Diatom Silica Oxygen Isotope Records from the Late Quaternary Antarctic Margin

南极洲及其冰盖已经并将继续在全球海洋-大气系统中发挥重要作用，因此，至关重要的是，我们必须充分了解南极洲及其冰盖过去的行为，以期了解它们在气候变暖下未来的潜在变化。南大洋是世界海洋热盐环流的关键组成部分，海洋周围热量和盐的重新分配是调节快速气候转变过程的组成部分。计算机模拟结果表明，充足的融水输入到南极大陆架区域，能够停止南极洲寒冷、含盐深水的形成，从而破坏了热盐环流和北半球海洋-气候系统的平衡。为了进一步研究这些源自南极洲的过程，有必要了解从南极冰盖穿过大陆边缘海进入南大洋的海洋气候信号的传递机制。在过去十年中恢复的保存非常完好的南极边缘沉积物岩心，包含了这些冰-海洋-气候相互作用的优秀档案，通常是在季节时间尺度上，从上一个冰河时代结束到整个最近的温暖间冰期（全新世）。岩心在脱冰作用时期呈季节性层状，在全新世时期呈间歇性层状，层状以浮游硅藻（藻类）化石为主；个别种类对海面情况敏感，包括海冰浓度、淡水流入和开阔海洋对边缘的影响。在末次冰期之后，这些全新世南极沉积物记录了长达数十年至数千年的气候波动，无论这些波动是由何种环境强迫机制造成的，这些变化可能首先在南极沿海地区感受到，而本研究提出的岩心位于记录这些变化的最佳位置。硅藻氧同位素测量是一种未充分利用的技术，它提供了一种在高纬度环境中获得氧同位素记录的手段。硅藻氧同位素的测量是湖泊历史研究中广泛使用的替代方法，然而，迄今为止，使用海洋硅藻氧同位素记录的尝试要少得多。已经进行的研究表明，极地和亚极地水域的硅藻氧同位素测量对表层海洋环境参数（如盐度、淡水输入和海面温度）的变化很敏感。这里提出的研究将是第一次尝试从南极边缘获取硅藻氧同位素记录，南极边缘是一个对南极冰盖的盛衰敏感的地区，就融化的水流入南大洋而言。我们建议通过对特定季节硅藻类群（即在春季或秋季特别繁盛的硅藻物种）的硅藻氧同位素测量，与来自融化的陆地冰或海冰的相对淡水流入海岸相关联，研究自最后一个冰川期以来南极边缘的季节性演变，以及产生沉积物记录的过程。我们还希望表明，硅藻氧同位素测量值在最后一个冰期结束时将会很低，因为大量的旧冰盖正在融化，而在全新世的温暖时期，当冰盖处于最小值时，测量值将会更高。

Antarctica and its ice sheets have played, and continue to play, a major role in the global ocean-atmosphere system, hence, it is critical that we have a sound understanding of the past behaviour of Antarctica and it's ice sheets with a view to understanding their potential future variability under a warming climate. The Southern Ocean is a key component of the thermohaline circulation of the world's oceans and the re-distribution of heat and salt around the oceans is integral to processes that regulate rapid climate transitions. Computer modelling results have shown that sufficient melt water input to the Antarctic continental shelf area is capable of shutting down the formation of cold, salty deep water in Antarctica hence upsetting the balance of the thermohaline circulation and the ocean-climate system of the Northern Hemisphere. In order to further investigate these processes that originate in Antarctica, it is necessary to understand the transfer mechanisms of ocean-climate signals from the Antarctic ice sheets, across the continental margin seas, into the Southern Ocean. Exceptionally well-preserved Antarctic margin sediment cores, recovered during the last decade, contain an excellent archive of these ice-ocean-climate interactions, often on seasonal timescales, from the end of the last ice age and throughout the recent warm interglacial (the Holocene). The cores are seasonally layered through the deglaication, intermittently layered through the Holocene, and the layers are dominated by fossil planktonic diatoms (algae); individual species of which are sensitive to sea surface conditions including sea ice concentration, fresh water influx, and open ocean influence upon the margin. Following the last ice age, these Holocene Antarctic sediments record climate fluctuations of tens to thousands of years long and whatever environmental forcing mechanism is responsible for these fluctuations, the changes are likely to be felt in the Antarctic coastal regions first, and the cores proposed for this research are located in prime positions to record these changes. Diatom oxygen isotope measurements represent an under-utilised technique that provides a means of obtaining oxygen isotope records in high latitude environments. The measurement of oxygen isotopes in diatoms is a widely used proxy in the study of the history of lakes, however, to date there have been many fewer attempts to use records of diatom oxygen isotopes in the oceans. Studies that have taken place have demonstrated the sensitivity of diatom oxyegn isotope measurements in polar and sub-polar waters to changes in surface ocean environmental parameters such as salinity, freshwater input and sea surface temperature. The research proposed here will be the first attempt to produce diatom oxygen isotope records from the Antarctic margin, a region sensitive to the waxing and waning of the Antarctic ice sheets in terms of melt water through-put to the Southern Ocean. We propose to investigate the evolution of seasonality along the Antarctic margin since the last ice age, and also the processes involved in producing the sediment record, by relating diatom oxygen isotope measurements on season-specific diatom taxa (i.e. diatom species that thrived particularly in spring or autumn) to relative freshwater influx to the coast, from either melted terrestrial ice or sea ice. We also hope to show that the diatom oxygen isotope measurements will be low at the end of the last ice age, as a large quantity of old ice sheets were melting, and will be higher during warmer time periods of the Holocene when ice sheets were at a minimum.