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

根据海岸沉积物等地质档案重建相对海平面，可以深入了解海平面在一系列地理(地方、区域和全球)和时间(几年到几千年)尺度上的变化。可以利用这些重建来限制海平面变化的长期、前人为部分，这些部分必须被量化，以产生建立沿海社区复原力所需的未来海平面上升的预测。观测记录太短，无法完成这项任务，现有的跨越过去约5000年的重建主要位于北大西洋周围的地点。热带太平洋的记录很少，部分原因是缺乏具有合适沿海沉积物的地点。小岛屿国家更容易受到海平面上升后果的影响，这让热带太平洋缺乏数据变得更加混乱。该项目将利用密克罗尼西亚联邦(密克罗尼西亚联邦丘克、波恩佩、科斯雷)红树林沼泽中沉积的沉积物，几乎连续地重建过去约5000年的相对海平面变化。将这些结果纳入统计框架，将能够对21世纪和22世纪期间密克罗尼西亚联邦的相对海平面变化进行区域范围的预测。这些预测将与密克罗尼西亚联邦和州政府机构和非政府组织等利益攸关方分享，以帮助规划未来海平面上升。还将为本科生、研究生和博士后科学家提供多学科培训。红树林沼泽与潮汐抬升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微生物也是如此。这种对特定海拔的生态偏好使红树林沉积物和有孔虫成为海平面上有价值的替代品。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，沉积了几米长的沉积物序列，可以收集和研究这些序列来重建相对海平面。然而，在大部分热带地区，长期的海平面下降阻碍了沉积物的积累。至关重要的是，密克罗尼西亚联邦长期的构造沉降导致红树林泥炭在过去约5000年里几乎连续堆积。该项目将恢复密克罗尼西亚联邦的沉积物岩心，并通过放射性碳测年以及确认污染和土地利用在岩心下部元素和同位素剖面中的已知年龄变化来确定沉积物积累的历史。保存在埋藏沉积物中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，以使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，以更好地理解短(十年)和长(几个世纪)时间尺度上局部、区域和全球趋势的原因。这项研究使用了一个统计框架，该框架结合了多种不确定性来源，并解释了区域尺度过程(例如，融水指纹和/或海洋动力学)的同时和共同变化的贡献，这项研究将为密克罗尼西亚联邦产生相对海平面预测，并将直接与当地主要利益攸关方分享。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。

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.