Showing papers by "R. S. W. van de Wal published in 2002"

Effect of periodic melting on geochemical and isotopic signals in an ice core from Lomonosovfonna, Svalbard

Abstract: [1] We examine the quality of atmospherically deposited ion and isotope signals in an ice core taken from a periodically melting ice field, Lomonosovfonna in central Spitsbergen, Svalbard. The aim is to determine the degree to which the signals are altered by periodic melting of the ice. We use three diagnostics: (1) the relation between peak values in the ice chemical and isotopic record and ice facies type, (2) the number of apparent annual cycles in these records compared with independently determined number of years represented in the ice core, and (3) a statistical comparison of the isotopic record in the ice core and the isotope records from coastal stations from the same region. We find that during warm summers, as much as 50% of the annual accumulation may melt and percolate into the firn; in a median year this decreases to similar to25%. As a consequence of percolation, the most mobile acids show up to 50% higher concentrations in bubble-poor ice facies compared with facies that are less affected by melt. Most of the other chemical species are less affected than the strong acids, and the stable water isotopes show little evidence of mobility. Annual or biannual cycles are detected in most parameters, and the water isotope record has a comparable statistical distribution to isotopic records from coastal stations. We conclude that ice cores from sites like Lomonosovfonna contain a useful environmental record, despite melt events and percolation and that most parameters preserve an annual, or in the worst cases, a biannual atmospheric signal.

Reconstruction of three centuries of annual accumulation rates based on the record of stable isotopes of water from Lomonosovfonna, Svalbard

Abstract: We use the upper 81 in of the record of stable isotopes of water from a 122 in long ice core from Lomonosovfonna, central Spitsbergen, Svalbard, to construct an ice-core chronology and the annual accumulation rates over the icefield The isotope cycles are counted in the ice-core record using a model that neglects short-wavelength and low-amplitude cycles We find approximately the same number of delta(18)O cycles as years between known reference horizons, and assume these cycles represent annual cycles Testing the validity of this assumption using cycles in deltaD shows that both records give similar numbers of cycles Using the delta(18)O chronology, and decompressing the accumulation records using the Nye flow model, we calculate the annual accumulation for the ice-core site back to AD 1715 We find that the average accumulation rate from 1715 to 1950 was on average 030 in we Accumulation rates increased about 25% during the later part of the 20th century to an average of 041 in we for the period 1950-97 The accumulation rates show highly significant 21 and 21 year periodicities, which gives credibility to our time-scale