210Po, 210Pb, and POC in the mesopelagic: multi-technique water

column sampling in MEDFLUX

G. StewartP. Masque, J.K. Cochran, J.C. Miquel, B. Gasser, D. Hirschberg, A. Rodriguez y Baena, and S. Fowler

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

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

210Pb, 210Po and Carbon Cycles

Modified from Bacon et al. 1996

ATM

PoloniumPoloniumPoloniumPolonium

PoPoPo

PoPb

Po

WHAT HAPPENS IN THE TWILIGHT ZONE?

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

Spring to Early Summer: Traps

March-May

3/11/2003

3/16/2003

3/21/2003

3/26/2003

3/31/2003

4/6/2003

4/12/2003

4/18/2003

4/24/2003

4/30/2003

5/6/2003

210 P

o (B

q/g)

0

1

2

3

4

5

6

200m800m

March-May

3/11/2003

3/16/2003

3/21/2003

3/26/2003

3/31/2003

4/6/2003

4/12/2003

4/18/2003

4/24/2003

4/30/2003

5/6/2003

PO

C ( g

/mg

)

0

10

20

30

40

50

200m800m

Not much loss of POC or 210Po between 200 and 800m

POC 210Po

Summer: Traps

May-June

5/14/2003

5/18/2003

5/22/2003

5/26/2003

5/30/2003

6/3/2003

6/7/2003

6/11/2003

6/15/2003

6/20/2003

PO

C ( g

/mg

)

0

10

20

30

40

50

May-June

210P

o (B

q/g)

0

1

2

3

4

5

6

200m1940m

Evidence of loss of POC and 210Po between 200 and 1940m

POC210Po200m

1940m

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

MarchMayJune

POC - Pumps % Particulate Po - Bottles

Bottle and Pump Results at Surface

Bottles capturedmore 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

May 2003

Po/Pb

0 5 10 15 20 25 30

0

500

1000

1500

2000

2500

3000

June/July 2003

Po/Pb

0 5 10 15 20 25 30

0

500

1000

1500

2000

2500

3000

Water Column ParticlesPump Particles

Swimmers Have High Po/Pb

PhytoplanktonArtemia

Artemia FP

Eupahusiids

Euphausiid FP

210 P

o to

210 P

b R

atio

0.1

1

10

100

Phytoplankton

Artemia

Euphausiids

Artemia FP Euphausiid FP

x 5

x 12

From Stewart et al. 2005

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

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 210Po in Bottle Particles

May 2003

210Po (Bq/m3)

0.0 0.2 0.4 0.6 0.8 1.0

0

500

1000

1500

2000

2500

3000

June 2003

210Po (Bq/m3)

0.0 0.2 0.4 0.6 0.8 1.0

0

500

1000

1500

2000

2500

3000

Water Column ParticlesPump Particles

Review of Surface Sediment Trap Material

Fecal Pellets

Bacterial Degradation

Fresh Phytoplankton

From Stewart et al. submitted DSR