“Fjord” for Thought: Regimes in Circulation at LeConte Glacier

Recent investigations of tidewater fjords have detailed unexpectedly high melt rates, highlighting the need for a better understanding of near-glacial processes and the dynamics that influence them. To offer insight into these processes, we deployed four moorings approximately 100 meters from the terminus of LeConte Glacier for 10 days in September 2018; these collected near-terminus velocity profiles along with hydroacoustic, temperature, pressure, and salinity data. In addition, we collected transects of velocity, salinity, and temperature from autonomous boats and time-lapse imagery of the terminus region. We find that fluctuations in the measured currents (speed and direction) are considerably higher near the terminus than those measured 500m down-fjord, indicating more complex flow patterns than have been reported previously. We divide the fjord circulation into four “regimes” (i.e. periods of time with distinct velocity and acoustic signals, characterized in terms of the mean and variance of these parameters) that demonstrate how the circulation can undergo abrupt changes from one state to another, creating distinct circulation patterns that persist on timescales from hours to several days. We propose that regime shifts reflect changes in the primary subglacial discharge outlet, and identify a possible relationship between large calving events and regime changes. The kinetic energy of the near-boundary flows, its distribution in space, and its change in time have significant consequence to predicted ice melt rates.