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）是地球年际气候变率的最大单一来源，由于大量研究表明，ENSO对大气和海洋表面的温室变暖很敏感，因此我们必须更好地了解ENSO在未来几十年和几个世纪内的反应。对海洋沉积物的研究考察了热带太平洋平均状态的百年至千年尺度的动态，但这些结果大多缺乏确定ENSO波段（2-7年）内变率所需的时间分辨率。珊瑚保存了海洋表面温度和上升流的记录在它们每年带状的文石骨架中，因此可以用于与ENSO一致的光谱频率。这项研究的结果将广泛有助于我们理解ENSO在一段时间内的性质，这段时间被认为是人为变暖世界的最新模拟。该研究项目将从多米尼加共和国古拉博地层的原始珊瑚化石中产生大约半个世纪的月分辨氧和碳同位素比率记录，作为中新世晚期ENSO变化的测试。该记录将允许研究人员测试中新世太平洋的三种状态：根深蒂固的厄尔尼诺条件，根深蒂固的拉尼娜条件，或现代ENSO模式。这些结果也可能对中美洲海道（CAS）最终关闭之前的流量建模产生影响。3.5 ma前后，中美洲地峡的完全形成（和CAS的关闭）导致了东太平洋和加勒比地区物种灭绝和物种形成的脉冲，并可能通过海洋环流的变化对北半球的冰川作用做出了贡献。然而，对这些影响的模拟受到通过CAS的流动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宽度和窗台深度的模糊性。一名来自康奈尔学院（一所小型的四年制文理学院，没有研究生课程）的本科生将通过积极参与该项目的各个方面，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.