Antarctic Ice Sheet dynamics and contribution to sea level rise during the Last Interglacial Helen Millman A thesis submitted in fulfilment for the degree of Doctor of Philosophy Climate Change Research Centre School of Biological, Earth and Environmental Sciences University of New South Wales Supervisors: Prof. Chris Fogwill, Prof. Chris Turney, Dr. Steven Phipps, Prof. Nick Golledge August 2018 Thesis/Dissertation Sheet Surname/Family Name : Millman Given Name/s : Helen Margaret Louise Abbreviation for degree as give in the University calendar : PhD Faculty : Science School : Biological, Earth and Environmental Sciences Antarctic Ice Sheet dynamics and contribution to sea level rise during the Thesis Title : Last Interglacial Abstract 350 words maximum: (PLEASE TYPE) The magnitude of future sea level rise remains uncertain due to a lack of understanding of feedbacks and tipping points in the climate system and cryosphere. As proxy records and current observations have limited spatial and temporal coverage, numerical modelling is needed to explore these crucial areas. It is thought that projected global mean surface temperatures will be ∼1-4°C above pre-industrial values by the end of this century, and whilst no past period truly reflects the potential future under anthropogenic climate change, past warm periods can be useful process analogues for future change. The Last Interglacial (LIG) was the last warm period before the present day, occurring 129-116 ka. It is thought that global mean sea level (GMSL) during the LIG was 5 to 10 m higher than present. With 60 m sea level equivalent (SLE) ice volume, the Antarctic Ice Sheets are the largest potential contributor to sea level rise, but they are also associated with the largest unknowns. Climate models consistently underestimate the level of warming during the LIG, and ice sheet modelling studies have been unable to reconstruct the apparent LIG sea level shown in the palaeo-records without significant changes to the model physics. LIG CO2 levels from ice core records show a variation of up to σ4, where σ represents standard deviation. It can take many years for bubbles of trace gases to become enclosed in the ice and so these uncertainties may be even greater if peak CO2 is not captured due to low precipitation and long closure periods. This study uses both climate and ice sheet modelling to assess the impact of elevated greenhouse gas (GHG) concentrations on Antarctic climate and ice sheet dynamics under LIG orbital forcing. Ice losses range from 16 to 648 cm SLE (sea level equivalent) over 20 kyrs of constant climate forcing, with the majority of this sea level rise stemming from the collapse of the West Antarctic Ice Sheet (WAIS). This mass loss was found to be driven by ocean-warming and is constrained by topography, with marine ice-sheet instability having significant impacts across key sectors of Antarctica. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral theses only). …………………………………………………………… ……………………………………..……………… ……….……………………...…….… Signature Witness Signature Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: COPYRIGHT STATEMENT ‘I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.' Signed ……………………………………………........................... Date ……30/08/18………………………………………........................... AUTHENTICITY STATEMENT ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.’ Signed ……………………………………………........................... Date ……30/08/2018………………………………………........................... ORIGINALITY STATEMENT ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed …………………………………………….............. Date ……………………………………………..............30/08/2018 INCLUSION OF PUBLICATIONS STATEMENT UNSW is supportive of candidates publishing their research results during their candidature as detailed in the UNSW Thesis Examination Procedure. Publications can be used in their thesis in lieu of a Chapter if: • The student contributed greater than 50% of the content in the publication and is the “primary author”, ie. the student was responsible primarily for the planning, execution and preparation of the work for publication • The student has approval to include the publication in their thesis in lieu of a Chapter from their supervisor and Postgraduate Coordinator. • The publication is not subject to any obligations or contractual agreements with a third party that would constrain its inclusion in the thesis Please indicate whether this thesis contains published material or not. This thesis contains no publications, either published or submitted for publication (if this box is checked, you may delete all the material on page 2) Some of the work described in this thesis has been published and it has been documented in the relevant Chapters with acknowledgement (if this box is checked, you may delete all the material on page 2) This thesis has publications (either published or submitted for publication) incorporated into it in lieu of a chapter and the details are presented below CANDIDATE’S DECLARATION I declare that: • I have complied with the Thesis Examination Procedure • where I have used a publication in lieu of a Chapter, the listed publication(s) below meet(s) the requirements to be included in the thesis. Name Signature Date (dd/mm/yy) Helen Millman 08/08/18 Postgraduate Coordinator’s Declaration (to be filled in where publications are used in lieu of Chapters) I declare that: • the information below is accurate • where listed publication(s) have been used in lieu of Chapter(s), their use complies with the Thesis Examination Procedure • the minimum requirements for the format of the thesis have been met. PGC’s Name PGC’s Signature Date (dd/mm/yy) i Abstract Sea levels have been rising since the early 20th century due to the increase in global temperatures predominantly caused by anthropogenic forcing. Although sea level rise is one of the major challenges we face today, the magnitude of future sea level rise remains uncertain due to a lack of understanding of dynamic feedbacks and tipping points in both the climate system and cryosphere. As proxy records and current observations are fragmentary and have limited spatial and temporal coverage, numerical modelling can help to explore these crucial areas. It is thought that projected global mean surface temperatures will be ∼1-4◦C above pre- industrial values by the end of this century, and whilst no past period truly reflects the potential future under anthropogenic climate change, past warm periods can be useful process analogues for future change. The Last Interglacial (LIG) was the last warm period before the present day, occurring 129-116k years ago. It is especially useful as a process analogue due to the relative abundance of proxy data from this time. Importantly, with amplified temperatures at high latitudes (polar amplification) global average temperatures during this period were up to 3◦C warmer than pre-industrial times. It is thought that global mean sea level (GMSL) during the LIG was 5 to 10 m higher than present. The Greenland Ice Sheet is believed to have contributed 0.6 to 4.3 m to LIG GMSL, and -0.2 to 0.4 m may be attributed to thermal expansion. With 60 m sea level equivalent (SLE) ice volume, the Antarctic Ice Sheets are the largest potential contributor to sea level rise, but they are also associated with the largest unknowns.