Greg Wiles

Decadal-Scale Climatic Variability Along the Extratropical Western Coast of the Americas: Evidence from Tree-Ring Records

Publisher Summary This chapter discusses the exactly dated tree-ring chronologies along the western coast of the Americas that have been used to track climatic variations, have simultaneously impacted the extra-tropical regions of North, and South America during the past four centuries. Tree-ring chronologies from precipitation-sensitive regions also reveal the occurrence of decadal-scale oscillations, have simultaneously influenced climatic conditions in the Midwest-southern United States, and central Chile. Spatial correlation patterns between tree-ring records, and sea surface temperatures (SSTs) over the Pacific show that variations in climate-sensitive records are strongly connected with SST anomalies in the equatorial Pacific, and off the western subtropical Americas. Correlations of opposite sign occur for the extra-tropical central North, and South Pacific. These correlation patterns resemble the spatial signature of the decadal mode of SST variability over the Pacific, which has recently been detected in instrumental records. The climate variations over the Pacific Ocean result from interactions among interannual, interdecadal, and secular modes of climatic variability. A detailed analysis in time, and frequency domains of the temperature- and precipitation-sensitive records for North, and South America indicates a major change within the decadal oscillatory mode. Some of the anomalies observed in SSTs over the Pacific during the last two decades may represent a recovery of the decadal mode of SST variability that prevailed in the Pacific before 1850.

Dendroclimatic studies: tree growth and climate change in northern forests.

A top priority in climate research is obtaining broad-extent and long-term data to support analyses of historical patterns and trends, and for model development and evaluation. Along with directly measured climate data from the present and recent past, it is important to obtain estimates of long past climate variations spanning multiple centuries and millennia. Dendroclimatic Studies at the North American Tree Line presents an overview of the current state of dendroclimatology, its contributions over the past few decades, and its future potential. The material included is not useful not only to those who generate tree-ring records of past climate-dendroclimatologists, but also to users of their results-climatologists, hydrologists, ecologists and archeologists.

Mentored undergraduate research in the geosciences

There is little argument about the merits of undergraduate research, but it can seem like a complex, resource-intensive endeavor [e.g., Laursen et al., 2010; Lopatto, 2009; Hunter et al., 2006]. Although mentored undergraduate research can be challenging, the authors of this feature have found that research programs are strengthened when students and faculty collaborate to build new knowledge. Faculty members in the geology department at The College of Wooster have conducted mentored undergraduate research with their students for more than 60 years and have developed a highly effective program that enhances the teaching, scholarship, and research of our faculty and provides life-changing experiences for our students. Other colleges and universities have also implemented successful mentored undergraduate research programs in the geosciences. For instance, the 18 Keck Geology Consortium schools (http://keckgeology.org/), Princeton University, and other institutions have been recognized for their senior capstone experiences by U.S. News & World Report.

Recent retreat of Columbia Glacier, Alaska: Millennial context

Columbia Glacier in Prince William Sound, Alaska, has retreated ∼20 km in the past three decades. We use marine sediment records to document the Columbia Glacier advance and retreat history over the past 1.6 k.y. in an effort to place its recent retreat in the context of the Common Era (C.E.). A change in magnetic mineralogy coincided with a shift in sediment geochemistry ca. 0.9 ka. This provenance change documents the advance of Columbia Glacier across a fault, resulting in glacial erosion of mafic rocks near the coast; this agrees with the timing of ice advance reconstructed using dendrochronology. Our marine provenance records show that Columbia Glacier remained advanced south of this fault into the 21st century. Columbia Glacier has now retreated north of this fault, making its recent retreat unprecedented since before ca. 0.9 ka. Southern Alaska temperatures have now warmed to pre–0.9 ka levels, based on tree-ring and reanalysis data. We show with glacier model simulations that the warming between C.E. 1910 and 1980, that includes anthropogenic forcing, was sufficient to trigger the recent retreat of Columbia Glacier from its extended position of the past 0.9 k.y., consistent with our data-driven assessment of the relationship between regional climate change and glacier extent. We conclude that the recent retreat of Columbia Glacier is a response to climate change rather than part of a natural internal tidewater-glacier oscillation.