Late Holocene Glacial Stratigraphy of Columbia Bay Alaska: Extending the Record

Matthew Beckwith-Laube

Department of Geology

The College of Wooster

*This material is based upon work supported by the National Science Foundation under Grant No. 9910805. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.

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Project Overview:

Supported by various sources, The College of Wooster has been able to work with other institutions such as Columbia University (Lamont-Doherty Earth Observatory), The University of Colorado (Institute of Arctic and Alpine Research), The University of Cincinnati, and many other organizations to conduct field work throughout Alaska since the mid-1990’s. The scope of this research has been to recreate climate histories through the use of dendrochronology. We have collected hundreds of tree samples that have provided insight into the periods such as the Medieval warming period, the Little Ice Age, and other climate changes occuring over the past  2,000 years. During the 2003 field season under funding provided by NSF grant 9910809*, Greg Wiles, Jim Figley (Cornerstone Elementary, Wooster Ohio) and Matthew Beckwith-Laube of the College of Wooster along with Thomas Lowell of the University of Cincinnati set out to Columbia Bay to examine and collect from two sites in the Columbia Fjord. The findings from this field season will be presented in a senior undergraduate thesis by Matthew Beckwith-Laube, at the 2003 Geological Society of America annual meeting in Seattle, Washington, and possible papers to come. This page hopes to provide an adequate overivew of the methodsof dendrochronology as well as the background of study in Columbia Bay.

Project Abstract:

Columbia Glacier, one of the largest tidewater glaciers in the northern hemisphere, began a drastic retreat from its terminus in 1979 where it had remained for over a century. The glacier has thinned over 300 hundred meters and retreated 13 kilometers to its present calving margin. This drastic retreat has uncovered a previously buried Mountain Hemlock forest that was run over by advance of the glacier. Preliminary tree-ring dating of the outer ring of tree sections collected in the Summer 2003 from up-fjord sites within 1 km of the present calving margin reveal glacial advance dating to the early 11th Century A.D. with outer ring dates ranging from 1020 and 1025 A.D. Seventy subfossil samples from 8 sites in the fjord are currently being analyzed and should provide details to this advance history. Estimates of advance rates from these up-fjord sites are consistent with previously tree-ring estimated rates of about 40 meters per year. In addition to logs obtained from these sites, wood samples are being radiocarbon dated to understand the complex glacial stratigraphy composed of superimposed till layers discovered during the 2003 field season. This stratigraphy could reflect earlier advance/retreat cycles and extend the glacial history prior to the tree-ring dated advance and observed retreat of the past 1000 years.

Previous Research:


This area represents a compilation of 5 years of field work and very successful and thorough data collection. We have aver 300 trees in various chronologies as well as dozens of samples yet to be processed. Work from our sites has been published in Quaternary , The Holocene, and various other major journals. The majority of previous research has focused on the influence of the North Pacific on climate variations.

Site Information and Sample Details:

We hope to see a succession of dates ranging from site to site (bottom to top of the valley). If we see progressively older outter ring dates up valley then we can deduct that the ice was thickening up valley as it advanced. On the other hand, if we see progressively younger dates up valley then we can deduct an advance of ice downvalley coming from above.  This model assumes that logs have been preserved in place and have not been transported a great distance. Another possibilty arises if we get dates that do not display any pattern. If this is the case we can assume that either logs have been transported or the ice did not simply thicken up or down valley. There could be a variety of movements that occured to deposit the till and logs in question. Further examination will provide additional clues as to the depositional history of this valley.
As we continue our examination of these sites we develop more and more ideas about what has been going on in this dynamic area. In the coming months i hope to continue with the construction of a master chronology of the area, determine advance rates, advance ‘style’, and possible figure out what these ideas mean both locally and globally.

About Me:

My name is Matthew Beckwith-Laube and my research interests are global climate change over the past 20,000 years (give or take a few thousand) and the role glaciers and other bodies of ice and oceans have in this global change. It is very important to understand what has been going on around us since humnan civilization took root. It is interesting to see what we are doing to our world to change the dynamics of our climate.

 

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