Collaborative Research: Interglacial climate in Bermuda and beyond

该项目将评估美国东海岸和加勒比地区过去一个关键的温暖气候时期--最后一次间冰期(MIS5e，130-11.6万年前)的海洋表面温度的变化。最后一次间冰期通常被认为是与预期的近期气候变化有关的最好的过去类比之一，因为全球海洋表面温度比今天略高，海平面上升了几米。此外，由于最后一次间冰期在地质上是最近的，保存完好的化石在贝壳的化学成分中记录了古气候信息，因此相对丰富。之前已经进行了绘制北大西洋过去海面温度的努力，但美国东海岸和远在1000公里外的海域存在着一个明显的数据差距。目前有超过4000万人生活在美国大西洋沿岸和加勒比海地区。除了气候变暖的直接影响外，沿海海温变暖还会加强大西洋飓风，增加对沿海基础设施的破坏。因此，在全球变暖的情况下，提高我们对沿海水温可能升高的认识具有重要的社会意义。通过研究最后一次间冰期的时间间隔，可以从化石中获得区域温度估计，这将有助于揭示这个人口稠密地区的海洋温度可能变暖多少。该项目将从海侵海滩沉积中发现的保存完好的软体动物化石和可追溯到最后一次间冰期的古生物礁沉积中产生新的高分辨率古温度重建。研究小组将进行实地工作，从百慕大、巴哈马群岛和美国东海岸从佛罗里达群岛到马萨诸塞州海角的多个地点的间冰期沉积序列中收集软体动物化石样本。收集的贝壳将被分析其稳定和成团的同位素组成，以确定过去的温度和每个地点海水的氧同位素组成(d18Osw；与盐度有关)。块状同位素古温度计代表了传统方法的进步，将产生更可靠的古气候信息，而不需要假设过去的d18Os值。由此得到的间冰期古温度和d18Osw的盆地尺度地图将有助于相互比较、模型替代和古今未来比较，并寻找间冰期中期融水事件的证据。较大的贝壳将以亚年度分辨率进行采样，以确定不同纬度温度的古季节性。因此，这项研究不仅应该得出研究区域间冰期水文的空间模式，而且将是第一次在季节时间尺度上这样做。在百慕大，还将对过去多个间冰期的间冰期沉积物进行采样，以比较较强和较弱的间冰期。作为该项目的一部分，一名或多名研究生和多名本科生将接受高级地球化学技术、野外工作和数据分析方面的培训。将通过密歇根州的科学活动将与化石和现代贝类有关的参与活动带给中小学生。该项目将支持两名早期职业科学家，他们将得到一名高级联合首席研究员的指导。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project will assess the variability of ocean surface temperatures along the U.S. East Coast and in the Caribbean for a key past warm climate period, the Last Interglacial (MIS 5e, 130-116,000 years ago). The Last Interglacial period is often thought to be one of the best past analogs to study in relation to expected near-future climate change because global sea surface temperatures were slightly warmer than today, and sea level was several meters higher. Additionally, because the Last Interglacial was geologically recent, well-preserved fossils that record paleoclimate information in the chemistry of their shells are relatively abundant. Previous efforts to map past sea surface temperatures across the North Atlantic have been undertaken, but a glaring data gap exists along the U.S. East Coast and as far as 1000 km out to sea. More than 40 million people currently live along the U.S. Atlantic seaboard and in the Caribbean. In addition to the direct impacts of a warmer climate, warming coastal sea temperatures can also strengthen Atlantic hurricanes, increasing damage to coastal infrastructure. Thus, it is of societal importance that we improve our knowledge of the potential for coastal water temperatures to increase in a warming world. By studying the Last Interglacial time interval, regional temperature estimates can be obtained from fossils that will help reveal how much ocean temperatures could potentially warm in this highly-populated region. This project will produce new high resolution paleotemperature reconstructions from well-preserved fossil mollusks found in transgressive beach deposits and raised paleo-reef deposits that are dated to the Last Interglacial. The research team will conduct field work to gather fossil mollusk samples from sedimentary sequences of interglacial age in Bermuda, the Bahamas, and multiple localities along the US East Coast from the Florida Keys up to the Massachusetts Cape. Collected shells will be analyzed for their stable and clumped isotopic compositions to determine past temperature and the oxygen isotopic composition of seawater (d18Osw; related to salinity) at each locality. The clumped isotope paleothermometer represents an advancement over traditional methods and will produce more robust paleoclimate information without the need to assume past d18Osw values. The resulting basin-scale map of interglacial paleotemperature and d18Osw will be useful for inter-proxy, model-proxy, and paleo-modern-future comparisons and to look for evidence of mid-interglacial meltwater events. Larger shells will be sampled at sub-annual resolution to determine paleo-seasonality in temperature at different latitudes. This research should thus not only yield a spatial pattern of interglacial hydrography in the study region but will be the first to do so at the seasonal time scale. In Bermuda, interglacial deposits from multiple past interglacials will also be sampled to compare stronger and weaker interglacial periods. As part of this project, one or more graduate students and multiple undergraduates will receive training in advanced geochemical techniques, field work and data analysis. Engaging activities relating to fossil and modern seashells will be brought to elementary and middle school students through science events in Michigan. The project will support two early career scientists who will receive mentoring from a senior co-principal investigator.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.