Dataset: Activities of 210Po and 210Pb on particles in two size classes obtained by in situ pumping on Leg 1 (Seattle, WA to Hilo, HI) of the US GEOTRACES Pacific Meridional Transect (PMT) cruise (GP15, RR1814) on R/V Roger Revelle from September to October 2018

Final no updates expectedDOI: 10.26008/1912/bco-dmo.892348.1Version 1 (2023-03-23)Dataset Type:Cruise Results

Principal Investigator: J. Kirk Cochran (Stony Brook University - SoMAS)

Co-Principal Investigator: Mark Stephens (Florida International University)

BCO-DMO Data Manager: Shannon Rauch ()


Program: U.S. GEOTRACES (U.S. GEOTRACES)

Project: US GEOTRACES Pacific Meridional Transect (GP15) (U.S. GEOTRACES PMT)

Project: Collaborative Research: Lead-210 and Polonium-210 as tracers for scavenging and export: GEOTRACES Pacific Meridional Section (PMT Lead-210 and Polonium-210)


Abstract

This project is part of the international GEOTRACES program, which was created to allow a comprehensive, coordinated study of trace elements and isotopes (TEIs) in the oceans. This project uses the radionuclide pair Lead-210 (210Pb) and its grand-daughter Polonium-210 (210Po) to provide important biogeochemical rate information pertinent to the TEIs that were measured during the US GEOTRACES Meridional Transect in the Pacific from Alaska to Tahiti in late 2018. Many processes in the ocean ca...

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Sampling was conducted in 2018 at various depths through the water column at eleven stations along the GEOTRACES Pacific Meridional Transect (GP15), carried out on R/V Roger Revelle (cruises RR1814 and RR1815). Particulate samples were collected by Phoebe Lam's group using McLane in-situ pumps (Lam et al., 2015). Two particle sizes were collected by pumping: a large particle fraction collected on a 142-millimeter (mm) 51-micrometer (μm) polyester mesh prefilters (Sefar 07-51/33) and a small particle fraction collected on paired 0.8-μm polyethersulfone Pall Supor 800 membrane filters. The filters were dried on board in a laminar flow hood, split, and placed in a polyethylene bag. Aliquots sent to Stony brook comprised 28-280 liters (L) (average ~100L) filtered for the small particle fraction and 60-330L (average ~250L) for the large particle fraction. More details on pump operation can be found in the GP15 Cruise Report (see Supplemental Files section).

The particulate filters were dried on board the ship in a laminar flow hood, split, and placed in a polyethylene bag. Aliquots sent to Stony Brook comprised 28-280 liters (L) (average ~100L) filtered for the small particle fraction and 60-330L (average ~250L) for the large particle fraction. Due to the equipment limitations and potential hazards when doing acid digestions at sea, on-board treatment was not possible for these samples. Instead, filter aliquots from Leg 1 were sent to the lab during the port stop in Hilo, Hawaii on 21 October. Leg 2 filters were sent back from Papeete, Tahiti at the conclusion of the cruise on 24 November.

In the laboratory, filters were placed in microwave digestion vessels and spiked with Polonium-209 (209Po) tracer (1.76 disintegrations per minute (dpm)) and 10 milligrams (mg) stable lead (Pb). 5 milliliters (mL) each of concentrated HCl, HNO3, and HF were then added to the vessel. The mixture was microwave-digested for 1 hour at 180° Celsius (C). After digestion, the resulting solution was decanted into a 25 mL Falcon tube, and the digestion vessels were rinsed with small aliquots of deionized (DI) water. The Falcon tubes were centrifuged for 10 minutes at 2000 rotations per minute (rpm) and the supernatant was pipetted into 50 mL Teflon beakers. The beakers were heated to almost complete dryness before 10 mL of concentrated HCl was added. This process was repeated to ensure that the HCl was the only acid present. 20 mL of 6 molar (M) HCl was added, the solution was decanted into a glass beaker and the Teflon beaker was rinsed with two aliquots of 30 mL DI water. The beakers were labeled, and ascorbic acid was added to the solution to reduce any Fe(III) to Fe(II) and prevent its plating. A silver planchet embedded in a Teflon stirring magnet was added to each sample, which was then plated at 80°C for 3 hours (Flynn, 1968; Lee et al., 2014), rinsed with DI water and acetone and counted in a Canberra/Mirion Quad Alpha spectrometer to determine initial 210Po. Residual Po was removed from solution by adding scrap silver for ~5 days and then transferring the samples to 125 ml polycarbonate bottles for storage and ingrowth of additional 210Po. The second plating was carried out after 6 to 8 months of storage. Data reduction was carried out using the methods reported in Rigaud et al. (2013).

Known Problems/Issues:
Calculation of the particulate 210Pb activity requires measurement of the concentration of stable Pb added during sample dissolution to determine the recovery of 210Pb from dissolution through plating. The sample solutions were stored for 6  to 8 months after the initial Po plating and removal of residual Po to permit ingrowth of additional 210Po from 210Pb decay. At the time of the second plating, aliquots were taken to measure the stable Pb. A discrete number of samples were completed in late 2019 to early 2020 and Pb recoveries were determined. However, Stony Brook University closed for an extended period starting in March 2020 due to the Covid-19 pandemic. Upon reopening, measurement of stable Pb in the stored aliquots showed losses in storage. As well, analytical instrumentation used to measure Pb (Element 2 ICP-MS) was no longer functioning and required extensive maintenance and repair. Because of these problems, it was decided to use average Pb recoveries for these samples, based on the Pb recoveries of samples analyzed before the shutdown.


Related Datasets

References

Dataset: GP15 Bottle Leg 1
Relationship Description: Cast_number, Event_ID, BTLNBR, and BTLNBR_FLAG were obtained from the bottle file and added to dataset 892348
Casciotti, K. L., Cutter, G. A., Lam, P. J. (2021) Bottle file from Leg 1 (Seattle, WA to Hilo, HI) of the US GEOTRACES Pacific Meridional Transect (PMT) cruise (GP15, RR1814) on R/V Roger Revelle from September to October 2018. Biological and Chemical Oceanography Data Management Office (BCO-DMO). (Version 6) Version Date 2021-05-05 doi:10.26008/1912/bco-dmo.777951.6

Related Publications

Results

Wei, Z., Cochran, J. K., Horowitz, E., Fitzgerald, P., Heilbrun, C., Kadko, D., Stephens, M., Marsay, C. M., Buck, C. S., & Landing, W. M. (2022). 210Pb and 7Be as Coupled Flux and Source Tracers for Aerosols in the Pacific Ocean. Global Biogeochemical Cycles, 36(8). Portico. https://doi.org/10.1029/2022gb007378
Methods

Flynn, W. W. (1968). The determination of low levels of polonium-210 in environmental materials. Analytica Chimica Acta, 43, 221–227. doi:10.1016/s0003-2670(00)89210-7
Methods

Lam, P. J., Ohnemus, D. C., & Auro, M. E. (2015). Size-fractionated major particle composition and concentrations from the US GEOTRACES North Atlantic Zonal Transect. Deep Sea Research Part II: Topical Studies in Oceanography, 116, 303–320. doi:10.1016/j.dsr2.2014.11.020
Methods

Lee, H. M., Hong, G. H., Baskaran, M., Kim, S. H., & Kim, Y. I. (2014). Evaluation of plating conditions for the recovery of 210Po on a Ag planchet. Applied Radiation and Isotopes, 90, 170–176. https://doi.org/10.1016/j.apradiso.2014.03.025
Methods

Rigaud, S., Puigcorbé, V., Cámara-Mor, P., Casacuberta, N., Roca-Martí, M., Garcia-Orellana, J., … Church, T. (2013). A methods assessment and recommendations for improving calculations and reducing uncertainties in the determination of210Po and210Pb activities in seawater. Limnology and Oceanography: Methods, 11(10), 561–571. doi:10.4319/lom.2013.11.561