OCE-PRF: Constraints on sea-level change over four glacial cycles through uranium-series dating of submerged Bahamian cave deposits

在最近的地质史上，地球的气候在冰河时代和像现在这样的暖期之间波动。这些冰期周期发生在大约10万年的时间尺度上，以全球海平面100米尺度的变化为标志，以回应大型大陆冰盖的增长和后退。冰河时代海平面波动的时间、持续时间和幅度在很大程度上受到地球表面温度变化的控制，这些变化是由于地球围绕太阳的轨道的变化以及大气中导致全球变暖的温室气体的数量造成的。我们对地球轨道和导致海平面变化的温室气体之间的复杂相互作用的理解仍然不完整。被称为洞穴的沿海洞穴沉积对过去的海平面变化提供了罕见但有价值的限制。洞穴提供了海洋表面位置的上限，因为它们是由洞穴滴水形成的，当淹没在海平面以下时不能生长，可以使用U-Th测年或地质年代学进行准确的测年。对于这个项目，研究人员将产生一个新颖的、基于洞穴的海平面记录，可以追溯到大约40万年前，涵盖最后四个冰川周期。这个项目将提高我们对冰河时代周期期间海平面变化的基本物理过程的理解，进而推动全球变暖中海平面的上升。这是一个及时的话题，因为“海平面变化的速度、机制、影响和地理变异性是什么？”已被美国国家科学院2015-2025年海洋科学十年调查重点列为八个优先科学问题之一。该项目将利用20世纪80年代末至90年代初巴哈马沿海目前被淹没的洞穴(蓝洞)中发现的大量洞穴，这些洞穴位于当前海平面以下4至77米的深度。这样的记录极其罕见，需要多年昂贵而危险的野外工作，并与有经验的洞穴潜水员进行协调。在实施该项目时，国际地球物理研究所将有机会利用(1)整个巴哈马的采集(~117个洞穴标本)，其中许多仍未确定年代，(2)最先进的U系列分析设备和(3)明尼苏达大学双城分校的尖端显微分析设备(如微型计算机断层扫描[CT]、电子探针显微分析[EPMA])，以评估生长间歇期边界的物理、化学和岩石学特征，这对于确定海平面上升导致的洞穴淹没的精确时间至关重要。最后，将使用GIA建模对结果进行评估，以便将数据放在全球平均海平面的更广泛背景下。总之，这种方法将极大地提高从基于洞穴的档案中提取的海平面信息的质量，为晚更新世海平面变化的时间和持续时间提供关键的限制。结果将有助于更广泛的海洋科学界做出强有力的海平面预测，以帮助沿海社区的政策制定者、利益攸关方和普通公众适应未来的海平面上升。向公众传播项目成果的潜在途径包括外联努力，如Skype a Science计划，在该计划中，PI有积极的参与记录。PI还将与NOAA的科学球体计划合作，开发数据可视化，有效地向非专业受众传达更新世晚期海平面变化的关键概念。PI还致力于扩大对海洋科学的参与，并将与主办机构合作，通过持续的K-12外展计划，促进包容性的工作环境，并鼓励历史上代表性不足的群体更多地参与STEM。该奖项反映了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。

In recent geologic history, the Earth’s climate has fluctuated between ice ages and warm periods such as the present. These ice age cycles occur on roughly 100,000 year timescales and are marked by 100 meter-scale changes in global sea level in response to the growth and retreat of large continental ice sheets. The timing, duration, and magnitude of ice age sea-level fluctuations is largely controlled by changes in Earth’s surface temperature due to variations in the Earth’s orbit around the sun and the amount of planet-warming greenhouse gases in the atmosphere. Our understanding of the complex interactions between Earth’s orbit and greenhouse gases that drive sea-level change remains incomplete. Coastal cave deposits called speleothems provide rare, but valuable constraints on past sea-level change. Speleothems provide an upper limit on the position of the ocean surface, as they form from cavern dripwaters and cannot grow when submerged below sea level and can be precisely dated using U-Th dating or geochronology. For this project, the researcher will produce a novel, speleothem-based sea level record extending back ~400,000 years, covering the last four glacial cycles. This project will improve our understanding of the fundamental physical processes that drive sea-level change during ice age cycles and, by extension, the sea-level rise in a warming world. This is a timely topic, as “what are the rates, mechanisms, impacts and geographic variability of sea level change?” has been highlighted as one of the eight priority science questions by the National Academy of Sciences’ 2015-2025 Decadal Survey of Ocean Sciences.The project will leverage an extraordinary collection of speleothems recovered from presently-submerged Bahamian coastal caves (blue holes) during the late 1980s/early 1990s at depths ranging from 4 to 77 m below present sea level. Such records are exceedingly rare, requiring many years of expensive and risky fieldwork and coordination with experience cave divers. In pursuing the project, the PI will have access to (1) the entire Bahamas collection (~117 speleothems), many of which remain undated, (2) state-of-the-art U-series analytical facilities and (3) cutting-edge microanalytical facilities available at University of Minnesota – Twin Cities (e.g., micro computed tomography [CT], electron probe microanalysis [EPMA]) to assess the physical, chemical and petrologic characteristics of growth hiatus boundaries, which is crucial for determining the precise timing of cave inundation due to sea-level rise. Finally, the results will be evaluated using GIA modelling to place the data in the broader context of global mean sea level. Taken together, this approach will greatly enhance the quality of sea-level information that can be extracted from speleothem-based archives, providing critical constraints on the timing and duration of late Pleistocene sea level change.Results will be useful to the broader Ocean Sciences community to produce robust sea-level projections to help policymakers, stakeholders and the general public in coastal communities adapt to future sea-level rise. Potential avenues for disseminating project results to the general public include outreach efforts such as the Skype a Scientist program, where the PI has an active record of participation. The PI will also partner with NOAA’s Science on a Sphere program to develop data visualizations that effectively convey key concepts of late Pleistocene sea-level change to a non-specialist audience. The PI is also committed to broadening participation in the Ocean Sciences and will partner with the hosting institution to foster an inclusive work environment and also encourage increased STEM participation from historically underrepresented groups through ongoing K-12 outreach initiatives.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.