Return to GPS/Tide Gauge home page

Background Images Information Links
Background Images Information Links


1. Sea Level Change and Post-Glacial Rebound in the Northeastern U.S.

When glaciers dominated North America in the last Ice Age, the crust and mantle beneath the ice suffered severe compression and bulging. Though the the ice is gone, the mantle and crust are still reshaping from the immense load in a process known as postglacial rebound (PGR). In the Northeastern U.S., a significant portion of the relative sea level rise is believed to be due to subsidence (crustal downward motion) caused by postglacial effects. The region lies in the dynamically supported "peripheral bulge" geologic structure surrounding the main post-glacial rebound area in Canada. As the glaciers retreated, the mechanism supporting the peripheral bulge vanished and the collapse of the bulge, which began roughly 10,000 years ago, continues today.

2. Correcting Tide Gauges by Vertical Positioning Using the Global Positioning System (GPS)

All recent estimates of global sea level rise derived from tide gauge data have depended on the use of a model to correct for the effects of post glacial rebound [Tushingham and Peltier, 1989]. These models, which depend on values of the lower mantle viscosity and the historical ice load, are subject to large uncertatinties [Davis and Mitrovica, 1996]. In addition, tide gauge records do not account for other sources of ground movement such as subsidence caused by fluid withdrawal (water, oil, gas, etc.) or other tectonic motion. In essence, even the best models are no substitute for monitoring the ground motion using precise geodetic techniques. The Global Positioning System (GPS) has emerged as a cheap alternative to laser ranging for providing accurate point positioning. It is now possible to continuously model the precise position of a significant number of tide gauges at relatively modest costs.

3. The Beginning: The Chesapeake Bay GPS Network - Project BAYONET

Fragile wetland ecosystems, which support an abundance of wildlife, are being lost around the Chesapeake Bay at an alarming rate due to an increase in sea level. The Blackwater National Wildlife Refuge in the Bay has suffered wetlands losses estimated at 25 percent in this century alone. The 1993-98 BAYONET study investigated the tide gauge data which recorded the sea level rise. The tide gauge data was corrected for land subsidence using a small network of GPS recievers placed near the gauges. This corrected data still shows sea level rising trends around 1.7-1.8 mm/yr [Schenewerk, et al., 1999] . The Chesapeake Bay, however, is only one piece of a global puzzle of tide gauge observations involving climate-induced sea level change convolved with vertical crustal motion. Eventually, a global network of GPS corrected tide gauge measurements may provide boundary conditions for the development of improved postglacial rebound models and foundational data for global warming investigations.

Davis, J. L., and J. X. Mitrovica, Glacial isostatic adjustment and the anomalous tide gauge record of Eastern North America, Nature, 379, 331-333, 1996.

EOS, Transactions, American Geophysical Union, Vol. 79, No. 12, March 24, 1998. pp 149, 156-157.

Schenewerk, M., vanDam, T., and Nerem, R.S., Monitoring Subsidence around Chesapeake Bay, GPS World, Vol. 10, No. 5, pp.34-41, May 1999.

Tushingham, A. M., and W. R. Peltier, ICE 3-G: A New Global Model of Late Pleistocene Deglaciation Based Upon Geophysical Predictions of Post Glacial Relative Sea Level Change, J. Geophys. Res., Vol. 96, No. B3, pp. 4497-4523, 1991.

Last modified June 07, 1999
Dr. Steve Nerem (
Dr. Mark Schenewerk (
Dr. Tonie vanDam (

Kwan-Dong Park (CSR graduate student)(

Return to the GPS/Tide Gauge home page


Page created by Greg Holt (CSR undergraduate assistant) (