Icelandic rhythmics:: Annual modulation of land elevation and plate spreading by snow load

We find strong correlation between seasonal variation in CGPS time series and predicted response to annual snow load in Iceland. The load is modeled using Green's functions for an elastic halfspace and a simple sinusoidal load history on Iceland's four largest ice caps. We derive E = 40 +/- 15 GPa as a minimum value for the effective Young's modulus in Iceland, increasing with distance from the Eastern Volcanic Zone. We calculate the elastic response over all of Iceland to maximum snow load at the ice caps using E = 40 GPa. Predicted annual vertical displacements are largest under the Vatnajokull ice cap with a peak-to-peak seasonal displacement of similar to 37 mm. CGPS stations closest to the ice cap experience a peak-to-peak seasonal displacement of similar to 16 mm, consistent with our model. East and north of Vatnajokull we find the maximum of annual horizontal displacements of similar to 6 mm resulting in apparent modulation of plate spreading rates in this area.