【作者】 聂亚光；

【导师】 谢周清； 刘晓东；

【作者基本信息】 中国科学技术大学 ， 环境科学， 2014， 博士

【摘要】 全球变化持续冲击着人类的居住环境,为了更好地理解各种驱动因子对气候系统的作用过程和机理以预测未来的变化趋势,就非常有必要对过去地球环境的变化进行系统地研究,达到以古论今论未来的目的。阿德利企鹅是南大洋食物链的顶级捕食者,广泛分布于南极地区,其生存状况受到多种环境因素的影响,是研究古生态对气候环境变化响应的理想对象。罗斯海地区是目前阿德利企鹅在南极最大的聚居地之一,同时也拥有着较长的企鹅居住历史,这些古生态信息有可能在粪土沉积物中得到较好的保存。利用这些珍贵的地质样品,通过定年、元素地球化学、同位素生态地质学等多种手段,本研究将讨论企鹅粪的输入对沉积物地球化学性质和同位素组成的影响,并从时间尺度上恢复企鹅的古生态,在空间记录对比的基础上,探讨企鹅数量变化对气候和环境变化的响应。1.罗斯海粪土沉积剖面年代序列的确立我们利用210Pb-137Cs和MS14C定年共同确定了罗斯海地区受企鹅粪影响的MB4、MB6、CL2、BI、CC、MB1、MR1、MR2等8个沉积剖面的年代序列。核素的分析结果显示剖面中过剩21opb的零点均可以达到,CRS模式适用于该地区表层沉积物年轻年代学的计算。沉积剖面过剩210pb的平均通量为5.88Bq/m2a,具有南极的区域性特征。137Cs活度较低,且多在剖面表层达到最大值,可能是受到气候变暖后冰川融水中蓄积137Cs输入的影响。根据平均沉积速率外推和210Pb与AMS14C定年结果拟合,MB4、MB6、CL2、BI、CC、MB1、MR1、MR2底部的年龄被分别确定为394、1281、572、1656、1796、574、1631、1530AD。2.企鹅粪土沉积物中生物标型元素的识别及其生态环境意义海鸟是海陆间物质传输的纽带,对海岸地带的元素地球化学循环有着重要的影响。我们测定了受企鹅粪影响的MB4, MB6、CL2、BI、CC、MB1、MR1、MR2等8个粪土沉积剖面中23种元素的含量。根据多种统计方法,在与环境介质样品对比分析基础上,我们发现企鹅粪是剖面中有机质和营养物质的主要来源,并且对As, Cd、Cu、F、P、S、Se、Zn这8种元素有着很强的富集作用,说明它们是该地区企鹅粪土标型元素组合。通过与南极其他地区、北极地区、南中国海西沙群岛地区海鸟生物标型元素的比较,我们发现它们在全球尺度上都存在重叠, As、Cd、Cu、P、Se、 Zn为共通的标型元素组合。这项比较工作加深了我们对于海鸟作为生物传输介质在海陆地球元素化学循环中所起作用的认识,为开展古环境和古气候重建工作奠定了基础。3.粪土沉积物中Hg元素对生物群落演替的记录及初步污染评价对MB4、MB6、CL2. BI、CC、MB1、MR1、MR2等8个剖面中总汞(Hg)含量的测试和分析显示Hg在沉积物中与TOC呈显著正相关关系,说明有机质是Hg的载体。企鹅粪中高含量的Hg以及剖面中Hg和企鹅粪土标型元素P之间的高度相关性证明了在受企鹅影响程度强烈的MB6、BI、CC、MR1、MR2中企鹅粪是Hg的主要来源。MB6底层海豹毛的出现伴随着Hg的升高,很可能是由于海豹粪的输入所引起的,显示出沉积物中的Hg具有区分不同营养级栖息物种(海豹与企鹅)的潜力。剖面中Hg富集系数的计算结果表明由于企鹅和海豹等生物传输介质的影响,罗斯海地区的粪土沉积物对Hg存在显著的富集,但通过比照沉积物环境质量基准,我们发现沉积物中的Hg还不足以对当地生物群落造成负面影响。4.沉积物中稀土元素的来源和地球化学分布特征我们对MB4、MB6、BI剖面中稀土元素的含量进行了分析,发现其在剖面上存在显著波动。通过对环境介质样品中稀土元素含量的测定以及剖面中稀土元素与岩性元素、企鹅粪土标型元素的相关性分析,我们认为沉积物中的稀土元素主要来源于基岩风化产物,而来自企鹅粪和藻类的生物源稀土元素则非常少。进一步对球粒陨石标准化后稀土元素分布模式中样品曲线斜率以及Ce、Eu异常的分析,揭示出沉积物中基岩风化产物、企鹅粪、藻类三个组分的混合过程是影响剖面中稀土元素分布的主要控制因素。我们利用端元混合模型计算了剖面中来自三个组分的稀土元素量,计算结果很好的区分出了来自基岩风化产物的稀土元素,并且能在一定程度上指示企鹅粪对沉积剖面影响的大小。总体来看,沉积物中的稀土元素与企鹅粪土标型元素呈相反的分布趋势,可以用来辅助恢复历史时期企鹅数量变化。5.粪土沉积物中碳、氮同位素地球化学特征及其生态环境意义我们对MB4、MB6、CL2、BI、CC这5个剖面沉积物碳、氮(分为酸处理和未处理两个组分)同位素的组成进行了分析。沉积物的碳同位素组成显示出明显的企鹅粪—藻类混合来源特征,使用同位素混合模型,我们重建了沉积剖面上不同深度企鹅粪输入和藻类生物量的大小。酸处理和未处理组分的氮同位素差值(△15N)在强烈受到企鹅粪影响的剖面较大,而在受到企鹅粪影响较小的剖面则不显著。分析结果表明企鹅粪和藻类是沉积物中主要的氮源,通过对两个特定剖面氮型态的分析我们发现在寒冷干燥的南极地区,企鹅粪沉积后的分解和氨挥发作用会造成显著的同位素分馏效应,使得沉积物中企鹅粪来源的无机氮同位素大幅上升,沉积物中无机氮占总氮的比例指示剖面受到企鹅粪影响的程度,也是控制△15N大小的关键因素。以上分析成功解释了其他剖面氮同位素组成的特征,因此我们认为在罗斯海地区,△15N是比传统δ15N更加有效的判断沉积物受企鹅影响程度的指标。6.罗斯海地区企鹅古生态的恢复企鹅对气候和环境变化反应敏感,因此常被用作指示古气候变化的生物指标。我们以MB4、MB6、CL2、MB1这4个沉积剖面中所确定的企鹅粪土标型元素为基础重建了罗斯岛Cape Bird地区过去1600年的企鹅数量变化。不同剖面的企鹅数量高峰在1400AD存在着明显的接替现象,很可能是区域内部企鹅迁徙的结果。接替现象在MB4剖面中沉积时间为1400～1900AD的砂质层中表现最为明显,多种理化指标的分析显示这一段沉积物并不是在淡水湖相环境下形成的,而是带有明显的海洋性来源特征。我们认为在小冰期寒冷气候的作用下罗斯岛的冰量积累上升,造成岛屿的地壳均衡下沉,海岸线向内陆推进。生存环境的剧烈变化使得栖息在Cape Bird中部海岸的企鹅放弃了它们的聚居地,向北部或者中部海拔更高的位置迁徙,显示出气候和环境的变化对企鹅生态的强烈影响。对采自Cape Crozier、Cape Royds和蒲福岛的较短沉积剖面中企鹅数量变化记录的恢复显示最近200年由于气候变暖,企鹅的数量在不断上升,这一结论与现代的观测资料一致。7. Marble Point海豹生态初探于Marble Point剖面中提取的海豹毛定年结果显示其年龄约为2700a BP左右,对应罗斯海南部地区温暖气候下的“海豹适宜期”。更多还原

【Abstract】 Global climate change is now laying substantial impact on the environment we are living in. To better understand the process and mechanism that how various drivers may influence the climate system of the earth, it is essential to study the historical change in the environment comprehensively, so that precise prediction for future climate change can be conducted. Adelie penguin is widely distributed around Antarctica, as one of the top predators in the Southern Ocean. The survival of Adelie penguin is heavily affected by many environmental factors, making the species an ideal target for research on the response of paleo-ecology to climate and environmental changes. The Ross Sea region has one of the biggest Adelie penguin concentrations nowadays with a long history of penguin occupation, and the ornithogenic sediments in the rookeries contain useful information of the past. In this study, we will analyze the samples with various techniques to interpret the influence that penguins imposed on the geochemical and isotopic composition of the sediments, and discuss the response of paleo-ecology of Adelie penguin to historical climate and environmental changes.1. Establishment of chronologies for the sediment profiles from the Ross Sea region210Pb-137Cs dating and AMS14C dating were employed to determine the chronologies of the ornithogenic sediment profiles from the Ross Sea region. Analysis for the activity of the radionuclides indicated that the zero point of210Pbex could always be reached in the profiles, and CRS mode was applied to calculate the age of the upper layers. Average flux of210Pbex in the profiles of this region is5.88Bq/m2a, similar to that of Antarctica region. Activity of137Cs in the sediments was generally low, and the maximum was often found in the surface, probably caused by additional137Cs brought by melt water from adjacent glaciers due to the warming climate in recent decades. According to the calculation of average deposition rate and combined analysis of210Pb-137Cs dating and AMS14C dating, the bottom layer of MB4, MB6, CL2, BI, CC, MB1, MR1and MR2were found dating back to394,1281,572,1656,1796,574,1631,1530AD, respectively.2. Identification of penguin bio-elements in the ornithogenic sediments and the eco-environmental implicationsSeabirds have substantial influence on geochemical circulation of elements, serving as a link for substance exchange between their foraging area and colonies. We investigated the elemental composition of eight penguin-affected sediment profiles including MB4, MB6, CL2, BI, CC, MB1, MR1and MR2. Among the three main constituents of the sediments (including weathered bedrock, guano and algae), guano was the main source of organic matter and nutrients, causing selective enrichment of several elements in each of the sediment profiles. In the23measured elements, As, Cd, Cu, F, P, S, Se and Zn were identified as penguin bio-elements in the Ross Sea region through statistical analysis and comparison with local end-member environmental media such as weathered bedrock, fresh guano and fresh algae. Compared with research in other parts of Antarctic, Arctic, and South China Sea, we found apparent overlap of avian bio-elements including As, Cd, Cu, P, Se, and Zn. Information on the composition and behavior of bio-elements in seabird guano on a global scale, and the role that bio-vectors play in the geochemical circulation between land and sea, will facilitate future research on avian ecology and palaeoclimatic reconstruction.3. Ecological succession recorded in sedimentary Hg and the preliminary pollution assessmentTotal mercury (Hg) concentrations were determined in profile MB4, MB6, CL2, BI, CC, MB1, MR1and MR2. Our data show significant positive correlations between Hg concentration and total organic carbon (TOC) content in all the profiles, suggesting the predominant role of organic matter (OM) as a Hg carrier. High Hg content in guano and a positive correlation between Hg and guano bio-element (phosphorus, P) in the ornithogenic sediment cores (MB6, BI, CC, MR1and MR2) indicate that Hg was strongly influenced by guano input. The bottom sediments of core MB6with seal hairs contain relatively high Hg. This increase is attributed to the input of seal excrement, suggesting that sedimentary Hg may be an effective trophic-level indicator from seals to penguins. The enrichment factors (EF) for Hg were calculated and the results indicated apparent Hg enrichment in the sediment cores from the Ross Sea region caused by bio-vectors such as penguins and seals. But sediment quality guidelines (SQGs) showed the total amount of Hg in the study area still rarely cause adverse effect to the local bio-communities.4. Distribution and sources of rare earth elements in ornithogenic sediments from the Ross Sea region, AntarcticaConcentrations of rare earth elements (REEs) were determined in profile MB4, MB6and BI. The distribution of REEs in each profile fluctuated with depth. REEs measured in environmental media and analysis on the correlations of∑REE lithological elements and∑REE-bio-elements in the profiles indicated that sedimentary REEs were mainly from weathered bedrock in this area, and the non-crustal bio-genetic REEs from guano and algae were minor. Further discussion on the slopes and Ce and Eu anomalies of chondrite-normalized REE patterns indicated that a mixing process of weathered bedrock, guano and algae was the main controlling factor for the fluctuation of REEs with depth in the sediments. An end-member equation was developed to calculate the proportion of REEs from the three constituents in the sediments. The calculation functioned well in estimating bedrock-derived REEs and the magnitude of ornithogenic influence in different profiles. In general, REEs in the ornithogenic sediments showed anti bio-element patterns and thus can be used as an additional proxy to reconstruct historical penguin populations.5. Environmental implication of carbon and nitrogen isotopic composition in ornithogenic sedimentsWe analyzed δ13C, and δ15N in both acid-treated and untreated sediments from profile MB4, MB6, CL2, BI and CC that were influenced by penguin guano. Carbon isotopic composition in the ornithogenic sediments showed a mixing feature of guano and algae. Using a2-member isotope mixing equation, we were able to reconstruct the historical change of guano input and algal bio-mass. The difference between treated and untreated δ15N (△15N) was significant in three profiles which were heavily impacted by guano, and minor in two profiles with less guano influence. We determined that total nitrogen in the sediments is primarily derived from penguin guano and algae, and used an N-species test to explain the variation of△15N in two profiles. It was found that post-depositional decomposition and ammonia volatilization, which have important roles in the cold and arid environment of Antarctica, would render an elevated δ15N through kinetic isotopic fractionation in the inorganic nitrogen from guano. N-species analysis revealed that the percentage of inorganic nitrogen in total nitrogen, indicative of the degree of guano influence, is the key factor controlling△15N in the sediments. This hypothesis successfully explained nitrogen isotopic composition in the remaining three sediment profiles. We conclude that the parameter A15N, rather than traditionally used untreated δ15N, can be taken as an effective proxy for the strength of avian influence on ornithogenic sediments in the Ross Sea region.6. Paleo-ecology of penguins and seals in the Ross Sea region and the comparison with ice-free areas around AntarcticaDue to the sensitivity to environmental changes, penguins in Antarctica are widely used as bio-indicators in paleoclimate research. On the basis of bio-element assemblages identified in ornithogenic sediments, we reconstructed the historical penguin population change at Cape Bird, Ross Island, for the past1600years. Clear succession of penguin population peaks were observed in different profiles at about1400AD, which suggested a high probability of internal migration within this region. The succession was most obviously marked by a sand layer lasting from1400to1900AD in profile MB4. Multiple physical/chemical analysis indicated this layer was not formed in a lacustrine environment, but was marine-derived. We believe that colder condition during the little ice age (LIA) would lead to increased ice mass on Ross Island, causing isostatic subsidence and inland-ward movement of the shoreline, which in turn resulted in the abandonment of the colonies. The penguins migrated from the coastal area of mid Cape Bird northward and to higher ground as documented in other sediment profiles, indicating an ecological response to global climate change and subsequent geological effects in Antarctica. Several shorter profiles from Cape Crozier, Cape Royds and Beaufort Island showed that the penguin population only stated to rise in the most recent200years due to a warming climate, corresponding to various geological and instrumental records.7. Preliminary research on seal ecology at Marble Point The seal hairs excavated from Marble Point, Victoria Land recorded the presence of seals at around2700a BP, in accordance with the "seal optimum" with warmer climate and open water.更多还原