Glacial history of Inglefield Land , north Greenland from combined in-situ 10 Be and 14 C exposure dating

Exposing the sensitivity of the Greenland Ice Sheet (GrIS) to Holocene climate changes is a key prerequisite for understanding the future response of the ice sheet to global warming. In this study, we present new information on the Holocene glacial history of the GrIS in Inglefield Land, north Greenland. We use 10Be and in-situ 14C exposure dating to constrain the 15 timing of deglaciation in the area and radiocarbon dating of reworked molluscs and wood fragments to constrain when the ice sheet retreated behind its present-day extent. The 10Be ages are scattered ranging from c. 92.7 to 6.8 ka whereas the in-situ 14C ages range from c. 14.2 to 6.7 ka. Almost half of the apparent 10Be ages predate the Last Glacial Maximum and up to 89 % are to some degree affected by nuclide inheritance. Based on the few reliable 10Be ages, the in-situ 14C ages and existing radiocarbon ages from Inglefield Land, we find that the deglaciation along the coast commenced c. 8.6-8.3 cal. ka BP in the 20 western part and c. 7.9 ka in the central part, following the opening of Nares Strait and arrival of warm waters. The ice margin reached its present-day position c. 8.2 ka at the Humboldt Glacier and c. 6.7 ka in the central part of Inglefield Land. Radiocarbon ages of reworked molluscs and wood fragments show that the ice margin was behind its present-day extent from c. 5.8 to 0.5 cal. ka BP. After 0.5 cal. ka BP, the ice advanced towards its Little Ice Age position. Our results emphasize that the slowly eroding and possibly cold-based ice in north Greenland makes it difficult to constrain the deglaciation history based 25 on 10Be ages alone unless it is paired with in-situ 14C ages. Further, combining our findings with those of recently published studies reveals distinct differences between deglaciation patterns of northwest and north Greenland. Deglaciation of the land areas in northwest Greenland occurred earlier than in north Greenland and periods of restricted ice extent were longer, spanning middle and late Holocene. Overall, this highlights past ice sheet sensitivity towards Holocene climate changes in an area where little information was available just a few years ago. 30 https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c © Author(s) 2020. CC BY 4.0 License.


Introduction
Information about the glacial history of the Greenland Ice Sheet (GrIS) is important to constrain its sensitivity to past and ongoing climate changes (Lecavalier et al., 2017;Larsen et al., 2018). Since the 1990s, mass loss from the GrIS has accelerated, 35 coinciding with atmospheric warming, and the ice sheet appears extremely sensitive to this warming, especially in north Greenland, where the ablation area has expanded with 46 % (Khan et al., 2015;Noël et al., 2019). As a result, the relative contribution to sea level rise from the north GrIS has increased significantly primarily through enhanced runoff as well as ice discharge via calving and melting at the Humboldt Glacier front (Mouginot et al., 2019;Noël et al., 2019).
With the introduction of cosmogenic nuclide exposure dating, previously glaciated areas of Greenland have been 40 systematically targeted and >1000 10 Be exposure ages have been published within the last two decades (Sinclair et al., 2016).
In consequence, the late glacial and Holocene glaciation history is well constrained in most areas of Greenland (Bennike and Björck, 2002;Funder et al., 2011;Sinclair et al., 2016). However, there are still areas where the deglaciation chronology is constrained by minimum limiting radiocarbon ages of mainly marine molluscs along the coast and where inland exposure ages are unavailable (Bennike and Björck, 2002;Funder et al., 2011). This is particularly true for north Greenland including 45 Inglefield Land where the current knowledge is primarily based on studies from late 1960s and 1970s (Nichols, 1969;Tedrow, 1970).
Despite that, 10 Be exposure dating has shown to be an efficient tool for constraining the deglaciation of the GrIS, but the use of this method is not without pitfalls. The method assumes that the measured 10 Be concentration was produced in one single post-glacial exposure period without surface erosion, but a number of studies have demonstrated that this assumption does not 50 always hold. A particular challenge arises when subglacial bedrock erosion is too slow to remove 10 Be inventories produced during earlier exposure periods, such as the previous interglacial. In such case, the resulting age is typically referred to as an apparent 10 Be exposure age in acknowledgment of the fact that this age typically exceeds the true exposure age (Kelly et al., 2008;Corbett et al., 2015;Farnsworth et al., 2018;Larsen et al., 2018;Søndergaard et al., 2019;Ceperley et al., 2020;Skov et al., 2020). This problem of 10 Be nuclide inheritance emphasizes the need for new methods in order to thoroughly constrain 55 the glacial history in parts of Greenland where the cold subglacial thermal regime in many places dictates inefficient erosion and widespread nuclide inheritance.
Here we use a combination of 10 Be and in-situ 14 C exposure dating of boulders and pebbles to overcome the problem of nuclide inheritance and constrain the Holocene deglaciation history of the GrIS in Inglefield Land, north Greenland. In addition, we use radiocarbon dating of reworked marine molluscs and wood fragments to constrain the Holocene timing of restricted ice 60 extent in the study area. Finally, we review and assess the glacial history in northwest and north Greenland with both local and regional climate records in order to expand our knowledge of the long-term sensitivity of the GrIS to climate changes. https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License.

Study site and previous work
Inglefield Land is situated in north Greenland, between 78. 2-79.1° N and 65.8-72.8° W and is bound to the south and east by 65 the GrIS, to the west by Smith Sound and to the north by Kane Basin and Humboldt Glacier (Fig. 1). Humboldt Glacier drains c. 5 % of the GrIS into Nares Strait and has a varied velocity profile due to diverse bed topography and drainage networks (Rignot and Kanagaratnam, 2006;Hill et al., 2017;Livingstone et al., 2017). In addition to the marine terminating Humboldt Glacier, the land-based Hiawatha Glacier is present in the eastern part of Inglefield Land. Together with the GrIS, this glacier overlie the newly discovered Hiawatha impact crater which makes the ice form a half circular structure, characterized by ice 70 that flows faster than the rest of the ice margin terminating on land in Inglefield Land (Kjaer et al., 2018).
The region is a high-Arctic desert, with low precipitation rates of c. 100-150 mm per year, falling mostly as snow (Blake et al., 1992;Dawes, 2004). The bedrock in the area is composed of Paleoproterozoic granite and gneiss, Late Proterozoic sedimentary and volcanic rocks and Lower Paleozoic sedimentary rocks and shelf carbonates with Quaternary deposits close to the present-day ice margin (Dawes, 2004;Kolb et al., 2016). The relief is gently declining from 600-700 m a.s.l. close to 75 the present-day ice margin towards the coast where meltwater channels and rivers cut the up to c. 400 m high plateaus composed of sedimentary rocks (Dawes, 2004).
During the Last Glacial Maximum (LGM) the GrIS and Inuitian Ice Sheet coalesced in Nares Strait and the ice flowed northand southward from a saddle in Kane Basin (England et al., 2006). The southward flowing ice formed the Smith Sound Ice Stream (England et al., 2006;Jennings et al., 2019) and it is believed to have extended to the 600 m depth contour in northern 80 Baffin Bay (Funder et al., 2011). Radiocarbon ages reveal that deglaciation of Nares Strait initiated at the northern entrance c. 11 cal. ka BP and southern entrance c. 10 cal. ka BP (Bennike and Björck, 2002;Jennings et al., 2011). The final deglaciation and opening of the Nares Strait have been debated but recent off shore studies together with a few terrestrial studies place the collapse of the ice saddle in Kane Basin and opening of Nares Strait between c. 9-8 cal. ka BP (Georgiadis et al., 2018;Jennings et al., 2019;Dalton et al., 2020). Recently, Jakobsen et al. (2018) and Reusche et al. (2018) proposed overall glacial retreat of 85 the GrIS in north Greenland during the Holocene, but with a possible stillstand of the ice sheet and its outlet glaciers as a response to the 8.2 cold events. These studies further suggested a restricted extent of the ice sheet in middle and late Holocene, until c. 0.3 ka where the ice reached its Little Ice Age (LIA) position.
The glacial history of Inglefield Land comprises the history of the Smith Sound Ice Stream along the coast, and the history of the GrIS in Inglefield Land, as described by Nichols (1969), Tedrow (1970) and Blake et al. (1992), with additional evidence 90 from the neighbouring Humboldt Glacier and Washington Land to the east by Bennike (2002) and Reusche et al. (2018). The deglaciation of the interior parts of Inglefield Land is less well known but a set of distinct moraine systems between the presentday ice margin and the coast line (Nichols, 1969) suggest that the GrIS made several stops or readvances during the overall deglaciation of Inglefield Land. Our current knowledge about the timing of deglaciation in Inglefield Land comprises a number of minimum limiting radiocarbon ages of raised marine deposits from the coastal areas that range from c. 8.6 to 6.6 cal. ka BP 95 (Nichols, 1969;Blake et al., 1992;Mason, 2010). The marine limit in Inglefield Land has been determined at several locations https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License. and decreases from c. 90 m in the southwestern part of Inglefield Land to c. 65 m in the northeastern part of Inglefield Land (Nichols, 1969;Funder and Hansen, 1996).

Cosmogenic nuclide exposure dating 100
Cosmogenic nuclide exposure dating is a widely used method to constrain the deglaciation history of former glaciated areas (Gosse and Phillips, 2001;Ivy-Ochs and Kober, 2008;Balco, 2020). One of the most common used nuclides is 10 Be as it forms in the abundant mineral quartz, and is fairly easy to extract and measure by accelerator mass spectrometry. However, due to its relatively slow decay and long half-life (1.4x10 6 yr), problems can arise in areas characterized by slow-moving cold-based ice as small rates of erosion hinder complete removal of nuclides "inherited" from prior exposures and thus, yield apparent 105 exposure ages exceeding the length pf the last ice-free period (Heyman et al., 2011). Nuclide inheritance is present in samples throughout Greenland, particularly at high elevations away from glacial troughs and fjords (Kelly et al., 2008;Corbett et al., 2013;Håkansson et al., 2016;Young et al., 2020) but it seems to be especially frequent in north Greenland where several studies have shown more widespread nuclide inheritance (Farnsworth et al., 2018;Larsen et al., 2018;Søndergaard et al., 2019;Ceperley et al., 2020;Larsen et al., in review). 110 Measurements of in-situ produced 14 C in boulders and bedrock can however circumvent the nuclide inheritance problem and help to obtain more reliable exposure ages (Hippe, 2017;Graham et al., 2019). Due to its shorter half-life (5730 yr), in-situ 14 C is sensitive to radioactive decay on late Quaternary and Holocene timescales as the concentration build up from prior exposure will rapidly decrease, when a surface is shielded from cosmic rays (Lifton et al., 2001;Hippe, 2017). As such, it is an optimal tool to solve the most recent deglaciation history of the GrIS. However, in-situ 14 C is still not the preferred nuclide 115 for exposure dating as the extraction process is demanding despite many improvements and developments within recent years (Lifton et al., 2015;Goehring et al., 2019;Lupker et al., 2019). Still more robust information on the deglaciation history can be achieved by using combined measurements of 10 Be and 14 C as shown by previous studies (Corbett et al., 2013;Hippe, 2017;Young et al., 2018;Graham et al., 2019). 120 3.1.1 10 Be exposure dating 10 Be exposure dating of boulders and pebbles was used to constrain the most recent glacial history of Inglefield Land. A total of 25 boulder samples were collected, all resting on bedrock except for sample GL1732-GL1735, which were on top of two moraines in the western part of Inglefield Land (Fig. 1c). In addition, two samples consisting of quartz pebbles (GL1715 and GL1716) were collected on an outwash plain in the northeastern part of Inglefield Land. Samples were collected using a rock 125 saw, hammer and chisel to cut out the top few centimetres of quartz bearing stable boulders (Fig. 2). With a hand-held Garmin e-trex 30 GPS, we recorded the latitude, longitude and elevation of each sample. The orientation of the rock surface and https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License.
shielding by the surrounding topography were measured using a compass and clinometer, respectively. Elevations of the sampled boulders were all between 65 m a.s.l. and 542 m a.s.l., and thus, were all at or above the local marine limit of the area (Nichols, 1969;Blake et al., 1992;Funder and Hansen, 1996). We measured sample thicknesses with a caliper before the 130 samples were crushed and sieved. This information was used to calculate the average thickness of each sample. For boulder and pebble samples we used the 250-700 µm fraction to isolate quartz and extract beryllium.
All samples were processed in the Cosmogenic Nuclide Laboratory at Department of Geoscience, Aarhus University following methods adapted from (Corbett et al., 2016). The 10 Be/ 9 Be ratios were measured at the Aarhus AMS Centre and all samples were blank corrected. Nuclide concentrations were normalized to the Beryllium standard ICN-01-5-4, with a 10 Be/ 9 Be value 135 of 2.851 x 10 -12 (Nishiizumi et al., 2007). Apparent 10 Be exposure ages were calculated using the online exposure age calculator formerly known as the CRONUS-Earth online exposure calculator v.3 (Balco et al., 2008) in combination with the Baffin Bay production rate (Young et al., 2013) and the Lm production scaling scheme (Lal, 1991;Stone, 2000). The rock density was set to 2.65 g/m 3 as it is representative for the boulders we sampled, and we assumed zero erosion. We did not correct for cover by vegetation or snow as the vegetation in the area is sparse and precipitation rates are low, c. 100-150 mm per year (Dawes, 140 2004). The sampled boulders were furthermore all positioned in open locations in the landscape making it highly unlikely that any snow cover persisted for long periods of time. As the glaciostatic uplift history is not well constrained in north Greenland, we present our 10 Be ages without any uplift correction, similarly to many other studies in Greenland which have shown the corrections to be negligible (Young et al., 2012;Sinclair et al., 2016;Larsen et al., 2018;Young et al., 2020).
All resulting apparent exposure ages and parameters used in the calculations can be seen in Table 1. The 10 Be ages are presented 145 with 1s analytical uncertainty and ages calculated using other scaling schemes deviate by <2 %.

In-situ 14 C exposure dating
We used in-situ 14 C exposure dating to further constrain the deglaciation history of Inglefield Land, primarily by testing for 10 Be nuclide inheritance in selected samples. Four of the quartz samples used for 10 Be exposure dating were chosen for in-situ 150 14 C exposure dating, GL1725, GL1712, GL1701 and GL1708. We chose these samples based on i) the resulting apparent 10 Be exposure ages within each sample location, ii) the amount of quartz left, and iii) the sample location in the study area to secure a broad spatial distribution (Fig. 1c). Approximately 4 g of purified quartz, the same used for 10 Be extraction, was used to extract the in-situ produced 14 C. Samples for in-situ 14 C measurements were processed using the in-situ 14 C extraction line at ETH Zürich (Hippe et al., 2009;Lupker et al., 2019). Samples were measured at ETH Zürich with the MICASAS AMS system 155 (Synal et al., 2007;Wacker et al., 2010) and sample in-situ 14 C concentrations were calculated from measured 14 C/ 12 C ratios (Hippe and Lifton, 2016). In-situ 14 C ages were calculated using the online exposure age calculator formerly known as the CRONUS-Earth online exposure calculator v.3 (Balco et al., 2008), the west Greenland production rate (Young et al., 2014), and the Lm production scaling scheme (Lal, 1991;Stone, 2000). All resulting ages and variables used in the calculations are https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License. listed in Table 2. In-situ 14 C exposure ages are presented with 1s analytical uncertainty and ages calculated using other scaling 160 schemes deviate by <4 %.

Radiocarbon dating of reworked molluscs and wood fragments
Radiocarbon dating of reworked organic material in glacial deposits can be used to determine when the ice extent was smaller than present (Bennike and Weidick, 2001;Briner et al., 2014;Farnsworth et al., 2018). For this purpose, we therefore collected 165 reworked marine molluscs at the southern margin of the Humboldt Glacier (Fig. 1c). From the samples site, 15 molluscs were chosen, pre-treated following the procedure of (Brock et al., 2010), and radiocarbon dated at the Aarhus AMS Centre (Olsen et al., 2016). In addition, four wood fragments were retrieved at 193 m a.s.l. on the meltwater plain in front of the Hiawatha Glacier (Fig. 1c). The wood fragments were pre-treated and radiocarbon dated at Beta Analytic.
Radiocarbon ages for the molluscs were calibrated using OxCal v4.3 (Ramsey, 2009) with the Marine13 calibration curve 170  and a marine reservoir effect of 550 14 C years (DR=150 14 C a) based on a couple of ages from molluscs collected alive before 1960 in north Greenland (Mörner and Funder, 1990). Radiocarbon ages for the wood fragments were calibrated with the IntCal13 calibration curve . Sample information, resulting radiocarbon ages, and calibrated ages are reported in Table 3. Throughout the text, we use the mean calibrated radiocarbon age ±2s.

Results 175
4.1 10 Be and in-situ 14 C exposure dating 10 Be exposure dating was carried out on 25 boulder samples and 2 samples consisting of pebbles to constrain the deglaciation of Inglefield Land (Fig. 3). The measured 10 Be concentrations in the 27 samples range from 3.0±0.9x10 4 to 60.3±0.9x10 4 10 Be at/g and result in apparent exposure ages ranging from 92.7±1.5 ka to 6.8±2.0 ka, with the oldest ages being from boulders on moraines in the western part of the area and the younger ages resulting from boulders closer to Humboldt Glacier and the coast 180 in the northeastern part of the area (Fig. 3, Table 1).
Although the 10 Be ages are scattered we see some structure in the dataset. The majority of ages sampled below 300 m a.s.l.
group within the post-LGM period, with a peak in early Holocene whereas most samples above 450 m a.s.l. predate the LGM.
Further, there also seem to be a vague pattern in spatial distribution, with the oldest 10 Be ages being from the two moraine ridges in western Inglefield Land and the youngest boulder ages closer to Humboldt Glacier. 185 In-situ 14 C exposure dating were carried out to better constrain the deglaciation of Inglefield Land from the scattered 10 Be ages.
The measured in-situ 14 C concentrations in the four samples range from 8.4±0.3x10 4 to 17.4±0.2x10 4 at/g and resulted in exposure ages ranging from 14.2±0.5 ka to 6.7±0.3 ka (Fig. 3, Table 2). All in-situ 14 C ages are younger than the 10 Be ages resulting from the same quartz sample, confirming that the 10 Be ages are generally affected by nuclide inheritance. However, https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License. the in-situ 14 C ages do to some degree match the youngest 10 Be ages from the same localities, except for GL1701, which 190 predate the Holocene. The remaining three in-situ 14 C ages group in middle Holocene.

Radiocarbon dating of reworked molluscs and wood fragments
Reworked marine molluscs were collected from the surface of and within diamictic sediments along the western margin of the Humboldt Glacier (Fig. 1c). Several species were identified and 15 samples of Mya truncata, Hiatella arctica and Astarte 195 borealis were used for radiocarbon dating. The calibrated mean radiocarbon ages range from 3.6±0.04 to 0.5±0.03 cal. ka BP ( Fig. 4, Table 3) and reflect the period when the Humboldt Glacier was behind its present-day extent. In addition, the wood samples collected on the outwash plain in front of the Hiawatha Glacier resulted in ages between 5.8±0.06 cal. ka BP and 1.9±0.04 cal. ka BP (Fig. 4, Table 3).

Indications of low erosion rates and cold-based ice in north Greenland
The 10 Be ages from Inglefield Land are scattered which makes it difficult to fully constrain the glacial history in the area. We consider the 12 10 Be ages older than the LGM as evidence of nuclide inheritance from prior exposure (Fig. 3)  We also consider the oldest in-situ 14 C age of c. 14.2 ka to be affected by inheritance as it is unlikely that Inglefield Land was deglaciated at that time. The only modelled scenario of nuclide build up that almost reach the measured concentration of the 210 sample and still follow the known glacial history of the GrIS in north Greenland is seen in Figure 5. In this scenario, Inglefield Land was deglaciated during MIS 3 from 45 to 23 ka and again in Holocene from 6.7 ka until present. This limits the expansion of the GrIS during the LGM to a narrow interval from c. 23 to 7 ka. This scenario is to some degree consistent with other studies in northern Greenland that suggest a restricted GrIS during MIS 3 Søndergaard et al., 2019) and a late coalescence of the GrIS and Inuitian Ice Sheet around 22 cal. ka BP (England, 1999). However, as we only have one 215 datapoint and the simulation is incapable of fully reaching the measured concentration we cannot make any firm conclusions on the timing of prior exposure of the sample and the implications for the ice sheet history.
The trend between apparent 10 Be ages and elevation of the samples points towards larger amount of inheritance in samples from higher elevations (Fig. 6). This pattern has also recently been observed in adjacent Washington Land as well as in Dove Bugt, northeast Greenland (Ceperley et al., 2020;Skov et al., 2020). In addition, there is an increasing amount of inheritance 220 in samples farther away from the Humboldt Glacier. This spatial distribution of samples with inheritance at higher elevations away from the Humboldt Glacier is expected as these locations represent areas outside troughs where erosion is low because of slowly moving or even cold-based ice. A similar relationship between nuclide inheritance and elevation and distance to deep fjords with large fast flowing outlet glaciers indicative of higher erosion rates has been demonstrated elsewhere in Greenland (Larsen et al., 2014;Søndergaard et al., 2019). 225 Overall, inheritance and the lack of sufficient nuclide resetting is a widespread problem especially in north Greenland, and have complicated several studies within recent years (Corbett et al., 2015;Farnsworth et al., 2018;Søndergaard et al., 2019;Ceperley et al., 2020;Larsen et al., in review). Thus, we conclude that large parts of the north GrIS were inefficient at eroding the subglacial topography during parts of or throughout the last glaciation probably because subglacial sliding were limited by cold-based thermal conditions and the overall low ice flux resulting from the relatively small precipitation rates of the region. 230 We note that cold-based zones are also considered to dominate the present-day thermal state of the GrIS (MacGregor et al., 2016).

Holocene glacial history of Inglefield Land
During the LGM, Inglefield Land was completely ice covered and the ice nourished the Smith Sound Ice Stream primarily 235 through the Humboldt Glacier until the opening of Nares Strait sometime between c. 9 and 8 cal. ka BP (Georgiadis et al., 2018;Jennings et al., 2019;Dalton et al., 2020). The outer coast at Kap Inglefield Land, Kap Grinell and Renselaer Bay in southwest Inglefield Land was deglaciated between c. 8.6 and 8.3 cal. ka BP (Nichols, 1969;Blake et al., 1992;Mason, 2010).
Farther north, the deglaciation of the outer coast at Marshall Bay in central Inglefield Land is constrained to c. 7.9 ka by a single in-situ 14 C age. This age is largely consistent with a radiocarbon age of marine molluscs of c. 8.2 cal. ka BP at Minturn 240 Elv located c. 20 km east of Marshall Bay (Nichols, 1969) (Fig. 7a).
After reaching the outer coast, the ice margin continued its retreat towards its present-day position which was reached by c. 6.7 ka in the central part of Inglefield Land. Farther north, the ice probably retreated somewhat slower as suggested by dating of a rearrangement of the meltwater drainage pattern from the Hiawatha Glacier. Initially, meltwater flowed from the Hiawatha Glacier towards Dallas Bay, but this changed when the ice margin was approximately halfway between the coast and present-245 day extent where a water divide then rerouted the meltwater towards Marshall Bay (Nichols, 1969). The timing of this change is constrained by a single 10 Be age of meltwater deposits (pebble sample) that yield an age of c. 6.8 ka (Fig. 7b). The 10 Be age is, however, consistent with a radiocarbon age of molluscs, presumably from lower lying prodeltaic sediments, which gave an age of c. 6.6 cal. ka BP at Dallas Bay (Nichols, 1969). This suggests that the ice margin was located north of the meltwater drainage divide around c. 6.8 ka. Farthest north in Inglefield Land, at the southern flank of the Humboldt Glacier the ice margin 250 reached its present-day extent already by c. 8.2 ka (Fig. 7a). This age is consistent with the 10 Be chronology from the northern flank of Humboldt Glacier where a moraine a few hundred meters outside the LIA moraine was abandoned c. 8.3 ka (Reusche et al., 2018).
After the ice margin reached its present-day position it continued to retreat farther inland. Wood fragments in front of the Hiawatha Glacier demonstrate that the land-based part of the GrIS in Inglefield Land was smaller than present between c. 5.8 255 and 1.9 cal. ka BP. In addition, the age distribution of the molluscs collected at the Humboldt Glacier margin indicates that it was behind its present-day position between c. 3.6 to 0.5 cal. ka BP (Fig. 7a). At the northern flank of Humboldt Glacier, radiocarbon ages of reworked marine molluscs suggest that the glacier retreated at least 25 km farther inland between c. 3.7 and 0.3 cal. ka BP (Bennike, 2002) possibly favoured by the bed topography being below sea level 10's of km inland (Morlighem et al., 2014;Morlighem et al., 2017). Thus, no later than c. 0.3 cal. ka BP, the GrIS in Inglefield Land re-advanced 260 towards its LIA maximum extent. The spatial extent of the late Holocene retreat of the Hiawatha Glacier behind its presentday ice margin is not known, but the ice retreat may possibly have exposed parts of the Hiawatha impact crater (Fig. 7b).

A review of the Holocene glacial history in northwest and north Greenland
In the following we review the new data from north and northwest Greenland to put our results into a broader context. We 265 focus on two stages of the deglaciation history of the GrIS, namely when it i) deglaciated from the coast towards its presentday extent and ii) when it was smaller than present (Fig. 8). For information about the offshore deglaciation history, the reader is referred to recent reviews by Georgiadis et al. (2018 and Dalton et al. (2020).
In the southern part of northwest Greenland, the ice margin reached the outer coast near Upernavik c. 11.3 ka (Corbett et al., 2013) coinciding with the overall ice retreat in Melville Bay initiating c. 11.6 ka (Søndergaard et al., in review) (Fig. 8b). The 270 ice reached the inner part of Upernavik Fjord c. 9.9 ka  and in Melville Bay the ice was at its present-day extent already c. 11.5 ka (Søndergaard et al., in review) (Fig. 8b). Farther north, coastal deglaciation near Thule and Delta Sø began c. 10.8 ka (Corbett et al., 2015;Axford et al., 2019) and the ice margin reached its present-day extent at Delta Sø c. 10.1 ka (Axford et al., 2019). In Inglefield Bredning north of Thule the ice reached the inner parts of the fjord c. 11.9 ka   (Fig. 8b). In north Greenland, results from Inglefield Land show that the deglaciation of the outer 275 coast commenced c. 8.6 cal. ka BP in southeast and c. 7.9 ka in the central part of the coast line and the ice reached its presentday position in central Inglefield Land c. 6.7 ka. The Humboldt Glacier deglaciated and reached its present-day extent c. 8.2 ka. In the adjacent Washington Land, deglaciation of the outer coast is constrained to c. 9.0 ka with widespread deglaciation of the entire area evident c. 8.6 ka (Ceperley et al., 2020). Farther north, Petermann Glacier was positioned at the outer sill in Hall Basin c. 8.7 (Jakobsson et al., 2018) and it reached its present day position c. 6.9 ka (Reilly et al., 2019). 280 Restricted ice extent behind the present-day ice margin in northwest and north Greenland was widespread during large parts of middle and late Holocene. In Upernavik and Melville Bay, the ice sheet was behind its present-day position between c. 9.1 and 0.4 cal. ka BP (Bennike, 2008;Briner et al., 2013;Briner et al., 2014;Axford et al., 2019;Søndergaard et al., in review) ( Fig. 8c). Farther north in the Thule area and around Qaanaaq, mosses from a local ice cap and subfossil plants from the GrIS show a smaller ice extent before c. 3.3 cal. ka BP (Farnsworth et al., 2018;Axford et al., 2019;Søndergaard et al., 2019). In 285 Inglefield Land, north Greenland, wood fragments in front of the Hiawatha Glacier suggest that the ice margin was behind its https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License. present-day extent from c. 5.8 and 1.9 cal. ka BP, whereas the Humboldt Glacier retreated at least 25 km inland c. 3.7 to 0.3 cal. ka BP (Bennike, 2002). The Petermann Glacier farther north also retreated farther inland of its present-day position and following readvance reached its LIA extent c. 0.3 ka (Reusche et al., 2018;Reilly et al., 2019) (Fig. 8c).
In summary, the timing of deglaciation along the coast in northwest Greenland is earlier than in north Greenland around Nares 290 Strait, but the timing is, however, in accordance with the overall deglaciation in Greenland (Bennike and Björck, 2002;Funder et al., 2011). Further, the periods of middle and late Holocene restricted ice extent of the larger outlet glaciers in north Greenland initiated later than in northwest Greenland and was shorter.

Holocene ice and climate interactions in northwest and north Greenland 295
The contrasting pattern of deglaciation between northwest and north Greenland, can in part be explained by different responses of the two sectors to Holocene climate changes (Fig. 9). The early deglaciation of the land areas in northwest Greenland from Upernavik to Inglefield Bredning coincides with the early Holocene Thermal Maximum (HTM) (c. 11-8 ka) in northwest Greenland (Lecavalier et al., 2017;Axford et al., 2019) which initiated earlier than in the rest of Greenland (Briner et al., 2016;Buizert et al., 2018) (Fig. 9a-c). This rapid increase in surface air temperatures has been suggested to be the main driver of the 300 widespread rapid deglaciation specifically in Melville Bay, the Thule area and Inglefield Bredning (Axford et al., 2019; Søndergaard et al., 2019;Søndergaard et al., in review), showing the sensitivity of marine based ice to rising air temperatures.
Although it has been suggested that warm Atlantic waters in Hall Basin, northern Nares Strait, assisted early Holocene ice retreat (Jennings et al., 2011), warm waters and increasing ocean temperatures in southern Nares Strait seemed to arrive later than along the west Greenland coast (Dyke et al., 1996;Levac et al., 2001;Lecavalier et al., 2017;Axford et al., 2019). This 305 delay in warming ocean conditions in southern Nares Strait might be the reason why the opening of Nares Strait and the deglaciation of the coastal areas in Inglefield Land and Washington Land happened 2-3 ka later than the land areas in northwest Greenland (Bennike and Björck, 2002;Larsen et al., 2014;Sinclair et al., 2016;Larsen et al., 2019).
After the ice margin reached its present-day extent in north and northwest Greenland it continued to retreat farther inland. In northwest Greenland, the period with restricted ice extent in Melville Bay c. 9.1 to 0.4 cal. ka BP, was driven by a strengthening 310 of the West Greenland Current and warm ocean waters arriving in middle Holocene (Levac et al., 2001;Caron et al., 2020) ( Fig. 9d). The presence of Chlamys islandica infers that the period with marine based outlets were behind their present-day extent in North Greenland coincides with the arrival of warm waters in Nares Strait (Bennike, 2002). The Neoglacial cooling are known to have affected ice on land in northwest Greenland and resulting in expansion of local ice caps, lake ice cover and even parts of the northwest GrIS (Blake et al., 1992;Lasher et al., 2017;Farnsworth et al., 2018;Søndergaard et al., 2019). 315 The Hiawatha Glacier in north Greenland show a re-advance after c. 1.9 cal. ka BP, as a possible response to the Neoglacial cooling, which also seems to have provoked a readvance of the Petermann Glacier c. 2.8 ka (Reusche et al., 2018). Finally, the ice in north and northwest Greenland show a near synchronous re-advance towards its LIA extents which coincides with the LIA cooling within the last millennium (Lasher et al., 2017;Lecavalier et al., 2017;Axford et al., 2019). https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License.

Conclusion
In this study we used in-situ 10 Be and 14 C cosmogenic nuclide exposure dating and radiocarbon dating of reworked organic material to constrain the Holocene glacial history of Inglefield Land, north Greenland. Our results revealed a large scatter in the 10 Be ages with c. 45 % of the ages predating the LGM and an overall 89 % of the samples being affected by inheritance possibly due to low-erosive cold-based ice. We find that the outer coast in Inglefield Land began to deglaciate between c. 8.6 325 and 8.3 cal. ka BP in the southeastern part, whereas the central part was deglaciated by c. 7.9 ka. Following initial deglaciation, the ice margin reached its present-day position c. 6.7 ka in central Inglefield Land, whereas Humboldt Glacier in the northern part of the study area reached its present extent already by c. 8.2 ka. After deglaciation the ice margin retreated behind its present-day extent from c. 5.8 to 1.9 cal. ka BP at the Hiawatha Glacier and c. 3.7 to 0.3 cal. ka BP at the Humboldt Glacier.
Thus, the readvance towards the LIA extent initiated between 1.9 and 0.3 cal. ka BP. 330 We furthermore reviewed new data from north and northwest Greenland to put our results into a broader context and assessed the findings with local and regional climate records. We find that the Holocene glacial history varies significantly between northwest and north Greenland. The deglaciation from the coast to the present-day ice extent in northwest Greenland occurred at the onset of the Holocene, possibly as a response to the relatively early HTM. Deglaciation continued and the ice sheet retreated behind its present-day extent in northwest Greenland throughout most of middle and late Holocene driven by 335 continued high air temperatures and the arrival of warm waters along the west Greenland coast. Contrary, the deglaciation of the outer coast in Nares Strait and north Greenland was delayed c. 2-3 ka and show a more restricted period of retreat behind its present-day extent. The observed difference in pattern of deglaciation in the two regions is most likely a consequence of the large marine based part of the northwest GrIS being more sensitive to climate changes as opposed to the largely land based north GrIS. Further, the late opening of Nares Strait could have delayed ice retreat in north Greenland, despite early 340 atmospheric warming. During the LIA cooling, the GrIS do though show a synchronous response with ice advance throughout north and northwest Greenland. Our findings highlight the complexity of the ice-climate system and show clear differences in ice sheet sensitivity between northwest and north Greenland. As such, this add new knowledge and possible constraints on the future state of the GrIS as a response to present-day global warming.         the outer coast (red) (Corbett et al., 2013;Corbett et al., 2015;Jakobsson et al., 2018;Ceperley et al., 2020;Søndergaard et al., in review) and following retreat towards the present-day ice margin (black) Reusche et al., 2018;Axford et al., 2019;Reilly et al., 2019;Søndergaard et al., 2019;Ceperley et al., 2020;Søndergaard et al., in review). (c) shows the period when the GrIS and its outlets (arrows) and local ice caps (circles) were smaller than the present-day extent (Bennike, 2002;Bennike, 2008;Briner et al., 2014;Farnsworth et al., 2018;Axford et al., 2019;Reilly et al., 2019;Søndergaard et al., 2019;Søndergaard et al., in review). A question mark means that the 615 upper limit of restricted ice extent has not been constrained.
b 10 Be ages were calculated using the online exposure age calculator formerly known as the CRONUS-Earth online exposure calculator v.3 (Balco et al., 2008), the Baffin Bay production rate (Young et al., 2013), and the St scaling scheme (Lal, 1991;Stone, 2000) under standard atmosphere. A rock density of 2.65 g cm -3 was used and we assumed zero erosion. Samples were normalized to the Beryllium standard ICN-01-5-4, with a 10 Be/ 9 Be value of 2.851 x 10 -12 (Nishiizumi et al., 2007) and blank corrected. 10 Be age uncertainties are reported as the 1s Be conc.
(atoms/g) 10 Be age (ka) b Table 2: Sample collection, 14 C isotopic information and resulting exposure ages for 4 boulders from Inglefield Land, north Greenland.
a Normalized to δ 13 C of -25‰ VPDB and AD 1950 b All samples were blank corrected (0.589±0.052 10 5 14 C atoms) c 14 C ages were calculated using the online exposure age calculator formerly known as the CRONUS-Earth online exposure calculator v.3 (Balco et al., 2008), the west Greenland production rate (Young et al., 2014), and the Lm scaling scheme (Lal, 1991;Stone, 2000) under standard atmosphere. A rock density of 2.65 g cm -3 was used and we assumed zero erosion. 14 C age uncertainties are reported as the 1s analytical uncertainty.  https://doi.org/10.5194/cp-2020-66 Preprint. Discussion started: 6 May 2020 c Author(s) 2020. CC BY 4.0 License. Table 3: Sample collection information, radiocarbon ages and calibrated ages for marine molluscs collected at the margin of the Humboldt Glacier and wood fragments collected in front of the Hiawatha Glacier, north Greenland.