LATE QUATERNARY SEA ICE, OCEAN AND CLIMATE RECORDS FROM ANTARCTICA: THE ADÉLIE BASIN

南环模（SAM）是影响南半球大气、海洋和气候变化的最重要因素，当它处于所谓的正态时，代表着中纬度急流和西风的南移和加强。在过去的几十年里，已经记录到一个持续向正SAM转移（西风带持续向南移动），这有可能显著改变SH海洋和海冰系统的特征。这一最近的趋势与全球气温前所未有的大规模上升同时发生。在这些全球温度变化的背景下，人们一直关注南大洋的二氧化碳封存作用——南大洋封存大气热量和温室气体的潜力受到中纬度西风带（即SAM）的位置和强度的强烈调节。鉴于当前的关注焦点，将近期向积极资产管理的强劲长期转变置于背景下是至关重要的。SAM的这种多年代际趋势是不寻常的，还是SAM内部自然变化的一部分？只有地质记录可以在足够长的时间尺度上（并超越仪器记录）提供SAM变化的代理时间序列来研究这个问题；来自IODP站点U1357的全新世沉积物提供了一个独特的机会，扫描电子显微镜背向散射电子成像提供了一个完美的工具。2010年2月，IODP 318考察队前往南极洲的Wilkes Land，在adsamlie盆地U1357遗址发现了一段约200米长的连续层状全新世硅藻泥。这个非凡的沉积物剖面代表了南极边缘唯一已知的完全层压的全新世序列，也是世界海洋已知的最长的全新世海洋序列。在年际时间尺度上，站点U1537对El Niño-Southern振荡（ENSO）强迫的敏感性较低，因此可能是一个更敏感的SAM动力学记录器。这与其他高分辨率的南极地点形成对比，如帕尔默深（南极半岛西部），它对ENSO和SAM强迫都有强烈的反应，使得强迫难以解开。在南极边缘，硅藻（单细胞海藻，硅质细胞壁）的丰度和组合与海冰环境密切相关，是季节性、年际和年代际时间尺度变化的敏感指标。近年来，adsamlie盆地区域卫星获得的海冰浓度与更积极的SAM同步显著增加。在化石记录中，随着SAM变为正值和海冰浓度的增加，硅藻将显示海冰相关分类群的增加，特别是Porosira glacialis和Thalassiosira antarctica之间的丰度比将显著增加到0.1以上（新建立的冬季海冰浓度高于或低于80%的测量值）。我也希望看到相对更多的冰川下层。较负的SAM将反映在较低的海冰浓度上，因此海冰硅藻的数量减少，冰川藻的数量减少。南极洲的比率降到0.1以下。利用硅藻数据，我希望重建过去SAM变异性的时间序列，从而评估最近向正SAM的长期移动是不寻常的还是全新世大气变异性的正常部分。

The Southern Annular Mode (SAM) is the most important factor in atmospheric, hence ocean and climate, variability in the Southern Hemisphere (SH) and, when it is in its so-called positive state, represents a southerly shift and strengthening of the mid-latitude jet and westerly winds. Over the past few decades, a consistent shift towards a positive SAM has been recorded (a persistent southerly shift of the westerlies) that has the potential to significantly modify the characteristics of SH ocean and sea ice systems. This recent trend is concurrent with unprecedented large scale increases in global temperature. In the context of these changes in global temperature, there has been a focus on the Southern Ocean for carbon dioxide sequestration - the potential of the Southern Ocean to sequester atmospheric heat and greenhouse gases is strongly modulated by the position and strength of the mid-latitude westerlies (i.e. the SAM). In light of this current focus it is crucial to place this recent and robust long-term shift towards positive SAM in context. Is this multi-decadal trend in the SAM unusual, or part of natural variability within the SAM? Only geological records can provide proxy time-series of SAM variability over long enough timescales (and beyond instrumental records) to investigate this issue; the annually-laminated Holocene sediments from IODP Site U1357 provide a unique opportunity and scanning electron microscope backscattered electron imagery provides a perfect tool. In February 2010, IODP Expedition 318 to Wilkes Land, Antarctica, recovered an ~200 m-long section of continuously laminated Holocene diatom ooze from the Adélie Basin, Site U1357. This remarkable sediment section represents the only known, fully laminated, Holocene sequence from the Antarctic margin and the longest known Holocene marine sequence from the world ocean. On interannual timescales, the location of Site U1537 makes it less sensitive to El Niño-Southern Oscillation (ENSO) forcing and, hence, a potentially more sensitive recorder of SAM dynamics. This is in contrast to other high-resolution Antarctic sites, such as Palmer Deep (west Antarctic Peninsula), that respond strongly to both ENSO and SAM forcing making forcings difficult to disentangle. Along the Antarctic margin, diatom (single-celled marine algae, siliceous cell walls) abundances and assemblages are intimately linked to sea ice environments and are sensitive indicators of change on seasonal to interannual and decadal timescales. Over recent years, satellite-derived sea ice concentrations in the Adélie Basin region have significantly increased concurrent with the more positive SAM. In the fossil record, as the SAM becomes positive and sea ice concentration increases, diatoms will show an increase in sea ice-related taxa and, in particular, an increase in the ratio of abundance between Porosira glacialis:Thalassiosira antarctica to significantly above 0.1 (newly established measure for winter sea ice concentration being above or below 80%). I would also expect to see relatively more occurrences of P. glacialis sub-laminae. A more negative SAM will be reflected in lower sea ice concentrations, hence less abundant sea ice diatoms and a reduction in the P. glacialis:T.antarctica ratio to below 0.1. Using the diatom data I hope to reconstruct time-series of past SAM variability, hence, to assess whether the recent long-term move towards positive SAM is unusual or a normal part of Holocene variability in the atmosphere.