Collaborative Research: P2C2--Extending Tree-Ring Based Reconstructions of Atlantic Gulf Basin Hydroclimate over the Common Era Using Old-Growth Sinker Wood

这项研究的总体目标是从19世纪末和20世纪初被砍伐的树木中收集年老的秃柏树和长叶松样本，以延长现有的秃柏树年轮在整个共同时代的年表。Baldcypress是美国东南部基于年轮的气候重建的关键树种之一，因为它的寿命长，对春夏季降水变化具有明显的敏感性。尽管它在区域和大陆尺度的高分辨率古气候研究中得到了广泛的应用，但其树气候学潜力的全部时空范围尚未得到探索。特别是缺乏残存的古老的秃顶柏树和长寿的树木，导致大西洋湾盆地（AGB）缺乏千年长度的年表。在19世纪和20世纪，整个AGB的原始森林，包括秃柏树和长叶松林，因蓬勃发展的建筑业而被过度开采，很少有森林幸存下来。在这一商业开发期间，许多原木在从沼泽采伐地到磨坊的运输过程中丢失，卡在河流拐弯处。一个世纪后，在许多AGB河流和滑坡的底部可以找到这种长寿的“下沉木”的贮藏，形成了唯一可靠的原始木材来源，也是扩大AGB树木年代学时空范围的独特来源。研究人员的目标是使用扩展的年表来开发跨越整个共同时代（1CE-present）的区域和季节性AGB水文气候重建。在年际至年代际尺度上，以白松为基础的重建结果表明，夏季AGB水文气候变化主要受大西洋多年代际变率（AMV）的影响。由此产生的AGB水文气候重建将以过去AMV的现有重建为基础，在三个重要方面：(a)时间扩展，(b)空间扩展和(c)分季节分辨率。常见的年代长度重建可以提高对过去全球尺度气候变率时期的区域表达的理解，特别是古小冰河期晚期（约536-660 CE）和罗马气候最佳期（约300 BCE -400 CE）。此外，AGB重建将为亚热带地区提供重要的锚点，而亚热带地区通常在陆地代理网络中代表性不足。此外，通过开发独立的早、晚木材宽度年表，研究小组计划在亚季节分辨率上重建AGB水文气候变率，这有助于提高对大尺度海洋-大气强迫气候的动力性质的认识。潜在的更广泛的影响包括加深对美国东南部水资源的了解，支持博士后研究人员，在亚利桑那大学开设以项目为基础的本科生研究经验课程，旨在吸引代表性不足的学生进行科学研究，以及为当地学校提供外联和实地考察。该奖项反映了美国国家科学基金会的法定使命，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。

The general goal of the research is to collect old-growth bald cypress and longleaf pine samples from trees that were cut in the late 19th and early 20th century to extend existing bald cypress tree-ring chronologies over the full Common Era.Baldcypress is one of the key tree species for tree-ring based climate reconstruction in the southeastern United States (U.S.), because of its longevity and its distinct sensitivity to spring and summer precipitation variability. Even though it has widespread applications in regional and continental-scale high-resolution paleoclimate research, the full spatiotemporal extent of its dendroclimatic potential is yet to be explored. The lack of remnant old-growth bald cypress stands with long-lived trees, in particular, contributes to the dearth of millennium-length chronologies in the Atlantic Gulf Basin (AGB). In the 19th and 20th century, old-growth forests, including bald cypress and longleaf pine stands, throughout the AGB were excessively exploited for the booming construction industry and few forests survived. During this commercial exploitation period, many logs were lost, stuck in river bends, in transport from the swamp harvest location to the mill sites. A century later, caches of such long-lived ‘sinker wood’ can be found on the bottoms of many AGB rivers and slips, forming the only reliable source of old-growth timber and a unique source for expanding the spatiotemporal reach of AGB dendrochronology.The researchers aim to use the extended chronologies to develop regional and seasonal AGB hydroclimate reconstructions that span the entire Common Era (1CE-present). On the interannual to decadal time scales best captured by bald cypress-based reconstructions, summer AGB hydroclimate variability is primarily influenced by Atlantic Multidecadal Variability (AMV). The resulting AGB hydroclimate reconstruction will build upon existing reconstructions of past AMV in three important ways: (a) temporal extension, (b) spatial extension, and (c) sub-seasonal resolution. Common Era-length reconstructions could improve the understanding of the regional expression of past periods of global-scale climate variability, specifically the Late Antique Little Ice Age (ca. 536-660 CE) and the Roman Climate Optimum (ca. 300 BCE -400 CE). Moreover, AGB reconstructions would provide important anchor points in the subtropics, a region typically underrepresented in terrestrial proxy networks. Furthermore, by developing independent earlywood and latewood width chronologies, the research team plans to reconstruct AGB hydroclimate variability at sub-seasonal resolution, which can help improve the understanding of the dynamical nature of large-scale ocean-atmosphere forcing of climate.The potential Broader Impacts include greater understanding of water resources in the southeastern United States, support for a post-doctoral researcher, a project-based undergraduate research experience course at the University of Arizona aimed at attracting under-represented students to scientific research, and outreach and field trips to the for local schools.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.