Rates of change in absolute sea level vary widely around the globe. In the Indo-Pacific, sea level is rising as fast as 10 mm per year. In the Gulf of Alaska and other areas, sea level is falling. These regional differences reflect differences in water temperature (warmer water is less dense and takes up more volume than colder water), current patterns, local addition of meltwater from ice sheets and glaciers, and other factors.
The Bad News
The VIMS study, based on a detailed analysis of simultaneous 35-year records from 10 tide gauges between Norfolk and Baltimore, shows that relative rates of sea-level rise in Chesapeake Bay range from 2.91 to 5.80 millimeters per year. That's the bad news, as even the lowest of these values is higher than the highest rise rates observed in many other localities along the U.S. East Coast. A rise rate of even 2.91 mm per year, when compounded over a century, equals a foot of sea-level rise (a 5.8 mm annual rise rate equals a two-foot rise).
The difference between these local rates of relative sea-level rise and the regional absolute average reflects sinking of the land surface. For instance, the measured rate of relative sea-level rise at Sewell's Point in Norfolk was 4.52 mm per year between 1976 and 2007. Because absolute sea-level rise only added 1.8 mm to the water level, the additional apparent rise in sea level of 2.72 mm (4.52 mm -1.8 mm) must instead be due to land subsidence. The authors write "on average, about 50% of the relative sea level rise measured at Bay water level stations is due to local subsidence."
The mid-Atlantic region is slowly sinking in response to land movements associated with melting of the polar ice caps following the last Ice Age, faulting associated with the Chesapeake Bay Impact Crater, local groundwater wit
|Contact: David Malmquist|
Virginia Institute of Marine Science