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 II)

Paper Session 4551
Friday, 4/20/07, from 4:00 PM - 5:40 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):

Catherine Helen Yansa - Michigan State University

Abstract(s):

• 4:00 PM Author(s):
  *Kathleen Nicoll - University of Utah
  

  Abstract Title: Recording a symphony in sand: assessing the fidelity of oceanic archives for terrestrial Quaternary climate change in the NE Sahara.

  
  

  Offshore records suggest that the ~15 ka cal BP onset and the ~5.5 ka cal BP termination of the “African Humid Period” was a rapid response to gradual insolation forcing. Although there is general agreement that an enhanced Afro- Asian monsoon profoundly affected the water balance of the continental landmass, it is evident that the delivery and tempo varied by location. This paper examines the synchronicity between the oceanic and terrestrial realms as interpreted from various proxy records, with emphasis on the palaeoenvironmental and geoarchaeological archives from the northeastern Sahara. A synthesis of available floral, faunal, and cultural records for the onset of wet conditions in Egypt and Sudan includes 500+ published radiocarbon dates from cultural contexts and various fluvio-lacustrine and Aeolian stratigraphies. At its wettest “monsoonal maximum”~10 - 6 ka cal BP, the interior of North Africa was a marginal drought-prone environment, barely sustaining human activities and a meager steppe-shrub desert flora/fauna with some Sudano-Sahelian elements. Recurrent dry phases are associated with abandonment, deflation, and sedimentation of Aeolian sand. The complexities in this highly continental terrestrial record reflect ascendant global, oceanic, and atmospheric changes, as well as other local feedback mechanisms that cannot be gleaned from the ocean archives. Abrupt hydroclimatic changes influenced resource availability across NE Sahara, and fostered technological innovation and adaptation, as well as the development of complex culture in Desert Peoples - one that displays linkages with the emerging Pharonic civilization in the Nile Valley ~ 5 ka cal BP.

  Keywords: Geoarchaeology, Africa, Monsoon, climate change, Nile

  
  
• 4:20 PM Author(s):
  *Frances Malamud-Roam - University of California
  B. Lynn Ingram - University of California
  Karl P Malamud-Roam - Contra Costa Mosquito and Vector Control District
  

  Abstract Title: Climate Variations Reflected in Changing Sediment Fluxes to Tidal Marshes of San Francisco Bay from Rivers Draining Regions in Northern and Southern California.

  
  

  This research has focused on changing fluxes of mineral sediments to tidal marshes surrounding San Pablo bay in the San Francisco Estuary from the three major source regions: the Sacramento river watershed, the San Joaquin river watershed and local streams that drain to San Pablo bay. Sediments are transregion relative to the others reflect changes in climate patterns over the state. A suite of 26 elements were measured in sediments collected from source rivers to characterize the potential end-member sources. Sediments were collected from marshes surrounding San Pablo Bay and cores were then collected from 4 tidal marshes. The pattern of sediment flux from the identified source end members has changed over time. Each marsh site reflects a large input from the watershed regions outside the Delta, but also a significant input from the local tributaries to San Pablo bay. Two longer cores, from Petaluma marsh and China Camp marsh, show that on long timescales, climate variability has impacts on the sediment fluxes to the Bay marshes. Of particular interest, the longer records reveal more variability between the two watershed regions draining the Sacramento and San Joaquin systems - an increase in some cores of 20%. An intriguing indication of overall decline in mineral sediments delivered to these marsh sites is apparent in the China Camp record occurring during the period of the Mediaeval Climate Anomaly, and an increase is apparent during the Little Ice Age.

  Keywords: climate variability, sediment flux, trace elements, tidal marsh, California climate

  
  
• 4:40 PM Author(s):
  *David E. Wilkins - Boise State University
  Richard L. Ford - Weber State University
  Kathleen Nicoll - University of Utah
  

  Abstract Title: Multiproxy Evidence for Late Holocene Climate Change, Coral Pink Sand Dunes, Utah.

  
  

  Dune fields can be highly sensitive to climatic change, as variability in effective moisture influences sediment supply and transport. The Coral Pink Sand Dunes, an active dune field in southern Utah, is the site of ongoing investigations into geomorphic system response to climate change in the Colorado Plateau. Stratigraphic exposures of crossbedded aeolian sand capped by a soil have been dated through optically-stimulated luminescence methods using single-aliquot regeneration (SAR) protocols. Those results identify three distinct episodes of aeolian deposition occurring 4.1 +/- 0.19 kyr, 2.8 +/- 0.22 kyr, and ca. 710 -510 kyr. The soil was radiocarbon dated (using the bulk organic matter) to 470 +/- 50 BP, and radiocarbon ages on plant matter in the surface matrix of the soil and from ponderosa pine snags in the dune field indicating more recent plant communities. Additional evidence of climatic variability is seen in a disjunct living pine stand (P. ponderosa) located within the dune field; dendrochronologic analysis of the trees places the oldest to the time when the 470 BP soil was formed. Evidence of aeolian activity is indicative of periods of drier climate resulting in dune surface activity, while the soils and pine stands indicate periods of increased moisture and resulting surface stability. The timing of these alternating episodes is broadly correlative to indications of drought and moisture in dune fields elsewhere in the Colorado Plateau, Rocky Mountains, Great Plains.

  Keywords: aeolian geomorphology, climate change, luminescence dating, dendrochronology

  
  
• 5:00 PM Author(s):
  *Dorian J. Burnette - University of Arkansas - Fayetteville
  

  Abstract Title: A New Daily Temperature Record for Kansas, July 1828 to August 2006.

  
  

  A 179-year record of daily mean temperature in Kansas has been developed from historical and modern instrumental data, extending from July 1828 to August 2006. Nineteenth century temperature data were obtained from original manuscripts of the U.S. Army Surgeon General, the Smithsonian Institution, and the Signal Service, and were carefully screened and corrected. Modern hourly temperature data were utilized to correct the historical temperature data for changes in observation time routines. Overlapping daily mean temperatures from sites with the best thermometer exposures were then attached to the modern record using regression methods. The resulting reference time series reflects coherent signals from the surrounding stations, assuring homogeneity. This new dataset is rich in temperature variability at all timescales, including positive and statistically significant trends in seasonal and annual temperature since 1828. The winter warming trend in Kansas has been almost double the summer warming. This record of daily temperature from Kansas is the only record to date that has been corrected at the daily timescale, and provides the longest and most detailed record of instrumental temperature in the continental interior of North America.

  Keywords: daily, temperature, Kansas

  
  
• 3:20 PM Discussant:
  Alan F. Arbogast - Michigan State University
  

  Abstract Title:.

Discussant:

Alan F. Arbogast - Michigan State University

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.