ABSTRACT TAYLOR, RICHARD STANLEY. Evaluating the Effects Of
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ABSTRACT TAYLOR, RICHARD STANLEY. Evaluating the Effects of Regional Climate Trends Along the West Antarctic Peninsula Shelf Based on the Distributions of Naturally Occurring Radiochemical Tracers within the Seabed. (Under the direction of Drs. David DeMaster and Christopher Osburn). Measurements of 230Th, 210Pb and 234Th activities were made on sediment cores collected along a N-S transect (exhibiting a sea-ice gradient) off the West Antarctic Peninsula. The resultant data, together with existing 14C sediment data, were used to evaluate the effects of regional warming on particle flux reaching the seabed on timescales from millennial to seasonal. Shelf samples were collected at five stations, over three cruises, between February 2008 and March 2009, as part of the FOODBANCS-2 Project. Sea-ice conditions (the number of days ice-free prior to core collection) were evaluated at the five stations to understand the relationship between ice abundance and particle flux. Based on the millennial tracer, 14C, particle flux along the peninsula decreases southward, consistent with the observed sea-ice gradient. 230Th data provide evidence that sediment focusing (i.e., lateral transport) occurs to a greater extent in the northern reaches of the study area as compared to the southernmost stations. 210Pb-based particle flux measurements (representing centurial trends) display a similar trend as 14C, showing higher particle flux in the northern study area stations (where sea-ice conditions are diminished) and lower flux southward as sea-ice conditions increase. Additionally, 210Pb data suggest that lateral transport plays an important role in sediment distributions on hundred-year timescales, which is explainable by the relatively short circulation times of peninsular waters relative to 210Pb’s half-life. On seasonal and annual time scales, 234Th data show an increase in particle flux at the southernmost stations. The observed increase in particle flux on seasonal and annual time scales is consistent with the increased warming trend along the peninsula and the reduction in sea-ice conditions over the past decade. However, a significant statistical relationship could not be established between sea-ice free days and 234Th-derived particle flux to the seabed. Thus, the fluxes/distributions of long-lived particle-reactive tracers (14C, 230Th, and 210Pb) off the West Antarctic Peninsula appear to be controlled primarily by the long- term pattern of increasing sea ice in the southward direction, whereas the fluxes of the short-lived tracer (234Th) appear to be affected most by the more recent decreases in sea ice extent (associated with Climate Change) that have occurred over the past decade primarily in the southern stations. © Copyright 2015 Richard Stanley Taylor All Rights Reserved Evaluating the Effects of Regional Climate Trends Along the West Antarctic Peninsula Shelf Based on the Distributions of Naturally Occurring Radiochemical Tracers within the Seabed by Richard Stanley Taylor A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Marine, Earth and Atmospheric Sciences Raleigh, North Carolina 2015 APPROVED BY: _______________________________ _______________________________ Dr. David J. DeMaster Dr. Christopher L. Osburn (Co-Chair of Advisory Committee) (Co-Chair of Advisory Committee) _______________________________ _______________________________ Dr. Elana L. Leithold Dr. Carrie J. Thomas DEDICATION For Science! ii BIOGRAPHY Richard was born in Columbus, Mississippi on November 23, 1979. His parents provided boundless support for his insatiable curiosity in everything he did - from exploring the sciences, to sports, to creative endeavors and beyond. His only limits have been those of personal safety (and those were pushed by the author often). Over the years he has worn many hats — to better his understanding of the unknown. In August 2009, after a long academic hiatus, Richard enrolled in the Marine Sciences program at North Carolina State University to finish his Bachelor’s Degree. The path to eventual success was long, but along the way he was rewarded with great gifts, each better than the last. Firstly, he was given the opportunity to assist in field and laboratory research —endeavors that further fueled his interest in the unknown. His newly gained field experience allowed his path to cross with that of his mentor, and eventual friend, Dave DeMaster. It was Dr. DeMaster who, through his inspiring work in Antarctica and his well-taught course on chemical oceanography, opened Richard’s eyes to the boundlessly interesting world of marinechemistry and radioisotopes. Lastly (and definitely the best), Richard met his future wife while completing his degree. Richard started his graduate career at North Carolina State University in the fall of 2012 under the guidance of Drs. DeMaster and Osburn. Upon completion of his master’s degree, he will be continuing on with Dr. DeMaster in pursuit of his doctorate. iii ACKNOWLEDGEMENTS The author would like to express his gratitude for the many people who contributed feedback and support throughout the writing process. In particular, he would like to thank his committee members: Doctors Carrie Thomas, Lonnie Leithold, Dave DeMaster and Chris Osburn for keeping his writing focused and honest. Financial support was provided by the National Science Foundation (Grant no. ANT-0636773, David J. DeMaster, Craig R. Smith and Carrie J. Thomas, principal investigators). The author also wishes to thank his friends Jen Dixon-Brown and Robert Duke for their open office doors (and the much needed breaks). Lastly, he would like to express his gratitude for his family and for their endless support (especially his wife - Emily Winchester Taylor). iv TABLE OF CONTENTS LIST OF TABLES ..................................................................................................... vii LIST OF FIGURES .................................................................................................. viii Chapter 1 Overview of Study Area and Overall Research Objective .................... 1 1. The West Antarctic Peninsula – Background ............................................. 1 2. General Circulation .................................................................................... 1 3. Sediment Transport ................................................................................... 4 4. Ecology ...................................................................................................... 7 5. Climate Change ....................................................................................... 10 6. Overall Research Objective ..................................................................... 11 Chapter 2 Documenting the Seabed Response to Climate Change Trends on the West Antarctic Peninsula Based on Naturally Occurring Radiochemical Tracers ............................................................................................... 13 1. Introduction .............................................................................................. 13 2. Methods ................................................................................................... 18 2.1 Study Sites ................................................................................... 18 2.2 Radiochemical Analysis ................................................................ 19 2.3 Sea-Ice Metric .............................................................................. 21 3. Results ...................................................................................................... 22 3.1 Radiochemical .............................................................................. 22 3.2 Millennial Trends .......................................................................... 25 3.3 Decadal-Centurial Trends ............................................................. 28 3.4 Seasonal Trends .......................................................................... 31 3.5 Annual Trends .............................................................................. 33 3.6 Sea-Ice Trends ............................................................................. 34 4.1 Discussion ............................................................................................... 37 4.2 Summary of Temporal Trends in Particle Flux.............................. 45 5. Conclusions ............................................................................................... 48 References ........................................................................................................... 50 v Appendices ........................................................................................................... 56 Appendix A .................................................................................................... 57 Appendix B .................................................................................................... 58 Appendix C .................................................................................................... 59 Appendix D .................................................................................................... 60 Appendix E .................................................................................................... 61 Appendix F .................................................................................................... 64 Appendix G