Climate and Short-Term Sea Level Change

Short-Term Sea Level Change (Decades to 100s of years)

As evidenced by our explorations and discussions above, global or eustatic sea level can also oscillate due to changes in the volume of water present within the ocean basins relative to storage of that water on land. Short-term sea level change can be driven by sudden tectonic events (i.e., earthquake-induced subsidence/uplift), and tidal processes, but sea level change on the scale of decades to 1000s of years is primarily driven by changes in the Earth's climate system that can be influenced by both intrinsic and extrinsic phenomena. 

Specific observations and facts to know about Short-Term Sea Level Change:

Factors influencing the volume of water within the ocean basins (or what are some ways that the ocean's water volume can change?):

Whether due to climate factors, or plate tectonic factors, water evaporated from the oceans can become locked up on land and prevented from cycling back to the ocean. The USGS estimates that some 8,500,000 cubic miles of water is trapped on land either as ice or as freshwater. When and if this water makes its way back to the ocean (and if it is not replaced on land), sea levels can rise significantly. The Greenland Ice sheet, if melted, is estimated by Byrd Polar Research Center and other scientists to produce a rise of between 6 and 7.4 meters to global sea level if it is not restored on land.

Rift lakes or large intra-continental seaways can trap liquid water that is temporarily removed from the global ocean (excellent examples include Lake Bonneville - the ancestral Great Salt Lake of the western U.S.). If precipitation of ocean-derived water is high on land, and this water is not able to return to the ocean, ocean water levels can drop over time.

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Figure 4.17: Significant water volumes can be locked up on continents and out of circulation from the global ocean in rift lakes like these the lakes of eastern Africa. In geologic time, especially during periods of significant rifting, even much larger lakes are thought to have existed. From left to right the lakes are: Lake Upembe, Lake Mwaru, Lake Tanganyika (largest), and Lake Rukwa. The lakes are located in the Democratic Republic of the Congo, NE Zambia, and southern Tanzania.
Credit: [link http://visibleearth.nasa.gov/view.php?id=54786" target="_blank 'NASA: Visible Earth: Lakes of the African Rift Valley']

Glaciers also trap and hold water in solid form. When ocean-derived moisture freezes and is held on land from year to year, they stockpile large volumes of water and ocean levels can drop.

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Figure 4.18: Map showing the global distribution of glaciers. Significant volumes of ice are held in mountainous terrains as well as in high latitude regions even down to sea level (i.e., Antarctica). At times in Earth's past, significantly larger glaciers existed including several that extended across significant portions of North America.
Credit: [link http://visibleearth.nasa.gov/view.php?id=81545" target="_blank 'NASA: Map by Robert Simmon'], using data from the Randolph Glacier Inventoryand Natural Earth.

Two main types of glaciers include alpine and continental glaciers.

• Continental glaciers or ice sheets similar to those on Greenland, Iceland, or Antarctica have been more widespread at times in Earth's history and trapped large volumes of water on land, so much so that continental areas subsided under the great thicknesses of ice built on top of them.
   
• Large numbers of alpine glaciers at high altitudes (i.e., Andes, Alps, Himalaya, Cascades, Rockies, etc.) collectively contain significant volumes of water that can also be released back to the global ocean if melted.

Continental aquifers will often hold volumes of water in the subsurface. As these aquifers are de-watered (pumped), the water is released back into the hydrologic system and can be returned to the ocean.

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Figure 4.19: Crop Circles in Kansas. Oceans are a long way from Kansas, yet the water used to irrigate these farm fields in central Kansas is headed there. Pumped from the large Ogalalla Aquifer that supplies much of the mid-west with its water supply, this water makes its way around the world in the form of food resources, as well as from evaporation. Water in the Ogalalla is being used at such a fast rate that it cannot be replenished. The end result is that this water ends up back in the ocean. So, whether you look at the mid-west or any desert on earth, humans are accessing and using water stored underground at incredible rates, and, in most cases, it is not going back into the ground.

Credit: https://commons.wikimedia.org/wiki/File:Crops_Kansas_AST_20010624.jpg  

Some areas in large desert regions (i.e., in Arizona, Nevada, California, etc.) have withdrawn substantial amounts of water from aquifers. This water is not replaced, ground subsidence occurs, and the aquifer becomes compacted. The withdrawn water is eventually lost to evaporation and ends up back in the ocean.

• Sedimentation and Sea Level
• Ocean Volume & Sea Level
• Ocean Currents & Sea Level