AN ABSTRACT OF THE THESIS OF Yip Chun for the degree of Master of Science in Oceanography presented on September 9. 1988 Title: Geochemistry of Thorium in Natural Water Systems Redacted for Privacy Abstract aunroved: Chih-An Huh 232Thisnon-radiogenic and hence issupplied tonatural water systems only by the weathering of crustal rocks.Like most other trace metals,itis delivered to the ocean by the usual fluvial and aeolian pathways.Therefore, 232Th can serve as a connection between trace metals and radiogenic thorium isotopes(i.e.,234Th,230Th, and 228Th). Knowledge of thedistributionof 232 in natural waters can therefore enhance the value of information on the distributionsoftheother Thisotopeswhen theyareappliedtovarious geochemical and geochronological studies. The activities of 230Th and 232Th in continental water (river and lake), seawater,andhydrothermalsolutionsaredeterminedbyneutronactivation analysis (NAA) and isotope dilution mass spectrometry (IDMS). Concentrations of dissolved and particulate 230Th and 232Th are presented for the Columbia River, the confluence of the John Day and Columbia Rivers, Crater Lake, Lost Lake, Oregon, and the Saanich Inlet, Canada.This data set indicates that there are large variations of thorium content in natural waters and of its partitioning between the dissolved and particulate forms.In surface waters, dissolved 232Th concentrations rangefrom0.02 1to0.708dpm/lO3kg,anddissolved230Th concentrations range from 0.039 to 0.917 dpm/lO3kg. Concentration ranges of particulate232Thand 230Thare0.0083to18.65dpm/lO3kg and0.03to 51.75 dpmllo3kg, respectively.The concentration levels in fresh waters are one (for dissolved Th) to four (for particulate Th) orders of magnitude larger than in seawater. Thorium is a very particle-reactive element.The partitioning of Th on particulates in the fresh waters are about 2 to 20 times higher than in seawater, reflecting higher particle concentration in fresh waters. Verticalprofilesarereportedforthree samplingsites:CraterLake, SaanichInlet,and off the coast of Washington and Oregon. A subsurface maximum of 232Th is observed in Crater Lake and Saanich Inlet, which may be produced by vertical particulate transport. The profiles in Saanich Inlet also show systematictrendsalongtheoxic/anoxicinterface;dissolved 232Th and 230Thincreasewithdepth whileparticulate232Th and 230Th decrease with depth. Chemical changesacrosstheredoxboundarystrongly affectthe partitioning of thorium between solution and suspended particles.When settling particles cross the redox boundary, Th is released into solution, enhancing the dissolved Th concentration in the anoxic water.The profile of 232Th in coastal seawaterclearly indicatesasurface sourceof232Thanditsscavenging throughout the water column. Inaddition,the remobilization and enhanced scavenging at land-sea boundaries may have a significant influence on thorium distribution,whichsuggeststhatfluvial inputismore importantincoastal regions, whereas aeolian input dominates in the open ocean. The concentrations of 232Th in hydrothermal solution from the Juan de Fuca Ridge range from 0.08to3.1dpm/lO3kg. Correlation between 232Th concentration and other properties indicatesthatthe hydrothermal end-member ishighly enrichedin232Threlativetodeep seawater. Thus, hydrothermal vents should constitute a source of 232Th to the deep ocean. Geochemistry of Thorium in Natural Water Systems by Yip Chun A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed September 9, 1988 Commencement June 1989 APPROVED: Redacted for Privacy Assistant Professor of Oceanography in charge of major Redacted for Privacy Head of departmftnt of Redacted for Privacy Dean of Date thesis is presented September 9. 1988 ACKNOWLEDGEMENTS First of all,I am indebted to all the people who edited this manuscript. Special thanks to Dabra Zahnle for her proofreading and helpful comments on thefirstdraftofthismanuscript. ThankstoCollinRoesler,Annette de Charon, Calven Mordy, and my host family Danetta and Mario Cordova for their emotional support, culture guidance and English editing. Most of allI am indebted to Chih-An Huh forhisfinancialsupport, scientific guidance, and his valuable time.Whenever I needed his advice, he always made time for me, no matter how busy he was.I couldn't have finished without his help.I would like to thank Fredrick G. Prahi for his constructive comments, advice and encouragement.Special thanks to Robert W. Collier for providing Crater Lake samples and data,suggestions,careful reading of the manuscript and helpful critique.I would also like to thank to David C. Kadko for supplying hydrothermal solution samples from the Juan de Fuca Ridge. Last, but not least, I would like to thank my husband, Ken Kwong for his understanding, patience, and the times he worked through the night with me on our computer. Withouthisemotionalsupport and computer knowledge,I couldn't have finished this thesis. This research was supported by NSF grants OCE-8515631. This thesis is dedicated to my mother who devotes all her life to her children. TABLE OF CONTENTS INTRODUCTION......................... 1 2. LITERATURE REVIEW...................... 7 2.1 Thermodynamic Properties of Thorium........... 7 2.2 Thorium Isotopes and the role of 232Th........... 15 2.3 Evolution of Methodoloj 20 2 ................. 2.4 Review and Update of Th Data in the Ocean........ 25 2.5 Implications From Manganese Nodules........... 29 2.6 Implications From Other Authigenic Deposits........ 35 3. METHODS AND MATERIALS.................. 36 3.1 General Introduction................... 36 3.2 Sampling and Shipboard Filtration............. 37 3.3 Neutron Activation Analysis................ 41 3.3.1 Principle......................... 41 3.3.2 Possible activation-induced interferences........... 42 3.3.3 Pre-irradiation chemistry.................. 43 3.3.4 Neutron activation.................... 48 3.3.5 Post-irradiation chemistry................. 49 3.3.6 Counting and data processing................ 51 3.4 Mass Spectrometric Analysis................ 54 3.4.1 Basic concepts...................... 54 3.4.2 Chemical procedure................... 54 3.4.3 Mass spectrometry.................... 55 3.4.4 Counting results and data reduction............. 57 4. THE DISTRIBUTION AND CONCENTRATIONS OF DISSOLVEDAND PARTICULATE THORIUM IN FRESH WATER AND SEAWATER .............. 59 4.1 General Introduction................... 59 4.2 Results and Discussion.................. 60 4.2.1 Transport of thorium from continents to the ocean and interactions at land-sea and air-sea interfaces 60 4.2.1.1 Comparison of Th concentrations and partitions......... between dissolved and particulate forms in fresh water and seawater . 60 232 4.2.1.2 Removal of fluvial in estuarine and coastal regions. 64 4.2.1.3 Interactions at the continental margin and seafloor 69 4.2.2 Subsurface maxima of 232Th in water columns: a common....... feature......................... 70 4.2.3 Redox reaction of thorium 76 .................. 4.2.4 Correlation between 230Th and 232Th and its implications 81 4.2.5 Hydrothermal influence on Th distribution.......... 83 4.3 Conclusion........................ 86 5. SUMMARY............................ 87 6. BIBLIOGRAPHY......................... 89 LIST OF FIGURES Figure Page 1.1. Map showing water sampling locations (solid square). 1. Bonneville Dam; 2. Confluence of the John Day & Columbia Rivers; 3. Lost Lake; 4. Crater Lake; 5. Saanich Inlet, Vancouver, B.C; and 6. Washington and Oregon coast.......................... 3 2.1. Equilibrium constants of the complexes versus (a) the charge of Th complex, and (b) the ionic strength of the medium (data source given in Table 1). Different lines indicate specific ionic strength........ 11 2.2.Distributionof Th complexes versus pH inasolutioncontaining inorganicand organicspeciesattheconcentrations indicatedand 25°C withTh = 0.01 ppb (from Langmuir and Herman, 1980).Under normal seawater pH conditions,the thorium-organic complexes and Th(OH)4° are the dominant dissolved species.............. 12 2.3. The Effect of thorium complexing on thesolubilityof thorianite, ThO (c)as a function of pH at 25°C (from Langmuir and Herman, 198?). The cross-hatched curve denotes the solubility ofTh02in purewater. Thoriumtendstoformstrongcomplexesgreatly increasingthesolubilityofthoriummineralsinwatersystems, especially organic complexes..................... 14 2.4.Chart showing the decay chain of the uranium and thorium series isotopes and the half-lives of each isotope.Alpha decays are shown bytheverticalarrows andbetadecaysbythediagonal(from Broecker and Peng, 1982)...................... 16 2.5. Reported 232Th concentration in seawater plotted versus distance from continents(data source given in Table3). The distancescaleis linear from 0 to 100 m and logarithmic thereafter.Various symbols indicate data determined by different analytical techniques.The clear trend that pre-1980 data (solid circles)are substantially higher than post-1980 data (open symbols)is primarily caused by sampling and analytical artifacts......................... 26 2.6. Map showing the distribution of initial 230Th/232Th activity ratio in manganese nodules and crusts (data source given in Table 4).Where replicate samples were collected and analyzed, mean values are given and the numbers in parentheses indicate number of samples........ 33 3.1. Flow diagram for separation and purification of thorium......... 44 3.2.Distribution of elements