Linking glacially modified waters to catchment-scale subglacial discharge using autonomous underwater vehicle observations

Abstract

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cryosphere 10 (2016): 417-432, doi:10.5194/tc-10-417-2016.Measurements of near-ice (<  200 m) hydrography and near-terminus subglacial hydrology are lacking, due in large part to the difficulty in working at the margin of calving glaciers. Here we pair detailed hydrographic and bathymetric measurements collected with an autonomous underwater vehicle as close as 150 m from the ice–ocean interface of the Saqqarliup sermia–Sarqardleq Fjord system, West Greenland, with modeled and observed subglacial discharge locations and magnitudes. We find evidence of two main types of subsurface glacially modified water (GMW) with distinct properties and locations. The two GMW locations also align with modeled runoff discharged at separate locations along the grounded margin corresponding with two prominent subcatchments beneath Saqqarliup sermia. Thus, near-ice observations and subglacial discharge routing indicate that runoff from this glacier occurs primarily at two discrete locations and gives rise to two distinct glacially modified waters. Furthermore, we show that the location with the largest subglacial discharge is associated with the lighter, fresher glacially modified water mass. This is qualitatively consistent with results from an idealized plume model.Support was provided by the National Science Foundation’s Office of Polar Programs (NSF-OPP) through PLR-1418256 to F. Straneo, S. B. Das and A. J. Plueddemann, PLR-1023364 to S. B. Das, and through the Woods Hole Oceanographic Institution Ocean and Climate Change Institute Arctic Research Initiative to F. Straneo, S. B. Das, and A. J. Plueddemann. L. A. Stevens was also supported by a National Science Foundation Graduate Research Fellowship. S. B. Das was also supported by the Woods Hole Oceanographic Institution James E. and Barbara V. Moltz Research Fellowship. M. Morlighem was supported by the National Aeronautics and Space Administration’s (NASA) Cryospheric Sciences Program through NNX15AD55G