In particular I worked to forecast the future trend of this series using feed-forward neural network and auto-regressive models. In spite the low signal-to-noise ratio of this series and its shortness, I succeeded in obtaining a reliable prediction for the next 15 years. The delta-O18 time series measured from the CT 85-5 deep-sea core has instead been used for studying climatic variations linked to the last deglaciation. The chronology of the series was made with the radiocarbon method in collaboration with the ETH of Zurich. This time series showed different climatic phases during the deglaciation and, during the cold event of the Younger Dryas, a delta-O18 local minimum on which I focused my attention. Possible causes of this event could be linked to a brief and sudden rise in temperatures or to a variation in isotopic composition of the water. In order to investigate this issue, I compared our series with measurements of other proxies, obtained from the Mediterranean area and also from the North Atlantic and Greenland.
Variazioni climatiche di scala 10-10^4 anni ricavate da misure di delta-O18 in sedimenti del Mediterraneo Centrale
PINCA, ELEONORA
2014/2015
Abstract
My thesis work was carried out at the Cosmogeophysics Group at the University of Turin, that studies climatic variations in the past, on the basis of the analysis of marine sediments from Central Mediterranean and in particular of the measurement of stable isotopes. Records deposited in sea and oceans are rich archives of information about climate evolution. In this thesis work I focused on the study of two Mediterranean cores, dated with high accuracy by radiometric methods and tephroanalysis. In both cores, delta-O18 measurement allowed to study climatic variations for the last 2,700 years (core GT 90-3) and for the last 60,000 years (core CT 85-5). The time series measured from GT 90-3 core, characterized by a high temporal resolution of 3,87 years, has been studied with various spectral methods (e.g., Singular Spectrum Analysis and Continuous Wavelet Transform), that allowed detecting high- and low-frequency climatic variations. In particular, a decennial component was detected, which is linked to the variations of Po River discharge. Thanks to the length of delta-O18 time series, the decennial component allowed to reconstruct the Po river discharge relative to the last 2,700 years, a period for which information is scarce. During my thesis work, I focused on the Po River discharge series measured during the last 200 years. In particular I worked to forecast the future trend of this series using feed-forward neural network and auto-regressive models. In spite the low signal-to-noise ratio of this series and its shortness, I succeeded in obtaining a reliable prediction for the next 15 years. The delta-O18 time series measured from the CT 85-5 deep-sea core has instead been used for studying climatic variations linked to the last deglaciation. The chronology of the series was made with the radiocarbon method in collaboration with the ETH of Zurich. This time series showed different climatic phases during the deglaciation and, during the cold event of the Younger Dryas, a delta-O18 local minimum on which I focused my attention. Possible causes of this event could be linked to a brief and sudden rise in temperatures or to a variation in isotopic composition of the water. In order to investigate this issue, I compared our series with measurements of other proxies, obtained from the Mediterranean area and also from the North Atlantic and Greenland.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14240/117899