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

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 Po-210 (T-1/2 = 138.4 days) and Pb-210 (T-1/2 = 22.3 years) in dissolved and particulate phases (snow, grab ice, ice core, surface seawater) to investigate the Po-210:Pb-210 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 Po-210/Pb-210 to quantify the atmospheric depositional input to the snow and surface waters. Falling snowfall is tagged with Po-210/Pb-210 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 Po-210 and Pb-210 input to the melt pond, and measured disequilibrium in ice core and ice-rafted sediment, we show Po-210/Pb-210 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 (n = 13), 13 +/- 11 (n = 6), 60 +/- 14 (n = 4), and 87 +/- 23 (n = 6) days, respectively. The average IRS age corresponds to an average drift velocity of sediment-laden ice of 0.18 +/- 0.06 (n = 6) m s(-1). We report highly elevated levels of Po-210 and Pb-210 in snow and melt pond compared to those in Arctic surface seawater and enrichment of Po-210 compared to Pb-210 onto particles extracted from snow, ice and melt ponds. The observed disequilibrium between Po-210 and Pb-210 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.