AUTHOR=Baskaran Mark , Krupp Katherine 

TITLE=Novel Application of 210Po-210Pb Disequilibria to Date Snow, Melt Pond, Ice Core, and Ice-Rafted Sediments in the Arctic Ocean

JOURNAL=Frontiers in Marine Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.692631

DOI=10.3389/fmars.2021.692631

ISSN=2296-7745

ABSTRACT=<p>We collected surface ocean water, snow, grab ice, ice core, melt pond and ice-rafted sediment (IRS) from 5 ice stations during the Western Arctic US GEOTRACES cruise (USGCG Healy; August 10 – October 7, 2015) and analyzed for <sup>210</sup>Po (T<sub>1/2</sub> = 138.4 days) and <sup>210</sup>Pb (T<sub>1/2</sub> = 22.3 years) in dissolved and particulate phases (snow, grab ice, ice core, surface seawater) to investigate the <sup>210</sup>Po:<sup>210</sup>Pb disequilibria in these matrices. Thirteen aerosol samples, using a large-volume aerosol sampler (PM10), from Dutch Harbor, AK to North Pole, were also collected and analyzed for <sup>210</sup>Po/<sup>210</sup>Pb to quantify the atmospheric depositional input to the snow and surface waters. Falling snowfall is tagged with <sup>210</sup>Po/<sup>210</sup>Pb ratio (AR) similar to that in the air column from the cloud condensation height to air-sea interface. From the measured AR in aerosol and snow, modeling the sources of <sup>210</sup>Po and <sup>210</sup>Pb input to the melt pond, and measured disequilibrium in ice core and ice-rafted sediment, we show <sup>210</sup>Po/<sup>210</sup>Pb AR is a novel chronometer to date snow, ice core, melt pond, and IRS. The calculated mean ages of aerosol, snow, melt pond and IRS are 12 ± 7 (<italic>n</italic> = 13), 13 ± 11 (<italic>n</italic> = 6), 60 ± 14 (<italic>n</italic> = 4), and 87 ± 23 (<italic>n</italic> = 6) days, respectively. The average IRS age corresponds to an average drift velocity of sediment-laden ice of 0.18 ± 0.06 (<italic>n</italic> = 6) m s<sup>–1</sup>. We report highly elevated levels of <sup>210</sup>Po and <sup>210</sup>Pb in snow and melt pond compared to those in Arctic surface seawater and enrichment of <sup>210</sup>Po compared to <sup>210</sup>Pb onto particles extracted from snow, ice and melt ponds. The observed disequilibrium between <sup>210</sup>Po and <sup>210</sup>Pb in ice could serve as a quantitative tool in delineating multiple-year ice from seasonal ice as well as a metric in quantifying the speed of ice/snow melting and delay in autumn freeze.</p>