This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Marshall, Matthew G Title: Assessing the impact of glacier retreat on organic matter export and cycling in Chilean Patagonia General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. Assessing the impact of glacier retreat on organic matter export and cycling in Chilean Patagonia Matthew Marshall School of Geographical Sciences University of Bristol A dissertation submitted to the University of Bristol in accordance with the requirements for the degree of Doctor of Philosophy in the Faculty of Science. January 2020 43,331 words Abstract Organic matter is an important component of global biogeochemical cycles, which are sensitive to processes of landscape change. The worldwide retreat of mountain glaciers is one of the most profound examples of such change. Chilean Patagonia represents a unique study region, which is both relatively untouched by direct human activity and undergoing significant rates of deglaciation. The biogeochemical role of glaciers in this region is relatively understudied and this thesis offers the first regional scale assessment of the sensitivity of organic matter in rivers and fjords to glacier retreat. This assessment comprises three complementary studies. The first adopts a space-for-time approach, in which the effects of spatial variations in landscape properties on organic matter flux and composition are used to infer the effects of ongoing glacier retreat over time. It was found that glaciers drive higher catchment yields for particulate organic matter and supply dissolved organic matter rich in protein-like and aliphatic substances. However, the influence of glaciers is dampened by non-glacial sources and sinks in the downstream landscape. The second study used incubation experiments to quantify the proportion of bioavailable dissolved organic carbon in river water from selected catchments. These incubations showed that bioavailability in these catchments is lower than that observed in glacial rivers of the northern hemisphere. This may be explained by prior processing and specific intrinsic compositional factors but is not systematically related to catchment glacier cover. The third study presents the first molecular level analysis of dissolved organic matter in a glaciated fjord. This analysis showed that riverine organic matter may comprise a significant proportion of the total organic carbon pool, which is sensitive to changes in glacier melt inputs. The relationships between organic matter cycling and landscape change in Chilean Patagonia established in this thesis highlight some potential implications of deglaciation for global biogeochemistry. Acknowledgements I would first like to thank Prof. Jemma Wadham for her enthusiastic supervision. It has been a privilege to work in such an interesting field and be supported in developing my own abilities by someone so positive and passionate about their work. Thanks also to Prof. Laura Robinson for keeping an eye on me when things looked a little bleak – your kindness was just enough to keep me going. Further thanks to Profs. Rachel Flecker, Alex Anesio and Martyn Tranter for helpful conversations along the way. I am indebted to Dr Anne Kellerman for taking me under her wing and sharing her expertise in organic geochemistry. Without her support, getting to grips with molecular data would not have been so enjoyable. Thanks also to Prof. Rob Spencer for allowing Anne to get involved in Patagonian fieldwork and for providing lab support. Much of my gratitude goes to Dr Jon Hawkings, whose dedication and diligence in field logistics and sample collection helped to make this thesis possible. Thanks also to the whole team at ‘Camp Washout’ (Alex Beaton, Ale Urra, Helena Pryer, Anne Kellerman and Rory Burford) for making great memories and Pisco hot chocolates. Especial thanks to Ale – I couldn’t have wished for better company to see out the full 50 days! I extend thanks to Dr Giovanni Daneri and the team at CIEP for invaluable logistical support. I am also grateful to Dr Sebastien Bertrand, Loïc Piret and their team for field support and ensuring that we didn’t starve! Thanks also to Don Rene, Rene Jr and Don Efrain for shipping us in and out of camp and topping us up with power from time to time. I thank Dr Fotis Sgouridis, James Williams and Dr Chris Yates for their lab support. I also thank the team at the MAGLAB, Tallahassee, for granting me time to run my field samples, and especially to Lyssa for fixing the glitch and helping make up for lost time! To all my office colleagues who made the tough times more bearable, especially Amy Sweet for boosting my confidence whenever it was needed and Helena Pryer for giving me a home when I was flooded out of my own. Thanks also to Ale (again!), Bea (and the dogs!), Sam, Miranda, Alex and the IcyBios team. Finally, to Mom, Dad, Mary and Ed for your love and encouragement throughout. And especially to Nick for your understanding and for keeping me sane. This thesis was funded through a studentship awarded by the NERC GW4+ DTP. Author’s declaration I declare that the work in this dissertation was carried out in accordance with the requirements of the University’s Regulations and Code of Practice for Research Degree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate’s own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. Signed Date Table of contents 1. Introduction and background ................................................................................. 1 1.1. Introduction ......................................................................................................... 1 1.2. Research objectives ............................................................................................. 3 1.2.1. Research objective 1..................................................................................... 3 1.2.2. Research objective 2..................................................................................... 4 1.2.3. Research objective 3..................................................................................... 4 1.3. Scientific background .......................................................................................... 5 1.3.1. Glaciers as sensitive stores of organic matter .............................................. 5 1.3.2. Accounting for the effect of glacial organic matter on aquatic systems ...... 9 1.3.3. Significance of the effect of glacial DOM on specifically marine systems12 1.4. Addressing key research opportunities ............................................................. 13 1.4.1. Global coverage.......................................................................................... 13 1.4.2. Integration of terrestrial and marine perspectives ...................................... 17 1.4.3. Potential of molecular level analyses ......................................................... 19 2. Methodology ........................................................................................................... 21 2.1. Study region ...................................................................................................... 21 2.1.1. Latitudinal river transect ............................................................................ 23 2.1.2. Steffen Glacier............................................................................................ 26 2.1.3. Baker-Martinez Fjord ................................................................................. 28 2.1.4. Other study sites ......................................................................................... 31 2.2. Sample filtration and storage............................................................................. 33 2.3. Analytical methods ............................................................................................ 34 2.3.1. Dissolved organic carbon (DOC) concentrations....................................... 34 2.3.2. Spectrofluorescence data ............................................................................ 36 2.3.3. Molecular determination of DOM.............................................................