Synchronous Retreat of Southeast Greenland's Peripheral Glaciers

Recently, scientific attention has focused on estimating Greenland's dynamic mass loss through changes to flow speeds, thickness, and length on its marine outlet glaciers. For the ice sheet outlet glaciers, dynamic mass loss has been found to be highly sensitive to changes in climate and individual glacier geometry. For the ice‐sheet‐independent marine glaciers around Greenland's periphery, dynamic mass loss is presently overlooked. Here, we apply an open‐source, automated method of measuring glacier length changes using satellite imagery, to produce highly detailed records of length changes for 135 peripheral marine glaciers in southeast Greenland. We find evidence for anomalous retreat across 56 glaciers coincident with elevated surface melt in 2016, with melt 22% above the 2013–2019 average. Our detailed observations resolve the widespread, rapid, and synchronous response of these independent marine glaciers to increased meltwater input in 2016, indicating that their dynamics may be more sensitive to atmospheric warming than currently thought. Plain Language Summary Mass loss from Greenland's ice sheet and surrounding glaciers contribute to global sea level rise and the freshening of regional ocean waters, which impacts ocean circulation patterns. Recent attention has turned to Greenland's mass loss through changes to its marine outlet glaciers' flow speeds, thickness, and length (i.e., dynamics). Outlet glacier dynamics are influenced by climate perturbations and glacier geometries, but little is known about the dynamics of the ∼600 ice‐sheet‐independent marine glaciers in Greenland. We use an automated method to measure glacier length changes using satellite imagery, leading to highly detailed records of length changes for 135 independent marine glaciers in southeast Greenland. We find evidence for anomalous retreat across 56 glaciers, which coincided with elevated surface melt in 2016. Our detailed observations and comparison with climate records demonstrate that independent marine glaciers can have a sensitive response to atmospheric warming. It is possible that other independent marine glaciers are also capable of widespread synchronous response to atmospheric forcing, but it may not be resolved with the limited study size and temporal resolution imposed by manual mapping methods. Key Points We produced detailed records of glacier length change for 135 marine glaciers in southeast Greenland using an efficient automated method 56 (∼41%) of the ice‐s