Coastal Erosion Responses for Alaska - the National Sea Grant ...

20 Motyka et al.—Global Sea Level Rise and Relative Sea Change in Alaska
Table 1. Contributions to sea level rise from the world’s glaciers.
Region
Sea level rise
equivalent
(mm yr-1) Years Reference
Alaska/NW Canada 0.14 ± 0.04 1950s-1990s Arendt et al. (2002)
Alaska/NW Canada 0.27 ± 0.10 1990s-2000/01 Arendt et al. (2002)
Alaska/NW Canada 0.31 ± 0.09 2002-2004 Tamisiea (2005)
Canadian Arctic Archipelago 0.064 1995-2000 Abdalati et al. (2004)
Patagonia 0.042 ± 0.002 1968/75-2000 Rignot et al. (2003)
Patagonia 0.105 ± 0.011 1995-2000 Rignot et al. (2003)
West Antarctica 0.12 ± 0.03 Late 1990s Rignot and Thomas (2002)
West Antarctica 0.2 2002-2003 Thomas et al. (2004)
East Antarctica 0.05 ± 0.06 Late 1990s Rignot and Thomas (2002)
Greenland 0.14 Late 1990s Krabill et al. (2000)
Greenland 0.20 ± 0.07 2002-2004 Velicogna and Wahr (2005)
Greenland 0.23 to 0.55 2002-2005 Rignot (2005)
not take into account the accelerated glaciodynamic response that tidewater
glaciers and polar outlet glaciers are now experiencing.
Relative sea level (RSL) change along coastal Alaska is a function of GSLR
and also the local and regional rates of crustal adjustments to isostatic rebound
from melting glaciers, tectonic processes, and the effects of gravity due to
changing ice masses. In the latter case, while ice melting adds water to the
oceans globally, reduced gravitational attraction exerted by the shrinking ice
masses can cause a drop in RSL locally. Estimates of this effect in regions
where glacier melting in Alaska is strong and ongoing, range from –2.3 mm
yr-1 (Tamisiea et al. 2003), to –0.4 mm yr-1 (Larsen et al. 2004), where negative
indicates a falling relative sea level. The loss of glacier ice is also driving
strong glacial isostatic rebound along much of southern coastal Alaska. The
effects of this rebound are clearly seen in tide gauge records and in GPS measurements.
The post–Little Ice Age collapse of the Glacier Bay ice field (Motyka
and Larsen 2005) and ongoing rapid melting of mountain glaciers throughout
the region (C.F. Larsen et al. submitted) has resulted in rebound rates of
as much as 32 mm yr-1 in Glacier Bay, with RSL falling as much as 5.7 m near
Glacier Bay since 1770 AD (Motyka 2003; Larsen et al. 2004, 2005). This broad
dome of uplift extends as far south as Sitka and as far north as Cape Yakataga,
where the ~20 mm yr-1 average uplift rate has also been attributed to glacier
rebound (Sauber and Molnia 2004).
Tectonically, the strike-slip margin along southeast Alaska contrasts
sharply with the collision of the Pacific Plate with the North American Plate