210Po, 210Pb, and POC in the mesopelagic: multitechnique water column sampling in MEDFLUX

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210Po, 210Pb, 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

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Outline

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

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210Po and 210Pb

• Ubiquitous Trace Natural Radionuclides
• Both Highly Particle-Reactive
• 210Po 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
• 210Pb Effective Surface Area Tracer
• Relationship between 210Po and 210Pb May Provide
  Additional Information Beyond 234Th

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210Pb, 210Po and Carbon Cycles
Modified from Bacon et al. 1996
ATM
Polonium
Polonium
Polonium
Polonium
Po
Po
Po
Po
Pb
Po
WHAT HAPPENS IN THE TWILIGHT ZONE?
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Sampling Techniques

• 210Po, 210Pb 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
• 210Po
• 210Pb

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Spring to Early Summer Traps
POC
210Po
Not much loss of POC or 210Po between 200 and 800m
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Summer Traps
POC
210Po
Evidence of loss of POC and 210Po between 200 and
1940m
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Disconnect POC and Particulate 210Po or Pumps
and Bottles?
POC - Pumps
Particulate Po - Bottles
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Bottle and Pump Results at Surface
From Liu et al. 2005
Bottles captured more POC than pumps during
spring, not summer Bottles and Pumps captured
Identical Chlorophyll a Differences were
attributed in part to zooplankton
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Po/Pb Ratios in Bottles and Pumps
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Swimmers Have High Po/Pb
From Stewart et al. 2005
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Bottles vs. Pumps

• Bottles capture high 210Po 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

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Mesopelagic Story

• 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

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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

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High Activity of 210Po in Bottle Particles
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Review of Surface Sediment Trap Material
From Stewart et al. submitted DSR
Bacterial Degradation
Fecal Pellets
Fresh Phytoplankton