|过去 2000 年新疆北部的湿度变化及其控制机理|
|Place of Conferral||新疆乌鲁木齐
Past 2000 Years
|Abstract||新疆北部过去 2000 年的气候变化一直备受相关研究者的关注，因为理解新疆北部过去2000年的气候变化有助于提高我们对大尺度气候-水资源内在关联的认知，也有助于提高我们应对新疆北部未来气候变化的能力。但是，新疆北部过去 2000 年气候变化的已有研究存在分辨率低、测年误差大的缺陷。而且，新疆北部也鲜有关于气候-水资源内在关联以及人类活动对水资源影响的报道。本文通过基于泥炭和湖芯的高分辨率代用指标，揭示了新疆北部过去 2000 年气候-水文变化之间的联系，探讨了最近百年来人类活动对水资源的影响。基于四个序列的资料，我们得出了下列结论：1）位于阿尔泰南部青河县的玉什库勒（YSKL）钻孔泥炭藓（非维管束植物）δ13Ccelluose所指示的土壤湿度表明：在约 170 BC 至 460 AD 期间，δ13Ccelluose所指示的湿度整体较高。在约 460 AD 至 870 AD 期间，湿度比前期（约 170 BC 至 460AD）更高。在约 870 AD 至 1590 AD 期间，湿度出现频繁的波动但整体偏低。在约 1590 AD 至 1830 AD 期间，湿度再次升高。在约 1830 AD 至 2010 AD 期间，泥炭芯的泥炭藓很匮乏，取而代之的是大量的苔草植物。偏正的苔草植物δ13Ccelluose 实际上指示了较低的土壤湿度。过去两千多年阿尔泰南部的暖季湿度变化主要受到降水量变化的影响，暖季温度也参与了湿度的变化过程。YSKL 的资料显示，北大西洋涛动（NAO）主导了 YSKL 的湿度变化过程，即正相的 NAO有利于湿度增加，负相的 NAO 导致了湿度下降。2）我们利用位于阿尔泰南部的黑阳坡（HYP）泥炭芯的纤维素 δ13Ccelluose和泥炭吸光度反演了 HYP 过去 650 年来的水文变化。HYP 泥炭 δ13Ccelluose所指示的地表湿度表明：在过去约 650 年来 HYP 的湿度一直是下降的。其中，在约1360 AD-1725 AD 期间，湿度下降可能是由低温条件下暖季降水下降引起的；在约 1725 AD-2013 AD 期间，湿度下降则可能是由高降水条件下暖季温度上升导致的蒸发增强引起的。泥炭吸光度所指示泥炭腐殖化程度表明：在约 1360 AD 至1725 AD 期间，泥炭的分解是增强的；在约 1725 AD 至 2013 AD 期间，泥炭的分解是减弱的。其原因可能是：在约 1360 AD 至 1725 AD 期间，暖季降水的减少使得地表湿度下降，从而改进了地表土壤层的氧化环境，更有利于有机质的分解，导致吸光度增加。在约 1725 AD 至 2013 AD 期间，随着湿度的继续下降，制约泥炭分解的因素由之前地下水位控制的氧化还原环境变成了地表土壤的可利用水的多寡。HYP 的资料表明该地区的降水在过去 650 年里很可能一直受到大西洋年代际振荡（AMO）的影响。3）我们对位于中天山的大龙池（DLC）湖芯进行了地球化学指标和硅藻组分的分析，并在这些分析的基础上重建了过去约 470 年的水文历史。作为温度代用指标的脆杆藻丰度（即 Fragilaria%）显示：约 1620 AD 至 1700AD 期间的温度接近过去约 470 年的平均值；约 1700AD 至 1825 AD 期间的温度显著偏低，其中约 1690 AD 至 1780 AD 为过去约 470 年以来的最低温度时段；约 1825 AD 至 2013 AD 期间的温度整体偏高并呈增加趋势。DLC 的温度变化很好地响应了北半球的温度变化，而后者是由太阳辐射和大气 CO2 所驱动的。过去约 470 年来，DLC 湖水盐度的变化受降水、温度、冰川融水量的控制。具体地讲，约 1540 AD 至 1570 AD 期间湖水中等水平的盐度是由适中的温度和适量的降水导致的。约 1570 AD 至 1700 AD 期间湖水极高的盐度是由极低的降水量导致的。约 1700 AD 至 1825 AD 年间湖水适中的盐度是由适中的降水和低温导致的低蒸发量共同调控的。约 1825 AD 至 1945 AD 年间极低的湖水盐度是由高温导致的冰川融化引起的。即前一时段（1700 AD 至 1825 AD）在低温条件下的冰川扩展为本时段（1825 AD 至 1945 AD）高温条件下的冰川融化提供了条件。约 1945 AD 至 2013 AD 期间的湖水盐度是由降水和温度二者调控的。较低的湖水盐度不仅是降水增加的结果，也是在高温条件下冰川融化的结果。我们的结论是：过去近 470 年来，天山中部的降水很可能一直受到 AMO 的影响。4）我们对位于新疆北部腹地的艾里克湖（ALK）的湖芯进行了地球化学和硅藻组分的分析，并据此重建了过去约 130 年的水文历史。我们重建的 ALK 湖面积的变化可分成两个主要阶段：自然因子控制阶段（约1884 AD 至 1960 AD）和人类因子控制阶段（约 1960 AD 至 2013 AD）。在自然因子控制阶段，ALK 湖依次出现了低湖面积（约 1884 AD 至 1920 AD）及高湖面积（约 1920 AD 至 1960 AD）的变化。我们推测，自然阶段的 ALK 湖面积很可能与新疆北部的暖季降水有关，而后者很可能受到 AMO 的影响。在人类因子控制阶段，湖面积完全受控于人类活动。由于人类开采地下水以及直接从 ALK上游的白杨河引水，ALK 湖出现了湖面积的逐渐缩小直至干涸（约 1960 AD 至2000 AD），之后通过引额济克人工沟渠调度了额尔齐斯河河水补充到 ALK 湖，湖面积才得到了恢复（2000 AD 至 2013 AD）。5）通过对比新疆北部及其周边地区（下称北疆）、新疆南部及其周边地区（下称南疆）过去 2000 年的湿度变化，我们发现，北疆和南疆的湿度变化具有较好的一致性。我们的比较结果显示，北疆和南疆过去 2000 年的湿度变化呈现如下特征：在约 0 AD 至 700 AD 期间，湿度偏高；在约 700 AD 至 1350 AD 期间，湿度偏低；在约 1350 AD 至 1900 AD 期间，湿度偏高，尤其是在约 1500 AD 至 1750AD 时段，北疆和南疆都进入了稳定的湿润期；在约 1900 AD 至 2000 AD 期间，湿度偏低，但是最近 50 年的湿度却是增加的。总得来说，北疆和南疆的湿度变化与东亚季风区的湿度表呈现了反相关系。6）新疆过去 2000 年来的湿度主要受到 NAO 和 AMO 的影响。其中 NAO可能更多的影响了新疆冬季降水而 AMO 可能更多的影响了北疆夏季降水。NAO通过与西伯利亚高压的交互作用，影响了西风环流中最大水汽传输轴的位置，最终影响到了新疆的冬季降水。正相的 AMO 有利于水汽进入西风系统，能够在北疆上空 1000-400 hPa 的区域形成了一个经向的水汽输送路径，将北太平洋的水汽输送到北疆，能够引起印度季风的强度以及持续时间增加，最终导致北疆地区夏季降水增加。|
|Other Abstract||The climate change during the past 2000 years has been one of the foci in the global change research. It is of particular importance for northern Xinjiang because understanding the climate change in northern Xinjiang during the past 2000 years can help us to comprehend the large-scale interactions between the climatic systems and hydrologic systems and can provide theoretical guidelines for mitigating the water-resource issues resulted from the projected further warming climate in northern Xinjiang. However, existing data are rather inadequate either because of too low sampling resolutions or/and because of inadequate chronologies. This dissertation focuses on four high-resolution sequences (peat and lake) with robust chronological supports and attempts to explore the interactions between the climatic systems and hydrologic systems in northern Xinjiang during the past 2000 years and also to assess the impact of human activities on the hydrologic systems during the past century.Followings are the major conclusions drawn from this research.1. Yushikule (YSKL) Peat Sequence：Peat carbon isotope of Sphagnum cellulose (δ13Ccellulose) at Yushikule (YSKL)Peat was used to estimate the warm-season moisture variations of the past ~2200 years in the southern Altai Mountains. The δ13Ccelluose-suggested moisture was generally high from ~170 BC to ~460 AD, distinctively high from ~460 BC to ~870 AD, generally low with frequent fluctuations from ~870 AD to ~1590 AD, much higher from ~1590 AD to ~1830 AD. It is rather notable that a Carex peat replaced the Sphagnum peat at ~1830 AD and the Carex peat dominated from ~1830 AD to ~2010 AD. The elevated δ13Ccelluose values derived from Carex peat actually suggest a lowered soil moisture from ~1830 AD to ~2010 AD. To sum up, the moisture of the past ~2200 years in the YSKL basin has been mostly associated with the precipitation.And the precipitation may be modulated by North Atlantic Oscillation (NAO)variations, exhibiting a positive relationship with NAO.2. Heiyangpo Peat (HYP) Sequence:Peat carbon isotope of cellulose (δ13Ccelluose) at Heiyangpo Peat (HYP) was used to estimate the warm-season moisture variations of the past ~650 years in the southern Altai Mountains and the humification (light absorbance) was used to constrain the δ13Ccelluose-based hydrological interpretation. The increasing trend of humification and the corresponding decreasing trend of δ13Ccelluose-suggested moisture within the depths spanning from 70 cm to 40 cm imply that a constant dropping in groundwater level under a constant drying condition may have promoted an aerobic environment and may thus more efficiently decomposed the peat from ~1360 AD to ~1725 AD. The groundwater-level dropping was most likely resulted from a constant decline of the precipitation. The decreasing trend of humification and the corresponding decreasing trend of δ13Ccelluose-suggested moisture within the depths spanning from 40 cm to 0 cm imply that the peat decay depended on the soil moisture level within the unsaturated layer above the groundwater level from ~1725 AD to ~2013 AD. That is, the decomposition of peat became weaker when the soil moisture became lower. The soil moisture-level dropping was most likely resulted from a constant rise of the warm-season temperature. In summary, it seems that the soil moisture in HYP basin has been modulated by the Atlantic Multidecadal Oscillation (AMO) and regional temperature during the past ~650 years.3. Dalongchi Lake Core (DLC) Sequence:A sediment core was drilled from an alpine lake (i.e., DLC) in the central Tianshan Mountains to reconstruct the past climate and the associated hydrology.Fragilaria-indicated temperature was moderate from ~1540 AD to ~1620 AD,relatively low with large-amplitude fluctuations from ~1620 AD to ~1700 AD,distinguishably lower from ~1700 AD to ~1825 AD with the coldest interval spanning from ~1690 AD to ~1780 AD, and averagely higher with a general rising trend during the past ~190 years. The temperature variation of Lake DLC in the central Tianshan Mountains was a general reflection of the Northern Hemisphere temperature anomaly,the latter being primarily driven by the total solar irradiance and the atmospheric CO2 concentration.The lake-water salinity was mainly controlled by precipitation from ~1540 AD to ~1700 AD. Specifically, a moderate level of the salinity from ~1540 AD to ~1570 AD was mainly associated with a moderate amount of precipitation under a mild temperature condition and the highest salinity of the entire core from ~1570 AD to ~1700 AD was most likely resulted from the extremely low precipitation. The lake-water salinity was modulated by both precipitation and temperature-dictated evaporation from ~1700 AD to ~1825 AD. Specifically, a stably moderate level of the salinity from ~1700 AD to ~1825 AD was achieved through an elevated precipitation/evaporation ratio. The elevated ratio was resulted from an increased precipitation and also from a decreased evaporation under a dramatically lowered temperature condition. The lake-water salinity was strongly affected by temperature-led glacier melting from ~1825 AD to ~1945 AD. The salinity reached the lowest level of the entire core and the lowest salinity seemed to be associated with the Fragilaria-indicated high temperature. That is, the lowest salinity might have been caused by temperature rising-resulted melting of glaciers that advanced massively during the preceding period (i.e., from ~1700 AD to ~1825 AD). The lake-water salinity was modulated by both precipitation and temperature-led glacier melting from ~1945 AD to ~2013 AD. The relatively low level of the salinity can be attributable to the increase in precipitation and also to the increase in glacier-melting water under a rising temperature condition during the past ~70 years. To sum up, the variation in the lake-water salinity of Lake DLC in the central Tianshan Mountains during the past ~470 years has been modulated by interplays among three factors:precipitation amount, temperature-dictated evaporation, and temperature-led glacier melting. It can also be concluded that the precipitation in the central Tianshan Mountains might have been modulated by AMO.4. Lake Ailike core (ALK) Sequence:A 42-cm-long sediment core was obtained from Lake Ailike (ALK) in northern Xinjiang to reconstruct the hydrological and ecological variations of the past 130 years and to decipher the modulating mechanisms. We reconstructed diatom-inferred conductivity (DI-Cond) and our reconstruction was based on the comparison between our fossil diatom assemblages from the ALK core and the modern diatom assemblages from the European Diatom Database.The scatter plot between the measured lake areas and the corresponding DI-Cond values showed a linear relationship with a high correlation coefficient, allowing for a quantitative reconstruction of the lake area. The reconstruction exhibited two major stages of lake-area variations: stage A (1884-1960 AD) was a “natural” stage and stage B (1960-2013 AD) was a “human” stage. The “natural” stage can be further divided into two sub-stages: A-1 (1884-1920 AD) was characterized by an averagely low lake area and A-2 (1920-1960 AD) was a stably high lake area period. The “human” stage can also be divided into two sub-stages: B-1 (1960-2000 AD) was a regressing stage and B-2 (2000-2013 AD) was a transgressing stage. Our reconstruction of lake area at stage A implied that the AMO might have influenced the precipitation of northern Xinjiang.5. Moisture comparison between northern Xinjiang and southern Xinjiang:Finally, we compared the regional moisture variation of northern Xinjiang and its adjacent areas (here referred as northern Xinjiang) with that of southern Xinjiang and its adjacent areas (here referred southern Xinjiang). Our comparison shows that the regional moisture variations in northern Xinjiang and in southern Xinjiang exhibited parallel trends during past 2000 years. The moisture variations can be divided into the following stages：(1) the moisture was generally high from ~0 AD to ~700 AD; (2) the moisture was distinguishably low from ~700 AD to ~1350 AD; (3) the moisture was generally high again from ~1350 AD to ~1900 AD with the highest interval spanning from ~1500 AD to ~1750 AD; (4) the moisture was quite low from ~1900 AD to ~2000 AD but it was relatively high during the recent ~50 years. The moisture variations of the past ~2000 years in Xinjiang (northern Xinjiang and southern Xinjiang) displayed an anti-phased relationship with the moisture variations in the monsoonal areas of China.6. Moisture relating modulated factors The regional moisture variation of Xinjiang was modulated by NAO and AMO during past 2000 years. Specifically, NAO can exert influences on cold season precipitation of Xinjiang and AMO can impose it effects on warm season precipitation of northern Xinjiang. NAO, which is interacting with Siberian High, impacts the winter precipitation variations in Xinjiang by controlling the position of the axis of maximum moisture transport. A positive AMO can enhance water evaporation into westerly circulation, lead to an anomalous northward moisture transport at 1000-400hPa geopotential height and induce an enhanced India Monsoon, ultimately results in an increasing warm season precitation in northern Xinjiang.|
兰波. 过去 2000 年新疆北部的湿度变化及其控制机理[D]. 新疆乌鲁木齐. 中国科学院大学,2017.
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