Terrestrial Holocene climate variability on the Antarctic Peninsula

南极大陆是地球系统的重要组成部分，影响并响应全球海洋和大气环流。冰盖在海平面变化中起着重要作用，目前冰盖相当于全球海平面上升了70米。因此，监测南极洲气候、冰冻圈和生物圈的变化是了解和预测未来全球变化的关键因素。在过去的50年里，南极洲大部分地区的气候保持相对稳定，但南极半岛经历了地球上升温速度最快的地区之一，自20世纪50年代以来上升了3摄氏度，在一些地方，冬季的升温速度甚至更高。气温的迅速上升与海冰面积减少、冰架崩塌、冰川退缩和冰流速率增加以及陆地和海洋生态系统的变化有关。然而，最近温度变化的原因和背景尚不清楚，尽管人们认为平流层臭氧消耗和温室气体增加都很重要。目前的全球气候模式没有充分捕捉到观测到的变化。理解和归因南极气候变化的一个关键问题是，与过去的自然气候变率相比，南极半岛记录的变化是否不寻常。然而，这个问题无法解决，因为仪器记录太短，现有的代用气候记录位置不合适，无法追踪随时间变化的空间特征。本项目将利用苔藓滩作为新的代用气候档案来验证三个关键假设：1)南极半岛最近的气温上升是全新世晚期前所未有的；2)变化的空间格局与以往气候变化时期相似。植物群落对近期气候变化的反应是生长率的提高和季节生长模式的改变。苔藓库是重建南极半岛陆地表面气候变化的理想沉积物，因为它们的位置与记录的温度变化有关，它们的年龄，以及它们的档案属性。在过去的5-6000年里，苔藓滩在整个南极半岛西部地区积累了泥炭。它们仅由一到两个物种组成，每年的生长可以在地表泥炭中追踪到，苔藓遗迹保存良好。我们将使用过去气候的多代理指标（稳定同位素、衰变测量、无证变形虫和苔藓形态），从观测到的690年至610年之间温度变化率梯度的关键位置重建气候变率。尽管这些技术在世界上更温带的地区进行了尝试和测试，但尚未在南极采用。我们在Signy岛进行了试点研究，结果表明这些代理对南极的苔藓库很有效，所以我们知道我们的方法将产生有价值的结果。我们的工作还将包括通过地表采样和测量计划来提高我们对代理气候关系的理解。这些记录将使用涵盖仪器观测期间的年度解析记录进行校准。连同Signy岛的记录，作为目前由研究小组成员监督的BAS博士项目的一部分，詹姆斯罗斯岛BAS冰芯的新结果和一些更高分辨率的海洋沉积物记录，我们的数据还将为更全面地了解更广泛地区的晚全新世气候变化提供基础。建立在BAS过去气候和化学项目的基础上，该项目旨在重建和理解南极半岛全新世的气候变化。

The Antarctic continent is an important part of the Earth system, both influencing and responding to global ocean and atmospheric circulation. The ice sheet plays a major role in sea-level change and currently holds the equivalent of 70m of global sea-level rise. Monitoring change in the climate, cryosphere and biosphere of Antarctica is therefore a critical element in understanding and predicting future global change. Over the past 50 years, the climate over most of Antarctica has remained relatively stable, but the Antarctic Peninsula has experienced one of the highest rates of warming anywhere on Earth, with increases of 3oC since the 1950s, and even higher rates for winter in some locations. The rapid increase in temperature has been associated with decreased sea-ice extent, ice-shelf collapse, glacier retreat and increased ice flow rates, and changes in ecosystems on land and sea. However, the causes and context of the recent temperature changes are unclear, although it is thought that stratospheric ozone depletion and increasing greenhouse gases are both important. Current global climate models do not capture the observed changes adequately at present. A key question in understanding and attribution of Antarctic climate change is whether the recorded changes on the Peninsula are unusual compared with past natural climate variability. However, this question cannot be addressed because the instrumental records are too short and existing proxy-climate records are not suitably located to be able to trace the spatial signature of change over time. The project proposed here will exploit moss banks as a new proxy-climate archive to test three key hypotheses: 1) The recent temperature rise on the Antarctic Peninsula is unprecedented in the late Holocene. 2) The spatial pattern of variability is similar to that which occurred during previous periods of climate change. 3) Plant communities are responding to recent climate change by increases in growth rates and altered seasonal growth patterns. Moss banks are ideal deposits for reconstructing climate change over the land surface of the Antarctic Peninsula because of their location in relation to recorded temperature changes, their age, and their attributes as archives. The moss banks have accumulated peat over the past 5-6000 years at locations throughout the western Antarctic Peninsula. They are formed of only one or two species, annual growth can be traced in the surface peats and preservation of moss remains is good. We will use multi-proxy indicators of past climate (stable isotopes, measures of decay, testate amoebae and moss morphology) to reconstruct climate variability from critical locations across the observed gradient in rate of temperature change between 69o and 61o S. Although these techniques are tried and tested in more temperate regions of the world, they have not been employed in the Antarctic. We carried out pilot studies on Signy Island which show that these proxies work well for the moss banks in the Antarctic so we know that our approach will produce valuable results. Our work will also involve improving our understanding of proxy-climate relationships by a programme of surface sampling and measurement. The records will be calibrated using annually resolved records covering the period of instrumental observations. Together with records from Signy Island being produced as part of a current BAS PhD project supervised by members of the research team, emerging results from the BAS ice core at James Ross Island and some of the higher resolution ocean sediment records, our data will also provide the basis for a more complete understanding of late Holocene climate variability in the broader region, building on the BAS Past climate and Chemistry programme directed at reconstructing and understanding Holocene climate variability in the Antarctic Peninsula.