Paleogene Climate and Deep-water Evolution in the Southwest Atlantic: Seismic Reflection and Coring Investigations in Support of IODP Proposal 862-Pre

今天的西南大西洋是一个关键区域：㈠太平洋和大西洋盆地之间的深水沃茨通过南极绕极流连通; ㈡南极边缘产生的深水沃茨扩散，填充海洋盆地的最深处。ACC是地球上最大的洋流系统，绕南极大陆顺时针方向畅通无阻。横跨德雷克海峡（南极洲和南美洲之间的一个狭窄但很深的海槽），ACC的平均运输量是巨大的，估计为每秒1亿至1.5亿立方米。因此，ACC是太平洋和大西洋之间水面和深水交通的主要管道。如果没有这种联系，全球翻转环流就不可能，在现代海洋中，它调节着全球热，盐，营养物质的运输，我们提出的项目旨在解决有关古近纪时间间隔的几个基本问题（约6600万至2300万年前），几十年来一直让海洋地质学家和古气候学家感到沮丧：ACC是什么时候开始的？它的建立对南极气候、翻转环流和全球纬向热量输送有什么影响？ACC的发展是3400万年前南极冰川形成的触发因素，还是其作用完全次于大气二氧化碳水平下降？对这些问题的新认识只能通过在关键区域的新地质研究来获得，例如西南大西洋。西南大西洋以前的古海洋学研究的一个主要问题是缺乏一个深度样带的网站，故意定位追踪古近纪水体性质的变化。在这一区域，复杂的海底水深测量限制和控制了与ACC相关的深水沃茨和舌状源底层沃茨的流动。在这一领域的深通道的演变，其连接到现代模式的深水环流的逐步发展，是unknow.We建议UK-IODP现场调查调查（SSI）进行地震反射调查和活塞取芯业务的福克兰高原东部地区的亚南极西南大西洋。这些调查数据将与阿尔弗雷德·韦格纳研究所（AWI）的同行巡航一起，为新的国际海洋发现计划（IODP）探险制定一个完整的建议，以钻探一个深度样带。这些地点被选为地质水质量测量站，将允许通过古近系深水循环模式的重建。我们的主要目的是测试长期存在的关于大气二氧化碳减少和ACC启动在驱动新生代冷却和南极冰川作用开始方面的相对作用的相互竞争的假设。UK-IODP SSI数据集以及AWI领导的同伴巡航获得的数据将有助于对深水沉积过程的新理解，漂流沉积和底流侵蚀的历史，结合深水水流的演变，以及西南大西洋的沉积特征。UK-IODP SSI和AWI巡航的综合结果将作为大型海洋地质学家和古海洋学家社区感兴趣的独立，可扩展的数据集，并为英国领导的IODP钻井提案提供坚实的基础，以便计划在南大西洋进行JOIDES Resolution操作。

The present-day Southwest Atlantic Ocean is a key region for: (i) the communication of deep waters between the Pacific and Atlantic ocean basins via the Antarctic Circumpolar Current (ACC); and (ii) the dispersal of deep waters produced on the Antarctic margin that fill the deepest parts of the ocean basins. The ACC is the largest oceanic current system on Earth and flows unimpeded clockwise around the Antarctic continent. Across the Drake Passage (a narrow, but deep trough between Antarctica and South America) the average volume transport of the ACC is enormous, estimated at 100 to 150 million cubic meters per second. The ACC is therefore the major conduit for surface and deep-water communication between the Pacific and Atlantic Oceans. Without this connection, global overturning circulation would not be possible, which, in the modern ocean, regulates the global transport of heat, salt, nutrients, and carbon and has a significant influence on global climate across all timescales.Our proposed project is developed to tackle several fundamental questions concerning the Paleogene time interval (~66 to 23 million years ago) that have frustrated marine geologists and palaeoclimatologists for decades: When was the ACC initiated? What was the impact of its establishment on Antarctic climate, on overturning circulation, and global latitudinal heat transport? Did the development of the ACC serve as the trigger for the initiation of Antarctic glaciation 34 million years ago or was its role completely secondary to that of declining atmospheric carbon dioxide levels? New insight into these problems can only be gained through new geological studies in key areas, such as the Southwest Atlantic Ocean.A major problem with previous palaeoceanographic studies in the Southwest Atlantic has been the lack of a depth-transect of sites, purposely situated to trace Paleogene changes in water mass properties. In this region, complex seafloor bathymetry restricts and controls the flow of both deep waters associated with the ACC and Antarctic-sourced bottom waters. The evolution of the deep passageways in this area, and their connection to the progressive development of the modern patterns of deep-water circulation, are unknown.We propose a UK-IODP Site Survey Investigation (SSI) to undertake seismic reflection survey and piston coring operations on the eastern Falkland Plateau region of the sub-Antarctic southwest Atlantic Ocean. Together with a companion Alfred Wegener Institute (AWI) cruise, these survey data will allow development of a full proposal for a new International Ocean Discovery Program (IODP) expedition to drill a depth transect of sites. These sites have been chosen to serve as a geological water mass gauging station that will allow reconstruction of deep-water circulation patterns through the Paleogene. Our primary aim is to test long-standing competing hypotheses on the relative roles of declining atmospheric carbon dioxide and the initiation of the ACC in driving the onset of Cenozoic cooling and Antarctic glaciation.The UK-IODP SSI datasets, together with data derived from the companion cruise led by AWI, will contribute new understanding of deep-water sedimentary processes, the history of drift sedimentation and bottom-current erosion in conjunction with the evolution of deep-water flow, and sediment characteristics of the Southwest Atlantic Ocean. The combined results of the UK-IODP SSI and AWI cruises will function as stand-alone, publishable datasets of interest to a large community of marine geologists and palaeoceanographers, and provide a robust foundation for a UK-led IODP drilling proposal in time for planned JOIDES Resolution operations in South Atlantic.