Palaeoclimate reconstructions from Tierra Del Fuego to detect Land-Ocean-Atmosphere Interactions

未来人类引起的气候变化的性质是高度不确定的，预计2100年全球气温上升幅度将在0.3-6.4摄氏度之间(IPCC 2007，AR4)。这种巨大的不确定性的部分原因是缺乏气候和替代气候数据来验证气候模型并限制地球系统对模拟强迫的敏感性，特别是在南半球(SH)。SH大气变率的一个重要组成部分是南环状模式(SAM)，它是一种大气质量的振荡，导致南大洋西风的变化。SH西风改变了富含碳的深水的上升流，从而影响了全球海洋和大气之间的二氧化碳平衡。目前尚不确定最近观测到的南部西风带的加强是否会导致南大洋成为大气二氧化碳的净来源或汇。人们对南部西风带大气二氧化碳的长期变化知之甚少，这使得人们很难区分内部和外部强迫的波动。必须纠正这一不足，以便产生和检验解释南部西风强度变化过程的假说&在已知的气候反差时期，例如中世纪气候异常和小冰期，这些西风强度如何与(半球间)气候变化有关。该项目将调查南美洲南部(SSA)的四个新地点。这一地区位于南部西风带的核心地带，地理位置非常适合捕捉其强度的变化。SSA基于陆地泥炭地的古气候档案能够记录西风带的长期变化，因为风的强度主要通过锋面和嵌入在盛行的西风环流中的低压系统影响冬季产生的降水。选定的地点都是雨水滋养的泥炭沼泽，提供了极好的气候档案。从这些沼泽中提取的定年岩心中保存的植物和原生动物化石将被用来重建过去~2000年来沼泽表面湿度(BSW，地表水平衡指数)的变化，时间分辨率为10-100年。将对相同的岩心样品进行氧和氢的稳定同位素分析。降水中这些元素重同位素的时空分布与气温有关，因此与大气环流有关。在泥炭藓纤维组分中捕捉到的同位素信号与植物用于合成纤维素的降水信号密切相关。因此，从凸起的泥炭中提取的泥炭化石保留了过去气候变化和大气环流的清晰信号。稳定的同位素数据将与海洋南极和南极半岛的苔藓库和冰芯的同位素测量结果以及北美东部的稳定水同位素数据和BSW重建数据进行比较。对同一岩心水平的化石和稳定同位素的分析将使我们能够重建区域陆地响应的时间、强度和空间格局，以及探索不同原因的因素，如大气和海洋环流的变化和太阳变率对研究区气候的影响。通过这种方式，我们将深入了解过去2000年来推动气候变化的机制。有待检验的假设：1南沙地区近2000年来的气候变化与北美东部和欧洲西北部的气候变化是同步的，代表了半球间的遥相关。2南沙地区近2000年来的气候变化与北半球的气候变化相反，表现为两极拉锯。3SSA近2000年来的气候变化与北半球气候变化不相关。

The nature of future human induced climate change is highly uncertain with projected global temperature increases in 2100 spanning 0.3-6.4 Celsius (IPCC 2007, AR4). Part of this large uncertainty is due to the paucity of climate & proxy-climate data to validate climate models & constrain Earth System sensitivity to simulated forcing, particularly in the Southern Hemisphere (SH). A key component of variability of the SH atmosphere is the Southern Annular Mode (SAM), which is an oscillation of atmospheric mass that results in changes in the westerly winds over the Southern Ocean. The SH westerly winds modify the upwelling of carbon-rich deep water & therefore influence the global balance of carbon dioxide between the ocean and the atmosphere. It is uncertain whether the recently observed intensification of the southern westerlies will cause the Southern Ocean to be a net source or sink of atmospheric carbon dioxide. Little is known about the long-term past variability of the southern westerlies & atmospheric carbon dioxide, making it difficult to separate internally & externally-forced fluctuations. It is imperative to rectify this deficiency in order to generate & test hypotheses to explain the processes of change in the strength of the southern westerlies & how these are related to (inter-)hemispheric climate change during known periods of contrasting climate change, for example the Medieval Climatic Anomaly & the Little Ice Age. This project will investigate four new sites located in southern South America (SSA). This region is located in the core of the southern westerlies and is ideally located to capture changes in their intensity. SSA terrestrial peatland-based palaeoclimate archives are capable of recording long-term changes in the westerlies, given that wind intensity affects precipitation mainly produced in winter by fronts & low-pressure systems embedded in the prevailing westerly circulation. The selected sites are all rain-fed peat bogs, which provide excellent climate archives. Plant & protozoan (testate amoebae) fossils preserved in well-dated cores extracted from these bogs will be used to reconstruct past changes in Bog Surface Wetness (BSW, an index of surface water balance) over the last ~2000 years, at a time resolution of 10-100 years. The same core samples will be analysed for stable isotopes of oxygen & hydrogen. The spatial & temporal distribution of the heavy isotopes of these elements in precipitation is related to air temperature, & hence to atmospheric circulation. The isotope signal captured in the cellulose fraction of Sphagnum moss closely tracks that of the precipitation used by the plant for cellulose synthesis. Hence, fossil Sphagnum from raised peat preserves a clear signal of past changes in climate & atmospheric circulation. The stable isotope data will be compared with isotope measurements from moss banks & ice cores from the maritime Antarctic and Antarctic Peninsula, in addition to stable water isotope data & BSW reconstructions from eastern North America. Analyses of fossils & stable isotopes from the same core levels will allow us to reconstruct the timing, magnitude & spatial pattern of the regional terrestrial response, as well as exploring the impact of different causal factors such as changes in atmospheric & ocean circulation & solar variability on the climate of the study area. In this way, insight will be gained into the mechanisms that have driven climate change over the last ~2000 years. Hypotheses to be tested: 1 Climate changes during the last ~2000 years in SSA are in phase with climate changes identified in eastern North America & NW Europe, & represent inter-hemispheric teleconnections. 2 Climate changes in SSA during the last ~2000 years are in antiphase with Northern Hemisphere climate changes & represent a bipolar seesaw. 3 Climate changes in SSA during the last ~2000 years are uncorrelated with Northern Hemisphere climate changes.