UC San Diego

The glacial fjords that connect the Greenland Ice Sheet to the North Atlantic control ocean heat transport toward the ice sheet and the downstream fate of glacier meltwater. This thesis builds on a growing body of research into Greenland fjord dynamics, focusing on aspects of glacier-fjord systems that are especially challenging to observe: sub-annual ocean variability beneath a floating ice tongue; iceberg meltwater properties and distribution; and the distribution and cycling of environmental mercury.

Ice discharge to the ocean can be moderated by ice tongues, floating extensions of glaciers that buttress the upstream ice flow. In Chapter 3, an ice-tethered mooring record from beneath the 79 North Glacier ice tongue shows that ocean warming observed on the continental shelf is advected into the fjord and reaches the glacier grounding line within 6 months, indicating that basal melt of the ice tongue is sensitive to regional ocean variability.

Icebergs calved from tidewater glaciers are a major component of fjord freshwater and heat budgets in fjords, but there are few observations to constrain iceberg melt models. In Chapter 4, meltwater plume intrusions are identified based on their temperature and salinity properties in two surveys of a large iceberg in Sermilik Fjord in southeast Greenland. The intrusions are distributed around the iceberg between 80-250 m depth and drive upwelling over vertical scales averaging 15-50 m, with the plume height primarily controlled by stratification. A standard melt plume model does not recreate the observed melt concentrations even with adjustments to the model coefficients, suggesting that more substantial modifications to the model physics are needed to accurately simulate iceberg melt and upwelling.

In Chapter 5, results from a recent survey in Sermilik Fjord show that glacially modified waters are depleted in the toxic trace element mercury relative to regional ocean waters, indicating that glacier melt is not a significant source of environmental mercury in that system. We hypothesize that mercury is removed from the water column in the ice melange region near the glacier terminus through scavenging and settling of suspended sediments from iceberg melt and runoff.