Assessing the Viability of Pristine Fossil Corals from the Dominican Republic as Indicators of ENSO at the Miocene/Pliocene Boundary

厄尔尼诺-南方涛动(ENSO)是地球上年际气候变率的最大来源，由于许多研究表明ENSO对大气和表层海洋的温室效应变暖非常敏感，因此我们必须更好地了解ENSO在未来几十年和几个世纪可能如何响应。对海洋沉积物的研究考察了热带太平洋平均状态百年至千年尺度的动态，但这些结果大多缺乏必要的时间分辨率，无法确定ENSO波段(2年至7年)内的可变性。珊瑚保存了它们每年带状的文石骨架中的海表面温度和上升流的记录，因此可以用于与ENSO一致的光谱频率。这项研究的结果将有助于我们广泛了解ENSO的性质，这段时间被认为是人类变暖世界的最新模拟。研究项目将从多米尼加共和国Gurabo组的原始化石珊瑚中产生大约半个世纪长的月分辨氧和碳同位素比率记录，作为对最近中新世ENSO变异性的测试。这一记录将允许研究人员测试中新世太平洋的三种可能状态：根深蒂固的厄尔尼诺条件、根深蒂固的拉尼娜条件或现代的ENSO模式。这一结果也可能对中美洲海道(CAS)最终关闭前的水流建模产生影响。在3.5 Ma左右，中美洲地峡的完全形成(以及CAS的关闭)导致东太平洋和加勒比海都出现了物种灭绝和物种形成的脉冲，并可能通过改变海洋环流来促成北半球的冰川作用。然而，这些影响的模拟受到流经CAS的水流性质仍然存在相当大的不确定性的限制，这主要是由于围绕开口的宽度(S)和基床的深度的模棱两可。康奈尔学院(一所小型的四年制文科学校，没有研究生课程)的一名本科生将通过积极参与该项目的所有方面，包括在全国会议上展示结果，接受古气候学研究方法的高级培训。

The El Nino-Southern Oscillation (ENSO) represents the single largest source of interannual climate variability on Earth, and because numerous studies have suggested that ENSO is sensitive to greenhouse warming of the atmosphere and surface ocean, it is critical that we better understand how ENSO may respond over coming decades and centuries. Studies of marine sediments have examined centennial- to millennial-scale dynamics of the mean state of the tropical Pacific, but these results have mostly lacked the temporal resolution necessary to identify variability within the ENSO band (2-7 yr). Corals preserve records of sea surface temperature and upwelling in their annually-banded aragonite skeletons, and thus can be used for spectral frequencies consistent with ENSO. The results of this study will contribute broadly to our understanding of the nature of ENSO during a time period considered the most recent analog for an anthropogenically-warmed world.The research project will generate a roughly half-century-long record of monthly-resolved oxygen and carbon isotopic ratios from a pristine fossil coral from the Gurabo Formation of the Dominican Republic as a test of ENSO variability in the latest Miocene. The record will allow the researchers to test three proposed states of the Pacific during the Miocene: entrenched El Nino conditions, entrenched La Nina conditions, or a modern ENSO pattern. The results may also have implications for modeling of flow through the Central American Seaway (CAS) prior to its final closure. Complete formation of the Central American Isthmus (and closure of the CAS) around 3.5 ma led to pulses of extinction and speciation in both the eastern Pacific and the Caribbean, and may have contributed to Northern Hemisphere glaciation through changes to ocean circulation. However, modeling these effects are limited by the still considerable uncertainties in the nature of flow through the CAS, largely owing to ambiguities surrounding the width of the opening(s) and depth of the sill. An undergraduate student from Cornell College (a small, four-year liberal arts school with no graduate programs) will receive advanced training in paleoclimatology research methods by actively participate in all aspects of this project, including presentation of results at a national meeting.