Plutonium isotopes in the North Atlantic

Abstract

The author hereby g r a n t s t o MIT and WHO1 permission t o reproduce and d i s t r i b u t e copies o f t h i s t h e s i s document i n whole o r i n p a r t . Signature o f Author / J o i n t Program i n Oceanography, Massachusetts I n s t i t u t e o f Technology and Woods Hole Oceanographic I n s t i t u t i o n , and t h e Department o f Earth, Atmospheric, and Planetary Sciences, Massachusetts I n s t i t u t e o f Technology C e r t i f i e d by Edward R. ~h o i k & i t z , ~h e s i s ~u -~e r v i sc6Accepted by -./,, , Edward Boyle, Chair, J o i n t tommlttee f o r Chemical Oceanography, Massachusetts I n s t i t u t e o f Technology/Woods Hole Oceanographic I n s t i t u t i o n ABSTRACT The a r t i f i c i a l r a d i o n u c l i d e Plutonium (Pu) has been introduced i n t o t h e environment p r i m a r i l y as f a l l o u t from atmospheric nuclear weapons t e s t i n g d u r i n g t h e 1950's and 1960's. E a r l i e r s t u d i e s o f Pu geochemist r y a r e g e n e r a l l y based upon t h e measurement o f t h e combined a c t i v i t i e s o f 2 3 9~u and 2 4 9~u (detected by alpha-counting and w r i t t e n as 239,240 Pu) and assume an i d e n t i c a l geochemical behavior f o r Pu from any o f i t s f a l l o u t sources. A major focus o f t h i s t h e s i s i s t h e development o f a mass spectrometric (m.s.) technique f o r t h e a n a l y s i s o f Pu i n marine sediments, pore waters, sediment t r a p m a t e r i a l and sea water from t h e North A t l a n t i c . With t h e m.s. technique, n o t o n l y i s t h e d e t e c t i o n l i m i t f o r 2 3 9 ' 2 4 0~u increased by over an order-of-magni tude, b u t t h e 2 4 0~u and 2 3 9~u isotopes can be separated as w e l l . The increased s e n s i t i v i t y f o r Pu provided by m.s. allowed me t o measure Pu i n deep-sea pore waters f o r t h e f i r s t time. Pore water studies a r e s e n s i t i v e i n d i c a t o r s o f e a r l y d i a g e n e t i c r e a c t i o n s , and can be used t o examine t h e unresolved question o f t h e e x t e n t o f Pu remobili z a t i o n out o f marine sediments. Along a t r a n s e c t o f cores ranging from h i g h l y reducing muddy sediments on t h e s h e l f t o more o x i c and carbonater i c h sediments i n t h e deep-sea, I have found t h a t t h e s o l u b i l i t y o f Pu i s predominantly c o n t r o l l e d by t h e d i s t r i b u t i o n o f Pu i n t h e s o l i dphase. The c a l c u l a t e d 2 3 9 9 2 4 0~~ distribution coefficients (Kd = dpm per kg on solids/dpm per kg i n s o l u t i o n ) range from 0.2-23 x lo4, w i t h some suggestion o f a t r e n d towards lower values i n t h e deeper cores 4 (Kdls 4 0 i n cores from water depths >2500m). D i f f u s i v e f l u x calcul a t i o n s based upon t h e observed Pu pore water g r a d i e n t s suggest t h a t since i t s i n t r o d u c t i o n , n e g l i g i b l e Pu has been r e m o b i l i z e d o u t o f t h e 2 3 sediments a t a l l o f t h e s i t e s . On a time scale o f 10 -10 years however, Pu r e m o b i ...

The Role of Sea Ice in the Fate of Contaminants in the Arctic Ocean: Plutonium Atom Ratios in the Fram Strait

“…Analyses of plutonium in bottom and sea-ice sediment samples were carried out following an adaptation of the procedure developed by Buesseler (1986) (27) and recently described by Kenna (2002) (28). Briefly, sediments (2-25 g dry mass) were digested with 8 N HNO3 after addition of 242 Pu as a yield tracer, and the leachate was purified through three ion exchange columns.…”