Radiometric Chronology of Neh–nar Glacier, Kashmir

Abstract

Surface and core samples of Neh–nar Glacier in the Kashmir Valley have been analysed for the radionuclides 32Si. 210Pb, 40K, and 137Cs. The lateral and vertical profiles (at an altitude of about 4 140 m) reveal:(1)32Si activity decreasing slowly from the accumulation zone to 4 050 m altitude and then abruptly towards the snout.(2)Five zones of alternating high and low 210Pb activity in the surface samples.(3)An horizon at between 2 and 3 m depth containing 210Pb activity above natural levels. This horizon is also associated with 137Cs and a maximum in total ß activity.The ice samples have been dated on the basis of a simplified two–component model, the “fresh“contribution determined by 2l0Pb and the old component by 32Si. The following conclusions can be drawn from these observations:(1)The model age of the snout ice is c. 850 years.(2)The average rate of ice movement in the lower glacier is about 2 m/year, which compares well with the annual movement rate of 2.65 m/year observed since 1974.

The Missing Silica Sink: Revisiting the Marine Sedimentary Si Cycle Using Cosmogenic 32Si

“…To date, given its very low activity and the difficult analytical procedures necessary for measurement, the use of natural 32 Si as a tracer has been limited. It has been used to determine particle mixing rates in the deep sea (DeMaster & Cochran, ), sedimentation rates in deltas and lakes (Nijampurkar et al, ; Morgenstern et al, , ; Suckow et al, ), and ages of glacier ice (Nijampurkar et al, , ; Morgenstern et al, , ). It has also been used as a tracer of stable silicon inputs into various water masses (Nijampurkar et al, , ; Lal et al, , ; DeMaster, ; Morgenstern et al, ) and to date groundwater ages in aquifers (Nijampurkar et al, ; Lal et al, ; Franke et al, ; Fröhlich et al, ; Morgenstern et al, ).…”

Oxygen isotopic ratios of some Himalayan glaciers

“…Nehnar, located in the Kashmir Valley (34O09'N, 75O3 I'E) in the western Himalayas is a small (3.4 km long and 0.35 km wide at the maximum) valley glacier extending over the altitude range of 3900-4700 m. Changme-Khangpu (CK) is another young and small valley type glacier located in the Sikkim valley (27O58'N, 88O42'E) in the altitude range of 4800-5500 m. It is 5.8 km long and drains into Tista river. The chronology and ice dynamics of these glaciers have been studied earlier (Bhandari et al, 1983;Nijampurkar et al, 1982).…”

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

“…The specific activities of 32 Si and 210 Pb in the snout-ice samples collected during August 1992 are calculated to be 3.7 ± 0.5 μ Bq kg −1 and 13.2 ±1.3 mBq kg −1 , respectively (Table 1). Using a two-component box model (Nijampurkar and others, 1982), the corrected value of 32 Si activity in the snout ice is calculated to be 2.5 μ Bq kg −1 . Using this value and assuming the average 32 Si concentration of the snowfall in the Himalayan region to be 11.7 μ Bq kg −1 , a radiometric age of 400 years is obtained for the snout ice of DB glacier.…”

“…During the 1992 expedition, large quantities (∼1000 kg) of surface snout ice were collected and processed for determination of 32 Si activity and dating of the snout ice. The chemical procedures adopted in the field as well as in the laboratory for the extraction, purification and estimation of 32 Si and 137 Cs are described in our earlier papers (Nijampurkar and others, 1982; Nijampurkar and Rao, 1992); 210 Pb was assayed by alpha spectrometry (Sarin and others, 1992).…”

“…In the laboratory, silica (along with 32 Si) was separated from Fe(OH) 3 and allowed to equilibrate with its daughter isotope, 32 P ( t 1 / 2 = 14.3 days). After 3–4 months, 32 P was recovered as Mg 2 P 2 O 7 and its activity was assayed on a low-background Geiger–Müller counter operated in anti-coincidence with a NaI(Tl) detector (Nijampurkar and others, 1982). The counting system had an efficiency of 27%.…”