| 引用本文: | 程 鹏 ，卢雪峰，杜 花，
BURR G S，宋少华，鲜 锋.2016.青海湖老碳效应的时空变化初步研究[J].地球环境学报,(4):357-365 |
| CHENG Peng, LU Xuefeng, DU Hua, BURR G S,
SONG Shaohua, XIAN Feng.2016.The preliminary study of spatio-temporal change of old carbon effect in Lake Qinghai (NE Tibet-Qinghai Plateau), China[J].Journal of Earth Environment,(4):357-365 |
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| 青海湖老碳效应的时空变化初步研究 |
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程 鹏 ，卢雪峰，杜 花，
BURR G S，宋少华，鲜 锋1,2,3,4
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1.中国科学院地球环境研究所 黄土与第四纪地质国家重点实验室，西安 710061;2.西安加速器质谱中心，西安 710061;3.陕西省加速器质谱技术及应用重点实验室，西安 710061;4. NSF-Arizona
AMS Laboratory, Physics Building, Department of Physics, University of Arizona, Tucson, Arizona 85721, USA
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| 摘要: |
| 本文通过对青海湖周边的湖水和河流DOC、DIC浓度、14C浓度，以及1F孔不同深度13个碳酸盐的14C年代分析，厘清青海湖老碳效应空间分布情况。研究表明：在空间上，青海湖DIC和DOC的14C的老碳各条河流分布极不均匀，南边的老碳效应明显比北边小，河流的老碳明显比湖水偏老，引起青海湖沉积物老碳效应的原因极有可能是由于北边主要河流将流域内的老碳输入湖区引起，并非由于湖水和大气的交换不畅引起的碳库效应。在时间尺度上，碳酸盐14C的老碳平均值比有机碳的14C老碳平均值偏老。由于入湖物质的变化，在全新世前，有机碳和碳酸盐的老碳比全新世后偏老。 |
| 关键词: 青海湖 溶解有机碳 溶解无机碳 14C测年 碳酸盐 |
| DOI：10.7515/JEE201604004 |
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| 基金项目:国家重点基础研究发展计划（973计划）（2013CB955900）；国家自然科学基金项目（41290254） |
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| The preliminary study of spatio-temporal change of old carbon effect in Lake Qinghai (NE Tibet-Qinghai Plateau), China |
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CHENG Peng, LU Xuefeng, DU Hua, BURR G S,
SONG Shaohua, XIAN Feng1,2,3,4
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment,
Chinese Academy of Sciences, Xi’an 710061, China;2. Xi’an AMS Center, Xi’an 710061, China;3. Shaanxi Key Laboratory of Accelerator Mass Spectrometry Technology and
Application, Xi’an 710061, China;4. NSF-Arizona AMS Laboratory, Physics Building, Department of Physics, University of Arizona, Tucson, Arizona 85721, USA
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| Abstract: |
| Background, aim, and scope The study of correction of old carbon is key to reliable 14C chorology in Qinghai Lake. There have been a number of studies in an attempt to estimate the past old carbon effects based on the cores drilled in Qinghai Lake. Various corrective methods have been employed with differing results. However, most of these chronologies were mainly based on a few 14C measurements on short cores and without considering the 14C variation of the modern water sample in the drainage basin of Qinghai Lake, which make us lack systemic understanding of the carbon cycle processes occurring in the lake. Materials and methods In this paper, river water samples were collected in main rivers such as Daotang, Heima, Buha, Quanji, Shaliu, Haergai, and Lake water samples were collected at the northwestern and southern lakeshores of Qinghai Lake in October 2009. The dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) water samples were then processed at Xi’an AMS Laboratory. Firstly, the DIC samples were placed in a container and acidified with H2PO3 on a vacuum line while those DOC samples were processed using the method of vacuum freeze extracting. The carbonate sample in the 1F core was acidified with H2PO3. Secondly, the evolved CO2 could be collected cryogenically transported to the storage for the further graphitization with a Zn/Fe catalytic reduction. Finally, the 14C were measured at Xi’an AMS Laboratory. Results Our results indicated that the distribution of old carbon of DIC and DOC in the river were not uniform. No matter concentration or 14C of DIC in the southern lakeshore was lower than that in the northern lakeshore as limestone was widely distributed. However, concentration of DOC in the southern river was higher than that in the northern river due to humic matter oozed from the grassland, but the 14C age was younger in the northern river. In short, for river water sample, the old carbon age was younger in the south than that in the north, for lake water sample, 14C age was modern, Furthermore, 14C age of a living naked carp (Gymnocypris przewalskii), algae in Qinghai Lake also were modern, indicated that the older 14C DIC, which is taken by rivers, have exchanged with atmospheric CO2 quickly, when it entered into the lake. So, the older 14C DIC in the river wasn’t main factor that result in the old carbon effect in the modern lake. Based on correction of old carbon method described by Zhou et al (2007, 2014), we attained the distribution of old carbon age with time in the carbonate and TOC of 1F core. After a comparative study, the results show that both old carbon age were changeable with time, and kept on decreasing since 32 ka. Compared with the old carbon age of TOC, the variation range of the old carbon age of carbonate got bigger. The average old carbon age of carbonate is 7000 years older than the average old carbon age of TOC. Discussion Before the Holocene period, the old carbon age is older than Holocene period, which indicated material source have changed. Before the Holocene period, the grain size in the core was consistent with that of aeolian loess accumulated in the drainage basin of Qinghai Lake. During this period, a large amount of pollen of cold-resistant and draught-enduring herb plants, especially Artemisia, Riemannian and Chenopodiaceae, were predominated in this region; the aquatic plant pollen and Lacustrine Ostracodes don’t existed in the sediment. All of these features suggested that it was drought in the drainage basin of Qinghai Lake, the climate was dry and cold, and grain size was coarse, the accumulated loess found in the core. In the Holocene period, the climate became wet and warm, the grain size was fine, most of material source derived from river. Conclusions Together with spatial and temporal distribution of the old carbon in the drainage basin of Qinghai Lake, we conclude that, in the space, the old carbon age was younger in the south than that in the north, and was younger in the river than that in the lake. All modern samples in the lake showed 14C age were modern, indicated older matter carried by river was main factor. Atmospheric exchange of 14C was the main process affecting surface dissolved inorganic carbon (DIC) in the lake, but dissolved organic carbon (DOC) can be explained as a combination of sources. The old carbon of carbonate was very intense and changeable in 1F core. In the timescale, before the Holocene period, the old carbon age was older than Holocene period due to the change of source input. For DOC extraction from water sample, it’s very possible to be contaminated by carbon from atmosphere during the experiment. It can be avoided by using the method of vacuum freeze extracting when we concentrated water sample and extracted DOC in the river and Lake of Qinghai. Recommendations and perspectives Combined the concentration of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) with 14C age, which enabled us to have a better understanding of the spatio-temporal distribution of old carbon effect in the watershed of Qinghai Lake and shed new insights on the carbon cycle processes occurring in the lake. |
| Key words: Qinghai Lake dissolved inorganic carbon (DIC) dissolved organic carbon (DOC) 14CC dating carbonate old carbon effect |
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