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Astronomical Forcing of Sub-Milankovitch Climate Oscillations During the Late Quaternary

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Astronomical Forcing of Sub-Milankovitch Climate Oscillations During the Late Quaternary Astronomical Forcing of Sub-Milankovitch Climate Oscillations during the Late Quaternary Alison Marguerite Kelsey Honours, Bachelor of Arts, Archaeology Bachelor of Arts, Archaeology Diploma of Information Technology, Software Development A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2017 School of Earth and Environmental Sciences ii Abstract A climate signal of ~1500-yr quasi-periodicity (e.g., Bond events) has been found from the Arctic to Antarctica, in palaeoclimatic data derived from a range of environmental proxy records. Solar and lunar forcing have individually been suggested as the cause of this millennial-scale signal, although some contend that it is little more than stochastic resonance within the climate system. Also debated is whether this climate signal is forced by the ocean-atmosphere dynamics of the North Atlantic or the tropical Pacific, as well as relevant climatic teleconnections. The cause of this cycle is elusive as no known solar cycle of this length exists, whilst forcing due to lunar gravitation has been dismissed as being too weak. The most likely cause of any periodic climate signal is an astronomical one, as demonstrated in Milankovitch cycles. This thesis explores a potential astronomical cause of millennial- and centennial- scale periodicities and variability, based on a combination of solar and lunar forcing. Conceptual and trigonometric models, physical models of insolation, solar irradiance, and gravitation, and astronomical data were used in this exploration. Identified as a possible cause of the ~1500-yr climate cycle is precession. Precession changes the timing of Earth’s seasons relative to our calendar and external reference points, such as the fixed stars and the closest point in Earth’s orbit to the Sun (the perihelion). The primary actors in precession are the Sun and Moon through their gravitational influence on the rotating Earth. Significant climatic impacts of precession are seen in the ~21-ky Milankovitch precessional cycle, the result of two interacting precessional cycles: equinoctial (associated with the seasonal/tropical year) and apsidal (associated the perihelion and anomalistic year). This thesis investigates precession at a high-frequency scale, enabling a more detailed tracking of the moving seasons relative to the moving perihelion at sub-Milankovitch scales through-out the last 5,500 yrs. This research found a statistically-significant, strong positive correlation between solar insolation reconstruction derived from Antarctic 10Be ice-core data and a normalised, chronologically-anchored model of superimposed astronomical cycles that emulates the ~1500-yr climate cycle. Pronounced millennial-scale signals were observed in Earth-Moon distances and gravitation data. Maximum forcing occurs at perihelion, close to lunar perigee and Bond events occur at these points during the range of the astronomical data. Previously identified potential components of the ~1500-yr climate signal, viz the 209-yr Suess de Vries cycle and a 133-yr cycle, can be clearly seen in the astronomical and physical data. Modelled, high- frequency, perigee-perihelion interaction by this research reinforces these results, reproducing and explaining the variability of millennial-scale climate signals. Such variability is also supported through the movement relative to the tropical year, in conjunction with mapping of Metonic lunation and perihelion positions. iii Supported by multiple lines of evidence, the results of this thesis suggest that the Sun and Moon act together through gravitation and insolation to produce millennial-, centennial-and decadal- scale climate signals through tidal forcing of Earth’s atmosphere and ocean. Key mechanisms and components are precession, perihelion, perigee, lunation, and nutation (wobble of Earth’s axis). Key inferences from these results are that astronomical forcing influences radiocarbon chronological variability, such as marine reservoir values, variability and time lag in radiocarbon data, and also suggest that the 209-yr SdV cycle is caused by combined solar and lunar forcing rather than previously inferred solar variability. iv Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. v Publications during candidature: KELSEY, A. M., MENK, F. W. & MOSS, P. T. 2015. An astronomical correspondence to the 1470- year cycle of abrupt climate change. Clim. Past Discuss., 2015, 4895-4915. Conference abstracts: KELSEY, A.M. 2015. The astronomy of the 1,470yr climate cycle: extending the Milankovitch connection. XIX INQUA-Congress, G01-03, 2015, Nagoya, Japan. KELSEY, A.M. 2015. Millennial Oscillations of the Late Quaternary and the Great Sandy Region of Southeast Queensland. XIX INQUA-Congress, P19-03, 2015, Nagoya, Japan. KELSEY, A. M. 2016. The Milankovitch connection: astronomical forcing of millennial-scale climate signals. AQUA Biennial Conference, 2016, P2, Auckland, New Zealand. Publications included in this thesis: Nil vi Contributions by others to the thesis: The supervisory team Patrick Moss and Fred Menk assisted with technical support, revisions and editing of the thesis. Peter Kershaw, Cian Brinkmann, and Janet McCoy assisted with editing of the thesis. Statement of parts of the thesis submitted to qualify for the award of another degree: None. vii Acknowledgements I firstly wish to thank my supervisors, Patrick Moss and Fred Menk, for their time, guidance, support, and encouragement during the course of my thesis. I greatly appreciate the opportunities they afforded me in allowing me to take this journey of discovery. To my family, and especially my children, Matthew Cole, Ross Cole, Cassie Robinson, Michael Kelsey, and Cian Brinkmann, thank-you from the bottom of my heart; your enduring patience, support and words of encouragement have made this achievement possible. My journey was plagued with obstacles, including breast cancer, broken bones, and multiple surgeries. Thank-you all for looking after me during those difficult times and helping me get across the finishing line, and feeding me when I forgot to eat, especially Cian and Matt Brinkmann, Cassie, Mick, and Anjuli Lansley. Cian, you were also a wonderful help in providing another set of eyes to edit my thesis. Although my parents, Max and Maureen Kelsey, are no longer of this world, I cannot forget them: to Mum and Dad I owe so much for encouraging and feeding my thirst for knowledge. I wish to say very big thank-you to my friends, all of whom provided encouragement, support and friendship throughout the course of my PhD research. In particular, I’d like to thank Phil Stewart, Janet McCoy, and Peter Kershaw for their friendship. You were all there when I needed a friend. Phil, your friendship, sense of humour, and words of encouragement helped me when I felt discouraged. Thank-you to Peter and Janet for editing my thesis, and Peter for your advice. I’d also like to thank Jamie Shulmeister, Lynda Petherick, Quan Hua, Jian-Xin Zhao, Patricia Gadd, and Matthew Fischer. Although our discussions were brief, you none-the-less provided guidance when I needed it. viii Keywords: Astronomy, Milankovitch precession, Bond events, ENSO, geochronology, cosmogenic isotopes, solar and lunar forcing Australian and New Zealand Standard Research Classifications (ANZSRC): ANZSRC code: 040605 Palaeoclimatology (33.33%) ANZSRC code: 020199 Astronomical and Space Sciences not elsewhere classified (33.33%) ANZSRC code: 040606 Quaternary Environments (33.33%) Fields of Research (FoR) Classification: FoR code: 0201 Astronomical and Space Sciences (50%) FoR code: 0406 Physical Geography and Environmental Geoscience (50%) ix Chapter Guide Chapter 1 - Introduction ....................................................................................................................... 1 1.1 Introduction ................................................................................................................................ 1 1.2 Scope and limitations ................................................................................................................
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