亚洲粉尘的源区分布、释放、输送、沉降与黄土堆积

根据亚洲粉尘关键区域(中国沙漠、黄土高原、青藏高原和中国历史降尘区)大气气溶胶中15～28种元素的浓度-粒度分布、沉降速率和通量分析,以及元素示踪系统的进一步解析,发现中国北方沙漠存在两个粉尘地-气交换较活跃区域,即中国西部沙漠和北部沙漠高粉尘区,且证明这两个区域及其邻区是亚洲粉尘和黄土高原黄土主要源区的中心区域;通过对5个亚太区域粉尘沉降量的模式估算,得出亚洲粉尘释放总量每年约为800Tg,约相当于全球沙漠排放总量的一半;粉尘与黄土的对比表明,亚洲粉尘区域尺度输送受季风环流控制,但间冰期时并不取决于尘暴过程,而全球尺度输送主要由高空西风完成,无论冰期、间冰期均受尘暴过程控制;粉尘通量的结果表明干沉降是粉尘在黄土区沉降的主要过程,且晚第四纪粉尘沉积的再改造份额不超过其沉积总量的10%;元素示踪系统应用于风成黄土,发现在间冰期北部沙漠源区输出的粉尘量增加,而在冰期西部源区输出的粉尘量增加.这种晚第四纪亚洲粉尘“源区摆动”的快速变化其实是全球千年尺度气候变化的一环,并可视为过去北半球大气环流长期变化的代用序列.

SOURCE DISTRIBUTIONS, EMISSION, TRANSPORT, DEPOSITION OF ASIAN DUST AND LOESS ACCUMULATION

On the basis of mass particle-size distributions,depositional velocities and fluxes of 15 to 28 elemental concentrations in ground-based aerosol over the key areas of Asian dust （Chinese desert regions, the Loess Plateau, Qinghai-Xizang Plateau and historical dust-fall regions）, two areas with high dust loading and fluxes are identified: the "Western High-Dust Desert" and the "Northern High-Dust Desert," with Taklimakan Desert and Badain Juran Desert as their respective centers. Further analyses of a chemical element balance model based on an elemental tracer system suggests that these apparently are the major source areas for Asian dust and loess deposited in the center of the Loess Plateau. Estimates of atmospheric dust deposition to five Asian / Pacific regions indicate that⁸00 Tg of Asian dust is injected into the atmosphere annually, accounting about half of global dust emission; about 30% of this is re-deposited onto the deserts, 20% is transported over regional-scales,primarily within continental China. The remaining 50% of the dust is subject to long-range transport to the Pacific Ocean and beyond. Particle-size distributions and depositional fluxes were investigated for the present-day Asian dust in dust storm and non-dust storm conditions and for the Late Quaternary loess / paleosol sequences from central China. The regional-scale transport of Asian dust during interglacial stages is mainly attributable to non-dust storm processes and is dominated by northwesterly surface winds. Conversely, during glacial stages the impact of dust storms on the accumulation of loess is enhanced. These regional effects are in contrast to the global-dispersal of dust that is associated with transport by upper-level westerly winds and is mainly the result of desert dust storms during both glacial and interglacial conditions. The calculations of dry and wet depositional fluxes to the Loess Plateau suggest that dry deposition dominated the total input of mineral dust. Only few percent of loess and paleosol particles were attributable to re-working process during the Late Quaternary. Elemental tracers based on several dust-derived elements （Al, Fe, Mg and Sc） reveal high-frequency variability in the contributions of the western high-dust sources vs. northern high-dust sources to eolian deposits from the center of the Loess Plateau. Comparisons of the patterns uncovered with climate signals from the remote North Atlantic region for the last glaciation show that shifts in source areas of Asian dust were synchronous with large-scale variations in atmospheric circulation, which play a part in millennia-scale global climatic change.