Satellite Gravity and the Geosphere Contributions to the Study of the Solid Earth and Its Fluid Envelopes (1997) / Chapter Skim
Currently Skimming:
7 SEA-LEVEL CHANGE
7 SEA-LEVEL CHANGE
Pages 67-78
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 67... ...
Satellite observations of time-dependent gravity could constrain changes in global sea-level in two ways. First, they could help identify the continental sources of water transferring into the ocean, through monitoring of Me mass of ice sheets, continental glaciers, and groundwater aquifers.
|
From page 68... ...
Contribution Thermal expansion Antarctica Greenland Glaciers and small ice caps Surface and groundwater Rate of Increase or Decrease (mm/yr) ~0.2to O.7 - 1.4 to 1.4 -0.4 to 0.4 0.2to O.5 0.5 to 0.7 The degree amplitudes from a 1 mm/yr rise in sea level do exceed (slightly)
|
From page 69... ...
land types in Blackwater National Wildlife Refuge, Chesapeake Bay, Maryland due, in part, to sea-level rise. From 1938 to 1980, an average of 17.3 hectares/yr of marsh was inundated.
|
From page 70... ...
A longs tea monitoring cabin would be d~sir~le. In addition to providing into on global Ed Ions se-level rise, seethe ~ data could be used to Bug charms on basin scales.
|
From page 71... ...
Thus again, satellite measurements of the increase in mass would be invaluable in sorting out the causes of sea-level rise. ICE MASS BALANCE The masses of glaciers, ice caps, and ice sheets (the term "ice sheet" is reserved for the vast ice covers of Antarctica and Greenland)
|
From page 72... ...
It is important to note, however, that there are ambiguities in interpreting gravity signals over ice sheets because of problems in separating the effects of ice-sheet changes from the effects of isostatic rebound, interannual variations in snow accumulation rates, and atmospheric pressure. These problems are discussed in turn below.
|
From page 73... ...
The first is by the calculation of broadly averaged snowfall rates from the atmospheric-moistureflux divergences over the ice sheets determined from atmospheric numerical analyses that incorporate satellite-based soundings of water vapor and winds over the surrounding oceans, as well as regular rawinsonde observations from a small number of surface stations. Meteorologists expect that by the year 2000 the total input can be known to + 10% for Antarctica and a few percent for Greenland (D.H.
|
From page 75... ...
Estimates of mass balance could be further improved if the present-day changes in the heights of the ice sheets could be determined separately using laser altimeter measurements from an orbiting satellite-specifically, NASA's planned Laser Altimetry Mission. For a given mass increase, the surface height changes would be in the ratio of 1:3.5:10 for isostatic uplift, changes in solid ice, and changes in snow accumulation at the surface, respectively, because the source of mass change in each of those cases is characterized by a different mean density.
|
From page 76... ...
The ice sheets are so large that satellite gravity can provide a valuable approach to the study of subdivisions like individual drainage systems as well as entire ice sheets. For example, the mass of ice in the large drainage system that empties into the east side of the Ross Ice Shelf is suspected to have fluctuated dramatically in the past because of unstable dynamic behavior, including a rapid retreat at the end of the last ice age that may even be continuing at present, albeit at a reduced rate.
|
From page 77... ...
(b) Separation of interannual mass changes from true secular changes will be aided greatly by the continually improving calculations of mass input to the ice-sheet surfaces from measurements of moisture-flux divergence around the perimeters of the ice sheets.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.