Low Gravity

Okay, this is like the coolest thing I've read in a science magazine in a long time! Taken from the highlight section of the current issue of Science:

Ice, the Mantle, and Canadian Gravity Lows

Terrestrial gravity above a point on Earth can vary with changes in theamount or density of underlying mass. In northern Canada, a largedepression of the continental craton has created a region ofanomalously low gravity. This topographic low may be the remnants ofthe depression made by the Laurentide Ice Sheet, in the case ofincomplete rebound of the crust (glacial isostatic adjustment, or GIA)after the melting of the ice sheet at the end of the Last GlacialMaximum, or the result of active downwelling of the mantle. Tamisiea et al. (p. 881)examine 4 years of data from the Gravity Recovery and ClimateExperiment (GRACE) satellites and conclude that GIA has contributed 40to 50% of the gravity anomaly over the area. They also infer that theLaurentide Ice Sheet had two large domes during the Last GlacialMaximum, rather than only one as some studies have suggested.