Description: Reconstructions of sea‐surface conditions during the Holocene were achieved using three sediment cores from northeastern Baffin Bay (GeoB19948‐3 and GeoB19927‐3) and the Labrador Sea (GeoB19905‐1) along a north–south transect based on sea‐ice IP25 and open‐water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III). In Baffin Bay, sea‐surface conditions in the Early Holocene were characterized by extended (early) spring sea ice cover (SIC) prior to 7.6 ka BP. The conditions in the NE Labrador Sea, however, remained predominantly ice‐free in spring/autumn due to the enhanced influx of Atlantic Water (West Greenland Current, WGC) from 11.5 until ~9.1 ka BP, succeeded by a period of continued (spring–autumn) ice‐free conditions between 9.1 and 7.6 ka BP corresponding to the onset of Holocene Thermal Maximum (HTM)‐like conditions. A transition towards reoccurring ice‐edge and significantly reduced SIC conditions in Baffin Bay is evident in the Middle Holocene (~7.6–3 ka BP) probably caused by the variations in the WGC influence associated with the ice melting and can be characterized as HTM‐like conditions. These HTM‐like conditions are predominantly recorded in the NE Labrador Sea area shown by (spring–autumn) ice‐free conditions from 5.9–3 ka BP. In the Late Holocene (last ~3 ka), our combined proxy records from eastern Baffin Bay indicate low in‐situ ice algae production; however, enhanced multi‐year (drifted) sea ice in this area was possibly attributed to the increased influx of Polar Water mass influx and may correlate with the Neoglacial cooling. The conditions in the NE Labrador Sea during the last 3 ka, however, continued to remain (spring–autumn) ice‐free. Our data from the Baffin Bay–Labrador Sea transect suggest a dominant influence of meltwater influx on sea‐ice formation throughout the Holocene, in contrast to sea‐ice records from the Fram Strait area, which seem to follow predominantly the summer insolation trend.

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Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Description: The morphometric and petrographic characteristics of the coarse-grained clasts (〉 1 cm) sampled from the sediments of the Amerasian Basin, Central Arctic Ocean, were studied. Most of the clasts are represented by dolomites (46,4%), sandstones (22,8%) and limestones (19,8%); the amount of other rocks fragments (chert, shale, igneous) is about 10%. A variety of lithological types were identified among the studied rock fragments. Limestones and dolomitic limestones often contain fragments of fauna. The majority of clasts is poorly rounded and characterized by a wide variety of shapes. More than half of the studied clasts have a size of 1-2 cm, a quarter - 2-3 cm, and larger clasts only occur in insignificant amounts. Geophysical surveys across the sampling sites showed a lack of bedrock outcrops, so the studied coarse-grained clasts are not of local origin. It is concluded that they were predominantly delivered from the Canadian Arctic Archipelago (likely from the platform area, e.g., Victoria Island), mainly due to iceberg rafting during deglaciation periods. The maximum possible contribution of the clasts from the Siberian sources is less than 23%. Distribution of the coarse-grained clasts argues for the existence of a quite stable ice drift path in the past, which is similar to the modern Beaufort Gyre.

Description: Hillaire‐Marcelet al. bring forward several physical and geochemical arguments against our finding of an Arctic glaciolacustrine system in the past. In brief, we find that a physical approach to further test our hypothesis should additionally consider the actual bathymetry of the Greenland–Scotland Ridge (GSR), the density maximum of freshwater at 3–4°C, the sensible heat flux from rivers, and the actual volumes that are being mixed and advected. Their geochemical considerations acknowledge our original argument, but they also add a number of assumptions that are neither required to explain the observations, nor do they correspond to the lithology of the sediments. Rather than being additive in nature, their arguments of high particle flux, low particle flux, export of 230Th and accumulation of 230Th, are mutually exclusive. We first address the arguments above, before commenting on some misunderstandings of our original claim in their contribution, especially regarding our dating approach.

Description: In the accompanying Comment1, Spielhagen et al. respond to our recent Article2, raising several issues concerning the perceived impossibility of a glacial freshwater ocean, focusing on the Nordic Seas and the North Atlantic south of the Greenland–Scotland ridge (GSR). They argue that no basin-wide 230Thex minima were seen in the Nordic Seas at the times proposed, and that they were due to dilution by high mass fluxes; that 10Be records closely resemble those of 230Thex, which they assume to support only the dilution hypothesis; that the reportedly continuous foraminiferal δ18O records were incompatible with freshwater under an ice shelf north of the GSR; and that no corresponding meltwater signal was seen in North Atlantic foraminiferal δ18O records south of the GSR. We highlight the circular arguments that result from the reliance on just one overstretched proxy for constraining age, temperature and salinity. Our interpretation is in line with observations and with the rapid melting during glacial terminations.

Description: Reconstructions of sea-surface conditions during the Holocene were achieved using three sediment cores from northeastern Baffin Bay (GeoB19948-3 and GeoB19927-3) and the Labrador Sea (GeoB19905-1) along a north– south transect based on sea-ice IP25 and open-water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III). In Baffin Bay, sea-surface conditions in the Early Holocene were characterized by extended (early) spring sea ice cover (SIC) prior to 7.6 ka BP. The conditions in the NE Labrador Sea, however, remained predominantly ice-free in spring/autumn due to the enhanced influx of Atlantic Water (West Greenland Current,WGC) from11.5 until ~9.1 ka BP, succeeded by a period of continued (spring–autumn) ice-free conditions between 9.1 and 7.6 ka BP corresponding to the onset of Holocene Thermal Maximum (HTM)-like conditions. A transition towards reoccurring ice-edge and significantly reduced SIC conditions in Baffin Bay is evident in the Middle Holocene (~7.6–3 ka BP) probably caused by the variations in the WGC influence associated with the ice melting and can be characterized as HTM-like conditions. These HTM-like conditions are predominantly recorded in the NE Labrador Sea area shown by (spring– autumn) ice-free conditions from 5.9–3 ka BP. In the Late Holocene (last ~3 ka), our combined proxy records from eastern Baffin Bay indicate low in-situ ice algae production; however, enhanced multi-year (drifted) sea ice in this area was possibly attributed to the increased influx of Polar Water mass influx and may correlate with the Neoglacial cooling. The conditions in the NE Labrador Sea during the last 3 ka, however, continued to remain (spring–autumn) ice-free. Our data from the Baffin Bay–Labrador Sea transect suggest a dominant influence of meltwater influx on sea ice formation throughout the Holocene, in contrast to sea-ice records from the Fram Strait area,which seem to follow predominantly the summer insolation trend.

Description: We present a regional seismic data set across the southeastern Lomonosov Ridge (LR) serving as pre-site survey for the upcoming drilling project IODP-377 (ArcOP). The overall goal of this drilling campaign is to recover a com¬plete stratigraphic sedimentary record of the southern ridge to meet the highest priority paleoceanographic objective, the continuous long-term Cenozoic climate history of the central Arctic Ocean. The seismic surveys provide basic information for the drilling, as the identification of undisturbed strata, location of slumps or hiatuses, depth-calculations of target reflectors, age estimations, and suggestions on the type of sedimentary rocks inferred from interval velocities of seismic units. On the LR the seismic lines confirm the presence of 1600 m thick, undisturbed, parallel sedimentary layers. 10 drilling locations can be proposed to recover the entire Miocene sedimentary sequence or even down to sediments of Lower Eocene age at about 900 mbsf. A prominent high-amplitude-reflector sequence (HARS) within the strata can be used to directly correlate to previous seismostratigraphic models for the eastern Arctic Ocean. Four major seismic units were identified which provide constraints on the coupled evolution of tectonic processes, palaeoceanography, and glaciation history of the Arctic Ocean. First, Mesozoic strata on the LR, its faulted flanks and the initial Amundsen Basin were covered with syn-rift sediments of Paleocene to early Eocene age. Numerous vertical faults indicate differential compaction of possibly anoxic sediments deposited in the young, still isolated Eurasian Basin. The second stage, as indicated by a prominent high-amplitude-reflector sequence covering the ridge, was a time of widespread changes in deposition conditions, likely controlled by the ongoing subsidence of the LR and gradual opening of the Fram Strait. Episodic incursions of water masses from the North Atlantic probably were the consequences and led to the deposition of thin sedimentary layers of different lithology. The third stage is marked by continuous deposition since the early Miocene. At that time, the ridge no longer posed an obstacle between the Amerasia and Eurasia Basins and pelagic sedimentation was established. Drift bodies, sediment waves, and erosional structures indicate the onset of circulation. Lastly, a sequence of high-amplitude reflectors marks the transition to the early Pliocene large-scale Northern Hemisphere glaciations. In a future step, the link of drilling data to the seismic net via synthetic seismograms shall enable a spatial extrapolation of findings, and serve to improve the seismostratigraphic models.