1. August 16-19, 2004 Woods Hole, MA Sponsored by the National Science Foundation

2. Settling Particles Phytoplankton Bacteria Zooplankton N,P,Fe DOM CO 2 Euphotic Zone 11-16 Gt C/y results in an atm CO 2 150 to 200 ppm lower than if all the phytoplankton in the ocean were to die

3. The purpose of the workshop is to bring together a number of international experts in the collection and application of 234 Th in aquatic ecosystems with diverse opinions and backgrounds to discuss and define current concepts in the use of 234 Th and a coherent strategy for future applications.

4. 1998 San Diego AGU/ASLO Ocean Sciences Meeting

5. New methodologies and techniques 1) What are the current methods for collecting and measuring 234 Th in fresh and marine ecosystems? 2) What is the best way to convert these measurements into integrated 234 Th deficiencies? 3) Can we assess and reduce the uncertainty in making this conversion?

6. C/ 234 Th ratios 1) How should C/ 234 Th ratios be collected and measured? 2) Are all phases of POC in equilibrium with 234 Th? 3) Can POC fluxes inferred from 234 Th be biased by cycling of 234 Th through a limited portion of the POC pool that has a turnover time significantly different from that of the "average" POC? 4) How should 234 Th results be compared to other indices of sinking particle flux?

7. Modeling 1) What are the appropriate models for understanding particle residence times, aggregation/coagulation rates, and sinking losses of 234 Th? 2) Do current models deal adequately with 3-D transport of 234 Th (both particulate and dissolved) and with temporal variability of the processes involved?

8. 234 Th speciation in seawater 1) What is the speciation of 234 Th with respect to dissolved and particulate inorganic and organic phases in seawater? How does 234 Th speciation impact aggregation and flux? 2) Can a better understanding of the geochemistry of 234 Th improve our use of 234 Th as a particle cycling and flux proxy? Are all phases of 234 Th in chemical equilibrium with one another? 3) What is necessary to achieve this better understanding?

9. Today: A series of introductory talks to provoke thought and discussion on each of the topics. Tuesday-Thursday: Discussion and plan for answering these questions

10. Outcome: A series of papers within a special volume that: 1) Address what was discussed at the meeting, i.e. overview and future directions 2) Current research being conducted by our community.