Isotope Stratification in High Mountain Glaciers: Examples from the Peruvian Andes and Himalaya

Abstract

ABSTRACT.18 0 and deuterium content was measured in snow and ice sampl es co llected from two c revasses on temperate glaciers hi gh in the Andes and in the Himalaya. The results show that, due to intense exposure to sun , a significant part of the annual accumulation of snow is re moved by melting and sublimation , the latter being predominant. There is strong empirical evi dence that in natural conditions which a re characteristic of both the glaciers studied sublimation of the snow cover can be approximated by the thermodynamic equilibrium process. The short-term fluctuations, though slightl y moderated, and lon ger-term variatio ns can sti ll be observed in the deeper parts of the glaciers in spite of firnifi catio n of the snow. RESU ME. Stratification des isotopes de halltes montagnes glaciaires: exemples tires des A ndes et de I'Himalaya.La teneur en oxygene-18 et en deuterium a ete etablie iI I'aide d'echa ntillo ns de neige et de glace recueillis iI partir de deux crevasses sur de hauts glaciers temperes des Andes et de I' Himalaya. Les resultats de cette etude ont prouve que sous l'eITet d ' une exposition ensoleillee intense un e gr a nde pa rtie de I'accumulation a nnuelle de neige est en levee par la fonte et la sublimation avec predomi nance de cette derniere. II existe une evidence empirique forte, que dans les conditions nat urelles qui so nt characteri stiqu es po ur tou s les deux glaciers etudies, la sublimation de la couche de neige peut ctre approxi mee par un processus d' equilibre thermodynamique.Les fluctu ations iI court terme quoique legerement moderees ainsi que les vari a tions iI plu s long terme peuvent faire encore I'objet d'observation iI des profonde urs plus gra n des des glaciers en depit de la firnification de la neige. temperierten Gletschern in den Hochanden und im Himal aya gemessen. Die Ergebni sse zeigen, dass wegen der starken Sonneneinstrahlung ein betriichtlicher Teil des jiihrlichen Schneeauft rag durch Schmelzung und Verdunstung abgetragen wurde, worbei der Einflu ss der Ve rdunstung iiberwiegt. In Naturverhiiltnissen, char ak teristisch fUr beide Gletsc her, die Subl imati on der Schneedecke an dem thermodynamischen Phasengleich gewicht kann approximiert sein . Kurzzeit-Fluktuationen, wenn auc h leicht moderiert, und Langzeitvariatio nen konnen noch in den tieferen Teil en der Gletscher trotz der Firnifikation des Schnees beobachtet werden.

Modeling δ18O in precipitation over the tropical Americas: 1. Interannual variability and climatic controls

“…As oceanic air masses move inland and lose water through precipitation, the remaining atmospheric water vapor therefore becomes progressively depleted in heavy isotopes (“continentality effect”). Once the water vapor reaches an orographic obstacle, the adiabatic cooling and precipitation associated with rising air masses (“altitude effect”) will further contribute to the depletion of this air mass [e.g., Grabczak et al , 1983; Gonfiantini et al , 2001].…”

Climatological significance of δ18 O in precipitation and ice cores: a case study at the head of the Ürümqi river, Tien Shan, China

“…Isotopic enrichment by partial melting of the snow cover can be roughly estimated by assuming a Rayleigh-type removal of meltwater from the system (Moser and Stichler, 1980). Nevertheless, such isotopic enrichment should influence the ice-core δ 18 O — T a records, in such a way that the final isotopic composition of the glacier ice is shifted in the same direction (Grabczak and others, 1983), or even enhance the climatic significance of ice-core δ 18 O records, because more enrichment in heavy isotopic content accompanies higher ablation, that is, generally due to higher air temperatures. This guarantees the climatic significance of ice-core δ 18 O records from areas of very heavy melt, especially on a long time-scale.…”

“…Simultaneously, isotopic fractionation occurs, leaving the solid phase enriched relative to the liquid phase (Arnason, 1969; Búason, 1972). Grabczak and others (1983), using the δ 18 O and δD profiles from two crevasses on temperate glaciers high in the Andes and in the Himalaya, suggested, however, that the short-and long-term isotopic variations can still be observed in the deeper parts of such glaciers.…”

Isotopic study on Dokriani Bamak glacier, central Himalaya: implications for climatic changes and ice dynamics

“…During the past 30 years, several studies have been carried out in polar and temperate regions, particularly Antarctic, Arctic and Alpine regions, using radioactive and stable isotopes (Dansgaard and others, 1969; Jouzel and others, 1987). Studies from the Indian and Nepal Himalaya are relatively sparse (Yasunari 1976; Grabczak and others, 1983; Nijampurkar and Bhandari, 1984; Mayewski and others, 1986; Wake, 1989; Nijampurkar and Rao, 1993). Recent studies based on δ 18 O in snow/ice and ice core from the Tibetan (Xizang) Himalaya have addressed the seasonal relationship between δ 18 O in snow/ice and air temperature and moisture sources (Aizen and others, 1996; Yao and others, 1996; Thompson and others, 1997).…”