Inter-and Intra-annual Surface Velocity Variations at the Southern Grounding Line of Amery Ice Shelf from 2014 to 2018

Abstract. The ice flow rate through the grounding line of the Amery Ice Shelf (AIS) is vital to understanding the mass discharge received from its three primary tributary glaciers. Previous studies have indicated a stable multiyear average surface velocity distribution in the convergence area of AIS. However, the surface velocity variations, especially short-term fluctuations, in the AIS have been relatively undocumented. This study investigated inter-annual and intra-annual surface velocity variations along the southern segment of AIS grounding line from 2014 to 2018. Using feature tracking to derive surface velocity for five consecutive austral summers and winters, it was found that AIS’s upstream end has experienced a steady ~ 5 % inter-annual increase in surface velocity. Surface velocity increases were observed in 2014/2015 (0.25 ± 0.02 m/d) and in 2017/2018 (0.21 ± 0.02 m/d) respectively. Surface velocities in winters were lower than the summers except for 2016, which had a 0.12 m/d surface velocity decrease from winter to summer. Although flowing slower than the other two glaciers, Fisher Glacier exhibited the highest inter-annual increase (8.56 ± 4.36 %) and the largest intra-annual variation (−5.41 ± 5.65 %) in surface velocity of the three studied glaciers. While the surface velocity observed in 2018 was generally close to the observed velocity in 1989, the magnitude of velocity variations observed during the 2014–2018 period is similar to the differences in velocities measured at the grounding line since 1989. This indicates continued relative stability in the surface velocities at the grounding line of these three tributary glaciers but also indicates that caution should be applied when interpreting long-term differences based on a limited number of measurements. This study demonstrated the capability of feature tracking to monitor the multidecadal changes of surface velocity.