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，预估2100年全球温度升高范围为0.3-6.4摄氏度（IPCC 2007, AR4）。这种巨大的不确定性部分是由于缺乏气候和代理气候数据来验证气候模式并限制地球系统对模拟强迫的敏感性，特别是在南半球（SH）。南半球大气变异性的一个关键组成部分是南环模（SAM），它是大气质量的振荡，导致南大洋上空西风的变化。SH西风改变了富含碳的深水的上涌，因此影响了海洋和大气之间的全球二氧化碳平衡。目前尚不确定最近观测到的南部西风带的增强是否会导致南大洋成为大气二氧化碳的净源或净汇。由于对过去南方西风带和大气二氧化碳的长期变化知之甚少，因此很难区分内部和外部强迫的波动。必须纠正这一缺陷，以便产生和检验假设，以解释在已知的对比气候变化时期（例如中世纪气候异常和小冰河期），南部西风带强度的变化过程以及这些变化与（半球间）气候变化的关系。该项目将调查位于南美洲南部（SSA）的四个新地点。该地区位于南部西风带的核心，是捕捉其强度变化的理想位置。SSA陆生泥炭地古气候档案能够记录西风带的长期变化，因为风强度主要在冬季影响西风带环流中嵌入的锋面和低压系统产生的降水。选定的地点都是雨养泥炭沼泽，提供了极好的气候档案。从这些沼泽中提取的岩心中保存的植物和原生动物化石将用于重建过去~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。同样的岩心样本将被用于分析氧和氢的稳定同位素。这些元素的重同位素在降水中的时空分布与气温有关，因此与大气环流有关。在苔藓纤维素组分中捕获的同位素信号与植物用于纤维素合成的降水密切相关。因此，从隆起的泥炭中发现的泥炭化石保存了过去气候和大气环流变化的清晰信号。稳定同位素数据将与来自南极海洋和南极半岛的苔藓滩和冰芯的同位素测量结果以及来自北美东部的稳定水同位素数据和BSW重建数据进行比较。通过对同一岩心水平的化石和稳定同位素的分析，我们可以重建区域陆地响应的时间、幅度和空间格局，并探索大气和海洋环流变化、太阳变率等不同原因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年来驱动气候变化的机制。待验证的假设：1 SSA过去~2000年的气候变化与北美东部和欧洲西北部的气候变化处于同一阶段，并表现出半球间的遥相关。2过去~2000年SSA的气候变化与北半球的气候变化呈反相，呈两极跷跷板状。近2000年SSA的气候变化与北半球的气候变化不相关。

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.