Polonium-210 and Lead-210 as tracers of particle export ...€¦ · Polonium-210 and Lead-210 as...
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From particle-reactive radionuclide fluxes to Particulate Carbon flux 0 100 200 300 400 500 0 50 100 150 200 250 300 Depth (m) PC/ 210 Po ratios (µmol C dpm -1 ) Aug 17 Aug 23 Sept 4 1-5 µm particles PC Flux = 210 Po Flux · PC/ 210 Po 234 Th Flux · PC/ 234 Th Acknowledgements The 210 Po/ 210 Pb research is funded by the WHOI’s Ocean Twilight Zone project while NASA is acknowledged for 234 Th and traps work. We thank the whole EXPORTS team, especially the Th and Trap groups, as well as the crew aboard the R/V Sally Ride and R/V Roger Revelle. OCB Summer Workshop, June 24 th to 27 th 2019, Woods Hole (MA) CONCLUSIONS ü Similar export depth for 210 Po and 234 Th (surface to 75-125 m) where Po<Pb and Th<U ü Low 210 Po fluxes were constant during 3 weeks ü The drop in 234 Th flux on September 4 th may indicate a recent decrease in particle export and increase in flux attenuation at this station ü 210 Po fluxes derived from the water column were at least 3 times higher than those measured with both trap designs ü Non-steady state & physical mixing not included in 210 Po model ü Does a single profile match particle source funnel for traps? ü Loss of particles attached to zooplankton when picking swimmers? ü Due to zooplankton diel vertical migration (particle removal in surface and release at depth)? ü Particulate Carbon (PC) flux at the base of the euphotic zone (110 m = 0.1% PAR) was ≈ 3 mmol C m -2 d -1 in good agreement with 234 Th estimates (2-5 mmol C m -2 d -1 ) ü Rapid decrease in PC fluxes below the euphotic zone leading to fluxes < 1 mmol C m -2 d -1 at 500 m ü The attenuation of PC fluxes between 100 and 500 m was 82 ± 8% ü Future work: quantify PIC, PN and bSi fluxes and explore what we can learn from different methods 1D SS model 210 Po Flux = ∫(A Pb –A Po ) · λ Po 1D SS model 234 Th Flux = ∫(A U –A Th ) · λ Th 0 50 100 150 200 0 500 1000 1500 2000 2500 Thorium-234 Flux (dpm m -2 d -1 ) Aug 17 Aug 23 Sept 4 STT STT STT NBST NBST NBST 0 50 100 150 200 0 10 20 30 40 50 Depth (m) Polonium-210 Flux (dpm m -2 d -1 ) Aug 17 Aug 23 Sept 4 STT STT STT NBST NBST NBST Export fluxes of 210 Po & 234 Th on sinking particles 0 100 200 300 400 500 -2 0 2 4 6 8 Carbon Flux (mmol C m -2 d -1 ) Po Aug 17 Po Aug 23 Po Sept 4 Th Aug 17 Th Aug 23 Th Sept 4 EUPHOTIC ZONE (0.1% PAR) traps traps 1D SS model 1D SS model TYPE OF SAMPLES • 3 seawater profiles • Sized-fractionated (1-5, 5-51, >51 µm) particles (in situ pumps) • Sinking particles (sediment traps) GOAL Provide quantitative estimates of sinking particle fluxes and attenuation with depth integrating a seasonal time scale ( 210 Po half-life = 138 days) Polonium-210 and Lead-210 as tracers of particle export and attenuation on the first EXPORTS cruise at Station PAPA Montserrat Roca-Martí 1 , Meg Estapa 2 , Pere Masqué 3,4 , Ken Buesseler 1 1 Woods Hole Oceanographic Institution (MA), 2 Skidmore College (NY) 3 Edith Cowan University (Western Australia), 4 Universitat Autònoma de Barcelona (Spain) The EXPORTS (EXport Processes in the Ocean from RemoTe Sensing) Program focuses on linking remotely sensed properties to the processes that control the export of ocean primary production from surface waters to depth. Here we present preliminary results from the naturally-occurring radionuclide pair 210 Po/ 210 Pb as part of the first NASA supported EXPORTS cruise in the NE Pacific at Station PAPA (August-September 2018). 210 Po and 210 Pb have been used to quantify sinking particle fluxes and their attenuation below the euphotic zone at a seasonal scale. These estimates will be compared to other methods with shorter time scales, 234 Th (weeks) and sediment traps (days), with the aim to provide a wider perspective into particle export and remineralization in the upper 500 m of the water column. Remarkable consistency between seawater profiles of 210 Po and 234 Th sampled over a period of three weeks suggests that the variability in the processes that lead to particle flux was relatively small over the summer. Particulate Carbon (PC) fluxes have been estimated using the PC/ 210 Po ratio on size-fractionated particles collected using in-situ pumps. Overall, we show low PC export fluxes (< 5 mmol C m -2 d -1 ) at 100 m decreasing rapidly below the well-lit surface ocean. 0 100 200 300 400 500 0 5 10 15 20 25 Depth (m) Po-210 & Pb-210 (dpm 100L -1 ) 210Pb 210Po 0 100 200 300 400 500 0 5 10 15 20 25 Po-210 & Pb-210 (dpm 100L -1 ) 210Pb 210Po 0 100 200 300 400 500 0 5 10 15 20 25 Po-210 & Pb-210 (dpm 100L -1 ) 210Pb 210Po 0 100 200 300 400 500 1.0 1.5 2.0 2.5 3.0 Depth (m) Th-234 & U-238 (dpm L -1 ) 238U 234Th 0 100 200 300 400 500 1.0 1.5 2.0 2.5 3.0 Th-234 & U-238 (dpm L -1 ) 238U 234Th 0 100 200 300 400 500 1.0 1.5 2.0 2.5 3.0 Th-234 & U-238 (dpm L -1 ) 238U 234Th Aug 17 Aug 23 Aug 17 Aug 23 Sept 4 Sept 4 Po<Pb EXPORT Po<Pb EXPORT Po<Pb EXPORT Th<U EXPORT Th<U EXPORT Th<U EXPORT 210 Po/ 210 Pb & 234 Th/ 238 U seawater profiles 10x10 km In situ pump Surface tethered trap Neutrally-buoyant sediment trap STT NBST Seawater samples Alyson Santoro Colleen Durkin
Polonium-210 and Lead-210 as tracers of particle export ...€¦ · Polonium-210 and Lead-210 as tracers of particle export and attenuation on the first EXPORTS cruise at Station
From particle-reactive radionuclide fluxes to Particulate Carbon
flux
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0 50 100 150 200 250 300
Dep
th (m
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PC/210Po ratios (µmol C dpm-1)
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Aug 23
Sept 4
1-5 µmparticles
PC Flux = 210Po Flux · PC/210Po234Th Flux · PC/234Th
AcknowledgementsThe 210Po/210Pb research is funded by the WHOI’s
Ocean Twilight Zone project while NASA is acknowledged for 234Th
and traps work. We thank the whole EXPORTS team, especially the Th
and Trap groups, as well as the crew aboard the R/V Sally
Ride and R/V Roger Revelle. OCB Summer Workshop, June 24th to
27th 2019, Woods Hole (MA)
CONCLUSIONSü Similar export depth for 210Po and 234Th (surface
to 75-125 m) where Po
