Special Sessions
Sponsored by the Geomorphology Specialty Group
Association of American Geographers 103rd Annual Meeting
San Francisco, California, April 17-21.

Climate Reconstructions: From Land to Sea (Session I)

Paper Session 4451
Friday, 4/20/07, from 2:00 PM - 3:40 PM

Sponsorship(s):

Biogeography Specialty Group
Climate Specialty Group
Geomorphology Specialty Group

Organizer(s):

Michelle Goman - Cornell University
Catherine Helen Yansa - Michigan State University

Chair(s):

Michelle Goman - Cornell University

Abstract(s):

• 2:00 PM Author(s):
  *Catherine Helen Yansa - Michigan State University
  Jennifer Nelson - Indiana University-Purdue University
  J. Elmo Rawling III - University of Wisconsin-Platteville
  Kathy Licht - Indiana University-Purdue University
  Aaron Young - University of Wisconsin-Platteville
  

  Abstract Title: Climate Changes in Southern Lower Michigan Over the Last 2000 Years: Differentiating Between "Lake Effect" and Regional Climate Patterns.

  
  

  A comparative study of the paleoclimate records of two lakes in southern Lower Michigan was conducted to reconstruct regional paleoclimate changes and to test for a localized “lake effect” signal. Multiple proxies (pollen, plant macrofossils, particle size, % organic matter, and % calcium carbonate) were analyzed from sediment cores collected from Miner Lake (42.7°N, 85.8°W), located close to Lake Michigan, and contrasted with those from Duck Lake (42.4°N, 84.8°W), which is situated in the interior of the state. Proxy data from Duck Lake show that this inland lake was responsive to large-scale climate perturbations, including the Medieval Warm Period (MWP, ca. 1200 to 800 cal yr BP) and Little Ice Age (LIA) cooling (ca. 500 to 150 cal yr BP). For example, the pollen record of this site indicates a shift from beech-maple forest to oakhickory forest during the MWP and the subsequent resurgence of beech-maple forest during the LIA. Spectral analysis of gray scale data for Duck Lake exhibits dominant periodicities of 207 and 96 years for cool/wet events, which may indicate a global climate signal, possibly induced by solar forcing. In contrast, the paleoclimate record of Miner Lake was invariant during the past several millennia, which suggests that a “lake effect” climate induced by Lake Michigan was more dominant than the regional climate pattern for sites located near the shore of this Great Lake.

  Keywords: climate change, Great Lakes, pollen, geomorphology, biogeography, climatology

  
  
• 2:20 PM Author(s):
  *Amy Hessl - West Virginia University
  Richard Stockton Maxwell - West Virginia University
  Ed Cook - Lamont-Doherty Earth Observatory, Columbia University
  Brendan Buckley - Lamont-Doherty Earth Observatory, Columbia University
  

  Abstract Title: Eastern Red Cedar (Juniperus virginiana): Millennial Length Tree Ring Records of the Mid-Atlantic Region?

  
  

  Unlike the western and central United States, the mid-Atlantic region has limited tree-ring records suitable for millennial length reconstructions of climate. A new source of climate history for the region may be derived from isolated stands of eastern red cedar growing in the headwaters of the Potomac River. Stands dominated by eastern red cedar populate the steep slopes of limestone “knobs” on the east side of the ridge and valley province of West Virginia. These are some of the driest locations in the region, receiving less than 90cm of precipitation per year, suggesting that these trees may be sensitive to drought. In this paper, we describe a set of sites that contain live and dead wood with treerings that extend back to 500 AD. More than 80 trees were sampled with increment cores (live trees) and cross sections (snags and logs) in an effort to build a long record of annually resolved drought information for the mid-Atlantic region. Results indicate a reasonable relationship with drought that may be suitable for identifying the frequency and duration of extreme drought events in the past. Additional sites containing these long-lived and well-preserved trees may exist in the area potentially allowing for a future network of tree ring sites suitable for climate reconstruction. Results may be especially relevant for the Washington DC metro area, located approximately 150 km east of the study area. The area’s population exceeded 5.9 million in 2005 and gets the majority of its water from the Potomac River.

  Keywords: drought, tree rings, mid-Atlantic

  
  
• 2:40 PM Author(s):
  *Chad S. Lane - University Of Tennessee
  Claudia I. Mora - University Of Tennessee
  Sally P. Horn - University Of Tennessee
  Kenneth H. Orvis - University Of Tennessee
  

  Abstract Title: Paleolimnological Evidence of Late-Holocene Precipitation Variability in the Dominican Republic and its Possible Impacts on Prehistoric Human Populations.

  
  

  High-resolution paleoclimate records from the circum-Caribbean region indicate a steady decrease in precipitation throughout the late Holocene with interspersed severe drought events. This precipitation variability has been primarily attributed to a southward shift in the mean annual position of the Intertropical Convergence Zone. The impact of this precipitation variability on Mayan society on the heavily populated Yucatan Peninsula has received significant attention. However, the impact of regional precipitation variability on smaller populations of the circum-Caribbean, including prehistoric island societies, has not been investigated. We have reconstructed a paleoprecipitation record using sediment characteristics, fossil pollen, aquatic macrofossils, and the oxygen isotope composition of ostracod valves preserved in sediment cores from Laguna Castilla and Laguna Salvador in the Cordillera Central of the Dominican Republic. Our paleoprecipitation record correlates well with regional records including those from the Yucatan Peninsula and the Cariaco Basin. The record indicates that the intervals 930-1550 and 125?300 cal yr BP were two of the most arid periods in the Dominican Republic during the late Holocene. The two most positive oxygen isotope excursions on record punctuate these extended dry periods and are coincident with paleolimnological evidence of human occupation, which was sporadic at the sites. Synchronous shifts in proxy indicators of human presence and extreme drought may indicate population migration into the interior of Hispaniola in search of dependable water sources during severe drought events. Further research is necessary to verify this hypothesis and to place these potential population migrations into archaeological and historical context.

  Keywords: lake sediment, isotope, ostracod, chara, pollen, charcoal

  
  
• 3:00 PM Author(s):
  *Bryan A. Black - Hatfield Marine Science Center, Oregon State University
  George W. Boehlert - Hatfield Marine Science Center, Oregon State Univeristy
  

  Abstract Title: Rockfish, tree rings, and climate: marine-terrestrial linkages in the Pacific Northwest, USA.

  
  

  We apply dendrochronology techniques to otolith growth increments of long-lived splitnose rockfish (Sebastes diploproa) in the northeast Pacific to i) generate multidecadal growth chronologies, ii) relate growth to ocean variability, and iii) compare with tree ring chronologies throughout the US Pacific Northwest. Rockfish otolith growth increments were thin sectioned, measured, and crossdating verified using COFECHA. The chronology was related to upwelling, sea surface temperatures, ENSO, and the PDO, and significantly (p < 0.01) correlated with indicators of cool, productive ocean conditions, especially during the winter and spring months. February upwelling accounted for 50% of the variance in the splitnose chronology. The chronology also significantly (p < 0.01) and negatively correlated with high elevation tree ring chronologies located throughout the Pacific Northwest. Tree-ring chronologies that correlated with the splitnose rockfish chronology shared a sensitivity to winter and spring ocean variability, and allowed a reconstruction of splitnose rockfish growth to the year 1600 AD. This approach revealed significant climate-driven linkages between the growth of organisms at 300 m depth in the Pacific Ocean with those at 2,000 m in the Cascade and Sierra-Nevada Mountains. We also report on pilot projects involving yelloweye rockfish, geoduck clams, and freshwater mussels.

  Keywords: dendrochronlogy, Pacific rockfish, climate

  
  
• 3:20 PM Discussant:
  Bryan Shuman - University of Minnesota - Minneapolis

Discussant:

Bryan Shuman - University of Minnesota - Minneapolis

Session Description: In these sessions the climate record is examined on a variety of timescales (i.e. historic to Pleistocene) and resolutions (i.e. annual to millennial), and through a variety of proxy (biologic and geomorphic) and instrumental analyses.