1. Dr. Claudia Benitez-Nelson University of South Carolina Radionuclides in Ocean: A General Introduction to Marine Radioactivity

2. Two Parts: Part 1: An introduction to radioactivity Part 2: Some examples of how radioactive elements are used to trace ocean processes

3. Proton Number (z) Neutron Number (N) Radioactivity – spontaneous change in the structure of the nucleus resulting in the loss of energy from the nucleus. Some lightweight isotopes are radioactive but, all elements that have an atomic number > 82 are radioactive.

4. Radiation is energy in the form of high speed particles or electromagnetic waves. Non-ionizing radiation lacks the energy to alter atoms (e.g., visible light and microwaves). Ionizing radiation has enough energy to change normal cellular functioning, such as cells death or transformation into a cancerous cell.

5.  particles, Most densely ionizing, but weakest form of ionizing radiation.  particles More energetic. Can travel several feet through air, but are stopped with denser materials such as wood, glass or aluminum foil.  rays High-energy electromagnetic energy waves and the most penetrating type of radiation. They travel at the speed of light through the air. Cells must be shielded from gamma rays with concrete, lead or steel. Ionizing radiation comes in several forms…..

6.   A single radioisotope can decay by many pathways….. but they are SET pathways! GAS

7. Every element decays with a specific half-life! t ½ = 0.693 /

8. Daughter = Parent * e (- * time) e (- * time)

9. Curie (Ci) –Originally based on disintegration rate of 1 g of radium, now defined as quantity of any radioactive nuclide in which the number of disintegrations per second (dps) is 3.7 x 10 10 (“Activity” = number of atoms * ) Becquerel (Bq) –The SI unit, defined as 1 dps, also often use Disintegrations per minute (dpm) Sieverts (Sv) –Effective Dose; 1 Sv = 100 rem = dose (rad) x quality factor (QF) –QF based on linear energy transfer, e.g. QF = 1 for x-rays, gamma rays; 10 for protons; 20 for alpha particles, fast neutrons Units of Radioactivity

10. Decays to stable Pb

11. Natural U-Th Series Artificial Radionuclides ( 90 Sr, 137 Cs) Cosmogenic ( 7 Be, 14 C) http://www.awi.de/en/research/research_divisions/geosciences/marine_geochemistry/research_themes/natural_radionuclides_and_geotrace s/tracers_for_transport_processes/

12. 40 mBq L -1 ~ 2.5 dpm L -1 11,000 mBq L -1 ~ 660 dpm L -1 137 Cs

13. So what do we use radionucldes in the ocean for??? As tracers of pretty much everything…. 1)Particle Scavenging 2)Groundwater Discharge 3)Ocean ventilation and mixing rates 4)Sediment accumulation & age dating

14. About 50% of anthropogenically produced CO 2 is taken up by the ocean. If all the phytoplankton in the ocean were to die, atm. CO 2 would be 150 to 200 ppm HIGHER than it is today. Vertical transport of other elements to depth Development of anoxia Benthic Food webs

15. As tracers of sinking particle export … 238 U 234 Th (t 1/2 = 24.1 d) 238 U is UNREACTIVE (soluble) in seawater. 234 Th is highly particle reactive.  Particles matter 238 U 234 Th

16. Radioactive Equilibrium Depth Activity (dpm/L) 238 U 234 Th Radioactive Disequilibrium 234 Th activity is low in surface ocean due to particle scavenging. 234 Th activity increases with depth as scavenging intensity decreases. 234 Th flux = particle flux…

17. 230 Th 232 Th 228 Th 227 Th 226 Ra 228 Ra 224 Ra 223 Ra 1600 years5.7 years3.66 days11.4 days The Radium Quartet highly particle reactive soluble in seawater As tracers of submarine groundwater discharge….

18. http://www.iaea.org/nael/page.php?page=2213 Ra adsorbs to particles in fresh water, but is mobile in salt water. Ra concentrations are usually high in salty submarine groundwater and low in ocean water.

19. South Carolina Atlantic Ocean t ½ = 1600 years Courtesy of Billy Moore

20. Assessing exchange of the coastal ocean with the open ocean South Carolina Atlantic Ocean t ½ = 11.4 days Courtesy of Billy Moore

21. t ½ = 5.7 years SGD flux = (2 to 4) x 10 16 L/yr River flux = 2.4 x 10 16 L/yr Moore et al. 2008

22. Tracers of ocean ventilation … The 14 C/ 12 C ratio relative to the natural level in the atmospheric CO 2 as a function of time in the second half of the 20th century. 14 C, 90 Sr, 3 H, 137 Cs 90 Sr Atm. Deposition at NYC

23. WHOI NOSAMS Facility 14 CO 2

24. Lima et al. 2004 As tracers of sedimentation & sediment age dating... 210 Pb Chernobyl Nuclear Accident Weapons Testing

25. Benitez-Nelson ASLO Nice 2009 Arigatou GozaimasuArigatou Gozaimasu! Conclusions Radionuclides are in situ clocks that can be used to trace a wide variety of oceanic processes ranging from gas exchange to sedimentation …