210 Po, 210 Pb, and POC in the mesopelagic: multi-technique water column sampling in MEDFLUX G. Stewart P. Masque, J.K. Cochran, J.C. Miquel, B. Gasser, D. Hirschberg, A. Rodriguez y Baena, and S. Fowler

Outline Review of 210 Po and 210 Pb behavior 210 Po and POC relationship What happens in the Mesopelagic? – Sediment traps indicate loss of 210 Po and POC – Water column POC decreases (Pumps) – No evidence of water column 210 Po decrease – Pumps vs. Bottles Possible explanations and conclusions

210 Po and 210 Pb Ubiquitous Trace Natural Radionuclides Both Highly Particle-Reactive 210 Po Specific Affinity for Organic Matter, Protein Correlated with Biological Activity – Predictable uptake by planktonic particles – Elevated concentrations in higher trophic levels – Highest dose of radiation to organisms 210 Pb Effective Surface Area Tracer Relationship between 210 Po and 210 Pb May Provide Additional Information Beyond 234 Th

210 Pb, 210 Po and Carbon Cycles Modified from Bacon et al ATM Polonium Po Pb Po WHAT HAPPENS IN THE TWILIGHT ZONE?

Sampling Techniques 210 Po, 210 Pb profiles in both pumps and bottles Water column profiles of POC only from pumps Sediment traps at 2 depths during 2 periods (Spring: 200m, 800m and Summer: 200m, 1940m) – POC – 210 Po – 210 Pb

Spring to Early Summer: Traps Not much loss of POC or 210 Po between 200 and 800m POC 210 Po

Summer: Traps Evidence of loss of POC and 210 Po between 200 and 1940m POC 210 Po

Disconnect: POC and Particulate 210 Po or Pumps and Bottles? POC - Pumps% Particulate Po - Bottles

Bottle and Pump Results at Surface Bottles captured more POC than pumps during spring, not summer Bottles and Pumps captured Identical Chlorophyll a Differences were attributed in part to zooplankton From Liu et al. 2005

Po/Pb Ratios in Bottles and Pumps

Swimmers Have High Po/Pb x 5 x 12 From Stewart et al. 2005

Bottles vs. Pumps Bottles capture high 210 Po swimmers at depth March through May Po/Pb differs June profiles are similar Neither pump nor bottle Po/Pb reflects evidence of POC remineralization Decoupling of water column measurements and sediment trap collection

No evidence of Polonium remineralization: WHY? – Long radioactive half-life? – Sorption with depth? – Mediterranean water bodies? – Rapid sinking? Need to investigate further Po/Pb as POC tracer below the euphotic zone Mesopelagic Story

Acknowledgements Funding for research from NSF to MEDFLUX, AAUW to GMS Funding for this conference from CUNY OEODP, Queens College DMNS Captain and Crew of R.V.Tethys (Monaco) and R. V. Seward Johnson (Harbor Branch) All the participants in MEDFLUX

High Activity of 210 Po in Bottle Particles

Review of Surface Sediment Trap Material Fecal Pellets Bacterial Degradation Fresh Phytoplankton From Stewart et al. submitted DSR