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Abstract Fjords are conduits for heat and mass exchange between tidewater glaciers and the coastal ocean, and thus regulate near‐glacier water properties and submarine melting of glaciers. Entrainment into subglacial discharge plumes is a primary driver of seasonal glacial fjord circulation; however, outflowing plumes may continue to influence circulation after reaching neutral buoyancy through the sill‐driven mixing and recycling, or reflux, of glacial freshwater. Despite its importance in non‐glacial fjords, no framework exists for how freshwater reflux may affect circulation in glacial fjords, where strong buoyancy forcing is also present. Here, we pair a suite of hydrographic observations measured throughout 2016–2017 in LeConte Bay, Alaska, with a three‐dimensional numerical model of the fjord to quantify sill‐driven reflux of glacial freshwater, and determine its influence on glacial fjord circulation. When paired with subglacial discharge plume‐driven buoyancy forcing, sill‐generated mixing drives distinct seasonal circulation regimes that differ greatly in their ability to transport heat to the glacier terminus. During the summer, 53%–72% of the surface outflow is refluxed at the fjord's shallow entrance sill and is subsequently re‐entrained into the subglacial discharge plume at the fjord head. As a result, near‐terminus water properties are heavily influenced by mixing at the entrance sill, and circulation is altered to draw warm, modified external surface water to the glacier grounding line at 200 m depth. This circulatory cell does not exist in the winter when freshwater reflux is minimal. Similar seasonal behavior may exist at other glacial fjords throughout Southeast Alaska, Patagonia, Greenland, and elsewhere.
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Regional Ocean Modeling System output for glacier geoengineering impact assessment in Greenland fjords
This dataset contains time series output from Regional Ocean Modeling System (ROMS) simulations investigating the impact of fjord sill depth on circulation and biogeochemistry in a Greenland fjord system. The data includes three scenarios with different sill depths (250m baseline, 200m, and 100m) and provides fjord-averaged temperature, dissolved inorganic nitrogen (DIN) fluxes at the fjord mouth, cumulative DIN export, and mean DIN concentrations at the fjord outlet. Temperature differences between the baseline and modified sill scenarios are also included. These results demonstrate how fjord sill depth controls water mass exchange, heat transport, and nutrient cycling in glacial fjord systems. Data is provided as a MATLAB structure with metadata describing variables and scenarios.
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- Award ID(s):
- 2212654
- PAR ID:
- 10642028
- Publisher / Repository:
- Zenodo
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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