Seismic observations of long-period ocean waves generated by calving icebergs, Jakobshavn Isbræ, Greenland

Tide gauges and broadband coastal seismometers regularly record low-frequency (0.001-0.01 Hz) ocean waves generated by large calving icebergs at Jakobshavn Isbræ, Greenland. The waves are observed up to 150 km from the glacier terminus, first arrive at the stations 10-30 minutes after calving initiates, can persist for several hours, and have distinct spectral peaks that vary between stations but not between calving events (suggestive of basin eigenmodes). The unique characteristics of the waves can be used to confidently identify large calving events. Furthermore, the energy of the waves can be used to estimate the size of a calving event and, if used in conjunction with visual imagery, place a maximum bound on the amount of energy lost to the ocean via turbulence and dissipation. Although the ocean wave signal is most easily identifiable in tide gauge data, seismometers have the added benefits of recording (1) very broadband seismic signals, including higher frequency (e.g., 2-5 Hz) seismic signals from calving events (not just their aftermath), (2) ocean waves in ice-choked fjords and bays that are impossible to instrument with tide gauges, and (3) continuous, real time signals over multiple years. We will present examples from Jakobshavn Isbræ to demonstrate how observations of calving-generated ocean waves can be used to gain insights into glaciologically-relevant processes.