UC Irvine

River deltas are fascinating, ecogemorphologically complex landscapes at the river-coastal interface which are rich in biodiversity, are economic hotspots due to their major food production and ports, and are home to more than $340$ million people, although composing only 0.57$ of the global land surface. They are vulnerable to sea level rise, human actions from upstream, and increased erosion from more severe storm activity. Arctic river deltas are especially at high risk from climate change induced impacts, in part due to their unique permafrost features. In particular, thermokarst lakes, which are formed by the thaw of ice-rich permafrost, are expected to both expand and drain under future warming, reconfiguring deltaic hydrology and impacting the arctic carbon cycle. Yet studies focusing on thermokarst lake dynamics and trends in deltaic environments are limited.

In this dissertation we first place arctic river delta morphologic variability in a global context through a multiscale characterization of river delta shoreline structure (Chapter 2). Then, we interrogated thermokarst lake processes in arctic river deltas through analysis of summertime surface water dynamics to infer permafrost presence (Chapter 3), development of a methodology for the extraction of perennially inundated lakes from a long remote sensing record to explore relationships of thermokarst lake size distributions with climate (Chapter 4), and characterization of thermokarst lake patterns towards inferring permafrost and geomorphic processes on arctic deltas (Chapter 5).

The results of this dissertation advance our understanding of the link between observed delta morphology and the dominant forcings which have formed deltas, provide the first quantitative framework for studying the spatial distribution of thermokarst lakes in terms of their size and location for delta comparison and for tracking their temporal changes, as well as for constraining and evaluating physics-based models. Some open questions are posed that require future study and targeted field observations to connect processes to their expression on the landscape and increase our confidence for future projections of the hydrogeomorphology of arctic deltas in response to global warming.