Presentation on theme: "Tlingit Legends and Tree Ring Dated Little Ice Age Maximum in Glacier Bay During the Early 18th Century Fetters, Caitlin 1, Wiles, Gregory 1, Lawson, Daniel."— Presentation transcript:
Tlingit Legends and Tree Ring Dated Little Ice Age Maximum in Glacier Bay During the Early 18th Century Fetters, Caitlin 1, Wiles, Gregory 1, Lawson, Daniel 2, Krivicich, Michael 1, and Koch, Johannes 3, (1) Department of Geology, The College of Wooster, 1189 Beall Ave, Wooster, OH 44691, firstname.lastname@example.org, (2) CRREL, 72 Lyme Rd, Hanover, NH 03755, (3) Department of Geology, Simon Fraser University, 8888 University Dr, Burnaby, B.C. Canada Acknowledgements We would like to extend our thanks to the Glacier Bay National Park and Preserve for allowing us to collect samples from this area. Also, we would like to thank The College of Wooster Geology Department and the Henry J. Copeland Fund for their generosity. Lastly, we would like to thank our boat captain Justin Smith for his smooth sailing and excellent guitar skills. Abstract Geological, geophysical and ethnographic studies in Glacier Bay are consistent with catastrophic rates of ice expansion into Tlingit communities and concomitant relative sea rise on the order of three meters as subsidence under ice loading. The timing of these changes dated to the late 1600s has been based on radiocarbon dating of submerged and now emerging forests buried by the ice or by inundations with subsidence. We report here on new tree-ring, calendar dates from the outer rings of logs recovered from the intertidal zones of the southern reaches of the Glacier Bay fiord complex. The ongoing tree-ring dating shows that ice expanded across the lower bay from 1704AD to 1735AD. The death of the forests may be due to multiple causes, including overriding by ice, proglacial sedimentation and possibly crustal deformation by ice loading. Our data indicate trees were killed along a 5 km flow line within a few decades, which suggests rapid ice expansion rates of about 2 km per decade. Such a rapid rate of advance is consistent with Tlingit legend of an ice advance forcing them to flee their village believed to be located near the 1704 margin in the Bartlett Cove area. In addition, Tlingit legends report two years of continuous winter conditions about the time of the Tlingit-evicting Little Ice Age ice advance. Interestingly, our tree-ring records show extreme cold between 1752 and 1754, possibly reflecting this event. Cooling during these years is not seen in other coastal Alaska series and thus may be a local effect amplified by the expanding Glacier Bay Icefield. Dendrochronology Results Study Area Over several years, samples have been collected all over Glacier Bay (Figure 1). Sites were chosen in areas that are suspected to have been run over by glaciers. Tlingit History Due to archeological record, it is believed that the Tlingits began living in Alaska 10,000 years ago. During the 1700s the Tlingits were displaced from Glacier Bay and forced to move due to advancing glaciers. “Glacier Bay History” legend tells a tale of a girl luring the glaciers down the bay with meat. Figure 4. Two living tree ring-width series from Glacier Bay that show a strong temperature signal. Both series correlate strongly with February through August average temperatures from Sitka, AK, in the 1800s and 1900s. The gap is due to a discontinuity in the station record during the transfer of Alaska from Russia to the United States. Note that both tree-ring series show abrupt changes (arrows) in temperature during the 1970s and early 1940s, known regime shifts (Ebbesmeyer et al., 1990; Mantua et al., 1997) and another possible shift about 1840. Further analyses of this record and its comparison to other records from GOA are currently being done for an undergraduate thesis (Erlanger, in progress). Note that both Beartrack and Excursion Ridge series tail off in their growth toward the end of the record (left panels); this appears due to a loss of climatic sensitivity (divergence). Blue shading in the left panels shows a cold interval that may be related to Tlingit legends that describe two years of continuous winter conditions (Connor et al., in review). References Connor, C., Streveler, G., Post, A., Monteith, D., and Howell, W., in review, The Neglacial landscape and human history of Glacier Bay, Glacier Bay National Park and Preserve, southeast Alaska, USA: The Holocene. Cruikshank, J., 2001, Glaciers and Climate Change: Perspectives from Oral Tradition: The Arctic Institute of North America, v. 54, p. 377-393. Dauenhauer, N.M., and Dauenhauer, R., 1987, Haa shuka, our ancestors: Tlingit oral narratives: Juneau, Alaska, Sealaska Heritage, 514 p. Mann, D.M., Streveler, G.P., 2008, Post-glacial relative sea level,, isostasy, and glacial history in Icy Strait, Southeast Alaska, USA: Quaternary Research, v. 69, p. 201-216. Monteith, D.M., Connor, C.L., Streveler, G.P., and Howell, W., 2007, Geology and oral history- -complementary views of a former Glacier Bay landscape, in Piatt, J.F. and Gende, S.M., eds., Proceedings of the Fourth Glacier Bay Science Symposium, October 26-28, 2004: U.S. Geological Survey Scientific Investigations Report 2007-5047, p. 50-53. Photos:Above right:http://www.alaskanativeartists.com/images/p rint_rainsplash.jpg Above: http://www.absc.usgs.gov/research/brownbears/gl acierbay/images/Tlingit_Haida_natives.jpg Left: http://upload.wikimedia.org/wikipedia/commons/8/ 8f/Tlingit_women_and_children.jpg Subfossil trees are found buried along the intertidal zone and are excavated (Figure 2). Cross sections of logs are taken from the lower part of the tree trunks. The tree ring-width pattern is used to discern climate. Each year a tree lives, it puts on a new growth ring. Radial growth is strongly impacted by precipitation and temperature during the growing season. Thinner rings are indicative of colder, dryer years while thicker rings indicate warmer, wetter years. Ring-width from a particular region can be cross-dated with living and sub-fossil trees. Cross-dating aids in the placement of an exact calendar date to each growth ring and acts to strengthen the climatic signals expressed by variation in radial growth by means of replication and verification (Figure 3). Figure 3. Cross-dating ring-width patterns from sub-fossil wood, recently deceased trees, and living trees extends the tree-ring record. Methods Figure 2. Samples were found by walking in the intertidal zone. The stump was then dug out to reach the bottom of the trunk. A cross-section was then taken using a chain saw. Obtained kill dates for all measured samples, which will allow us to calculate advancement rates for the advancing glacier. The preliminary chronology links to other calendar dated data from Glaicer Bay. At this time we estimate the advancement rate to be ~300 m/per year during the Little Ice Age. Still need to obtain kill dates for samples located in the western coast of Glacier Bay. Conclusions Figure 1. Map of Glacier Bay showing the locations of samples including their kill dates if available.