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The Greenland Ice Sheet has been losing mass at an accelerating rate over the past 2 decades. Understanding ice mass and glacier changes during the preceding several hundred years prior to geodetic measurements is more difficult because evidence of past ice extent in many places was later overridden. Salt marshes provide the only continuous records of relative sea level (RSL) from close to the Greenland Ice Sheet that span the period of time during and since the Little Ice Age (LIA) and can be used to reconstruct ice mass gain and loss over recent centuries. Salt marsh sediments collected at the mouth of Dronning Marie Dal, close to the Greenland Ice Sheet margin in southeastern Greenland, record RSL changes over the past ca. 300 years through changing sediment and diatom stratigraphy. These RSL changes record a combination of processes that are dominated by local and regional changes in Greenland Ice Sheet mass balance during this critical period that spans the maximum of the LIA and 20th-century warming. In the early part of the record (1725–1762 CE) the rate of RSL rise is higher than reconstructed from the closest isolation basin at Timmiarmiut, but between 1762 and 1880 CE the RSL rate is within the error range of the rate of RSL change recorded in the isolation basin. RSL begins to slowly fall around 1880 CE, with a total amount of RSL fall of 0.09±0.1 m in the last 140 years. Modelled RSL, which takes into account contributions from post-LIA Greenland Ice Sheet glacio-isostatic adjustment (GIA), ongoing deglacial GIA, the global non-ice sheet glacial melt fingerprint, contributions from thermosteric effects, the Antarctic mass loss sea level fingerprint and terrestrial water storage, overpredicts the amount of RSL fall since the end of the LIA by at least 0.5 m. The GIA signal caused by post-LIA Greenland Ice Sheet mass loss is by far the largest contributor to this modelled RSL, and error in its calculation has a large impact on RSL predictions at Dronning Marie Dal. We cannot reconcile the modelled RSL and the salt marsh observations, even when moving the termination of the LIA to 1700 CE and reducing the post-LIA Greenland mass loss signal by 30 %, and a "budget residual" of +∼3 mm yr -1 since the end of the LIA remains unexplained. This new RSL record backs up other studies that suggest that there are significant regional differences in the timing and magnitude of the response of the Greenland Ice Sheet to the climate shift from the LIA into the 20th century. [ABSTRACT FROM AUTHOR]

To put recent Greenland Ice Sheet (GrIS) ice loss into a longer-term context, we must understand its behavior during late-glacial and Early Holocene warming. Previous results seem to suggest that there is a large contrast in the timing of deglaciation between South and Southeast Greenland. However, because of lack of available data, in particular in Southeast Greenland, it is difficult to assess how the ice sheet responded to major late-glacial and Early Holocene climate changes. In this study, we use 41 new 10Be ages to constrain the deglaciation chronology in 12 new locations from the coast to the present ice margin in South and Southeast Greenland. We find that South Greenland (south of 61.5°N) deglaciated between ∼14.8 and 11.9 ka, whereas Southeast Greenland (61.5°N to 68.2°N) deglaciated between ∼11.4 and 11.3 ka. The deglaciation of the coastal, low-intermediate topography in South Greenland coincides with increased air surface temperatures during the Bølling-Allerød with fjords continuing to deglaciate into the Early Holocene. In contrast, the ice sheet persisted at the coast until the late-glacial and Early Holocene in Southeast Greenland, likely because of increased precipitation in the high alpine topography and fjord geometry and bathymetry (e.g. width of fjords and presence of sills). This multi-phased deglaciation demonstrates a contrasting response of the southern GrIS to changes in climate and variations in topographic setting, and that the spatial deglaciation of the GrIS was complex and likely did not respond to a single external climate forcing. • Deglaciation began in South Greenland by 14.8 ka coeval with rising air temperature. • Warm Atlantic water likely drove deglaciation during the Younger Dryas. • Ice retreated from Southeast Greenland coast by 11.3 ka when air temperatures rose. • Evidence of a Neoglacial advance occurs in Southeast Greenland by ∼1.9 ka. • Local climate, topography and fjord geometry/bathymetry likely mediated ice retreat. [ABSTRACT FROM AUTHOR]

Knowledge about the future response of the Greenland Ice Sheet to global climate change, including ice sheet contributions to sea level rise, is important for understanding the impact of climate change on society. Such studies rely in ice sheet model predictions and improved chronological constraints of past ice sheet extents and paleoclimatic trends. Many regions in Greenland are well studied, but northwest Greenland and especially Melville Bay, being one of the most important regions in terms of dynamical ice mass loss, lack a firm chronology of Holocene ice marginal fluctuations. In this study, we present the first comprehensive chronology for Melville Bay spanning 73.1–75.7°N based on 36 new 10Be exposure ages of boulders and 39 new radiocarbon ages of marine molluscs in Little Ice Age moraines. From weighted mean 10Be exposure ages, excluding 6 outliers, we find that the outer coast in Melville Bay was deglaciated ∼11.6 ± 0.3 ka (n = 15) and the ice margin reached its present-day position 40 km farther inland ∼11.5 ± 0.3 ka (n = 15). Our results suggest an interval of rapid ice-marginal retreat (i.e. collapse) of the northwest GrIS in Melville Bay, most likely triggered by rapidly rising atmospheric temperatures in early Holocene. Additionally, combining the comprehensive dataset of new radiocarbon ages with 26 radiocarbon ages from previous studies shows a restricted ice sheet extent from 9.1 ± 0.2 to 0.4 ± 0.1 cal ka BP, which coincides with increased sea surface temperatures. Our results highlight past ice sheet sensitivity towards climate changes in one of the least explored and most vulnerable regions of Greenland. Furthermore, comparing our new results to already existing ice sheet models (Huy3 and Huy3b) emphasize the proximal relevance of the Agassiz ice core temperature reconstruction for Melville Bay, which indicates the possible sensitivity of the ice sheet to a warming climate and place improved constraints on ice sheet simulations. • The northwest Greenland Ice Sheet was very sensitive to past climate changes. • The marine-based part of the ice sheet collapsed in Early Holocene. • The ice sheet was smaller than present throughout middle and late Holocene. • Rising atmospheric and sea surface temperatures drove deglaciation. • Ice sheet models do not fully capture this behaviour and improvements are needed. [ABSTRACT FROM AUTHOR]