Bering Sea diatom isotope records during the onset of Northern Hemisphere Glaciation

上新世晚期北半球冰盖的逐渐推进和第四纪间冰期-间冰期旋回的发展标志着地球气候史上一个重要的开端。特别值得注意的是与北半球大冰期（约2.85-2.73 Ma）开始有关的转变，当时格陵兰岛、欧亚大陆和北美洲出现了大冰原。调查这段时间内发生的变化是了解全球气候系统长期功能和时间变率的一个关键目标。在温室气体浓度增加的情况下，上新世及其期间的气候事件有可能成为未来全球变暖的类似物，这进一步强调了这一点。尚待详细考虑的一个方面是北大西洋以外的高纬度海洋位置的作用。特别是，由于沉积物记录中缺乏其他上新世岩心和/或碳酸盐化石，对北太平洋地区的认识主要局限于西北亚北冰洋的ODP站点882。来自该地区的其他记录的缺乏意味着ODP站点882记录与融水输入的时间及其对水柱的影响之间的空间代表性仍然未知。特别是，生物泵在这段时间内的响应以及随后在冰期-间冰期旋回中的变化是不受约束的。IODP第323次考察（2009年7月至9月）代表了对白令海上新世/第四纪的第一次重要尝试。在对收集到的岩心进行分析的同时，由于缺乏2.0 Ma之前的碳酸盐化石，对上新世/早第四纪的大部分区域进行同位素记录的工作受到了阻碍。该项目旨在通过测量白令海U1341站点3.2-2.5 Ma硅藻d13C， d18O和d30Si来解决这个问题。位于鲍尔斯山脊西侧海冰范围的南部，该位置适合监测最终将通过阿留申岛弧输送到北太平洋的水的变化。这些结果将补充考察队正在进行的工作，从而可以评估太平洋和白令海之间在融水流入和生物泵方面的联系。建立对后者的理解对于确定海洋在这段时间内调节大气二氧化碳浓度方面的作用至关重要。

The progressive advancement of ice-sheets across the Northern Hemisphere in the late Pliocene and the development of glacial-interglacial cycles which punctuate the Quaternary era marks a significant threshold in the Earth's climate history. Of particular note are the transitions associated with the onset of major Northern Hemisphere Glaciation (NHG), c. 2.85-2.73 Ma, when large ice-sheets developed across Greenland, Eurasia and Northern America. Investigating the changes that occurred over this time-frame represents a key objective for understanding the long-term functionality and temporal variability of the global climate system. This is further emphasised by the potential for the Pliocene and the climatic events within it to act as an analogue for future global warming under enhanced greenhouse gas concentrations. One aspect yet to be considered in detail is the role of high latitude marine locations outside of the North Atlantic Ocean. In particular, knowledge on the North Pacific region is primarily restricted to ODP Site 882 in the North West Subarctic Ocean, due to an absence of other Pliocene cores and/or carbonate fossils in sediment records. The paucity of other records from the region means that it remains unknown how spatially representative the ODP Site 882 record is in relation to the timing of meltwater inputs and their impact on the water column. In particular, the response of the biological pump over this interval and subsequent changes in glacial-interglacial cycles is unconstrained. IODP Expedition 323 (July to September 2009) represents the first significant attempt to investigate the Pliocene/Quaternary in the Bering Sea. Whilst work is ongoing to analyse the collected cores, efforts to generate isotope records are hindered for large sections of the Pliocene/Early Quaternary by a lack of carbonate fossils prior to c. 2.0 Ma. This project aims to address this by measuring diatom d13C, d18O and d30Si from 3.2-2.5 Ma at Site U1341 in the Bering Sea. Situated south of the sea-ice extent at the western flank of Bowers Ridge, the location is suitable for monitoring changes in waters which will ultimately be transported into the North Pacific Ocean across the Aleutian Island Arc. Results, complementing ongoing work by the Expedition Party, will permit an assessment of linkages between the Pacific Ocean and Bering Sea with regards to meltwater influx and the biological pump. Establishing an understanding of the latter is critical for determining the role of the oceans in regulating atmosphere CO2 concentrations over this time-frame.