CL4.7

Since the mid-20th century, the Arctic has experienced two major impacts of climate change: a warming at a faster rate than the global mean surface temperature and a reduction of both winter and summer sea ice cover. However, the impact of the Arctic sea ice loss on global climate remains under debate, in particular the impact on the Atlantic meridional overturning circulation (AMOC). Specifically, some studies find that in response to Arctic sea ice decline, the AMOC weakens on multi-decadal timescales, reaching a new equilibrium state with a significantly reduced AMOC, while others studies see a weak AMOC reduction followed by a partial or full recovery. To further investigate the impact of sea ice loss on the climate, ensemble simulations are performed with the coupled atmosphere-ocean general circulation model CM5A2 from the Insitut Pierre Simon Laplace (IPSL-CM5A2). To induce the change in sea ice, the Arctic sea ice albedo is reduced by about 23%, previously shown to be consistent with the sea ice changes expected to occur by approximately the year 2040. The experimental design compares the response to sea ice loss starting from AMOC minimum and neutral phases, respectively. The objective of our experiment is to further investigate the AMOC-sea ice relationship in the transient and equilibrium responses to decreased sea ice and the robustness within a coupled model. The initial 30-year response results in similar spatial patterns in sea ice volume and 500mb potential height responses (inducing a negative NAO-like pattern) for both types of initial conditions. In both cases, the AMOC reduces by 0.5 to 1.5Sv Sv (about 15% of the model mean AMOC) during the first ~100 years of the experiment. Yet, there are differences in the response depending on the AMOC initial state, for example, in the magnitude and timing of the AMOC reduction. The AMOC eventually recover towards years 151-200. Our results give insight into the importance of decadal variability for anticipating the response of the next decades to climate change, as well as improves the understanding of the long-term transient and equilibrium responses between AMOC and Arctic sea ice.

How to cite: Simon, A., Ferster, B., Fedorov, A., Mignot, J., and Guilyardi, E.: The Transient and Equilibrium Response of the AMOC to Arctic sea decline in a coupled model., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7416, https://doi.org/10.5194/egusphere-egu21-7416, 2021.

We compare the response of a coupled atmosphere-ocean-Greenland Ice Sheet (GrIS) model forced with an abrupt quadrupling of CO₂ from greenhouse gas concentrations in 1970 with the response of the atmosphere-ocean model with a static GrIS . The model, UKESM1.ice.N96.ORCA1, consists of HadGEM GC3.1 coupled to the BISICLES ice sheet model with mean annual surface mass balance (SMB) passed to BISICLES and orography and cumulated iceberg flux passed back to the atmosphere and ocean, respectively, at the end of each year. The differences in the surface temperature and atmospheric fields between the two experiments are confined to Greenland, with no discernible global effects from the evolving orography. The volume of the GrIS decreases by 15 % in 330 years. The surface height decreases the most (over 800m in 330 years) in southwest GrIS due to surface melting enhanced by feedbacks between elevation, air temperature and albedo. The input of freshwater to the ocean from Greenland is enhanced due to increased meltwater runoff, but the flux from melting icebergs decays to zero as calving from glaciers declines. The resulting sea level rise is dominated by SMB, where the equivalent sea level rise is 1179 mm (5.0 mm/yr) for the static GrIS and 1120 mm (4.4 mm/yr) for the interactive ice sheet at 2300.  There is less sea level rise in the interactive GrIS experiment, even though more mass is lost through surface melting, because the amount lost through iceberg calving decreases as the grounding line of marine-terminating glaciers retreat inland whereas calving in the static experiment is constant.    

How to cite: Lee, V., Smith, R. S., and Payne, A. J.: The role of an interactive Greenland Ice Sheet in abrupt 4xCO2 forcing experiments., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13327, https://doi.org/10.5194/egusphere-egu21-13327, 2021.

Extended and intense wildfires occurred in Northern Canada and, unexpectedly, on the Greenlandic West coast during summer 2017. The thick smoke plume emitted into the atmosphere was transported to the high Arctic, producing one of the largest impacts ever observed in the region. Evidence of Canadian and Greenlandic wildfires was recorded at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5°N, 68.8°W, www.thuleatmos-it.it) by a suite of instruments managed by ENEA, INGV, Univ. of Florence, and NCAR. Ground-based observations of the radiation budget have allowed quantification of the surface radiative forcing at THAAO. 

Excess biomass burning chemical tracers such as CO, HCN, H2CO, C2H6, and NH3 were  measured in the air column above Thule starting from August 19 until August 23. The aerosol optical depth (AOD) reached a peak value of about 0.9 on August 21, while an enhancement of wildfire compounds was  detected in PM10. The measured shortwave radiative forcing was -36.7 W/m2 at 78° solar zenith angle (SZA) for AOD=0.626.

MODTRAN6.0 radiative transfer model (Berk et al., 2014) was used to estimate the aerosol radiative effect and the heating rate profiles at 78° SZA. Measured temperature profiles, integrated water vapour, surface albedo, spectral AOD and aerosol extinction profiles from CALIOP onboard CALIPSO were used as model input. The peak  aerosol heating rate (+0.5 K/day) was  reached within the aerosol layer between 8 and 12 km, while the maximum radiative effect (-45.4 W/m2) is found at 3 km, below the largest aerosol layer.

The regional impact of the event that occurred on August 21 was investigated using a combination of atmospheric radiative transfer modelling with measurements of AOD and ground surface albedo from MODIS. The aerosol properties used in the radiative transfer model were constrained by in situ measurements from THAAO. Albedo data over the ocean have been obtained from Jin et al. (2004). Backward trajectories produced through HYSPLIT simulations (Stein et al., 2015) were also employed to trace biomass burning plumes.

The radiative forcing efficiency (RFE) over land and ocean was derived, finding values spanning from -3 W/m2 to -132 W/m2, depending on surface albedo and solar zenith angle. The fire plume covered a vast portion of the Arctic, with large values of the daily shortwave RF (< -50 W/m2) lasting for a few days. This large amount of aerosol is expected to influence cloud properties in the Arctic, producing significant indirect radiative effects.

How to cite: Calì Quaglia, F., Meloni, D., di Sarra, A. G., Di Iorio, T., Ciardini, V., Pace, G., Muscari, G., Becagli, S., Cacciani, M., Ortega, I., Hannigan, J. W., and Holben, B. N.: Radiative forcing of aerosols over the Arctic from the August 2017 Canadian and Greenlandic wildfires, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7405, https://doi.org/10.5194/egusphere-egu21-7405, 2021.

The Arctic Ocean is at the frontier of the fast changing climate in the northern latitudes. As the first study, we assessthe different mass and steric components of the observed sea level trend from both absolute sea level (ASL) from altimetryand tide gauges, without using gravimetric observations from GRACE. This approach permits a longer time series and avoidsproblems with errors from leakage effects in GRACE-products. ASL is equal to mass-driven sea level added with steric sealevel, while tide gauge based sea level are also corrected with novel estimates of vertical land movement. Calculations of the5mass component from present-day deglaciation, shows that deglaciation rises Arctic sea level with more than 1 mm y−1, whilethe steric contribution is between -5 and 15 mm y−1 with large spatial variability, with the halosteric signal dominating thepattern. A dynamic mass contribution is derived from the Estimating Circulation and Climate of the Oceans (ECCO)-model(version 4 release 4), which varies between -1 and 2 mm y−1. The combined mass and steric product agrees (within uncertainty)with ASL-trends observed from altimetry in 99% of the Arctic, although large uncertainties originate from poor data coverage in the steric data and large variability in the dynamic product. A comparison with ASL trends observed at tide gauges agreeswith mass+steric at 11 of 12 tide gauge sites.

How to cite: Ludwigsen, C. A., Rose, S. K., and Andersen, O. B.: Climate contributions to Arctic coastal sea level change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16215, https://doi.org/10.5194/egusphere-egu21-16215, 2021.

As air temperatures in the Arctic continue to rise, permafrost thaw intensifies, and discharge from the Arctic rivers increases. These drastic changes are likely to accelerate mobilization of organic matter and its export through rivers into the Arctic Ocean. Therefore, thorough monitoring of these processes becomes increasingly important. The Lena River with its large catchment area is one of the major sources of the organic carbon in the Arctic Ocean and, therefore, plays a crucial role in the Arctic carbon cycle. 
To observe current and future changes of carbon transport via the Lena River, a new monitoring program has been initiated in 2018. In situ water samples are collected from the one of the Lena Delta branches every several days. Since generally the in situ sampling in the Arctic is challenging and costly, in this study, we test the potential of remote sensing to complement the field observations. Remote sensing provides synoptic spatial coverages and high temporal resolution at high latitudes. 
We test the retrieval of dissolved organic carbon (DOC) from satellite-derived chromophoric dissolved organic matter (CDOM). For this, we use measurements of the Ocean & Land Colour Instrument (OLCI) on board the Sentinel-3 satellites in combination with beforehand tested atmospheric correction algorithms and CDOM retrieval algorithms. The quality of the satellite retrieved DOC of the Lena River water is assessed by DOC, measured in the in situ samples. Remotely sensed DOC contributes to an improvement of DOC fluxes monitoring, which can potentially be extended to all big Arctic rivers.

How to cite: Preusker, R., El Kassar, J., and Juhls, B.: Evaluating Dissolved Organic Carbon Retrieval in the Lena River Delta using Sentinel 3 OLCI Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15997, https://doi.org/10.5194/egusphere-egu21-15997, 2021.

The Copernicus Climate Change Service (C3S) regional reanalysis for the Arctic consists of two datasets of Essential Climate Variables (ECVs) for the 24 year period from 1997 to 2021. The high resolution (2.5x2.5 km²) datasets cover Greenland, Iceland, Svalbard, the Barents Sea and Northern Scandinavia. Several islands in the Russian Arctic and a few islands in the Canadian Arctic are also covered. The produced datasets are freely available to all. A first subset of the data has been published on the Copernicus Data Store (CDS) in early 2021.

The reanalysis is perfomed with state-of-the-art data assimilation techniques that include many local quality-controlled observations that have not been included in previously published reanalysis datasets. The weather forecasting model HARMONIE-AROME cy40h1.1.1 has been used to produce the dataset. The model computations have additionally been optimized for processes essential in the Arctic. Estimated uncertainty data have been produced at atmospheric pressure levels, and validation statistics have been made for synoptic weather stations.

How to cite: Nielsen, K. P., Schyberg, H., Yang, X., Støylen, E., Dahlgren, P., Amstrup, B., Peralta, C., Køltzow, M., and Bojarova, J.: 24 years of C3S Arctic regional reanalysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15178, https://doi.org/10.5194/egusphere-egu21-15178, 2021.

Atmospheric water vapour is a critical component of both meteorological and climatological processes. It is the dominant gas in the greenhouse effect and its diurnal cycle is an essential component of the hydrological cycle. Diurnal water vapour cycles are complex and are a product of several mechanisms, including (but not necessarily limited to): evapotranspiration, advection, large-scale vertical motion, and precipitation. They are dependent on local geography, as well as latitude. Numerical Weather Prediction (NWP) models rely on high-quality water vapour input to provide accurate forecasts, which is particularly difficult in the Arctic due to its extreme weather and harsh environment. Diurnal water vapour cycle observations are also excellent tools for evaluating NWPs due to their complex nature and dependence on multiple processes. Integrated water vapour (IWV), or total column, diurnal water vapour cycles, usually calculated with Global Navigation Satellite Systems (GNSS) instruments, have been the focus of most previous diurnal WV studies; however, height-resolved diurnal cycles provide a more complete picture of the diurnal mechanisms and include vertical motion, which cannot be discerned via IWV measurements. Differential Absorption Lidars (DIALs) are well suited to providing height-resolved diurnal cycles in the boundary layer due to their high vertical and temporal resolution.

We use the novel Vaisala pre-production DIAL, installed in Iqaluit, Nunavut (63.75 N, 68.55 W), to calculate seasonal height-resolved diurnal WV cycles from 100 m to 1500 m altitude. We also calculate the surface and total column WV diurnal cycles using co-located surface station and GNSS measurements. We find that the first 250 m of the DIAL diurnal cycle magnitudes agree well with the surface station measurements. The phases of the cycle do shift with altitude, and the amplitudes generally increase with altitude. In the summer, all instruments observe a strong 24 hr cycle. As the amount of solar radiation decreases over the year, the 24 hr cycle weakens and the 12 hr cycle begins to dominate in all instruments. While we find a strong correlation between the 24 hr cycle and the solar cycle, we do not observe any correlation between the 12 hr cycle and the solar cycle. Finally, we also compare the DIAL observations to the Environment and Climate Change Canada (ECCC) NWP model. We evaluate both the assimilation of the humidity input and initial water vapour fields, as well as the diurnal cycle over the 24 hour forecast. Future work will include case study comparisons with the Canadian NWP model to assess the model’s ability to resolve rapid changes in diurnal water vapour.

How to cite: Hicks-Jalali, S., Mariani, Z., Casati, B., Leroyer, S., Lemay, F., and Crawford, R.: First model evaluations of height-resolved diurnal water vapour cycles using lidar observations in an Arctic environment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10175, https://doi.org/10.5194/egusphere-egu21-10175, 2021.

The dramatic decrease in Arctic sea ice has resulted in a corresponding increase in the seasonal freshwater flux due to melt water in the Canada Basin. This source of freshwater can be quite patchy as sea ice breaks aparts and melts, resulting in freshwater fronts that are strained and stirred by the mesoscale eddy field. We would like to understand the relevant processes that determine the evolution of these freshwater fronts and how heat and salt are exchanged between the fresh melt water and the background water masses. In particular we investigate the importance of submesoscale processes for the lateral and vertical exchange of heat and salt, using high resolution observations of a freshwater front in the Arctic to initialise idealised simulations of frontal evolution. We isolate the effect of submesoscale dynamics by comparing high resolution submesoscale-resolving simulations with lower resolution simulations permitting only larger-scale eddies. Comparisons with observed temperature wavenumber spectra will be presented to investigate whether the simulated dynamics are representative of observations. Heat and salt budgets are presented for the simulations and the impact of submesoscale dynamics on the balance between across-front ageostrophic and geostrophic transports will be discussed. We will also discuss the implications of these results on the seasonal redistribution of heat over the upper ocean, specifically do submesoscale dynamics lead to an increase in the vertical transport of heat across the base of the summer mixed layer, therefore increasing the heat content within the winter mixed layer and delaying the formation of sea ice in the fall?

How to cite: Alberty, M., Legg, S., Hallberg, R., MacKinnon, J., Sprintall, J., Alford, M., Mickett, J., and Fine, E.: Quantifying the impact of submesoscale dynamics on the evolution of Arctic freshwater fronts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10372, https://doi.org/10.5194/egusphere-egu21-10372, 2021.

In the last two decades, rising ocean temperatures have significantly contributed to the increased melting and retreat of marine-terminating glaciers along the coast of Greenland. Warming subsurface waters have also been shown to interact with the glaciers in Northeast Greenland, which until recently were considered stable, and caused their rapid retreat. The main source of these waters is the westward recirculation of subducted Atlantic Water (AW) in Fram Strait, which has shown a warming of up to 1° C over the past few decades.

In this study, the connection between the subsurface warm Atlantic Intermediate Water (AIW) found on the wide continental shelf of Northeast Greenland and in the fjords, and AW within the West Spitsbergen Current (WSC) is investigated using historical hydrographic observations and high-resolution numerical simulations with the Finite-Element Sea-ice Ocean Model (FESOM). We find that AW from the WSC takes between 10 – 14 months to recirculate across Fram Strait and reach the shelf break where it moves southwards. The pronounced inter-annual variability in the WSC is preserved as the water recirculates. However, the variability of temperature and AIW layer thickness on the shelf at seasonal or inter-annual time scales is at best weakly controlled by the AW temperature in the WSC. There is no significant correlation between AIW and the WSC anywhere on the shelf, suggesting advection from the WSC alone does not control AIW signals. The role of wind-driven, episodic upwelling is then investigated as a driver of transport of AIW from Fram Strait onto the shelf (following an approach by Münchow et al., 2020) where it then may follow the deep trough system towards the glaciers.

How to cite: McPherson, R., Kanzow, T., and Wekerle, C.: Large-scale connections between Fram Strait recirculation and warm water pathways towards Greenland fjords, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8695, https://doi.org/10.5194/egusphere-egu21-8695, 2021.

Despite the contribution of the Greenland Ice Sheet (GrIS) to global sea level rise, the lack of a complete understanding of its driving mechanisms largely constrains future model projections. Brief observational records limit model development efforts, however, the assimilation of paleoclimatic proxy data in climate models provides new opportunities to place recent climate changes in and around the Arctic in the context of long-term high-latitude variability. Building off of previous work, we investigate the relative role of internal atmospheric variability in modulating GrIS surface mass balance (SMB) using the newly available Ensemble Kalman Fitting Paleo-Reanalysis (EKF400) version 2, with monthly resolution for the period 1602-2003 AD, and the Last Millennium Reanalysis (LMR) version 2, which has an annual resolution from 0-2000 AD. We apply maximum covariance and empirical orthogonal function analyses on these two datasets to reveal co-varying patterns of Arctic upper-tropospheric changes and the GrIS SMB over centennial and millennial timescales with a special focus on remote tropical drivers of this local coupling. In light of these tropical-Arctic linkages in shaping GrIS conditions over the past two millennia, the application of proxy-assimilated model experiments provides deeper insights into the formation of such atmospheric dynamical connections that may impact GrIS SMB in the future.

I.G.H is supported by the Ministry of Human Capacties (NTP-NFTÖ-20-B-0043).

How to cite: Topal, D., Ding, Q., Hatvani, I. G., and Ballinger, T. J.: Multi-decadal tropical-Arctic atmospheric teleconnections and their influences on Greenland Ice Sheet melt, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9736, https://doi.org/10.5194/egusphere-egu21-9736, 2021.

Certain past climatic events act as an analogue for future climatic conditions. The Holocene epoch featured a number of climatic variations of which Holocene Thermal Maximum (HTM) stands out as a recognizable phenomenon, especially in the North Atlantic and the Arctic. Similar to modern warming, HTM in Svalbard recorded extreme warmth along with intense deglaciation and sea ice retreat. Therefore, predictions of future climate using HTM depends on understanding the changes in interactions between ocean, sea ice, and atmospheric conditions. While many studies exist on this period, only few have reconstructed ocean surface conditions in the Arctic at high resolution. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from Kongsfjorden, Svalbard covering the period of ca. 10.5 to 7.5 cal. kyr BP. Our reconstructions of sea surface temperature (SST) and sea ice conditions are based on diatom microfossil records from a 454 cm long marine sediment core from Kongsfjorden, Svalbard. The section from 454 to 300 cm was used for reconstructions owing to the lack of availability of diatom microfossils. Owing to their high sensitivity towards SST and sea ice, diatoms act as excellent proxies of these environmental conditions in the past. The SST record from Kongsfjorden reveals moderately warm open water conditions and highly variable sea ice conditions during the HTM. The SST achieves maximum values during the early Holocene insolation maxima ca. 10.5 to 7.5 cal. kyr BP, followed by a slow cooling trend simultaneously with the decreasing insolation intensity. Our results emphasize the regional heterogeneity observed in ocean surfaces during the HTM and how modern warming in the study area has already reached sea surface temperatures comparable to the HTM. 

How to cite: Guruvayoorappan, H., Miettinen, A., Divine, D., and Mohan, R.: Modern warming exceeds sea surface temperatures of the Holocene Thermal Maximum in Kongsfjorden, Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14024, https://doi.org/10.5194/egusphere-egu21-14024, 2021.

Climatological studies show that Baffin Island ice caps (Barnes and Penny) are highly sensitive to global climatic changes. However, there is little high temporal resolution data available to study the long-term response of Baffin Island ice caps to climate change. While most of the sedimentary climate records in the region are obtained from lake sediments, there is less information from glaciomarine sediments. High sedimentation rates that characterize fjords in glaciomarine environments make these sites ideal to study the impact of climate and oceanographic changes on tidewater glacier dynamics at high-temporal resolution. In this context, a piston core (AMD2019-804-12PC) recovered in the Coronation Fjord (Baffin Island, Nunavut, Canada) in an ice-proximal environment was investigated using physical, grain-size, mineralogical, geochemical, and magnetic properties to document changes in sediment transfers from the Penny Ice Cap (PIC) in relation to Late Holocene climate variability. The chronostratigraphic framework of this core was developed by combining AMS ¹⁴C and paleomagnetic analysis. The physical and sedimentological analysis show that core 12PC is characterized by laminated mud sediments interspersed with fine sand and disseminated ice-rafted debris (IRD). The biotite+chlorite-plagioclase-feldspar ternary diagram reveals a homogeneous detrital input with a composition characteristic of the Cumberland Batholith. These sedimentary characteristics are interpreted as a product of suspension settling and muddy density flows from turbid meltwater plumes related with the PIC dynamic. Results also reveal two lithofacies (LF) related with distinct glacial regimes. LF1 (601-280 cm; 1500-1800 AD), which covers the Little Ice Age period, is characterized by a high IRD content, below-average values in biotite+chlorite/quartz, low variations in Zr/Ti and Fe/Al, suggesting enhanced tidewater glacier discharge likely associated with the growth of the PIC. LF2 (280-0 cm; 1800 AD to present) is defined by a decrease in IRD content, above-average values in biotite+chlorite/quartz, and high variations in Zr/Ti and Fe/Al, interpreted as representing the retreat of the glacier to its present-day extent in response to modern warming. Similar trends observed between our detrital proxies and the Arctic surface air temperature anomalies, the chironomid-inferred summer-temperature from a nearby lake, and melt feature record from the PIC, suggest high connectivity between atmospheric temperatures variations and the sedimentary dynamics of the PIC during the last 400 years.

How to cite: Rodríguez-Cuicas, M.-E., Montero-Serrano, J.-C., St-Onge, G., and Normandeau, A.: A 400-year record of glaciomarine sedimentation associated with the dynamics of the Penny Ice Cap (Baffin Island, Nunavut, Canada), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6840, https://doi.org/10.5194/egusphere-egu21-6840, 2021.

The polar regions exhibit some of the most visible signs of climate change globally; annual mass loss from the Greenland Ice Sheet (GrIS) has quadrupled in recent decades, from 51 ± 65 Gt yr⁻¹ (1992-2001) to 211 ± 37 Gt yr⁻¹ (2002-2011). This can partly be attributed to the widespread retreat and speed-up of marine-terminating glaciers. The Zachariae Isstrøm (ZI) is an outlet glacier of the Northeast Greenland Ice Steam (NEGIS), one of the largest ice streams of the GrIS (700km), draining approximately 12% of the ice sheet interior. Observations show that the ZI began accelerating in 2000, resulting in the collapse of the floating ice shelf between 2002 and 2003. By 2014, the ice shelf extended over an area of 52km², a 95% decrease in area since 2002, where it extended over 1040km². Paleo-reconstructions provide an opportunity to extend observational records in order to understand the oceanic and climatic processes governing the position of the grounding zone of marine terminating glaciers and the extent of floating ice shelves. Such datasets are thus necessary if we are to constrain the impact of future climate change projections on the Arctic cryosphere.

A multi-proxy approach, involving grain size, geochemical, foraminiferal and sedimentary analysis was applied to marine sediment core DA17-NG-ST8-92G, collected offshore of the ZI, on  the Northeast Greenland Shelf. The aim was to reconstruct changes in the extent of the ZI and the palaeoceanographic conditions throughout the Early to Mid Holocene (c.a. 12,500-5,000 cal. yrs. BP). Evidence from the analysis of these datasets indicates that whilst there has been no grounded ice at the site over the last 12,500 years, the ice shelf of the ZI extended as a floating ice shelf over the site between 12,500 and 9,200 cal. yrs. BP, with the grounding line further inland from our study site. This was followed by a retreat in the ice shelf extent during the Holocene Thermal Maximum; this was likely to have been governed, in part, by basal melting driven by Atlantic Water (AW) recirculated from Svalbard or from the Arctic Ocean. Evidence from benthic foraminifera suggest that there was a shift from the dominance of AW to Polar Water at around 7,500 cal. yrs. BP, although the ice shelf did not expand again despite of this cooling of subsurface waters.

How to cite: Davies, J., Møller Mathiasen, A., Kristensen, K., Pearce, C., and Seidenkrantz, M.-S.: Early Holocene ocean conditions off the Zachariæ Isstrøm, Northeast Greenland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15076, https://doi.org/10.5194/egusphere-egu21-15076, 2021.

Periodic mass discharges of icebergs from the Laurentide ice-sheet into the North Atlantic Ocean during the last glacial period deposited abundant ice-rafted detritus (IRD) accumulated in sequences of typically six major Heinrich Event layers, each with some tens of cm thickness, at all eastern slopes of the Grand Banks submarine platform of Newfoundland. Compositionally, it is well established that these IRD layers consist of varied rock contents emanating from distinct, but not yet clearly defined bedrock provinces of the Canadian Shield. The, most prominently reported constituent is detrital dolomite, but the entire lithological range of the IRD is much broader. Rock magnetic records, e.g. magnetic susceptibility logs of SE Grand Banks cores, therefore depict complex and partly repeating internal substructures across the Heinrich Event layers owing to distinct successions in IRD lithology over the course of every mass calving event.

We investigated IRD sieve fractions (1mm – 4cm) of the entire glacial section (550–1054 cm) of SE Grand Banks slope gravity core GeoB 18530-1, sampled in 2.3 cm steps. Therefrom, we identified and classified distinct IRD rock types as well as monocrystalline rock-forming mineral particles, for which we established so far 24 well-defined lithological categories of sedimentary, igneous and metamorphic origin. This initial identification of IRD lithology was performed based on all available visual criteria including texture (crystallinity, grain-size), color and translucency (mineralogy), hardness and surface structures (e.g., cleavage) using a binocular microscope. This rock type classification is now being substantiated by polarized light microscopy of exemplary thin sections created from larger IRD clasts.

To established cumulative rock magnetic fingerprints of all IRD magnetic mineral assemblages, isothermal remanent magnetization acquisition curves of all sieve fractions as well as individual specimens of all the classified rock types have been measured. These records systematically revealed higher concentrations of magnetic minerals at the tops and bottoms of most Heinrich Event layers and also clear variations in coercivity spectra. This finding is mirrored by the IRD rock count records, where magmatic rock types predominate mostly at Heinrich Event layer boundaries. Preferred deposition of these IRD rock types during the initiation and ending of events and their variation from older to younger events,- highlight repetitive patterns in the cyclic Laurentide ice-sheet collapses to be further explored.

How to cite: Bukar, S., von Dobeneck, T., and Lisker, F.: Investigating the internal lithological structure and rock magnetic signature of Heinrich Event layers at SE Grand Banks Slope, Newfoundland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15610, https://doi.org/10.5194/egusphere-egu21-15610, 2021.

Sea ice provides strong feedback in the climate system, and it plays an important role in modulating the strength of the Thermohaline Circulation through glacials, and even interglacials. The warmer than present Last Interglacial (LIG, ~116-128 ka) is thought to have a less stable climate than the current interglacial. Proxies from the deep- and surface subpolar North Atlantic Ocean show prominent instabilities pointing toward coupled ocean-climate variability.  Here we reconstruct sea surface and sea ice changes of the subpolar gyre through the penultimate deglaciation and LIG in order to evaluate sea ice’s role as a driver and amplifier of these ocean circulation and climate changes. We reconstruct the sea ice and sea surface conditions using biomarkers (IP₂₅, sterols) and dinoflagellate cyst assemblages from the Eirik Drift. Low productivity combined with an absence of IP₂₅ could indicate a potential full sea ice cover through MIS 6. The surface ocean experienced large variability through the first half of the LIG, including an early cooling with potential seasonal sea ice cover evident from the dinoflagellate cyst assemblage and IP₂₅. The peak warm period of the LIG is seen in the second half, followed by a brief cooling period towards the end. Following the LIG, MIS 5d is characterized by an IP₂₅ signal and high relative abundances of round brown dinocysts indicating cooling with seasonal sea ice cover. Initial comparisons with deep ventilation proxies (benthic foraminiferal δ¹³C data) indicate a potential close link between sea ice, surface hydrography and deep circulation. In future studies, we aim to compare the sea ice record to benthic foraminiferal δ¹³C data from the same samples to better understand the connection between surface and deep-ocean variability.

How to cite: Steinsland, K., Ninnemann, U., Fahl, K., Stein, R., Grant, D., and De Schepper, S.: Last Interglacial sea ice variability and paleoceanography of the Labrador Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10594, https://doi.org/10.5194/egusphere-egu21-10594, 2021.