HR: 0800h
AN: PP21C-1592    [Abstracts]
TI: Evidence for Coupled Paleotemperature and Sea-Level Change, 600 to 1600 AD: Insights From the Mississippi Delta
AU: * Gonzalez, J L
EM: jgonza30@uic.edu
AF: Department of Earth and Environmental Sciences, Tulane University, 6823 St. Charles Avenue, New Orleans, LA 70118-5698 United States
AU: Tornqvist, T E
EM: tor@tulane.edu
AF: Department of Earth and Environmental Sciences, Tulane University, 6823 St. Charles Avenue, New Orleans, LA 70118-5698 United States
AB: An expanding archive of high-resolution paleotemperature data, particularly from the Northern Hemisphere, suggests the widespread occurrence of several climatic anomalies over the past two millennia. The best known are the Medieval Warm Period (MWP) (900 to 1200 AD) and the Little Ice Age (LIA) (1400 to 1900 AD). Critical to future sea-level predictions, particularly in the wake of hurricane Katrina, is to understand the extent to which such climate anomalies have influenced the rate of eustatic sea-level rise. To address this issue we constructed an exceptionally detailed sea-level chronology for the time interval 600 to 1600 AD. This new record is based on 27 index points from basal peat, tracking 60 cm of sea-level rise. Our study area is in the Mississippi Delta where the spring tidal range is less than 0.6 m, the impact of ocean currents on sea-surface topography is limited, and rates of tectonic subsidence are negligible, providing unprecedented opportunities for establishing high-resolution sea-level records. Age control was obtained by AMS 14C dating; most ages are weighted means of two subsamples. Sample elevations were determined by combining differential GPS measurements with optical surveying. All index points were plotted as error boxes using 2 sigma confidence intervals for the ages, plus all vertical errors involved in sampling and surveying. A striking clustering of sea-level index points around 1100 AD suggests an acceleration of sea-level rise. A third order polynomial (r2=0.78) was fitted through the central point of each error box. The first derivative of the polynomial provides an approximation of the rate of sea-level change. Sea level rose at an average rate of 0.4 mm/yr between 600 and 650 AD and increased to 0.7 mm/yr from 900 to 1200 AD, culminating between 950 and 1050 AD. After 1200 AD and for the next 400 years (i.e., into the LIA), sea level continued rising but at a gradually slowing rate, approaching zero towards the end of our record. It is important to note that regression analysis tends to generate a smoothed trend curve, and the stacking of error boxes during the time interval 1000 to 1300 AD does not rule out sea-level rise at a rate of 1 to 2 mm/yr during this period. Nevertheless, it appears that the rate of sea-level rise during the MWP did not exceed the modern (past 60 to 90 years) rate (1.4 to 2.2 mm/yr) along the Gulf Coast, as derived from well-anchored tide-gauge records in Florida. Our evidence lends support to a close coupling between elevated surface temperatures and accelerated sea-level rise, and we conclude that the rate of sea-level rise during the past century ranks among the highest of the past two millennia.
DE: 0497 Wetlands (1890)
DE: 1105 Quaternary geochronology
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 4217 Coastal processes
DE: 4556 Sea level: variations and mean (1222, 1225, 1641)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005