Levoglucosan has been extensively used as a biomarker for tracing vegetation fire emissions in atmospheric aerosols, ice cores, and lake sediments. Precipitation can scavenge levoglucosan from the atmosphere to the Earth's surface. However, almost no previous research has investigated the variability of levoglucosan in precipitation. This research reports levoglucosan records in precipitation samples collected from March 2018 to September 2019 in Lhasa, on the southern Tibetan Plateau. Although the event-based levoglucosan variations seem random, the variability on monthly or seasonal time scales is highly correlated to vegetation fire changes along the Himalayas and surrounding regions. In addition, extreme wildfires in southern Central Asia also affect levoglucosan records in precipitation at Lhasa, especially during the summer. Our results indicate that local vegetation fires are not the major sources of levoglucosan in precipitation in Lhasa. In addition, the annual levoglucosan flux at Lhasa is much higher than that in ice cores on the Tibetan Plateau. This study provides important insights into levoglucosan records in precipitation over the Tibetan Plateau, highlighting how levoglucosan variations could reflect fire changes from a single event to seasonal or annual time scales.
Abstract. This study investigated the daily δ18O variations of water vapour (δ18Ov) and precipitation (δ18Op) simultaneously at Nagqu on the central Tibetan Plateau for the first time. The data show that the δ18O tendencies of water vapour coincide strongly with those of associated precipitation. The δ18O values of water vapour affect those of precipitation not only on the same day, but also for the following several days. In turn, the δ18O values of precipitation also affect those of water vapour. Hence, there exists an interaction between δ18Ov and δ18Op, and the interaction decreases gradually with time. During the entire sampling period, the variations of δ18Ov and δ18Op at Nagqu did not appear dependent on temperature, but did seem significantly dependent on the joint contributions of relative humidity, surface pressure, and precipitation amount. In addition, the δ18O changes in water vapour and precipitation can be used to diagnose different atmospheric trajectories, especially the influences of the Indian monsoon and convection. Moreover, intense activities of the Indian monsoon and convection may cause the enrichment of δ18Op relative to δ18Ov at Nagqu (on the central Tibetan Plateau) to differ from that at other stations on the northern Tibetan Plateau. These results indicate that the effects of different moisture sources, including the Indian monsoon and convection currents, need be considered when attempting to interpret paleoclimatic records on the central Tibetan Plateau.
[1] Whether stable oxygen isotope (δ18O) in precipitation obeys the temperature effect and/or amount effect in the monsoon region has long been controversial. An intensive, precipitation event-based sampling project has been carried out at Guangzhou and Changsha stations in southeast China under the Asian monsoon influence. By dividing a year into summer and winter half years at respective station, we find prevalence of amount effect at both stations throughout the year. δ18O-temperature presents complex correlations, with the positive correlation significant at Guangzhou during the summer half year and at Changsha during the winter half year, but vague at either station during the rest of the year; the former attributable to a third mode of convection, while the latter indicative of the weakening monsoon influence accompanied by intensified local recycling. Our high-resolution data demonstrate a significant coexistence of temperature and amount effects of precipitation δ18O in the monsoon domain, conducive to climatic interpretation of δ18O in paleoclimate proxies in mid/low latitudes.
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