Seasonal Flow Types of Glaciers in Sermilik Fjord, Greenland, Over 2016–2021.

Greenland glaciers have three primary seasonal ice flow patterns, or "types": terminus‐driven, runoff‐driven, and runoff‐adapting. To date, glacier types have been identified by analyzing flow at a single location near the terminus; information at all other locations is discarded. Here, we use principal component (PC)/empirical orthogonal function (EOF) analysis to decompose multi‐year time series of glacier speed, combined from three satellite‐derived products at four glaciers feeding Sermilik Fjord, Greenland. This improves on single‐point methods by yielding spatial patterns (EOFs), which ensure the result reflects data at all locations on the glacier, and associated temporal patterns (PCs), which allow identification of glacier type. We find that the leading EOF is uniformly signed over the entire glacier domain, that this mode explains the majority of the variance in speed, and therefore that glacier type can be inferred from the leading PC. We find that Helheim Glacier was terminus‐driven, Fenris Glacier and Midgard Glacier were runoff‐adapting, and Pourquoi Pas Glacier was runoff‐driven over 2016–2021. Our classification agrees with previous work for Helheim and Midgard Glaciers, but differs at the other two. At all but Fenris Glacier, the leading PC correlates significantly with the speed pattern observed at the single point used in previous analyses. Thus, Fenris Glacier has more complex flow patterns than single‐point analysis can capture, and wider spatial analysis techniques such as EOF/PC are required. We suggest that, due to its low computational cost and inclusion in standard analysis packages, EOF/PC analysis should be used for assessing glacier type. Plain Language Summary: Glaciers change their flow speed throughout the year. Most glaciers move slowest in winter and more quickly during summer, but subtle differences in the timing give us clues as to what controls the speed of the glacier. Some glaciers respond to ocean conditions ("terminus‐driven"), others respond to ice melting at the top surface of the glacier ("runoff‐driven"), and still others adjust their water systems as the ice melts, responding to the same melt in a different way ("runoff‐adapting"). We do not know the types of all glaciers, nor what causes a glacier to be a certain type. Previous work identified the types of a few dozen glaciers around Greenland by manually examining ice flow at a single point on each glacier. Here, we take a wider approach by mathematically extracting patterns in ice flow across the entire glacier, not just a single point. We analyze four glaciers that flow into the same fjord in East Greenland. Our results broadly agree with the previous simpler analyses, but differ at two glaciers and identify possible "multi‐type" glaciers. Thus, our method holds promise in the quest to discover what controls the seasonal flow patterns of Greenland glaciers. Key Points: Glacier type varies across Sermilik Fjord: Helheim is terminus‐driven, Fenris and Midgard are runoff‐adapting, and Pourquoi Pas is runoff‐drivenDecomposition by empirical orthogonal functions and principal components reveals glacier type using data at all points in the glacier domainInferred glacier types differ slightly from previous work because we weight all locations equally and isolate the seasonal component [ABSTRACT FROM AUTHOR]