Concentration, sources and light absorption characteristics of dissolved organic carbon on a typical glacier, the northeastern Tibetan Plateau

Abstract

Light-absorbing dissolved organic carbon (DOC) constitutes a major part of the organic carbon in the glacierized region. It has important influences on the carbon cycle and radiative forcing of glaciers. However, currently, few data are available in the glacierized region of the Tibetan Plateau (TP). In this study, DOC characteristics of a typical glacier (Laohugou glacier No. 12 (LHG glacier)) in the Northeastern TP were investigated. Generally, DOC concentrations on LHG glacier were comparable to other glacierized regions around the world. The average DOC concentrations in snowpits, surface snow, surface ice (superimposed ice) and proglacial streamwater were 332.4 ± 132.3 μg L −1, 229.3 ± 104.4 μg L −1, 425.8 ± 269.9 μg L −1, and 237.5 ± 95.6 μg L −1, respectively. It was estimated that the annual DOC flux released from this glacier was 6949.4 kg C yr −1, of which 43.2 % DOC was bioavailable and could be decomposed into CO2 within 28 days of its release. The mass absorption cross section (MAC) of DOC at 365 nm was 1.4 ± 0.4 m 2 g −1 in snow and 1.3 ± 0.7 m 2 g −1 in ice, similar to those of dust transported from adjacent deserts. Based on this finding and the significant relationship between DOC and Ca2 +, it was proven that the main source of DOC of this glacier was mineral dust. The radiative forcing of DOC relative to black carbon (BC) was calculated to be 9.5 ± 8.4 % in snow and 0.1 ± 0.1 % in ice, respectively, implying the necessity of accounting for DOC in future radiative forcing investigations in the glacierized region on the TP, especially when these areas are covered by fresh snow.