Scientists have calculated the speed of glacioisostatic movements of the earth's crust, which occurred as a result of the degradation of the Earth's ice sheet in the 21st century, taking into account the horizontal component of movements for regions remote from glaciers for the first time. The melting of the Greenland ice sheet provokes an uplift in the north of the Eurasian and North American continents at a rate of 1.0-0.4 millimeters per year. Average horizontal movement rates range from 0.3 millimeters per year in northern Canada to 0.05 millimeters per year in the southern United States and Europe. The research is published in Geophysical Research Letters.
Since the turn of the century, the rate of degradation of the Earth's ice sheet has skyrocketed, with ice loss from shields at the poles and mountain glaciers increasing by 57 percent. Such a large-scale deglaciation of the planet not only accelerates the rise in the level of the World Ocean, but also causes deformation of the earth's crust. The ice sheet pushes the lithosphere into the underlying viscous asthenosphere, and when the ice melts, the earth's crust seeks to restore an equilibrium state. There is a process of glacioisostasis, when the vertical and horizontal movements of the earth's crust compensate for the glacial load. A striking example of glacioisostasis is the uplift of Fennoscandia after the degradation of the Pleistocene Scandinavian ice sheet. Currently, the north of the Gulf of Bothnia is rising at a rate of one centimeter per year.
The development of global navigation satellite systems has made it possible to measure the vertical movements of the crust both near modern ice sheets and at a distance from them. However, the horizontal component of glacioisostatic movements was rarely taken into account, despite the fact that it may exceed the rate of uplift in peripheral regions.
Researchers in Australia and the United States, led by Sophie Coulson of Harvard University, modeled the rate of deformation of the earth's crust resulting from changes in the mass of ice on the planet. Geologists took into account both vertical and horizontal movements. The calculations of deformations were based on a spherically symmetric model of the Earth, and the elastic and density structures of the planet were specified by the preliminary reference Earth model (PREM). Also used were satellite altimetry data from ICESat, which provided monitoring data for the mass balance of the Antarctic, Greenland ice sheets and mountain glaciers in the period from 2003 to 2013.
According to the results of calculations, the thinning of the Greenland ice sheet provokes an uplift in the south of the island of the same name at a rate of three millimeters per year. At a distance from the ice sheet, vertical velocities drop from 0.4-1.0 (Iceland, Baffin's Land) to 0.0-0.4 (northern Europe, continental Canada) millimeters per year. Tangential movements of the earth's crust proceed in a northerly direction. On the Eurasian continent, the maximum horizontal velocities are 0.2 millimeters per year in Norway, which decrease to 0.05 millimeters per year in southern Europe. When moving from the northeast of Canada to the west of the United States, the speed of tangential movements decreases from 0.3 to 0.05 millimeters per year.
Thinning of the Arctic glaciers leads to widespread horizontal movements in high latitudes at speeds up to 0.15 millimeters per year. The magnitude of the crustal deformations due to the change in the mass of the Antarctic ice sheet is less than that caused by the melting of Greenland: the loss of ice mass in the west of Antarctica was partially compensated by an increase in its eastern part during the study period. The rates of vertical uplifts reach maximum values of one millimeter per year in the Antarctic Peninsula and decrease to 0.02 millimeters per year in the Falkland Islands.
Glacioisostatic crustal deformations for five locations. Colored lines show the individual contribution of the Greenland (green), Antarctic (blue) ice sheets and mountain glaciers (orange) and their sum (black)
The horizontal and vertical velocities of the earth's crust are highest in places close to the regions of ice mass loss. This is illustrated by calculations for Norilsk, where the high rates of deformation in the period from 2003 to 2013 are explained by researchers by the rapid degradation of glaciers on Svalbard and the islands of the Russian Arctic. After analyzing the velocities of glacioisostatic movements in the London and Boston area, the authors also concluded that these two areas demonstrate sensitivity to the melting of the Greenland Ice Sheet, although they are located at a great distance from it. Scientists concluded that the calculated speeds of horizontal and vertical movements of the earth's crust can complement satellite geodetic measurements.
