Tides, seiches, and specific flood events all represent short-term variations in water levels in estuaries over the course of a day, while long term variations can track changes in water level over several years. Understanding long term trends in sea level, as well as the relationship between global and local sea level change, provides critical information about the impacts of the Earth's climate on our estuaries.
Global sea level rise is primarily attributed to changes in ocean volume due to two factors: melting of land-based ice and thermal expansion of saltwater molecules. Melting of glaciers and continental ice masses, which are linked to changes in air temperature, can contribute significant amounts of freshwater input to the Earth's oceans. Additionally, a steady increase in global air temperature creates an expansion of salt water molecules, thereby increasing ocean volume. Local sea levels in estuaries are impacted by global sea level trends as well as regional factors such as ocean circulation, wind and atmospheric pressure, tectonic subsiding or rebounding, and human activities like oil extraction or building of levees.
As the sea rises, the wetlands and marshes of estuaries will erode, and new wetlands will form inland as previously dry areas are flooded by the higher water levels. The amount of newly created wetlands and marshes will most likely be much smaller than the lost area of wetlands - especially in developed areas protected with bulkheads and other structures that keep new wetlands and marshes from shifting inland. The “drowning” of marshes represents a significant loss of important estuarine habitat.
To learn more about the estuary and climate change connection, check out Climate Extensions main page.
Websites Used with this Activity:
Additional Web Resources:
To further understand sea level using NOAA's data, check out this middle school module.