Collaborative Research: Multi-proxy sea-level reconstructions and projections in the middle Pacific Ocean

从沿海沉积物等地质档案中重建相对海平面，可以深入了解一系列地理（地方，区域和全球）和时间（几年到几千年）尺度上的海平面变化。这些重建可以用来限制海平面变化的长期、人为活动前的组成部分，这些组成部分必须量化，以预测未来海平面上升，从而建立沿海社区的复原力。观测记录太短，无法完成这项任务，现有的重建跨越过去5000年，主要位于北大西洋周围的网站。热带太平洋的记录很少，部分原因是缺乏合适的沿海沉积物。热带太平洋缺乏数据的另一个原因是，小岛屿国家更容易受到海平面上升的影响。该项目将利用密克罗尼西亚联邦（FSM;楚克、波恩佩、科斯雷）红树林沼泽中沉积的沉积物，对过去约5000年的相对海平面变化进行近乎连续的重建。将这些结果纳入统计框架，就可以对密克罗尼西亚联邦21世纪和22世纪的相对海平面变化作出区域规模的预测。这些预测将与密克罗尼西亚联邦的利益攸关方分享（例如，联邦和州政府机构以及非政府组织），以帮助规划未来的海平面上升。还将向本科生和研究生以及一名博士后科学家提供多学科培训。红树林沼泽与潮汐高度有系统和可量化的关系，生活在红树林沉积物表面并留下化石记录的有孔虫等微生物也是如此。 这种对特定海拔高度的生态偏好使得红树林沉积物和有孔虫成为有价值的海平面替代物。随着相对海平面的上升，红树林沼泽会积累沉积物，以保持其在潮汐框架中的高度。在100到1000年的时间里，沉积物的多米序列可以被收集和研究，以重建相对海平面。然而，在许多热带地区，长期的海平面下降阻止了沉积物的积累。重要的是，密克罗尼西亚联邦长期的构造沉降导致了红树林泥炭在过去约5000年中几乎连续的积累。该项目将在密克罗尼西亚联邦回收沉积物岩心，通过放射性碳测年和确认底层元素和同位素剖面中已知年代的污染和土地使用变化，确定沉积物积累的历史。埋藏沉积物中保存的有孔虫将通过化石组合与现代类似物的定量比较来估计以前的海平面高度。新的重建将与现有的（和更新的）晚全新世相对海平面重建数据库相结合，利用现有的时空模型估计全球平均海平面趋势。该模型还将有助于将相对海平面信号划分为其组成部分，以更好地了解短（十年）和长（世纪）时间尺度上的局部，区域和全球趋势的原因。使用一个统计框架，该框架包含多个不确定性来源，并考虑到区域尺度过程（例如，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Reconstructions of relative sea-level from geological archives such as coastal sediment offer insight into sea-level changes on a range of geographic (local, regional, and global) and time (years to millennia) scales. These reconstructions can be leveraged to constrain the long-term, pre anthropogenic components of sea-level change, which must be quantified to produce projections of future sea-level rise needed to build resilience in coastal communities. Observational records are too short to perform this task and existing reconstructions spanning the past ~5000 years are primarily located at sites around the North Atlantic Ocean. There is a scarcity of records from the tropical Pacific Ocean, in part due to a lack of sites with suitable coastal sediment. Confounding the lack of data in the tropical Pacific Ocean is the heightened vulnerability of small island nations to the consequences of sea level rise. This project will produce near-continuous reconstructions of relative sea-level change during the past ~5000 years using sediment that was deposited in mangrove swamps in the Federated States of Micronesia (FSM; Chuuk, Pohnpei, Kosrae). Incorporation of the results into a statistical framework will allow regional-scale projections of relative sea level change in FSM during the 21st and 22nd centuries to be developed. These projections will be shared with stakeholders in FSM (e.g., federal and state government agencies and non-governmental organizations) to help plan for future sea level rise. Multi-disciplinary training will also be provided to undergraduate and graduate students and a postdoctoral scientist.Mangrove swamps have a systematic and quantifiable relationship to tidal elevation, as do micro-organisms such as foraminifera that live on the sediment surface in mangroves and leave a fossil record. This ecological preference for specific elevations makes mangrove sediment and foraminifera valuable sea-level proxies. As relative sea level rises, mangrove swamps accumulate sediment to preserve their elevation in the tidal frame. Over 100s to 1000s of years, multi-meter sequences of sediment are deposited that can be collected and studied to reconstruct relative sea level. In much of the tropics, however, long-term sea-level fall prohibits the accumulation of sediment. Crucially, long-term tectonic subsidence in FSM has resulted in near-continuous accumulation of mangrove peat over the past ~5000 years. This project will recover sediment cores in FSM and establish a history of sediment accumulation through radiocarbon dating and recognition of pollution and land-use changes of known age in downcore elemental and isotopic profiles. Foraminifera preserved within the buried sediment will be used to estimate the height of former sea-level through quantitative comparison of fossil assemblages with modern analogs. The new reconstructions will be combined with an existing (and updated) database of late Holocene relative sea-level reconstructions to estimate global mean sea-level trends using an existing spatio-temporal model. This model will also facilitate partitioning of the relative sea level signal into its constituent parts to better understand the causes of local, regional, and global trends on short (decadal) and long (multi century) timescales. Using a statistical framework that incorporates multiple sources of uncertainty and accounts for simultaneous and co varying contributions from regional scale processes (e.g., meltwater fingerprints and/or ocean dynamics), this research will produce relative sea-level projections for FSM that will be shared directly with key local stakeholders.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.