The dynamics of shelf forcing in Greenlandic Fjords

TitleThe dynamics of shelf forcing in Greenlandic Fjords
Publication TypeJournal Article
Year of Publication2018
AuthorsJackson R.H, Lentz S.J, Straneo F
JournalJournal of Physical Oceanography
Date Published2018/11
Type of ArticleArticle
ISBN Number0022-3670
Accession NumberWOS:000450407900001
Keywordsbaroclinic flows; Coastal flows; coastal-trapped waves; driven; east greenland; estuaries; glaciers; heat delivery; ice-sheet; Kelvin waves; oceanic heat; oceanography; outlet glaciers; Regional models; simple-model; subglacial discharge; tidewater glaciers

The fjords that connect Greenland's glaciers to the ocean are gateways for importing heat to melt ice and for exporting meltwater into the ocean. The transport of heat and meltwater can be modulated by various drivers of fjord circulation, including freshwater, local winds, and shelf variability. Shelf-forced flows (also known as the intermediary circulation) are the dominant mode of variability in two major fjords of east Greenland, but we lack a dynamical understanding of the fjord's response to shelf forcing. Building on observations from east Greenland, we use numerical simulations and analytical models to explore the dynamics of shelf-driven flows. For the parameter space of Greenlandic fjords, we find that the fjord's response is primarily a function of three nondimensional parameters: the fjord width over the deformation radius (W/R-d), the forcing time scale over the fjord adjustment time scale, and the forcing amplitude (shelf pycnocline displacements) over the upper-layer thickness. The shelf-forced flows in both the numerical simulations and the observations can largely be explained by a simple analytical model for Kelvin waves propagating around the fjord. For fjords with W/R-d > 0.5 (most Greenlandic fjords), 3D dynamics are integral to understanding shelf forcingthe fjord dynamics cannot be approximated with 2D models that neglect cross-fjord structure. The volume flux exchanged between the fjord and shelf increases for narrow fjords and peaks around the resonant forcing frequency, dropping off significantly at higher- and lower-frequency forcing.

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