Precipitation isoscape of high reliefs: interpolation scheme designed and tested for monthly resolved precipitation oxygen isotope records of an Alpine domain

摘要

Stable oxygen isotope composition of atmospheric precipitation (δO) was scrutinized from 39 stations distributed overSwitzerland and its border zone. Monthly amount-weighted δO values averaged over the 1995–2000 period showed theexpected strong linear altitude dependence (−0.15 to −0.22‰ per100 m) only during the summer season (May–September). Steeper gradients(~ −0.56 to −0.60‰ per 100 m) were observed for wintermonths over a low elevation belt, while hardly any altitudinal difference wasseen for high elevation stations. This dichotomous pattern could be explainedby the characteristically shallower vertical atmospheric mixing height duringwinter season and provides empirical evidence for recently simulated effectsof stratified atmospheric flow on orographic precipitation isotopic ratios.This helps explain "anomalous" deflected altitudinal water isotope profilesreported from many other high relief regions. Grids and isotope distributionmaps of the monthly δO have been calculated over thestudy region for 1995–1996. The adopted interpolation method took intoaccount both the variable mixing heights and the seasonal difference in theisotopic lapse rate and combined them with residual kriging. The presenteddata set allows a point estimation of δO withmonthly resolution. According to the test calculations executed on subsets,this biannual data set can be extended back to 1992 with maintained fidelityand, with a reduced station subset, even back to 1983 at the expense of fadedreliability of the derived δO estimates, mainly inthe eastern part of Switzerland. Before 1983, reliable results can only beexpected for the Swiss Plateau since important stations representing easternand south-western Switzerland were not yet in operation.