We quantifed post depositional losses of methanesulfonate (MSA-), nitrate, and chloride at the EPICA drilling site in Dronning Maud Land (DML, 75°S, 0°E). Analyses of four interme-diate deep firn cores and 13 snow pits were considered. We found that about 26±13% of the once deposited nitrate and typically 51±20% of MSA- were lost, while for chloride no signifi-cant depletion could be observed in firn older than one year. Assuming a first order exponen-tial decay rate, the characteristic e-folding time for MSA- is 6.4±3 a and 19±6 a for nitrate. It turns out that for nitrate and MSA- the typical mean concentrations representative for the last 100 years were reached after 5.4 a and 6.5 a, repectively, indicating that beneath a depth of around 1.2-1.4 m post depositional losses can be neglected. With a simple approach we esti-mated the partial pressure of the corresponding free acids MSA, HNO3, and HCl based on Henrys law assuming that ionic impurities of the bulk ice matrix are localised in a quasi brine layer (QBL). From this approach it stands to reason that a nearly quantitative loss of MSA-, NO3-, and Cl- should occur. We suggest that firn metamorphosis and fractional dissolution of electrolytes in in the QBL and the ice matrix are the decisive processes leading to the observed partial losses.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL1-Processes and interactions in the polar climate system
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL6-Earth climate variability since the Pliocene