Tectonic Gateways and Paleogene Southern Ocean Circulation: The Proto-Antarctic Circumpolar Current

强烈的西风驱动着南大洋的南极绕极流（ACC）。 ACC将南极洲热隔离在冷水环中，并通过南极分歧处的上升流将富含营养的温跃层沃茨带到表面。ACC在新生代行星冷却中的作用是未知的，主要是由于关键构造门户开口的时间不确定性。 通过对南大洋大西洋区沉积物岩心的钕同位素测量，揭示了中始新世晚期德雷克海峡开放的早期阶段。 不同的太平洋海水Nd同位素信号的传播到大西洋部门与古生产力代理的增加是我们的假设，即一个原ACC（浅到中间深度）的基础上开发的始新世晚期。 为了验证这一假设，我们将测量Nd同位素从沉积物芯在印度和太平洋部门跟踪新的interocean连接沿着环南极路径的影响。 认识到大西洋和印度部门之间类似的环流模式将有力地支持我们的假设。塔斯马尼亚门户的早期开放历史也是一个重要的古海洋学目标。最近在塔斯曼海的钻探支持两个相互冲突的古循环重建。 "暖情景"表明，塔斯曼海的海水来自低纬度印度洋后，门户打开，而"冷情景"表明高纬度来源。对塔斯曼海隆南部沉积物岩芯的钕同位素测量将检验这些相反的假设。这项研究将提供一个更详细的了解相对于新生代气候演化的ACC的演变。 该项目提供博士后支持和职业发展，其结果将被纳入西摩海洋发现中心（Seymour Marine Discovery Center）的演讲中，该中心是UCSC的一个公共教育设施。

Strong westerly winds drive the Antarctic Circumpolar Current (ACC) in the Southern Ocean. The ACC thermally isolates Antarctica in an annulus of cold water and brings nutrient-rich thermocline waters to the surface through upwelling at the Antarctic Divergence. The role of the ACC in Cenozoic planetary cooling is unknown, largely due to uncertainties in the timing of critical tectonic gateway openings. Neodymium (Nd) isotope measurements from sediment cores in the Atlantic sector of the Southern Ocean have revealed the early stages of Drake Passage opening during the late middle Eocene. The propagation of the distinct Pacific seawater Nd isotope signal into the Atlantic sector in association with increases in paleoproductivity proxies is the basis for our hypothesis that a proto-ACC (shallow to intermediate depths) had developed by the late Eocene. To test this hypothesis, we will measure Nd isotopes from sediment cores in the Indian and Pacific sectors to track the effects of new interocean connections along the circum-Antarctic pathway. The recognition of similar circulation patterns between the Atlantic and Indian sectors will strongly support our hypothesis. The early opening history of Tasmanian Gateway is also an important paleoceanographic objective. Two conflicting paleocirculation reconstructions are supported by recent drilling in the Tasman Sea. The 'warm scenario' suggests seawater in the Tasman Sea was derived from the low latitude Indian Ocean after the gateway opening while the 'cold scenario' suggests a high latitude source. Nd isotope measurements of sediment cores from the south Tasman Rise will test these opposing hypotheses. This study will provide a more detailed understanding of the evolution of the ACC relative to Cenozoic climate evolution. This project provides postdoctoral support and career development, and results will be incorporated into presentations given to docents at the Seymour Marine Discovery Center, a public education facility at UCSC.