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

南半球环形模态（SAM）是南半球（SH）大气、海洋和气候变率中最重要的因素，当它处于所谓的正状态时，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，一个一致的转向积极的SAM已被记录（西风带的持续向南移动），有可能显着修改SH海洋和海冰系统的特性。最近的这一趋势与全球气温前所未有的大规模上升同时发生。在全球气温发生这些变化的背景下，人们一直把重点放在南大洋的二氧化碳封存上--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制。鉴于目前的关注重点，将这种最近和强劲的向积极SAM的长期转变置于背景下至关重要。SAM中的这种数十年趋势是不寻常的，还是SAM中自然变化的一部分？只有地质记录可以提供代理时间序列的SAM变化在足够长的时间尺度（和超越仪器记录）来调查这个问题，每年层合全新世沉积物IODP网站U1357提供了一个独特的机会和扫描电子显微镜背散射电子图像提供了一个完美的工具。2010年2月，前往南极洲威尔克斯地的IODP第318次考察队在阿德利盆地（地点U1357）发现了一段约200米长的连续分层全新世硅藻软泥。这一非凡的沉积物剖面代表了南极边缘唯一已知的、完全分层的全新世层序，也是世界海洋中已知的最长的全新世海相层序。在年际时间尺度上，站点U1537的位置使其对厄尔尼诺-南方涛动（ENSO）强迫不太敏感，因此可能是SAM动态的更敏感记录器。这与其他高分辨率南极站点形成对比，例如帕尔默深海（南极半岛西部），对ENSO和SAM强迫反应强烈，使强迫难以解开。沿着南极边缘，硅藻（单细胞海藻，硅质细胞壁）丰度和组合与海冰环境密切相关，是季节到年际和十年时间尺度变化的敏感指标。近年来，卫星推算的阿德利盆地地区海冰密集度在更积极的SAM的同时显着增加。在化石记录中，随着SAM变为正值和海冰浓度增加，硅藻将显示出与海冰相关的类群的增加，特别是冰川孔链藻与南极海链藻之间的丰度比增加到显著高于0.1（新建立的冬季海冰浓度高于或低于80%的措施）。我还希望看到相对更多的P. glacialis亚层的出现。更负的SAM将反映在较低的海冰浓度，因此海冰硅藻的丰度较低，P. glacialis：T. anaerotica的比例降低到0.1以下。使用硅藻的数据，我希望重建过去的SAM变化的时间序列，因此，评估是否最近长期走向积极SAM是不寻常的或正常的一部分，在大气中的全新世变化。

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.