Changing Ice Morphology as a Driver for Highly Energetic Near-Terminus Ocean Dynamics

Jonathan D Nash1, Erin C Pettit2, Rebecca H Jackson3, Marguerite Shaya4, David Sutherland5, Christian Keinholz6, Jason M Amundson6, Eric D Skyllingstad7, Nicole Abib8, Meagan E. Wengrove9 and Dylan Winters7, (1)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (2)Oregon State, Corvallis, Oregon, United States, (3)WHOI, Woods Hole, MA, United States, (4)Carleton College, Northfield, MN, United States, (5)University of Oregon, Department of Earth Sciences, Eugene, OR, United States, (6)University of Alaska Southeast, Juneau, AK, United States, (7)Oregon State University, Corvallis, OR, United States, (8)University of Oregon, Eugene, United States, (9)University of New Hampshire Main Campus, Durham, United States
Abstract:
Recent studies find ambient ice melt rates at a tidewater glacier in Alaska significantly higher than predicted by the standard melt/plume models. This implies that either the model parameters are incorrect or that the assumed near-boundary flows are too weak or oversimplified. In this study we analyze data from 4 moorings deployed autonomously within 100 m of the terminus of Leconte Glacier Alaska along with multibeam acoustics, time-lapse imagery and autonomously-collected profiles of velocity and density to get a new understanding of the fluid dynamics influencing the ice-ocean boundary.

Here we focus on the velocity variability and its relationship to the ice dynamics away from the primary subglacial discharge plume. At Leconte, the ice flow is rapid (10-30 m/d) leading to significant changes in terminus morphology over short time periods, with dramatic consequences to the ocean fluid dynamics. In particular calving events lead to >1 m/s instantaneous currents, persistent internal seiching in the fjord (with 5-10 minute periods), and down-fjord exchanges telecommunicated at the surface wave speed, each of which have consequences to heat transports and ice melt. In addition, changes in the terminus geometry (over time periods of minutes to days) alter the location of subglacial discharge flows that influence the structure of large-scale near-terminus eddies. Together, these control the kinetic energy near the terminus, which is enhanced by an order of magnitude compared to that 500-m downstream, and hence has significant consequences to terminus ice melt.