Deciphering postglacial rebound and groundwater processes in Canada & US mid-continent using absolute gravity, GPS and GRACE dataLambert, Anthony 1; Henton, Joseph 2; Huang, Jianliang 2; Mazzotti, Stephane 1; Courtier, Nicholas 1 We examine similarities and differences in long-term trends and inter-annual signals between absolute gravity, vertical GPS, and GRACE time series at mid-continent North American sites. We find good agreement between the GPS and absolute gravity trends at most sites (both based on data acquired over more than a decade). The resulting gravity and uplift rates are compatible with ongoing postglacial rebound from the Laurentide ice sheet. In contrast, we find significant differences between the absolute gravity, corrected for vertical movement, and the GRACE trends at about half of the sites. This is possibly due to the difference between the two techniques in spatial averaging of the dominant postglacial rebound processes. At some of the sites (e.g., Pinawa and International Falls), both the absolute gravity and GRACE time series show a significant inter-annual signal, with a good agreement in phase and amplitude between the two techniques. Comparison with flow rate data of the Winnipeg River suggests that this inter-annual signal may be related to large-scale variations in groundwater storage. Preliminary analysis does not show a significant inter-annual signal in the GPS time series for the same sites. The difference in response between gravity and GPS, and how it may relate to groundwater storage, will be investigated. |