Contrasting modes of deglaciation between fjords and inter‐fjord areas in eastern North Greenland

Abstract

Knowledge about the deglaciation history of the Greenland Ice Sheet (GrIS) is important to put the recent observations of ice loss into a longer‐term perspective. In southern Greenland, the deglaciation history is generally well constrained. In this study, we use 43 new 10Be surface exposure ages combined with existing minimum‐limiting 14C ages to constrain the deglaciation history of eastern North Greenland, including the three major fjord systems – Independence Fjord, Hagen Fjord and Danmark Fjord. The 10Be ages are generally scattered and many of the samples are significantly older than expected, with pre‐LGM ages being a result of inheritance from previous exposures. By using a Bayesian statistical approach to combine the new 10Be ages and existing 14C ages, we are able to constrain the deglaciation history. We find that the outer coast and deep fjords were rapidly deglaciated between ̃11 and 10 ka. Subsequently, the deglaciation progressed far inland up the fjords, probably as a result of increased summer surface temperatures and subsurface ocean temperatures during the Holocene Thermal Maximum. The rapid retreat of the Middle Holocene slowed when the ice sheet became land‐based in the central and southern part of the study area where the ice margin first reached its present extent by ̃6.7 ka. As the onset of Neoglacial ice advance had already commenced at ̃5 ka this limits the period when the ice margin could retreat farther inland and it probably remained within max. 30–40 km of its present extent. The contrasting behaviour between the fjords and inter‐fjord areas shows a clear topographic effect on the stability of the GrIS. These results inform how the GrIS may respond to a warmer climate in various topographic settings and may provide useful constraints for future ice‐sheet models.

Permafrost Thermal Dynamics and Cryostratigraphy at Villum Research Station, Station Nord, Eastern North Greenland (81°N)

“…The Unit 1 diamicton, only present at SN2, is interpreted as till, presumably from when the Prinsesse Ingeborg Halvø was glaciated before 11 cal. ka BP (Larsen et al., 2020). This till is likely found across the whole peninsula, and thus we expect it would have been found at SN1 had the borehole been drilled to the same depth as SN2, relative to sea level.…”

“…A similar environment exists in outer Danmark Fjord today, but a more expansive calving glacier front was likely present during the early stages of deglaciation. Iceberg production and influx of ice‐rafted sediment was likely at a maximum during the most rapid period of ice retreat from 11 to ∼8.2 ka (Larsen et al., 2020). Given the location of the boreholes in beach ridges and the marine limit of at least 81 m a.s.l.…”

“…ka BP, with relatively rapid ice retreat continuing until the ice sheet became land‐based around ∼8.2 ka (Larsen et al., 2020). The Greenland Ice Sheet reached its present extent around ∼6.7 ka in Kronprins Christian Land, and further retreat inwards of the present extent was limited during the Holocene Thermal Maximum (Larsen et al., 2020). After becoming an independent ice cap during deglaciation, Flade Isblink persisted throughout the entire Holocene, but reached a minimum extent (smaller than today) between ∼8.7 and 3.1 cal.…”

“…Additional work on lake sediments and radiocarbon dating of moraine material has elucidated the ice‐marginal fluctuations of local ice caps (Larsen et al., 2019), and Larsen et al. (2020) presented the overall deglaciation history of eastern North Greenland.…”

“…Strunk et al (2018) established the minimum marine limit and Holocene sea level history of Finderup Land, adjacent to the Prinsesse Ingeborg Halvø in the west, based on cores from five isolation lakes. Additional work on lake sediments and radiocarbon dating of moraine material has elucidated the ice-marginal fluctuations of local ice caps (Larsen et al, 2019), and Larsen et al (2020) presented the overall deglaciation history of eastern North Greenland.…”