A mysterious gravity dip in the Hudson Bay, Canada area has been a weighty topic for scientists for years. Now satellite data reveal a thick ice sheet that once cloaked the region partially resolves this so-called gravitational anomaly. Reported in the May 11 issue of the journal Science, the new results provide a crude map of the ice sheet's structure as it was during the last ice age. The melted ice left behind an imprint from which the Earth is still rebounding, and that imprint contributes to the weird gravity.
Past studies have searched endlessly for the missing gravity, but according to one explanation, convection within the Earth's mantle tows the continental plate downward. The problem with this theory is that such a process occurs on the order of a million years or so and wouldn't show up in the GRACE measurements as they detect only geologically "quick" gravity changes on the order of years.
Another theory blames the anomalous gravity on glacial rebounding, which occurs on much shorter time scales. During the Ice Age, the two-mile-thick Laurentide Ice Sheet stretched from the Arctic down through eastern Canada to the northern half of the Midwestern United States, spanning 5 million square miles. The massive sheet pressed down on the Earth, deforming the crust somewhat like a Sumo wrestler on a trampoline surface.
Even though the ice has all but vanished, the Earth still feels the burden and like a slowly rebounding memory-foam pillow, it has yet to snap back to its ice-free shape. The gravity measurements reveal that the slight deformation could explain about 25 to 45 percent of the unusually low gravity that has persisted over a large section of Canada.
The rest of the "missing gravity" can be explained by some sort of mantle tugging, the scientists say.
This new discovery will help scientists ice-sheet dynamics and how climate affects the mass and distribution of ice over the Earth.
Source: Live Science via AOL News