Ocean driven retreat of the Northeast Greenland Ice Stream following the Last Glacial Maximum

Domain: physics
Published: 2025-11-29
Editorial outcome: minor_revision

Abstract
The Northeast Greenland Ice Stream (NEGIS), the largest ice stream draining the Greenland Ice Sheet (GrIS), is losing mass at an accelerating rate due to atmospheric and ocean-to due to atmospheric and ocean-driven melting. Holding the equivalent of 1.1–1.4 metres of sea-level rise, its collapse will have a significant impact on global sea levels making it crucial to understand the controls on its dynamic behaviour.
The NEGIS retreated from the continental shelf edge by 21.6 ka BP, with this study confirming continued grounding line retreat to ~100 km from the shelf edge by 20.3 ka BP, earlier than previously reported. This early retreat was driven by warm Return Atlantic Water (RAW) and amplified by a retrograde seabed, which together drove initial grounding line retreat. The presence of a series of grounding zone wedges indicates a quasi-stable grounding line, which was fronted by an ice shelf. Grounding-line retreat took place between 20.3 and 15.2 ka BP. However, ice-shelf breakup caused by enhanced sub-ice shelf melt rates driven by RAW ingression, coupled with surface thinning instigated by atmospheric warming during Greenland Interstadial I, triggered rapid retreat of the ice stream after 15.2 ka BP. Our findings confirm the dominant role of oceanic forcing in grounding line stability and ice-shelf breakup.

Introduction
The greatest uncertainty to future sea-level projections, yet potentially the largest contribution, stems from the uncertain response of the Antarctic and Greenland ice sheets to future warming1,2. The Northeast Greenland Ice Stream (NEGIS) extends more than 600 km into the interior and drains approximately 12% of the Greenland Ice Sheet (GrIS). Complete collapse of the NEGIS would raise global sea level by 1.1–1.4 m3,4. The NEGIS is fronted by three marine-terminating glaciers: Nioghalvfjerdsfjorden Glacier (79N), Zachariae Isstrøm (ZI) and Storstrømmen Glacier (SG). These fringing glaciers and ice shelves were relatively stable up until the mid-2000s, but since then, 79N and ZI have shown significant flow acceleration and dynamic thinning5 with complete loss of the ice shelf fronting ZI in late 2012 and early 2013 (up to 40 km loss3). 79N still retains its 70 km long, 20 km wide ice shelf, which buttresses the ice stream. However, a significant calving event observed in 2022 indicates ongoing ice shelf instability, with models predicting that the collapse of the ice shelf would increase grounding line flux by over 160%6. Enhanced atmospheric- and particularly ocean-driven melting has been identified as the primary driver of retreat3–5,7,8. Numerous studies have indicated that Return Atlantic Water (RAW, also referred to in the literature as Return Atlantic Current, RAC) is reaching the grounding line of 79N and driving both grounding line and sub-ice shelf melt7,9–12 (Fig. 1b).
Given these recent changes, it is increasingly important to understand the future evolution of the NEGIS in order to assess future sea-level rise. While numerical simulations provide a powerful predictive tool, their reliability depends on an accurate parameterisation of ice-sheet dynamics and key boundary conditions such as bathymetry and climate forcing. This issue is particularly acute at the ice sheet grounding line, where there is often a dearth of reliable bathymetric data or information on ocean heat transport. Alternatively, the palaeo record provides an unparalleled archive of past changes, enabling an understanding of ice-ocean interactions, and particularly the threshold of ice sheet variation in response to thermal drivers, bathymetry and internal ice-sheet dynamics. This palaeoperspective is essential to assess the significance of recent changes, to provide empirical evidence to refine models of change, and to gain an understanding of the overall stability of the NEGIS system13.

Results
Early deglacial and Atlantic water influence (>20.3 ka BP–17.6 ka BP)
The sediments obtained from cores 144GC and 146GC provide evidence for ice-stream activity during deglaciation from the end of the LGM in the outer Norske Trough. Four lithofacies (LF1-LF4) represent subglacial conditions during ice advance, followed by glaciomarine and sub-ice shelf conditions during retreat (Fig. 3). Foraminiferal analysis conducted on core 144GC supports the lithofacies interpretation with the assemblage being split into five foraminiferal assemblage zones (FAZ’s) (Fig. 4).
Lithofacies 1 (LF1) is the basal lithofacies in both cores. It is characterised by a matrix-supported, consolidated dark-grey diamicton with variable grain size, absence of foraminifera (FAZ1), high wet bulk density, medium magnetic susceptibility, and relatively high shear strength (11–32 kPa, Figs. 3 and 4). Sub-bottom profile data (Fig. 2) reveal this unit to be streamlined and ubiquitous across the seafloor. It is interpreted as a subglacial traction till15, an interpretation supported by López-Quirós et al.22 at other adjacent sites in the outer Norske Trough (Fig. 1). Core 146GC contains a duplication of LF1 in the lower stratigraphy, suggesting grounding line oscillation and the deposition of a re-advance till (Fig. 3). In contrast, based on its upper stratigraphy (sub-ice shelf to glaciomarine transition), core 144GC records the grounding line migration west of the core site with no re-advance over the site. The geomorphic and chronological evidence from other studies indicates that the outer Norske Trough was deglaciated by 21.6 ka BP18.
Lithofacies 2 (LF2) consists of a finely laminated to crudely stratified silt clay and is colour banded (Fig. 3). It drapes LF1 and infills lows in the seafloor topography (Fig. 2). Shear strength is low (<10 kPa). This lithofacies is largely devoid of gravel/pebble-sized clasts and is faulted in places. It is characterised by medium-low wet bulk density, medium magnetic susceptibility values and low shear strength (Fig. 3). The benthic foraminiferal assemblage in LF2 can be split into three assemblage sub-zones (Fig. 4). FAZ2a is dominated by Stetsonia horvathi (50–90%) with abundance increasing to a maximum of 90% at the top of this unit. Stainforthia. feylingi (4–14%), Cassidulina neoteretis (0–22%) and Cassidulina reniforme (1–14%) are common but decreasing in abundance up core. Benthic foraminiferal abundance through this zone is relatively low (foraminiferal accumulation rate (FAR) under 3000 indiv. cm−2 kyr−1) except for the lowermost sample where FAR exceeds 31,000 indiv. cm−2 kyr−1 (Fig. 4). Planktic foraminifera are also present in low concentrations (<500 indiv. cm−2 kyr−1), although again exceeding 2500 indiv. cm−2 kyr−1 in the lower-most sample (Fig. 4). The planktic δ18O record in 144GC records low values through this zone (~2‰) except for an isolated spike 175 cm (Fig. 4).
These sediments are interpreted as proximal glaciomarine plumites24,29. A radiocarbon date of 18.6 ka BP toward the base of LF2 (15 cm above the subglacial till) provides a minimum age for deglaciation of the site of 144GC and, hence, retreat from the shelf edge. The age-depth model provides a date of 20.3 ka BP for the transition from subglacial till to glaciomarine sedimentation (see Supplementary Information 3 and 4). Core 144GC, which is located ~100 km from the continental shelf edge, supports continued early deglaciation and retreat across the outer continental shelf during this early deglacial period. This date is significantly earlier than published chronologies at a similar core location (16.6 ka BP in core 135, Fig. 1) and takes place during the global LGM30. While these cores cannot constrain whether ice was grounded at the shelf edge, geomorphic evidence consisting of mega-scale glacial lineations (MSGLs), GZWs, and glaciogenic debris flows on the continental slope all indicate ice extended to the shelf edge16,18, with radiocarbon dates indicating ice retreat from the shelf edge underway by 21.6 cal ka BP18. The age of the first occurrence of LF2 in core 146GC is not well constrained, but its presence between two till layers indicates that glacimarine conditions occurred between the periods of ice grounding at the site.
The benthic foraminiferal assemblage (FAZ2a) within core 144GC indicates harsh surface water conditions indicative of an ice shelf, with a dominance of S. horvathi and a secondary assemblage of S. feylingi31,32 (Fig. 4). These conditions persist throughout FAZ2a until c. 17.6 ka cal BP. An ice-shelf interpretation is further supported by the fine-grained nature of this unit and lack of IRD (Fig. 3), implying the presence of an ice shelf precluded the movement of icebergs over the core site (c.f. 29). However, the occurrence of C. neoteretis is evidence of RAW presence immediately on deglaciation33, the influence of which decreases up core. This indicates that RAW was present in the trough at depth during this early deglacial phase. This is consistent with observations from core GR02-GC19, which records the presence of C. neoteretis from 35 ka BP to present at the continental shelf edge. Where the two records differ is the strength of the RAW signal, which is more variable on the continental shelf (this study) compared to the continental slope record19. The presence of C. reniforme, a glaciomarine species found at present on the northeast Greenland continental shelf, is associated with chilled Atlantic water32,34. It covaries with C. neoteretis and provides further support for an Atlantic water presence during initial deglaciation. The occurrence of planktic foraminifera species, albeit in low concentrations, within FAZ2a does indicate open water conditions nearby, which suggests these species were advected to the core site under an ice shelf. Furthermore, the planktic δ18O record in 144GC shows low values, indicating there was a significant meltwater signal during this early deglacial period.

Grounding line stability and continued ice-shelf presence (17.6 ka–15.2 ka BP)
The early deglaciation from the continental shelf edge was followed by slow retreat and subsequent grounding line stabilisation as indicated in shelf bathymetry, geophysical data22 and the sediment cores reported here (144GC and 146GC). From 17.6 ka BP to 15.2 ka BP, both cores consist of fine-grained, laminated sediments containing no IRD (LF2). The foraminiferal assemblage transitions from FAZ2a to FAZ2b and is characterised by very low benthic foraminiferal abundances (ranging between 16–2522 indiv. cm−2 kyr−1), with foraminiferal numbers being too low (3–25 individuals counted) for a statistically robust count. However, although in very small numbers, S. horvathi and S. feylingi are most abundant, with occasional occurrences of C. neoteretis and C. reniforme.
FAZ2c is characterised by a significant increase in benthic foraminiferal concentration and is dominated by S. horvathi (46–53%) with S. feylingi also being common (4–32%). The abundance of C. neoteretis (3–13%) also increases in this section of the core, but C. reniforme is present in low abundance (2–4%), and planktic foraminifera remain absent. Both 144GC and 146GC continue to reflect sedimentation in an ice-proximal glaciomarine environment derived from meltwater plumes29. The lack of large clasts in the X-radiographs and fine particle size distribution (containing no sand component, Supplementary Fig. 1) indicates ice-berg rafting was suppressed (Fig. 3). Indeed, when combined with the very low abundances of benthic foraminifera and the absence of planktic foraminifera, this suggests the continued presence of an ice shelf at the time of deposition35,36.
Alternative explanations for the low abundance or absent foraminiferal counts include high sedimentation rates and/or poor preservation. However, there is no clear evidence of a change in sedimentation rate that could reduce benthic foraminiferal productivity37. We also rule out poor preservation as there are no agglutinated foraminifera or test linings present in this section of the core (evidence of poor preservation37), and the occasional calcareous species that are present are well preserved. Therefore, the presence of an ice shelf is the most likely explanation for the low species concentrations (c.f. 31). The substantial reduction in foraminiferal concentrations in FAZ2b and the lack of any planktic specimens may indicate the distance of the core site to the ice-shelf margin increased and, thus, inhibited the advection of foraminifera to the core site.
FAZ2c is characterised by an increase in benthic foraminiferal concentrations, dominated by the ice shelf and indicator species. However, S. horvathi decreases in abundance up core whilst S. feylingi and the RAW indicator species C. neoteretis and C. reniforme increase in abundance. The decrease in S. horvathi up core and the increase in S. feylingi suggest the ice shelf may have retreated, with the site becoming more proximal to the ice-shelf margin. The increase in C. neoteretis and C. reniforme indicates an increase in RAW ingress potentially due to the edge of the ice shelf retreating (calving) closer to the core site, leading to more favourable light and nutrient conditions38. However, the continued absence of planktic foraminifera, combined with the lack of IRD, indicates that the ice shelf was still present over the core site during this period.
It should be noted that an alternative hypothesis to an ice shelf is the presence of sea-ice, and S. feylingi is often associated with sea-ice edge/seasonal sea-ice conditions38,39. However, ice-shelf presence is reinforced by the geomorphological record within Norske Trough16,22. GZWs are considered to be a critical, diagnostic feature of ice streams that terminate into floating ice shelves40. Furthermore, there is evidence of tabular iceberg keel marks on the margins of the Norske Trough in front of GZW1 and GZW2 and near core 144GC16,18,22. It is likely that these icebergs calved from floating ice shelves41,42. The keel marks are noted at <300 m water depth16 indicating a thick ice shelf fronting the grounding line at GZW1 and GZW2. The maximum extent of the ice shelf is unknown. However, if the NEGIS was pinned on GZW2, it would have extended at least 60 km to cover both 146GC and 144GC core locations. The presence of a floating ice shelf in the Norske trough is also supported by foraminiferal assemblages, including the presence of the ice-shelf indicator species Glomulina oculus, and laminated lithofacies in core 92G26, which shows that an ice shelf fronted the NEGIS as it retreated along Norske Trough from the outer to inner shelf.
Together, cores 144GC and 146GC indicate that the grounding line receded to the mid-trough GZW2 between 20.3 and 15.2 ka, where it stabilised. This is supported by sedimentological variations in core 146GC, which contain two dark grey diamicton units separated by finely laminated mud, suggesting that ice retreated west of the core location, depositing the laminated unit, followed by a readvance that deposited the uppermost diamicton in 146GC. Absence of similar diamictons in 144GC indicates that the margin did not extend seaward of GZW1, and instead implies an oscillating margin likely anchored to GZW2.

Destabilization of the grounding line and ice-shelf breakup
Between 15.2 and 14 ka BP, a significant shift from a fine-grained laminated mud of LF2 to a gritty, massive sandy silty clay with coarser gravel to pebble-rich layers of Lithofacies 3 (LF3) occurs in both cores. Core 144GC contains two discrete LF3 layers at 98–98.5 and 90–94 cm that consist of a reddish brown coarse sandy-silt containing granules and larger clasts (see Supplementary Fig. 1). The lower boundaries of both layers are sharp. Between these layers is a finer, gritty, massive silt. High magnetic susceptibility measurements (Fig. 3) characterise this section of the core and correspond with the coarse and clast-rich units. From 78 to 90 cm, the stratigraphy is a gritty, sandy clay that fines upwards (Fig. 3). Core 146GC also contains a transition from LF2 to LF3, with alternating layers of fine massive mud and IRD-rich fine massive mud between 350 and 315 cm, prior to 15.2 ka BP. This is then overlain by two thick (34 cm and 200 cm), clast-rich, soft (<10 kPa) diamictons in sandy silty clay. These thicker diamicton layers are faintly stratified and have sharp, convoluted, upper and lower boundaries (Fig. 3).
The foraminiferal assemblage in LF3 (FAZ3) is characterised by continued increase in C. neoteretis, reaching a maximum abundance of 50%. C. reniforme abundance also increases from 14% at the base of FAZ3 to between 22–25% in the upper section of FAZ3 (Fig. 4). S. feylingi and S. horvathi decrease from 55–35% to 20–5%. Both the benthic and planktic foraminiferal abundances are generally very high (peaking at 30,000 indiv. cm−2 kyr−1 for benthic foraminifera and 20,000 indiv. cm−2 kyr−1 for planktic foraminifera), although abundances are lower within the IRD-rich layers (57 indiv. cm−2 kyr−1 benthic and 114 indiv. cm−2 kyr−1 planktic specimens). The δ18O record from planktic foraminifera return to relatively low values in this unit (generally <2‰). Towards the top of this biostratigraphic unit (88 cm, 12.4 ka BP), Cibicides lobatulus increases in abundance to a maximum of 18%.
Overlying LF3 in both cores is a massive brown fine-grained mud (LF4), deposited during the past 10 ka BP (Fig. 3). This lithofacies in core 144GC consists of two foraminiferal zones (FAZ4 and 5). FAZ4 (6.2-10 ka BP) is characterised by a decrease in both C. neoteretis and C. reniforme and a significant increase in abundance of S. feylingi (from 36% to 100%). Overall, the benthic foraminiferal abundance decreases from 4100 indiv. cm−2 kyr−1 to 108 indiv. cm−2 kyr−1. Planktic abundances also decrease from 2200 indiv. cm−2 kyr−1 to 54 indiv. cm−2 kyr−1 at the top of FAZ4. The planktic δ18O values return to comparatively high values (3–3.5‰). The overlying foraminiferal assemblage, FAZ5, is characterised by low benthic (<350 indiv. cm−2 kyr−1) and planktic (<7 indiv. cm−2 kyr−1) abundances, with the benthic assemblage dominated by agglutinated species with very few calcareous specimens.
The lithostratigraphic and foraminiferal data from cores 144GC and 146GC are interpreted as recording the destabilisation of the grounding line and ice shelf that occurred sometime between 15.2 and 14 ka BP. The coarser units at 94–98 cm and 90–94 cm represent deposition of IRD. A similar lithofacies change is observed in core 135G22, which occurs at a similar time (14.6 ka BP (13617–15670 yrs BP) age is recalibrated using the method in this paper). This sedimentological and faunal signature is interpreted as evidence of ice shelf breakup, allowing the rafting and deposition of coarse material from icebergs. The transition from LF2 to LF3 in core 144GC is comparable to sub-ice shelf sedimentary sequences reported from Antarctica35,43, and represents grounding line migration and ice-shelf breakup.
The alternating fine, massive mud and IRD-rich, fine, massive mud layers in 146GC represent a similar sedimentary process to that captured in core 144GC, and are similarly interpreted to mark the retreat of an overlying ice shelf back across the core site35. The thick diamicton layers captured in core 146GC are interpreted as debris flow deposits produced during grounding line retreat and redistribution of material upslope of the core site across GZW2. The near synchronous timing of the deposition of LF3 in both cores, which are ~60 km apart, points to a rapid breakup and retreat of the fronting ice shelf and grounding line.
Foraminiferal assemblage data support our interpretation of environmental conditions during this phase of grounding line retreat (Fig. 4). The biostratigraphic change from FAZ2 to FAZ3 indicates a shift from sub-ice shelf conditions to more seasonal sea-ice conditions and a continued strengthening of the RAW influx. This is further supported by the rapid increase in planktic/benthic ratios and planktic concentration, indicating open water and productive surface water conditions27. The δ18O record from planktic foraminifera returns to relatively low values (<2‰) through FAZ3, suggesting significant meltwater input from the disintegrating ice shelf and grounding line retreat. The increase in Cibicides lobatulus towards the top of FAZ3 (88 cm, 12.4 ka BP) suggests relatively strong currents in a high-energy environment44 coinciding with the high meltwater signal inferred from the δ18O values. This also coincides with the clast-rich unit (LF3; Fig. 4), with the coarse-grained detritus likely released during ice shelf/sea ice break-up.
The timing of ice-shelf breakup, ~15.2–14 ka BP, corresponds with an increased RAW signal on the continental shelf (increase in C. neoteretis shown in 144GC) suggesting that ocean-driven melting played an important role in ice-shelf breakup. Furthermore, the prolonged meltwater signal at this time indicates that there was a large amount of freshwater released from the ice front. This likely acted to enhance the inflow of RAW across the shelf to the grounding line, as has been shown for the present-day 79N7. The significant increase in abundance of C. lobatulus indicates comparatively strong bottom currents in the area of core 144GC in the latter stages of grounding line retreat. When planktic foraminiferal δ18O values are lowest, C. neoteretis and, therefore RAW signal, were high.
After 10 ka BP, the core lithostratigraphy suggests the ice margin retreated away from both core sites, reducing the sedimentation rate and sediment size fraction, with only very fine muds being deposited. The decrease in C. neoteretis and C. reniforme indicates a reduced RAW influence, whilst the high planktic δ18O values indicate a reduced meltwater influence as the grounding line retreated further from the core site. The increase and dominance of S. feylingi through FAZ4 (Fig. 4) indicate unstable conditions with seasonal sea ice present38. The overlying foraminiferal record, FAZ5, is characterised by low benthic and planktic concentrations, with only agglutinated species present in the samples, indicating poor preservation due to dissolution37. As foraminifera preservation is so poor in this section of the core, constraining ocean circulation during the mid-to-late Holocene is not possible.

Methods
Marine geophysical analysis
Sub-bottom profiler data was collected using a hull-mounted Parasound DSIII-P70 system operating at a pulse mode of between 4 and 20 kHz and a pulse length of 0.5 ms. The seismic profiles were visualised using PS3 file formats on SeNTv2.02. This data was used to guide core site locations.

Core collection and CTD
Marine geophysical data and gravity cores were collected across the northeast Greenland continental shelf during cruise PS100 on the RV Polarstern in 2016. The cores were recovered from the outer section of Norske Trough within a basin that lies between the shelf edge and the GZW2. Core PS100-144GC (77 7.495N, 10 34.239W, 496 m bsl) lies within a basin located between the outer shelf edge and GZW1 (Fig. 1b). The total length of this core is 216 cm. Core PS100-146GC (77 31.381N, 12 20.131W, 505 m bsl) is located on the outer/seaward edge of GZW2 and is 575 cm long.
Each core was cut into 1 m sections, split, photographed, and described onboard. Core description recorded information on grain size, colour, sorting, bed contacts, clast abundance, sedimentary structures, and the presence of macrofossils. Shear strength measurements, using a handheld Torvane, were also taken at 10 cm intervals down core.

Physical properties analysis
Post-cruise physical property analysis was conducted on all cores at Durham University. Each core was X-rayed using a GEOTEK CT scanner. The X-rays were used to augment the core descriptions for more detailed lithofacies analysis and allowed clearer identification of IRD content. Magnetic susceptibility, wet bulk density and p-wave velocity measurements were collected using a GEOTEK Multi-Sensor Core Logger at 1 cm resolution down core. Additionally, 47 samples were collected from core PS100-144GC for particle size analysis using a laser particle size analyzer. Samples were prepared by removing organic material using 10% Hydrogen peroxide. Sodium hexametaphosphate was used to deflocculate the sediment, and samples were sieved through a 2 mm mesh sieve prior to putting through the laser scanner. This data was used to calculate the proportion of clay, silt, and sand-sized particles.

Foraminiferal analysis
Detailed foraminiferal analysis was conducted on core PS100-144GC with 46 samples analysed down core. Samples were volumetrically measured, then wet-sieved through a 500 µm and 63 µm sieve to remove the coarse and fine material. The 63–500 µm fraction was used for foraminiferal analysis. Each sample was counted wet and on the same day as sample preparation to prevent the dissolution of small foraminiferal species and destruction of agglutinated species.
Absolute abundances of both benthic and planktic foraminiferal counts are presented as both concentrations (number of species per 1 cc of sediment; Fig. 4) and as foraminiferal accumulation rates (FAR) or fluxes. FAR (as individuals cm−2 ky−1) was calculated using the following equation:
Equation 1: FAR = TSAR * FN
Where TSAR is the total sediment accumulation rate (g cm−2 kyr−1) and FN the number of foraminifera per gram56.

Foraminiferal stable isotope analysis
Oxygen and carbon isotope analysis was conducted on the benthic foraminifera Cassidulina neoteritis (28 samples) and planktic Neogloboquadrina pachyderma (32 samples). Analysis was conducted at the NERC Isotope Geosciences Laboratory at the British Geological Survey. Analysis was conducted using an IsoPrime mass spectrometer with a Multicarb preparation system. Stable isotope results were calibrated to the VPDB scale of international standards with an analytical precision of >±0.05‰.

Chronology
The chronology of the two cores is based on 6 accelerator mass spectrometry (AMS) 14C ages (Table 1) measured on mixed species of benthic foraminifera although Miliolina and Quinqueloculina species were avoided. AMS 14C samples were submitted to the NERC radiocarbon facility in East Kilbride, where they were prepared to graphite and passed to the SUERC AMS laboratory (SUERC publication codes) or the Keck CCycle AMS laboratory, University of California, Irvine (UCIAMS publication codes) for 14C measurement. The radiocarbon dates were corrected for isotopic fractionation and then calibrated to calendar years (cal a BP) using Calib 8.20 (Stuiver and Reimer, 1993) and the Marine20 radiocarbon calibration curve (Heaton et al., 2020). We have followed the approach presented in Heaton et al. (2023) for calibrating in polar regions to calibrate the ages presented here. This takes into account the temporal uncertainties, with most likely larger reservoir ages in the marine reservoir correction for high latitudes during glacial periods. For radiocarbon dates with a calibrated age younger than the start of the Holocene (taken here as from 11,500 cal a BP), we calculate ΔR and ΔR error based on the 8 closest samples from the Marine Reservoir Correction Database (http://calib.org/marine/, Reimer and Reimer, 2001). This gives a marine reservoir correction (ΔRHol) of 2 ± 66 used in calibration (Table 1). For pre-Holocene-aged samples, we perform two calibrations to provide a more realistic estimate of the age and age uncertainty. The first calibration assumes minimal polar 14C glacial depletion and uses the ΔRHol estimate as above. The second calibration uses an estimated latitude-dependent maximal polar 14C glacial depletion from Heaton et al. (2023). This is added to the Holocene value to give the glacial correction: ΔRGS. We then take the conservative approach of using the full calibrated range from these two calibrations to calculate the median and range of ages used in the discussion (all calibrations are shown in Table 1).
The three calibrated AMS ages from core PS100-144GC were then used in the Bayesian accumulation age-depth modelling program Bacon 2.2 to develop an age-depth model. We performed two age-depth models. The first using the ΔRHol to calibrate all ages, the second using ΔRGS for the two older ages as described above (Supplementary Figs. 3 and 4). We then took the average of the two models for each cm to develop the age-depth model used in this study. The lowest radiocarbon date from PS100-144GC constrains the base of the glacimarine unit at 190 cm to 20347 cal yr BP (full range of 18673–22689). Due to the poor chronological control in the upper section of the core, an assumed age of 0 was used for the core top. This is likely to be incorrect due to loss of the surface sediment through the coring process. We therefore only compare the proxy datasets from 20,000-10,000 cal yr BP, where the age model is more confidently constrained. No age-depth model was produced for core 146GC due to the limited chronological control constraining the older section of the core. Foraminiferal abundance was too low to allow additional radiocarbon ages to be measured.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript presents new data on the history of the NEGIS from the LGM through early Holocene. It builds on previous work that has shown that the ice margin reached the shelf edge at the Westwind Trough and that it had already retreat off the outer shelf during the LGM. What this manuscript adds is faunal evidence from a key core (144GC) and lithofacies analysis plus dating on two cores (144 and 146GC) to gain more detailed understanding of the further retreat history and what forcings were at play. The core sites target important ice marginal features (grounding zone wedges) on the mid/outer shelf. The lithfacies and foraminifera assemblage data are used to reconstruct important aspects of the NEGIS in the past: the configuration of the ice front (i.e. ice shelf fronted or ice cliff fronted); emissions of meltwater, advection of relatively warm RAC water, and sea-ice cover. I was struck by two key findings. The first is firm indication that the ice retreated during the LGM and during the oldest part of deglaciation, HS-1. The cores do not contain a complete record of this retreat as they were ice covered until c. 19 ka. A basal diamicton interpreted as subglacial deposit is overlain by fine grained laminated sediment lacking ice rafted clasts and containing a fauna consistent with an ice shelf fronted margin. The second key result to my mind is that the GZWs record relative stability of the grounding zone during the interval of c. 19ka to c. 15.8 ka. After c. 15.2 ka, the lithofacies indicate a calving margin lacking an ice shelf and the faunas indicate strong inflow of RAC and relative ocean warmth at the seabed that would influence ice instability. The GZWs had been thought to be Younger Dryas in age, so this is a key finding! The conclusion is that ice retreat from the GZW 2 may have been driven both by warm atmosphere and ocean forcing. I think that the data exist in this paper to make these points. However, there are some structural problems and some lack of clarity in the manuscript that hurt its ability to make these points clearly.\nThe Results section does not clearly distinguish previous work and background information from new results presented in this study. I would argue that the first 3 paragraphs are actually part of an introduction, setting the stage for the problems that the core data can attempt to solve. The fourth paragraph is meant to indicate how the lithofacies and foraminifera in the two cores can be associated with environments, but it was confusing because it goes immediately to interpretations without presenting the characteristics of the lithofacies and fauna and how these progress upcore and in association with the chronology. In a sense, there is no results section in this paper. The data are not described in a systematic way before interpretations are made. It is difficult to separate what is new and what is previously published.\nLine 189 there is an error in the sedimentation rate calculation…I think it is off by two orders of magnitude. Maybe what is meant is 0.2 cm per year rather than per kyr.\nThe figures are nicely drawn, but they fall short of helping to convey the points being made in some cases.\nOn Figure 1, the map of the area, two GZWs are shown. Core 144 is shown immediately in front of the outer GZW. I was however, confused that on the acoustic profile of the core site in Figure 3, that core 144 is shown to the NW of GZW1. Is this is a matter of the directions being misplaced on the figure? I am unsure, but think this profile needs to be turned around. It would help as well if Figure 1 showed where the two profiles are in the trough so that the orientation and locations are clear. In addition, it would help the introduction if there was a panel added to show the modern NEGIS, maybe using flow speed. Otherwise it is not easy for uninitiated readers to match the outlet glaciers with the main ice stream.\nFigure 4 could benefit from having the Lithofacies along the depth axis as in Figure 2 so a reader does not need to flip back and forth. Suggest you include planktic forams per ml and benthic forams per ml. You could use the planks per ml instead of the P:B ratio if space is an issue. The ice species are in purple not blue…at least in the reviewer pdf. I presume that faunal analyses were not made on core 146 which is too bad.\nFigure 5. needs some additional annotation such as chrons (LGM, HS1, B-A, YD etc). Maybe add the modern average air temperature to the summer air temp panel. Might be useful as well to tie in the faunal zones and lithofacies as these are important as well as the fuana.\nFigure 6 shows schematic profiles of the reconstructed NEGIS through time. Panel a indicates that the ice margin retreated by calving back and that dirty ice bergs were released. Early in the paper there is evidence of IRD in slope cores during this period. Panel b is the starting point of this study. But this panel does not match the data. GZW 1 is a bump on the seafloor but no association made with the core. Is GZW 1 associated with deposition of the laminated facies lacking IRD? Does that suggest that this is an ice shelf fronted margin beginning from the very start of the core record? This schematic does not explain GZW 1 and how it relates to results presented for 144GC. Panel C makes sense except that the story either is missing the IRD interval of ice retreat to GZW 1, or that the formation of GZW 1 is ignored. Presumably the GZWs are formed as the ice stabilizes, so perhaps they should not appear until the panel in which they form.", "reviewer_2": "Review of Callard et al (2025) - ‘Ocean driven retreat of the Northeast Greenland Ice Stream following the Last Glacial Maximum’\nSummary\nThis study presents data and conclusions from two new sediment cores taken on the Norske Trough that are used to describe the early deglaciation of the Northeast Greenland Ice Stream (NEGIS) from its LGM position. The paper has numerous interesting findings that are used to describe the evolution of the paleo-ice stream by tying in sediment facies, analysis of foraminifera assemblages and glacial landforms. Chief among them is the important role that ocean melt, driven by warm Return Atlantic Water Current (RAC), played in the initial retreat of NEGIS from its LGM by ~20 ka BP, a retreat that occurred without a rise in atmospheric temperature and that was much earlier than previously thought. RAC is further linked with the collapse of the ice shelf after 15.7 ka BP when surface air temperatures began to rise during the onset of the Bølling-Allerød. Furthermore, Grounding Zone Wedges in the Norske Trough provided vital pinning points and stability during the early deglaciation after the trough deepens into a retrograde slope inland of the shelf edge.\nI found this paper very enjoyable to read and believe is shares valuable insights into the evolution of the NEGIS from the LGM. This is especially topical as constraining the future response of the contemporary NEGIS to climate warming is crucial. The manuscript is well-written and well-structured, with the authors clearly explaining their interpretations of sediment record which I, for the most part, agree with.\nMy comments below mainly relate to interpretations made around the early retreat/deglaciation of the NEGIS, specifically whether an ice shelf existed before 18 ka BP, and the role the bathymetry and fjord topographically played in the initial retreat. I will state here that my opinions are far from set in stone, and hopeful adding a few sentences to further explain their interpretations would alleviate any of my concerns and lead me to recommend this paper for publication.\nMajor Comments\n• Ice Shelf Interpretation: I agree with the authors interpretation that an ice-shelf existed in the Norske Trough with the grounding line on GZW2 between 18-15ka BP. However, I’m curious why the authors believe an ice shelf wasn’t present before NEGIS retreat to GZW2 (for example in Figure 6B). Instead, during the early deglaciation (>20 ka BP to 18 ka BP), the high levels of S. horvathii and lack of IRD and are presented as reasons for thick sea-ice conditions. These same arguments are then used as evidence for an ice shelf between 18-15 ka BP. Furthermore, as the authors rightly mention, the occurrence of GZWs are indications of shelf ice conditions, therefore I would expect it likely that an ice shelf was present with the grounding line on GZW1 during the early deglaciation (López-Quirós et al., 2024). I also wonder why the keel marks from tabular ice bergs must have been formed after 18 ka BP, could they not have been formed from an earlier ice shelf?\nLater in the discussion it is stated ‘… that NEGIS was fronted by an ice shelf when it stabilised on GZW2’. This is not what it shown in Figure 6B when the retreat is shown as a calving cliff face with harsh sea-ice conditions when it reached GZW2. It is then said that the presence of an ice shelf was of ‘negligible’ importance to the initial stability of NEIGS and that the bathymetric high was more important. I think that a reference or two is required here, as I’m not entirely convinced by that conclusion.\n• Bathymetry and Fjord Geometry: I agree with the authors that RAC was likely the cause of early retreat and echo that this is a great finding of the paper. However, I’m not sure I fully agree with the authors comments on the fjord geometry and slope angle regarding this initial retreat, where the initial slow retreat rates (23 to 19 m/yr) on a retrograde slope are used to conclude the bathymetry was not a principal control. Firstly, I think it would be great to have a comparison against retreat rates from other paleo-ice streams in Greenland, is 23 m/yr considerably slower? Secondly, I see that the Norske Trough immediately narrows from the shelf edge, could this have slowed initial retreat through increased lateral drag, similarly as the authors later discus with the narrowing of the trough around GZW2. Finally, while the bathymetry deepens from 320 m at the shelf edge to 560 m 100 km in land, the majority of this deepening (210 m) happens ~50km from the shelf edge, therefore, wouldn’t it be reasonable to while retrograde in nature, the initial shallow slope may have contributed to the slower retreat rates?\nMinor Comments\n• Figure 1: I think the polygons for GZW1 and 2 should only have the outlines and not be filled, it would then be possible to see how the GZWs look in comparison to the sea floor. I also wonder is the scale for the bathymetry could be clipped to range from 0 to 1500 m, just to make it the variations in depth slightly clearer.\n• Figure 5: JJA air temperatures. I think this should be made clear is if for the contemporary NEGIS region or the paleo domain of the ice stream? I’m also curious if the temperatures are any different in the newer Badgeley et al., 2020 dataset?\n• l.34: It would be worthwhile mentioning that 79N still has an ice tongue that is providing significant buttressing to the interior ice (Humbert et al., 2023), especially as you discuss ice shelf evolution and collapse in the results/discussion.\n• l.24: ice shelf break ‘up’?\n• l.29: Redefine the Greenland Ice Sheet acronym - GrIS.\n• l.36: Capital W for ‘with’.\n• l.40 – 42: Sentence is a bit sloppy. ‘There’ should be ‘their’, and maybe reads better as ‘… their reliability depends on an accurate parametrisation of ice-sheet physics, including key boundary conditions such as…’\n• l.45: ‘enabling a better understanding of ice-ocean interactions’ – We already have some understanding of how ice-ocean, but the paleo record definitely improves this.\n• l.51: double ‘from’ – maybe better as ‘Recent evidence from marine cores taken on the continental shelf…’\n• l.57: ‘… initial retreat of NEGIS and critically…’\n• l.94: I am presuming that the moraine ridge referred to here as not GZW1? I think this could be made a little clearer by also stating that 144GC is also in front of GZW1.\n• L.138: Missing full stop.\n• l.146 where is core CR02-GC? I don’t see it in Figure 1.\n• l.149: Incorrect capitalisation of D.\n• l.164: Full stop within the brackets when it should be outside.\n• l.180: Add reference to Fig.4 at the end of the sentence.\n• l.258: Missing bracket\n• l.259: ‘Driven melting’ and ‘driven ice shelf breakup’, choice of words could be improved in this sentence.\n• l.282: Missing full stop.\n• l.287: Missing full stop.\n• L.291: 23 m/yr is for the Norske Trough while 19 m/yr is the Westwind trough in reference 20. This should be made clearer (Ó Cofaigh et al., 2025).\n• l.334: ‘melting was an important driver’\n• l.353: Should AWI not be AW?\n• l.353: Missing spaces and doubles spaces in this sentence.", "reviewer_3": "Callard et al., provide new information relating to the role oceans played in governing the retreat of the Northeast Greenland Ice Steam on the mid/outer continental shelf. Key results are:\n- Deglaciation began at around 20ka BP on the mid/outer Northeast continental shelf, this is earlier than previously reported in the Norske Trough.\n- Analysis of foraminiferal assemblages suggests this was primarily driven by the intrusion of warm Return Atlantic Water onto the shelf, amplified by a retrograde seabed.\nOverall, I liked that paper, and I found it interesting; the discussion was enjoyable to read. I believe that the contribution is important in this region, particularly given the impact of warming ocean waters on the fate of the Greenland Ice Sheet today and in the future. I think that the methodologies and science are sound, I have some comments on this in the ‘main comments’ section of this review.\nOne of the main comments I have relates to the quality of the writing and mistakes throughout. I believe that these detract from the overall manuscript. I therefore list those small changes first here. However, I recommend that the entire manuscript be carefully proofread edited prior to subsequent review.\nComments relating to quality of writing and figures\n- Sometimes the authors use ‘the’ NEGIS sometimes ‘the’ is excluded – it should be consistent\n- Type in figure 1a caption – ‘value’ coldest, I think this should be blue.\n- Line 41 – their reliability not there reliability\n- RAC never defined. I think it would be more correct to use Return Atlantic Water (RAW) to describe the water mass in some instances. E.g. like 309. This should be checked throughout\n- The full core name of 135G should be given in the figure caption of 1b, as per the other cores listed\n- What is AWI Bank – not defined anywhere\n- The Rasmussen et al., 2022 core should be marked on the map (19G), it is in the caption but not on the map. 39G is also listed in the caption but not on the map. Please check all of these again.\n- I think fig 2 and 3 should be switched as fig 3 is introduced in the text first and this is confusing\n- Fig 4: foraminifera species names should always be in italics, also in Fig 5\n- Fig 4 caption, should this not be <300 counts\n- Please check the spelling of all species throughout the manuscript. I noticed some mistakes (e.g. s. hovathi has two I’s on line 141)\n- No references linked to S. feylingi inferences – it is my understanding that this species is linked to productivity (e.g. Seidenkrantz, 2013).\n- Typo line 149 – capital D\n- Space missing line 258 after 144GC\n- Typo line 259, remove driven\n- Full stop missing from line 282\n- Full stop missing line 287\n- I would start a new paragraph for “as previously.” (line 320).\n- Foraminifera should be foraminiferal when it is used as a adjective (e.g. foraminiferal assemblages, line 323 and foraminiferal species, line 409). This should be checked throughout the manuscript and changed accordingly\n- References required for ice shelf statement – line 328\n- What is AWI (Line 353)\n- Indicate not indicates (line 353)\n- Space after 270GC (Line 254)\n- Indicate not indicated (Line 358)\n- Constraints not constrains (Line 360)\n- Extra l before planktic in fig caption 5a\n- I think it would be better to be consistent using line graphs or bar charts for the foraminifera data in Fig 4 and 5\n- The end of Figure 6 caption needs removing. And the correct description of the figure included.\nMain comments\n- I very much enjoyed reading the discussion, I think the argument for RAC is strong with the nuances discussed and previous evidence well incorporated!\n- There is a wealth of recent literature highlighting past changes to the NEGIS, for me, the fact that deglaciation began earlier than previously reported needs to be stated in the abstract as I think it is a very important finding and differentiates this paper from those previously published. This is clear in your summary at the end of the paper (Line 360 start), but could be better stated in the abstract. Simply adding ‘Radiocarbon dating shows deglaciation began ~20 ka BP, earlier than previously reported, etc’ would suffice.\n- I think it is important to present the foraminiferal data as concentrations, (e.g. no. taxa/g dry sed), given the impact of compaction downcore. As volumetric data associated with the samples (as listed in the methods) was taken, I think it think this is possible if bulk sediment weights are/were made. If this is not possible, I think foraminifera fluxes could be useful to include.\n- I think that this paper should be cited, given that it examines the distribution of modern benthic foraminifera in the exact study area being investigated here and the proxies used:\no Davies, J., Lloyd, J., Pearce, C. and Seidenkrantz, M.S., 2023. Distribution of modern benthic foraminiferal assemblages across the Northeast Greenland continental shelf. Marine Micropaleontology, 184, p.102273. Useful inferences about specific species should be added from this (e.g. stetsonia horvathi)\n- Fig. 2. I do not understand the reasoning behind the order of the xray images in the red box. I think it make more sense to list this in order of appearance in the cores. It would also be helpful if the lithofacies abbreviations were defined in the caption.\n- I think this reference is also important to include: Tabone, I., Robinson, A., Montoya, M. and Alvarez-Solas, J., 2024. Holocene thinning in central Greenland controlled by the Northeast Greenland Ice Stream. Nature communications, 15(1), p.6434. It provides useful information relating to the importance of constraining timing and speed of retreat of the NEGIS and I believe would be useful for the introduction.\n- To me it seems like these cores are located on the mid/outer shelf, I wouldn’t describe 146GC as being on the outer continental shelf (Line 71).\n- Given the high abundance of C. reniforme, I think more focus needs to be given to its interpretation in the results and discussion. Broadly, it seems to covary with C. neoteretis and previous studies have linked it to chilled Atlantic water. I think this should be included and discussed.\n- I would find it helpful to have the Faunal zones marked on Fig 5.\n- Why is the age model for 146GC not included (e.g. as part of supplementary figure 3)?\n- Were all benthic foraminifera species included in the radiocarbon samples? Or were some species (e.g. Miliolina) excluded. This is important to outline these details in the methodology."}, "author_response": "Response to reviewers’ comment\nThe authors would like to thank the reviewer for their constructive comments. We have responded to each reviewer’s comments below with our response in blue.\nReviewer #1 (Remarks to the Author):\nThis manuscript presents new data on the history of the NEGIS from the LGM through early Holocene. It builds on previous work that has shown that the ice margin reached the shelf edge at the Westwind Trough and that it had already retreat off the outer shelf during the LGM. What this manuscript adds is faunal evidence from a key core (144GC) and lithofacies analysis plus dating on two cores (144 and 146GC) to gain more detailed understanding of the further retreat history and what forcings were at play. The core sites target important ice marginal features (grounding zone wedges) on the mid/outer shelf. The lithfacies and foraminifera assemblage data are used to reconstruct important aspects of the NEGIS in the past: the configuration of the ice front (i.e. ice shelf fronted or ice cliff fronted); emissions of meltwater, advection of relatively warm RAC water, and sea-ice cover. I was struck by two key findings. The first is firm indication that the ice retreated during the LGM and during the oldest part of deglaciation, HS-1. The cores do not contain a complete record of this retreat as they were ice covered until c. 19 ka. A basal diamicton interpreted as subglacial deposit is overlain by fine grained laminated sediment lacking ice rafted clasts and containing a fauna consistent with an ice shelf fronted margin. The second key result to my mind is that the GZWs record relative stability of the grounding zone during the interval of c. 19ka to c. 15.8 ka. After c. 15.2 ka, the lithofacies indicate a calving margin lacking an ice shelf and the faunas indicate strong inflow of RAC and relative ocean warmth at the seabed that would influence ice instability. The GZWs had been thought to be Younger Dryas in age, so this is a key finding! The conclusion is that ice retreat from the GZW 2 may have been driven both by warm atmosphere and ocean forcing. I think that the data exist in this paper to make these points. However, there are some structural problems and some lack of clarity in the manuscript that hurt its ability to make these points clearly.\nThe Results section does not clearly distinguish previous work and background information from new results presented in this study. I would argue that the first 3 paragraphs are actually part of an introduction, setting the stage for the problems that the core data can attempt to solve. The fourth paragraph is meant to indicate how the lithofacies and foraminifera in the two cores can be associated with environments, but it was confusing because it goes immediately to interpretations without presenting the characteristics of the lithofacies and fauna and how these progress upcore and in association with the chronology. In a sense, there is no results section in this paper. The data are not described in a systematic way before interpretations are made. It is difficult to separate what is new and what is previously published.\nWe have made structural changes throughout the manuscript. We have moved and adapted the first three chapters of the results section into a new sub-section of the introduction titled ‘Background to study site’. We have incorporated the 4th paragraph into the section titled ‘Early deglacial and Atlantic water influence (>20.3 ka BP – 17.6 ka BP)’.\nWe have restructured each results sub-section so the results from this study are described first then interpreted. The paper now has a much clearer logical progression that we hope does justice to the findings of the paper.\nLine 189 there is an error in the sedimentation rate calculation…I think it is off by two orders of magnitude. Maybe what is meant is 0.2 cm per year rather than per kyr. This is indeed incorrect. We have also modified the chronology using a new calibration method that has changed the original sedimentation rate. Instead, we have adapted the text to state ‘However, there is no clear evidence of a change in sedimentation rate that could reduce benthic foraminiferal productivity.’ (Lines 204-205)\nThe figures are nicely drawn, but they fall short of helping to convey the points being made in some cases.\nOn Figure 1, the map of the area, two GZWs are shown. Core 144 is shown immediately in front of the outer GZW. I was however, confused that on the acoustic profile of the core site in Figure 3, that core 144 is shown to the NW of GZW1. Is this is a matter of the directions being misplaced on the figure? I am unsure, but think this profile needs to be turned around. It would help as well if Figure 1 showed where the two profiles are in the trough so that the orientation and locations are clear. In addition, it would help the introduction if there was a panel added to show the modern NEGIS, maybe using flow speed. Otherwise it is not easy for uninitiated readers to match the outlet glaciers with the main ice stream.\nThis was confusing so we have now rewritten and clarified it. The feature to the east of 144GC is not GZW1 and we confirm that the direction of the line in the original image is correct. Instead, this is another ice marginal feature that lies to the east of the core 144GC and closer to the shelf edge. It therefore formed prior to GZW1. Given its geometry and acoustic properties, we believe this to be an additional GZW (cf. Batchellor and Dowdeswell, 2015). It is now labelled it as an additional GZW on Figs. 2 and 6. Location of the two acoustic lines are marked on Fig1 in orange. We have added the Ice sheet velocity measurements to Fig 1a and labelled the location of NEGIS which is evidence by the section of fast flowing ice.\nFigure 4 could benefit from having the Lithofacies along the depth axis as in Figure 2 so a reader does not need to flip back and forth. Suggest you include planktic forams per ml and benthic forams per ml. You could use the planks per ml instead of the P:B ratio if space is an issue. The ice species are in purple not blue…at least in the reviewer pdf. I presume that faunal analyses were not made on core 146 which is too bad.\nWe have added the lithofacies along the depth access as requested. We have removed P:B ratio. Both planktic and benthic foraminifera per ml is added to the figure. The colour of the ice species is supposed to be blue, but we have adopted the colour to a different blue colour so it doesn’t appear purple on screens or printouts.\nFigure 5. needs some additional annotation such as chrons (LGM, HS1, B-A, YD etc). Maybe add the modern average air temperature to the summer air temp panel. Might be useful as well to tie in the faunal zones and lithofacies as these are important as well as the fuana.\nWe have added both the lithofacies, including the IRD layers in core 144GC, as well as the faunal zones to the figure. We have annotated on the figure the timing of Greenland stadial 1 and 2, Greenland interstadial 1 and Holocene. We have not added modern air temperature to eth panel as there is already a lot in this figure.\nFigure 6 shows schematic profiles of the reconstructed NEGIS through time. Panel a indicates that the ice margin retreated by calving back and that dirty ice bergs were released. Early in the paper there is evidence of IRD in slope cores during this period. Panel b is the starting point of this study. But this panel does not match the data. GZW 1 is a bump on the seafloor but no association made with the core. Is GZW 1 associated with deposition of the laminated facies lacking IRD? Does that suggest that this is an ice shelf fronted margin beginning from the very start of the core record? This schematic does not explain GZW 1 and how it relates to results presented for 144GC. Panel C makes sense except that the story either is missing the IRD interval of ice retreat to GZW 1, or that the formation of GZW 1 is ignored. Presumably the GZWs are formed as the ice stabilizes, so perhaps they should not appear until the panel in which they form.\nWe have redrawn Figure 6 so that it aligns more closely to the timing of events as written in the text. We have removed GZWs in the panels where ice is grounded and only included them in the panels in which they are formed. We have included the new GZW that lies in front of core 144GC in panel B. Panels b and c now show the persistent presence of an ice shelf which account for the lack of IRD in panel C that the reviewer highlighted.\nReviewer #2 (Remarks to the Author):\nReview of Callard et al (2025) - ‘Ocean driven retreat of the Northeast Greenland Ice Stream following the Last Glacial Maximum’\nSummary\nThis study presents data and conclusions from two new sediment cores taken on the Norske Trough that are used to describe the early deglaciation of the Northeast Greenland Ice Stream (NEGIS) from its LGM position. The paper has numerous interesting findings that are used to describe the evolution of the paleo-ice stream by tying in sediment facies, analysis of foraminifera assemblages and glacial landforms. Chief among them is the important role that ocean melt, driven by warm Return Atlantic Water Current (RAC), played in the initial retreat of NEGIS from its LGM by ~20 ka BP, a retreat that occurred without a rise in atmospheric temperature and that was much earlier than previously thought. RAC is further linked with the collapse of the ice shelf after 15.7 ka BP when surface air temperatures began to rise during the onset of the Bølling-Allerød. Furthermore, Grounding Zone Wedges in the Norske Trough provided vital pinning points and stability during the early deglaciation after the trough deepens into a retrograde slope inland of the shelf edge.\nI found this paper very enjoyable to read and believe is shares valuable insights into the evolution of the NEGIS from the LGM. This is especially topical as constraining the future response of the contemporary NEGIS to climate warming is crucial. The manuscript is well-written and well-structured, with the authors clearly explaining their interpretations of sediment record which I, for the most part, agree with.\nMy comments below mainly relate to interpretations made around the early retreat/deglaciation of the NEGIS, specifically whether an ice shelf existed before 18 ka BP, and the role the bathymetry and fjord topographically played in the initial retreat. I will state here that my opinions are far from set in stone, and hopeful adding a few sentences to further explain their interpretations would alleviate any of my concerns and lead me to recommend this paper for publication.\nMajor Comments\n• Ice Shelf Interpretation: I agree with the authors interpretation that an ice-shelf existed in the Norske Trough with the grounding line on GZW2 between 18-15ka BP. However, I’m curious why the authors believe an ice shelf wasn’t present before NEGIS retreat to GZW2 (for example in Figure 6B). Instead, during the early deglaciation (>20 ka BP to 18 ka BP), the high levels of S. horvathii and lack of IRD and are presented as reasons for thick sea-ice conditions. These same arguments are then used as evidence for an ice shelf between 18-15 ka BP. Furthermore, as the authors rightly mention, the occurrence of GZWs are indications of shelf ice conditions, therefore I would expect it likely that an ice shelf was present with the grounding line on GZW1 during the early deglaciation (López-Quirós et al., 2024). I also wonder why the keel marks from tabular ice bergs must have been formed after 18 ka BP, could they not have been formed from an earlier ice shelf?\nReviewer 2 is correct, and we have now clarified and amended this aspect of the paper. We agree with the reviewer that the core lithology and foraminiferal evidence point to the presence of an ice shelf throughout the whole early deglacial period until 15.2 ka BP. This is clearly supported by the geomorphic evidence (GZW’s) on the sea floor. An extensive iceshelf was over both core 146 and 144 prior to 15.2 ka, when it subsequently broke up leading to the IRD layers of the same age recorded in both cores. We have adjusted the wording throughout the manuscript to reinforce this message. It is the most critical aspect of this story. Changes in the foraminiferal assemblage and flux data indicate a change in the distance of the ice-shelf front to the core site and we have added this detail to the text. In our initial submission we also considered the likelihood of sea-ice cover as an alternative to the presence of an ice shelf, but this was a weaker argument and overly complicated. It has now been de-emphasised.\nLater in the discussion it is stated ‘… that NEGIS was fronted by an ice shelf when it stabilised on GZW2’. This is not what it shown in Figure 6B when the retreat is shown as a calving cliff face with harsh sea-ice conditions when it reached GZW2. It is then said that the presence of an ice shelf was of ‘negligible’ importance to the initial stability of NEIGS and that the bathymetric high was more important. I think that a reference or two is required here, as I’m not entirely convinced by that conclusion.\nWe thank the review for their comment and have addressed this in the text to state that the ice-shelf acted to stabilise the retreating NEGIS. We have included a reference to the modern ice-shelves from the area to support this. However, the location of the bathymetric high is also an important control on stability of the ice stream as well as the ice shelf.\n• Bathymetry and Fjord Geometry: I agree with the authors that RAC was likely the cause of early retreat and echo that this is a great finding of the paper. However, I’m not sure I fully agree with the authors comments on the fjord geometry and slope angle regarding this initial retreat, where the initial slow retreat rates (23 to 19 m/yr) on a retrograde slope are used to conclude the bathymetry was not a principal control. Firstly, I think it would be great to have a comparison against retreat rates from other paleo-ice streams in Greenland, is 23 m/yr considerably slower? Secondly, I see that the Norske Trough immediately narrows from the shelf edge, could this have slowed initial retreat through increased lateral drag, similarly as the authors later discus with the narrowing of the trough around GZW2. Finally, while the bathymetry deepens from 320 m at the shelf edge to 560 m 100 km in land, the majority of this deepening (210 m) happens ~50km from the shelf edge, therefore, wouldn’t it be reasonable to while retrograde in nature, the initial shallow slope may have contributed to the slower retreat rates?\nWe have added two examples. During the early deglaciation of the Ummannaq Ice Stream that has retreat rates were 121 to 94 ma−1. During the early deglaciation of Jakobshavn Isbrae retreat rates were 104 to 137 ma−1 (Roberts et al. 2024). Both are order of magnitude higher than the rates reported in this paper and highlights that the NEGIS retreat was comparatively slow. We agree that lateral drag could influence the retreat rate. We have added additional wording to this effect in the manuscript.\nMinor Comments\n• Figure 1: I think the polygons for GZW1 and 2 should only have the outlines and not be filled, it would then be possible to see how the GZWs look in comparison to the sea floor. I also wonder is the scale for the bathymetry could be clipped to range from 0 to 1500 m, just to make it the variations in depth slightly clearer.\nThe polygons have been changed to outlines and we have clipped the bathymetry to 0-1500.\n• Figure 5: JJA air temperatures. I think this should be made clear is if for the contemporary NEGIS region or the paleo domain of the ice stream? I’m also curious if the temperatures are any different in the newer Badgeley et al., 2020 dataset?\nThe modelled data is for a specific location rather that the whole NEGIS region. We have added some extra detail in the caption. We have not made a comparison between temperature reconstructions as we are interested in timing and pattern of change as a clue to possible drivers opposed to absolute temperature changes.\n• l.34: It would be worthwhile mentioning that 79N still has an ice tongue that is providing significant buttressing to the interior ice (Humbert et al., 2023), especially as you discuss ice shelf evolution and collapse in the results/discussion.\nWe have added the following text ‘79N still retains its 70 km long, 20 km wide ice shelf, that buttresses the ice stream. However, a significant calving event observed in 2022 indicates ongoing ice-shelf instability, with models predicting that collapse of the ice shelf would increase grounding line flux by over 160%6.’(lines 38-41)\n• l.24: ice shelf break ‘up’? This is corrected\n• l.29: Redefine the Greenland Ice Sheet acronym - GrIS. This is redefined in line 32\n• l.36: Capital W for ‘with’. Corrected\n• l.40 – 42: Sentence is a bit sloppy. ‘There’ should be ‘their’, and maybe reads better as ‘… their reliability depends on an accurate parametrisation of ice-sheet physics, including key boundary conditions such as…’\nWe have changed the wording to ‘While numerical simulations provide a powerful predictive tool, their reliability depends on an accurate parameterisation of ice-sheet dynamics and key boundary conditions such as bathymetry and climate forcing.’ (lines 48-50)\n• l.45: ‘enabling a better understanding of ice-ocean interactions’ – We already have some understanding of how ice-ocean, but the paleo record definitely improves this.\n• l.51: double ‘from’ – maybe better as ‘Recent evidence from marine cores taken on the continental shelf…’ We have changed the wording to ‘Recent evidence from marine cores, bathymetric and geophysical observations from the continental shelf provides a longer-term reconstruction of the behaviour of the NEGIS.’ (lines 68-69)\n• l.57: ‘… initial retreat of NEGIS and critically…’ Corrected\n• l.94: I am presuming that the moraine ridge referred to here as not GZW1? I think this could be made a little clearer by also stating that 144GC is also in front of GZW1. We have adapted the text and figures so that this is clearer. (lines 100-101: ‘Core PS100-144GC (hereafter 144GC) lies between two GZW’s (a newly identified GZW and GZW1; Fig. 1 and Fig. 2).’\n• L.138: Missing full stop. Corrected\n• l.146 where is core CR02-GC? I don’t see it in Figure 1. We have added GR02-GC to Figure 1.\n• l.149: Incorrect capitalisation of D. Corrected\n• l.164: Full stop within the brackets when it should be outside. Corrected\n• l.180: Add reference to Fig.4 at the end of the sentence. We have changed the wording to demonstrate how low the foraminiferal counts where in the shaded sections.\n• l.258: Missing bracket Corrected\n• l.259: ‘Driven melting’ and ‘driven ice shelf breakup’, choice of words could be improved in this sentence. This section has been rephrased ‘The timing of ice-shelf breakup, ~15.2-14 ka BP, corresponds with an increased RAW signal on the continental shelf (increase in C. neoteretis shown in 144GC) suggesting that ocean-driven melting played an important role in ice-shelf break up.’ (lines 314-316)\n• l.282: Missing full stop. Corrected\n• l.287: Missing full stop. Corrected\n• L.291: 23 m/yr is for the Norske Trough while 19 m/yr is the Westwind trough in reference 20. This should be made clearer (Ó Cofaigh et al., 2025). We have removed reference to the 19ma-1 in Westwind Trough (Lines 348-350)\n• l.334: ‘melting was an important driver’ Corrected\n• l.353: Should AWI not be AW? Corrected\n• l.353: Missing spaces and doubles spaces in this sentence. Corrected\nReferences\nBadgeley, J.A., Steig, E.J., Hakim, G.J., Fudge, T.J., 2020. Greenland temperature and precipitation over the last 20000 years using data assimilation. Clim. Past 16, 1325–1346. https://doi.org/10.5194/cp-16-1325-2020\nHumbert, A., Helm, V., Neckel, N., Zeising, O., Rückamp, M., Khan, S.A., Loebel, E., Brauchle, J., Stebner, K., Gross, D., Sondershaus, R., Müller, R., 2023. Precursor of disintegration of Greenland’s largest floating ice tongue. The Cryosphere 17, 2851–2870. https://doi.org/10.5194/tc-17-2851-2023\nLópez-Quirós, A., Junna, T., Davies, J., Andresen, K.J., Nielsen, T., Haghipour, N., Wacker, L., Olsen Alstrup, A.K., Munk, O.L., Rasmussen, T.L., Pearce, C., Seidenkrantz, M.-S., 2024. Retreat patterns and dynamics of the former Norske Trough ice stream (NE Greenland): An integrated geomorphological and sedimentological approach. Quat. Sci. Rev. 325, 108477. https://doi.org/10.1016/j.quascirev.2023.108477\nÓ Cofaigh, C., Lloyd, J.M., Callard, S.L., Gebhardt, C., Streuff, K.T., Dorschel, B., Smith, J.A., Lane, T.P., Jamieson, S.S.R., Kanzow, T., Roberts, D.H., 2025. Shelf-edge glaciation offshore of northeast Greenland during the last glacial maximum and timing of initial ice-sheet retreat. Quat. Sci. Rev. 359, 109326. https://doi.org/10.1016/j.quascirev.2025.109326\nJamie Barnett\nStockholm University\nReviewer #3 (Remarks to the Author):\nCallard et al., provide new information relating to the role oceans played in governing the retreat of the Northeast Greenland Ice Steam on the mid/outer continental shelf. Key results are:\n- Deglaciation began at around 20ka BP on the mid/outer Northeast continental shelf, this is earlier than previously reported in the Norske Trough.\n- Analysis of foraminiferal assemblages suggests this was primarily driven by the intrusion of warm Return Atlantic Water onto the shelf, amplified by a retrograde seabed.\nOverall, I liked that paper, and I found it interesting; the discussion was enjoyable to read. I believe that the contribution is important in this region, particularly given the impact of warming ocean waters on the fate of the Greenland Ice Sheet today and in the future. I think that the methodologies and science are sound, I have some comments on this in the ‘main comments’ section of this review.\nOne of the main comments I have relates to the quality of the writing and mistakes throughout. I believe that these detract from the overall manuscript. I therefore list those small changes first here. However, I recommend that the entire manuscript be carefully proofread edited prior to subsequent review.\nWe have worked hard to improve the quality of writing and remove mistakes.\nComments relating to quality of writing and figures\n- Sometimes the authors use ‘the’ NEGIS sometimes ‘the’ is excluded – it should be consistent We have added the to all occurrences of NEGIS.\n- Type in figure 1a caption – ‘value’ coldest, I think this should be blue. We have corrected this to blue\n- Line 41 – their reliability not there reliability Corrected\n- RAC never defined. I think it would be more correct to use Return Atlantic Water (RAW) to describe the water mass in some instances. E.g. like 309. This should be checked throughout We have changed all RAC to RAW in the text and figures for consistency.\n- The full core name of 135G should be given in the figure caption of 1b, as per the other cores listed Full core name has been added in caption\n- What is AWI Bank – not defined anywhere. This is a name for the Shoal that runs on the southeastern edge of inner Westwind Trough as published in Arndt et al 2015 and 2017. This is not defined but assumed to be Alfred Wegner Institute bank.\n- The Rasmussen et al., 2022 core should be marked on the map (19G), it is in the caption but not on the map. 39G is also listed in the caption but not on the map. Please check all of these again. We have added 19G to the map. Mention of 39G has been removed from the caption as this core is not referred to in the main text\n- I think fig 2 and 3 should be switched as fig 3 is introduced in the text first and this is confusing We have switched the figures\n- Fig 4: foraminifera species names should always be in italics, also in Fig 5 This has been corrected\n- Fig 4 caption, should this not be <300 counts Yes, the reviewer is correct, but we have also changed the wording at the end of this caption.\n- Please check the spelling of all species throughout the manuscript. I noticed some mistakes (e.g. s. hovathi has two I’s on line 141) We have checked the spelling of all species names throughout the text and corrected those that were misspelled.\n- No references linked to S. feylingi inferences – it is my understanding that this species is linked to productivity (e.g. Seidenkrantz, 2013). In the original text we used reference 38 Knudsen, K. L. & Seidenkrantz, M.-S.,1994. Stainforthia feylingi new species from arctic to subarctic environments, previously recorded as Stainforthia schreibersiana (Czjzek). In H.P. Sejrup, K.L. Knudsen (Eds.), Late Cenozoic Benthic Forminifera: Taxonomy, Ecology, and Stratigraphy.Cushman Foundation for Foraminiferal Research, Special Publication, vol. 32 (1994), pp. 5-13.\nWe have since added Patterson, R. T., et al. (2000). \"Oxygen level control on foraminiferal distribution in Effingham inlet, Vancouver Island, British Columbia, Canada.\" The Journal of Foraminiferal Research 30(4): 321-335.\n- Typo line 149 – capital D corrected\n- Space missing line 258 after 144GC corrected\n- Typo line 259, remove driven corrected\n- Full stop missing from line 282 corrected\n- Full stop missing line 287 corrected\n- I would start a new paragraph for “as previously.” (line 320). corrected\n- Foraminifera should be foraminiferal when it is used as a adjective (e.g. foraminiferal assemblages, line 323 and foraminiferal species, line 409). This should be checked throughout the manuscript and changed accordingly. We have checked and corrected all occurrences where this change is required.\n- References required for ice shelf statement – line 328 We have included reference 53: Gudmundsson, G. Ice-shelf buttressing and the stability of marine ice sheets. The Cryosphere 7, 647-655 (2013).\n- What is AWI (Line 353) This is corrected to RAC\n- Indicate not indicates (line 353) corrected\n- Space after 270GC (Line 254) corrected\n- Indicate not indicated (Line 358) corrected\n- Constraints not constrains (Line 360) corrected\n- Extra l before planktic in fig caption 5a corrected\n- I think it would be better to be consistent using line graphs or bar charts for the foraminifera data in Fig 4 and 5 After making comparison figures we have decided to keep the different styles between figures as it made the figures clearer. Similar approaches have been used in other published articles (e.g., Lloyd et al, 2023)\n- The end of Figure 6 caption needs removing. And the correct description of the figure included. An appropriate figure caption has been added: ‘Figure 6: Conceptual model representing the interaction between the marginal position of the NEGIS, ocean circulation and ice shelf activity. Panels a) to h) represent key time periods discussed in the manuscript and consists of a cross-sectional view of the NEGIS and the fronting ice shelf as well as a top-down view showing extent in relation to the current NEGIS continental shelf. Bathymetry, position of GZWs and position of sediment cores analysed are illustrated and are estimations.’\nMain comments\n- I very much enjoyed reading the discussion, I think the argument for RAC is strong with the nuances discussed and previous evidence well incorporated! Thank you for this comment.\n- There is a wealth of recent literature highlighting past changes to the NEGIS, for me, the fact that deglaciation began earlier than previously reported needs to be stated in the abstract as I think it is a very important finding and differentiates this paper from those previously published. This is clear in your summary at the end of the paper (Line 360 start), but could be better stated in the abstract. Simply adding ‘Radiocarbon dating shows deglaciation began ~20 ka BP, earlier than previously reported, etc’ would suffice. We have edited the abstract, but it is important to note that O Cofaigh et al 2025 have published the oldest age for deglaciation (21.6 ka BP). However, this record provides the oldest reconstruction of RAW and confirms the continued retreat of the NEGIS back 100 km from the continental shelf edge to the core location and during the global LGM and we can link that retreat to RAW. We have adapted the abstract and text, so this is clearly stated.\n- I think it is important to present the foraminiferal data as concentrations, (e.g. no. taxa/g dry sed), given the impact of compaction downcore. As volumetric data associated with the samples (as listed in the methods) was taken, I think it think this is possible if bulk sediment weights are/were made. If this is not possible, I think foraminifera fluxes could be useful to include. Sample were volumetrically measured not weighted and therefore we cannot calculate the taxa/g dry weight. However, we have calculated the foraminiferal fluxes and referred to this throughout the results section and added the data to Fig 4 and 5.\n- I think that this paper should be cited, given that it examines the distribution of modern benthic foraminifera in the exact study area being investigated here and the proxies used:\no Davies, J., Lloyd, J., Pearce, C. and Seidenkrantz, M.S., 2023. Distribution of modern benthic foraminiferal assemblages across the Northeast Greenland continental shelf. Marine Micropaleontology, 184, p.102273. Useful inferences about specific species should be added from this (e.g. stetsonia horvathi)\nThank you for highlighting this omission. We have referenced this paper where appropriate throughout the manuscript.\n- Fig. 2. I do not understand the reasoning behind the order of the xray images in the red box. I think it make more sense to list this in order of appearance in the cores. It would also be helpful if the lithofacies abbreviations were defined in the caption. The order of the lithofacies have been changed in the figure so they are in order of appearance.\n- I think this reference is also important to include: Tabone, I., Robinson, A., Montoya, M. and Alvarez-Solas, J., 2024. Holocene thinning in central Greenland controlled by the Northeast Greenland Ice Stream. Nature communications, 15(1), p.6434. It provides useful information relating to the importance of constraining timing and speed of retreat of the NEGIS and I believe would be useful for the introduction. This is indeed a useful paper to cite, and we have included reference to this paper (reference 28) in the introduction (Lines 92-96)\n- To me it seems like these cores are located on the mid/outer shelf, I wouldn’t describe 146GC as being on the outer continental shelf (Line 71). We have changed the text to outer continental shelf. (Lines 109-110)\n- Given the high abundance of C. reniforme, I think more focus needs to be given to its interpretation in the results and discussion. Broadly, it seems to covary with C. neoteretis and previous studies have linked it to chilled Atlantic water. I think this should be included and discussed. We agree and have added more detailed about C. reniforme and its covariance with C. neoteretis as well as it’s link to chilled Atlantic Water.\n- I would find it helpful to have the Faunal zones marked on Fig 5. These have been added to the figure\n- Why is the age model for 146GC not included (e.g. as part of supplementary figure 3)? We did not conduct an age model for core 146GC due to the limited chronological constraint, particular for the older section of the core. We have added a line in the methods explaining this.\n- Were all benthic foraminifera species included in the radiocarbon samples? Or were some species (e.g. Miliolina) excluded. This is important to outline these details in the methodology. It was mixed but we did avoid Miliolina and Quinqueloculina species, I have added this detail in the methods.\nReferences:\nArndt, J.E., Jokat, W., Dorschel, B., Myklebust, R., Dowdeswell, J.A. and Evans, J., 2015. A new bathymetry of the Northeast Greenland continental shelf: Constraints on glacial and other processes. Geochemistry, Geophysics, Geosystems, 16(10), pp.3733-3753.\nArndt, J.E., Jokat, W. and Dorschel, B., 2017. The last glaciation and deglaciation of the Northeast Greenland continental shelf revealed by hydro-acoustic data. Quaternary Science Reviews, 160, pp.45-56.\nLloyd, J. et al. Ice-ocean interactions at the Northeast Greenland Ice stream (NEGIS) over the past 11,000 years. Quaternary Science Reviews 308, 108068 (2023).\nÓ Cofaigh, C., Lloyd, J.M., Callard, S.L., Gebhardt, C., Streuff, K.T., Dorschel, B., Smith, J.A., Lane, T.P., Jamieson, S.S.R., Kanzow, T., Roberts, D.H., 2025. Shelf-edge glaciation offshore of northeast Greenland during the last glacial maximum and timing of initial ice-sheet retreat. Quat. Sci. Rev. 359, 109326. https://doi.org/10.1016/j.quascirev.2025.109326"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revised manuscript is much better and I do not have any additional comments or suggestions. I think it is well written and illustrated and the conclusions are noteworthy.", "reviewer_2": "2nd Review of Callard et al (2025) - ‘Ocean driven retreat of the Northeast Greenland Ice Stream following the Last Glacial Maximum’\nSummary:\nThe authors have done an excellent job in responding to the comments from myself and the other reviews. This new version of the manuscript is both an improvement in structure and writing; while also further emphasising, valuable insights gained from the paleo-evolution of NEGIS and crucially the importance of ocean melt in the stability of ice shelves and grounding line behaviour.\nMy previous comments mainly concerned the interpretations of glacial dynamics at the beginning of the deglaciation, whether an ice shelf existed during retreat from the shelf edge, as well as the role of bathymetry in driving retreat. Both concerns have been alleviated through added references and greater context in the discussion, as well as improvements to Figures 1 and 6. Furthermore, there are numerous small changes throughout the manuscript that address all my minor comments completely. I would also like highlight the restructuring of the manuscript to include the ‘Background to study site’ section after the Introduction. This was in response to Reviewer #1, and I believe this greatly improves the readability of the manuscript and enhances the story of NEGIS retreat of the LGM and the importance of warm Atlantic water.\nTo conclude, I believe this piece of work provides novel and crucial insight into the deglaciation of the Greenland Ice Sheet from the LGM and importantly the role of warm Atlantic water is driving grounding line retreat and ice shelf instability. The early retreat of the NEGIS (~20 ka BP) despite a lack of atmospheric warming, plus the enhanced Atlantic water signal around the collapse of the ice shelf are vital conclusions that stress the importance of the ice-ocean boundary as we strive to understand the retreat of contemporary ice sheets through both observations and modelling efforts.\nI just have a few minor comments relating to grammar:\n- In the response to reviewers there is mention of a “Background to Study Site” section, however I can’t see this sub-heading. Maybe an issue with the PDF but I want to highlight in case.\n- Line 31-32: Maybe could be re-written to avoid saying the Greenland Ice Sheet twice in quick succession.\n- Line 195: Missing space between cores and 114GC\n- Line 217: Comma should be a full stop\n- Line 349: Missing space after ‘approximately’\n- Lune 357: Missing space after GZW\n- Line 357: Miss placed bracket after “moraine ridges”\n- Line 364: Missing bracket and full stop after Fig 5.\n- Line 393: Missing bracket before Figs\nJamie Barnett\nStockholm University", "reviewer_3": "I think the author's have adequately addressed the comments made on their manuscript. However, I could not see this reference in the reference list:\nReferences required for ice shelf statement – line 328\nWe have included reference 53: Gudmundsson, G. Ice-shelf buttressing and the stability of marine ice sheets. The Cryosphere 7, 647-655 (2013).\nI could not see this reference in the text. Reference 53 refers to Aagaard-Sørensen, S. et al. A late glacial–early holocene multiproxy record from the eastern 912 fram strait, polar north atlantic. Marine Geology 355, 15-26 (2014).\nApart from that omission, I enjoyed reading the revised manuscript."}, "author_response": "Response to reviewers’ comment\nThe authors would like to again thank the reviewer for their comments. We have responded to each reviewer’s comments below with our response in blue.\nREVIEWERS' COMMENTS\nReviewer #1 (Remarks to the Author):\nThe revised manuscript is much better and I do not have any additional comments or suggestions. I think it is well written and illustrated and the conclusions are noteworthy.\nReviewer #2 (Remarks to the Author):\n2nd Review of Callard et al (2025) - ‘Ocean driven retreat of the Northeast Greenland Ice Stream following the Last Glacial Maximum’\nSummary:\nThe authors have done an excellent job in responding to the comments from myself and the other reviews. This new version of the manuscript is both an improvement in structure and writing; while also further emphasising, valuable insights gained from the paleo-evolution of NEGIS and crucially the importance of ocean melt in the stability of ice shelves and grounding line behaviour.\nMy previous comments mainly concerned the interpretations of glacial dynamics at the beginning of the deglaciation, whether an ice shelf existed during retreat from the shelf edge, as well as the role of bathymetry in driving retreat. Both concerns have been alleviated through added references and greater context in the discussion, as well as improvements to Figures 1 and 6. Furthermore, there are numerous small changes throughout the manuscript that address all my minor comments completely. I would also like highlight the restructuring of the manuscript to include the ‘Background to study site’ section after the Introduction. This was in response to Reviewer #1, and I believe this greatly improves the readability of the manuscript and enhances the story of NEGIS retreat of the LGM and the importance of warm Atlantic water.\nTo conclude, I believe this piece of work provides novel and crucial insight into the deglaciation of the Greenland Ice Sheet from the LGM and importantly the role of warm Atlantic water is driving grounding line retreat and ice shelf instability. The early retreat of the NEGIS (~20 ka BP) despite a lack of atmospheric warming, plus the enhanced Atlantic water signal around the collapse of the ice shelf are vital conclusions that stress the importance of the ice-ocean boundary as we strive to understand the retreat of contemporary ice sheets through both observations and modelling efforts.\nI just have a few minor comments relating to grammar:\n- In the response to reviewers there is mention of a “Background to Study Site” section, however I can’t see this sub-heading. Maybe an issue with the PDF but I want to highlight in case. This has been added, thank you.\n- Line 31-32: Maybe could be re-written to avoid saying the Greenland Ice Sheet twice in quick succession. This has been reworded to: The Northeast Greenland Ice Stream (NEGIS) extends more than 600 km into the interior and drains approximately 12% of the Greenland Ice Sheet (GrIS).\n- Line 195: Missing space between cores and 114GC : added\n- Line 217: Comma should be a full stop corrected\n- Line 349: Missing space after ‘approximately’ corrected\n- Lune 357: Missing space after GZW corrected\n- Line 357: Miss placed bracket after “moraine ridges” corrected\n- Line 364: Missing bracket and full stop after Fig 5. corrected\n- Line 393: Missing bracket before Figs corrected\nJamie Barnett\nStockholm University\nReviewer #3 (Remarks to the Author):\nI think the author's have adequately addressed the comments made on their manuscript.\nHowever, I could not see this reference in the reference list:\nReferences required for ice shelf statement – line 328\nWe have included reference 53: Gudmundsson, G. Ice-shelf buttressing and the stability of marine ice sheets. The Cryosphere 7, 647-655 (2013).\nI could not see this reference in the text. Reference 53 refers to Aagaard-Sørensen, S. et al. A late glacial–early holocene multiproxy record from the eastern 912 fram strait, polar north atlantic. Marine Geology 355, 15-26 (2014). This paper has been referenced and is number 53. Aagaard-Sorensen is number 54. (line 678)\nApart from that omission, I enjoyed reading the revised manuscript."}]

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