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Abstract At tidewater glaciers, the ocean supplies heat for submarine ice melt and the glacier supplies freshwater that impacts ocean circulation. Models that employ buoyant plume theory are widely used to represent the effects of subglacial discharge on both glacier melt and freshwater export, but a scarcity of observations means that these models are largely unvalidated. The challenges and inherent risks of working near actively calving glaciers make it difficult to collect in situ observations. This study, conducted at Xeitl Sít’ (LeConte Glacier) in southeast Alaska, reports the first observations of velocity and geometry of the upwelling core of a subglacial discharge plume. This subglacial discharge plume rises along an overcut ice face, with vertical velocities in excess of 1 m s−1, and a plume shape consistent with subglacial discharge emerging from a narrow outlet. Buoyant plume theory, as commonly applied, fails to replicate the observed entrainment, underestimating the plume's volume flux by more than 50%. Large eddy simulations reveal that over half of this mismatch can be attributed to the overcut slope of the ice, which enhances entrainment. Enhanced mixing near the grounding line may account for the additional entrainment. Accurate representation of plume geometry and entrainment is critical for understanding plume‐driven melt of the terminus and the initial mixing of glacial meltwater as it is exported into the ocean.
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Turbulent Dynamics of Buoyant Melt Plumes Adjacent Near‐Vertical Glacier Ice
Abstract At marine‐terminating glaciers, both buoyant plumes and local currents energize turbulent exchanges that control ice melt. Because of challenges in making centimeter‐scale measurements at glaciers, these dynamics at near‐vertical ice‐ocean boundaries are poorly constrained. Here we present the first observations from instruments robotically bolted to an underwater ice face, and use these to elucidate the interplay between buoyancy and externally forced currents in meltwater plumes. Our observations captured two limiting cases of the flow. When external currents are weak, meltwater buoyancy energizes the turbulence and dominates the near‐boundary stress. When external currents strengthen, the plume diffuses far from the boundary and the associated turbulence decreases. As a result, even relatively weak buoyant melt plumes are as effective as moderate shear flows in delivering heat to the ice. These are the firstin‐situobservations to demonstrate how buoyant melt plumes energize near‐boundary turbulence, and why their dynamics are critical in predicting ice melt.
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- PAR ID:
- 10503596
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 51
- Issue:
- 9
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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