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.