Jessie Pearl Abstracts
Jessie Pearl
Ph.D. Candidate
Global Change GIDP
World Dendrochronology Conference
Thimphu, Bhutan
June 2-22, 2018
High-resolution paleoclimate records are essential for improving detection and attribution of internal and forced climate system responses. The densely populated northeastern United States is at high risk from increasing temperatures, droughts, and extreme precipitation events. The region has limited annual and seasonal-scale proxy climate records beyond the instrumental record. Atlantic white cedar, a wetland conifer found within 200km of the Atlantic coastline of the United States, is a promising new temperature proxy that can fill in these data gaps. However, certain cedar chronologies contain multivariate climate signals. Here, we present a dense network of Atlantic white cedar tree ring chronologies across the northeastern United States and demonstrate how site selection is extremely important for regional paleoclimate reconstructions. Ring width variability reflects winter through summer temperatures at inland and ‘hydrologically stable’ sites in the northernmost section of the species’ range. Ombrotrophic sites along the coast of the Northeast contain hydrologic signals and correlate with growing season precipitation. We demonstrate skillful climate reconstructions for the last several centuries and the potential to use sub-fossil samples to extend these records over the entire Common Era. This comprehensive understanding of the species’ climate sensitivity and environment leads to a tree-ring network that provides the long-term context at multi-decadal and centennial time scales for the large-scale ocean-atmospheric processes that influence the climate of the region.
Abstract for Lay Audience
To adequately predict future climate and ensure the resilience of our Earth, we need to better understand the geological, climatological, and biological systems of the past. Paleoclimate (past climate) data provide opportunities to observe the climate system at timescales that are not available using instrumental data. The densely populated Boston to New York corridor is vulnerable to many climate-change related risks, notably sea level and temperature rise, but lacks precise temperature, precipitation, and drought records prior to the era of instrumental data. Many climatological phenomena in the Northeastern United States (the ‘Northeast’) are thought to have periodicities of a century or longer, therefore short instrumental records of only 100 years are insufficient to characterize return intervals or the range of variability. Reconstructing past conditions requires “proxy” data: data in the natural system that can approximate direct measurements. To address the significant paleoclimate data gap in the Northeast, I create climate records using tree-ring width and geochemistry from living and preserved (“sub-fossil”) Atlantic white cedar forests.
Trees are incredible climate proxies; each year they put on an annual ring that contains information about that years’ growing environment. As such, tree-ring width records can give us annually resolved climate records that go back centuries to millennia. The Northeast, however, is infamously difficult for dendrochronology (the study of tree-rings) research. The mesic forests of the Northeast are home to many ‘difficult’ tree species; ones that do not have strong climate signals or contain multivariate climate signals. At this conference I will present to the dendrochronology community my paleoclimate records using Atlantic white cedar tree-rings. These are important results as they are some of the first statistically robust, annually resolved, climate reconstructions for the region.
Atlantic white cedar is a hardy, wetland species found 200km from the Atlantic coastline. Due to its durability, we find intact, well-preserved, sub-fossil cedar trunks along the coastline where ancient cedar swamps have fallen into the ocean. As such, we are able to extend our proxy records back thousands of years. Here, I show that annual tree-ring width of inland Atlantic white cedar are sensitive to temperature, and therefore are successful proxies for past temperatures. I also show how Atlantic white cedar swamps that grow in special geologic environments close to the coastline have tree-ring widths that reflect precipitation. This is because their environment restricts groundwater penetration and runoff, and the trees are dependent on rain for fresh water. My data represent a novel and highly precise paleoclimate proxy that extends the known climate history of New England and helps to identify long-term context of large-scale ocean-atmospheric processes that influence the climate of the region. This data will be valuable to academics and resource managers who are working to understand regional climate trends and improve northeastern climate projections. Additionally, the data is critical for many national and international paleoclimate and climate modeling groups doing large scale, northern hemisphere, climate reconstructions and climate sensitivity experiments.