i A GLACIOCHEMICAL STUDY OF THE MILL ISLAND ICE CORE by Mana Inoue, B.Eng, B.AntStd. Hons Submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy Institute for Marine and Antarctic Studies University of Tasmania August, 2015 ii I declare that this thesis contains no material which has been ac- cepted for a degree or diploma by the University or any other institution, except by way of background information and duly ac- knowledged in the thesis, and that, to the best of my knowledge and belief, this thesis contains no material previously published or written by another person, except where due acknowledgement is made in the text of the thesis, nor does the thesis contain any material that infringes copyright. Signed: Mana Inoue Date: 12 January 2016 iii This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968 Signed: Mana Inoue Date: 12 January 2016 iv ABSTRACT The IPCC 5th Assessment Report states that there are insufficient South- ern Hemisphere climate records to adequately assess climate change in much of this region. Ice cores provide excellent archives of past climate, as they con- tain a rich record of past environmental tracers archived in trapped air and precipitation. However Antarctic ice cores, especially those from East Antarc- tica, are limited in quantity and spatial coverage. To help address this, a 120 m ice core was drilled on Mill Island, East Antarctica (65◦ 30' S, 100◦ 40' E). Mill Island is one of the most northerly ice coring sites in East Antarctica, and is located in a region with sparse ice core data. The specific project aims were: 1) To produce a high resolution, well- dated record of water stable isotopes (δ18O, δD), and trace ion chemistry (sea salts, sulphate, methanesulphonic acid); 2) to investigate the seasonal and interannual variability of sea salts, in order to reveal which climate factors influence the Mill Island record; 3) to perform a regional comparison of δ18O and snow accumulation rate with nearby existing climate records from ice cores, observational stations, and atmospheric models, in order to seek the optimal method for temperature reconstruction using the Mill Island ice core record. Hydrogen peroxide, water stable isotopes, and trace ion chemistry were measured at high resolution throughout the entire core. The ice core was dated using a combination of chemical species, but primarily using water sta- ble isotopes. The Mill Island ice core contains 97 years of climate record (1913 { 2009), and has a mean snow accumulation of 1.35 metres (ice-equivalent) per year (mIE/yr). Concentrations of trace ions were generally higher than at other Antarctic ice core sites (e.g., mean sodium levels were 254 µEq/L). The full trace ion record contained a mix of periods with well-defined seasonal cycles and periods with weak seasonality and a higher baseline. An abrupt change was observed in the sea salt record in the mid-1930s. This may be related to a significant change in the local ice-scape. Sea salts were compared with instrumental data, including atmospheric models and satellite-derived sea ice concentration, to investigate influences on the Mill Island ice core record. The mean annual sea salt record did not show a correlation with wind speed. Instead, sea ice concentration to the east of Mill Island was found to be likely influencing the annual mean sea salt record, at least during the period of 1979 to 2009. A mechanism involving formation of frost flowers on sea ice was pro- v posed to explain the extremely high sea salt concentration. Post-depositional migration of magnesium and methanesulphonic acid were observed in the trace ion record, and for the first time, migration of sodium and chloride were ob- served. Snow accumulation rate was compared with snow accumulation or pre- cipitation record from nearby sites. The Mill Island snow accumulation was found to be influenced by local orography, i.e., the annual snow accumulation record is not strongly related with precipitation in nearby sites. The Zonal Wave Three (ZW3), large scale atmospheric mode, modulates precipitation at nearby Law Dome, and to a lesser extent, modulates Mill Island precipitation. Snow accumulation and δ18O were compared with precipitation and tem- perature data from atmospheric models. The climatology of precipitation at Mill Island shows evidence of higher snowfall during winter, consistent with other Antarctic sites. The linear monthly ice core dating was adjusted us- ing the precipitation climatology, and the adjusted δ18O record resulted in a warmer annual signal. This finding indicates that without this adjustment, there is a small cold bias in annual temperature reconstructions from ice cores that share this elevated winter precipitation. This bias should be considered when reconstructing temperatures where climate trends differ with season and when comparing with other temperature reconstructions (e.g., terrestrial or ocean based records). In situ temperature data (e.g., a co-located Automatic Weather Station) are not available at Mill Island. Instead, the annual mean δ18O record was compared with atmospheric reanalysis model output temperature at Mill Is- land. The correlation was found to be statistically insignificant. To attempt a more accurate palaeothermometer reconstruction, the annual record was di- vided into summer and winter \windows" with the maximum δ18O value set as the summer window centre, and the minimum δ18O value set as the winter window centre. It was found that when using narrow summer and winter win- dows, the δ18O value was significantly correlated with December to April mean model temperatures and May to July mean model temperatures, respectively. vi ACKNOWLEDGEMENTS Firstly, I would like to thank all of my supervisors: Mark Curran, An- drew Moy, Tas van Ommen, Alex Fraser, Helen Phillips, and Ian Goodwin. Especially, huge appreciation to Alex for your lightning speed responses any time, and for wise suggestions not only as a supervisor but also as a good friend; also to Mark for giving me many opportunities during my Ph.D., and such an amazing field work experience. I also would like to thank the glaciology team, Meredith Nation, Sam Poynter, Jason Roberts, Alan Elcheikh, Tessa Vance, Chris Plummer, Shavawn Donoghue, and Ben Domensino for their support; and to the Mill Island field work (AAS project 1236) crew, including Mark Curran, Ian Goodwin, Andrew Moy, Ben Domensino, Troy Baker, and Tim Gill, for their hard work. My appreciation also goes to Andrew Klekociuk for the HYSPLIT sup- port; Jan Lieser for the sea ice data; Scott Carpentier for useful and helpful climate discussions; Melissa Nigro for the AMPS data; Jan Lenaerts for the RACMO data; Mike Summer and Tom \Tank" Remenyi for the LATEX support; the ACE CRC and IMAS administration teams, especially Wenneke ten Haout and Kate Maloney for their amazing support and leadership; Guy Williams and the Young Antarctic Scientist (YAS) team (Ben, Nick, Eva, Julie, Molly, Margaux, David, Lavy, Tom, Delphi, Merel, Pearse), it was great fun to visit schools and talk about Antarctic science to kids! Christine Weldrick for proof- reading, your fresh eye saved me a lot of work! Huge thank to the Aurora Basin North (ABN) ice core drilling project crew: Mark Curran (Science leader), Sharon Labudda (Field leader), Tas van Ommen, Noel Paten, Malcolm Arnold, Simon Sheldon, Trevor Popp, Jerome Chappellaz, David Etheridge, Chunlei An, J. P. Steffensen, Andrew Moy, Meredith Nation, Jenny Carlisle, Tony Fleming, Joe \captain" McConnell, Wang Feiteng, Peter Campbell \Bloo", Jason Roberts, Olivia Maselli, Nerilie Abram, Holly Winton, Chris Plummer, Olivier Alemany and Tessa Vance; all the people who supported us from Casey, Kingston, Hobart and all over the world. I had such a great experience during the field work. This was definitely a highlight of my life, and strong motivation for the next steps. I would like to acknowledge the International Postgraduate Research Scholarship (IPRS), the Australian Postgraduate Awards (APA), and the Antarctic Climate & Ecosystems Cooperative Research Centre (ACE CRC) for my Ph.D. scholarship, and the Institute for Marine and Antarctic Studies (IMAS) for travel funds. And of course, enormous thank to all my friends. My Ph.D. life would not be this colourful, meaningful, or joyful without your laughs, love and hap- piness. In particular, Lucho, my Chilean brother and best friend, thank you very much for looking after me, for all your support, suggestions, help, and for hiking, cooking, movie, playing music, drinking, chatting, everything. What you have done for me is way more worthy than quite few bottles of whisky and shochu! I can't express enough how much I appreciate you. Thank you. Manu, my French brother, thank you for caring for me, listening all my com- plaints and giving me French solutions which opened my eyes many times! Without my two brothers, the last six month of my Ph.D. would have been much harder. I loved the swimming time with you two. Thank you, Onichans. Eva, thank you for the multiple tea times, complaining together about every- thing, and kidnapping me for breaks. Julie, thank you for making me laugh and encouraging me when I was really down. You rescued me from dark- ness many times. Nicole, thanks for the connection between us, laughing and smiling. I miss you and love you so much. You are just amazing! Maurito, Andre, thank you for the countless precious evenings. I miss those times with you guys in Lower Sandy Bay and in Japan! Molly and Lara, the \original friends", thank you for your endless love since my Honours degree. You have been always there when I needed you. Thank you. Amelia, Tania, Nick, Daniela, Malinda, Camila, Max, Pearse, PaPas (Pablo and Pamela), Giulia, and Luchita, thank you for feeding me both food and love.