210Po/210Pb Activity Ratios as a Possible ‘Dating Tool’ of Ice Cores and Ice-rafted Sediments from the Western Arctic Ocean – Preliminary Results
210Po/210Pb Activity Ratios as a Possible ‘Dating Tool’ of Ice Cores and Ice-rafted Sediments from the Western Arctic Ocean – Preliminary Results
Abstract:
We have collected and analyzed a suite of surface snow samples, ice cores, ice-rafted sediments (IRS) and aerosol samples from the Western Arctic for Po-210 and Pb-210 to examine the extent of disequilibrium between this pair to possibly use 210Po/210Pb activity ratio to date different layers of ice cores and time of incorporation of ice-rafted sediments into the sea ice. We have earlier reported that the activity concentrations of 210Pb in IRS vary over an order of magnitude and it is 1-2 orders of magnitude higher than that of the benthic sediments (1-2 dpm/g in benthic sediments compared to 25 to 300 dpm/g in IRS). In this study, we have measured 210Po/210Pb activity ratios in aerosols from the Arctic Ocean to constrain the initial 210Po/210Pb ratio at the time of deposition during precipitation. The 210Po activity concentration in recent snow is compared to surface ice samples. The ‘age’ of IRS incorporation can be calculated as follows:
[210Po]measured = [210Po]initial + [210Pb] (1 – exp(-λt)) (1)
where λ is the decay constant of 210Po, 138.4 days, and ‘t’ is the in-growth time period. From this equation, ‘t’ can be calculated as follows:
t = (-1/λ) [ln (1- ((210Po/210Pb)measured – (210Po/210Pb)initial)] (2)
The assumption involved in this approach are: i) there is no preferential uptake of 210Po (highly biogenic – S group); and iii) both 210Po and 210Pb remain as closed system. The calculated age using equation (2) will be discussed and presented.