Displays

For the period between 14.7 and 11.5 cal. (calibrated) kyr B.P, the sediment flux of Bindschadler Ice Stream (BIS; West Antarctica) averaged 1.7 × 10⁸ m³ a⁻¹. This implies that BIS velocity averaged 500 ± 120 m a^-1. At a finer resolution, the data suggest two stages of ice stream flow. During the first 2400 ± 400 years of a grounding-zone stillstand, ice stream flow averaged 200 ± 90 m a^-1. Following ice-shelf breakup at 12.3 ± 0.2 cal. kyr B.P., flow accelerated to 1350 ± 580 m a^-1. The estimated ice volume discharge after breakup exceeds the balance velocity by a factor of two and implies ice mass imbalance of ~40 Gt a^-1 just before the grounding zone retreated >200 km. We interpret that the paleo-BIS maintained sustainable discharge throughout the grounding-zone stillstand first due to the buttressing effect of its fringing ice shelf and then later (i.e., after ice-shelf breakup) due to the stabilizing effects of grounding-zone wedge aggradation. Major paleo–ice stream retreat, shortly after the ice-shelf breakup that triggered the inferred ice flow acceleration, substantiates the current concerns about rapid, near-future retreat of major glaciers in the Amundsen Sea sector where Pine Island and Thwaites Glaciers are already experiencing ice-shelf instability and grounding-zone retreat that have triggered upstream-propagating thinning and ice acceleration.

How to cite: Bart, P. and Tulaczyk, S.: A significant acceleration of ice volume discharge preceded a major retreat of a West Antarctic paleo-ice stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5875, https://doi.org/10.5194/egusphere-egu2020-5875, 2020.

The Eocene-Oligocene Transition (EOT), approximately 34 Ma ago, marks a period of major global cooling and inception of the Antarctic ice sheet. Proxies of deep circulation suggest a contemporaneous onset or strengthening of the Atlantic meridional overturning circulation (AMOC). Proxy evidence of gradual salinification of the North Atlantic and tectonically driven isolation of the Arctic suggest that closing the Arctic-Atlantic gateway could have triggered the AMOC at the EOT. We demonstrate this trigger of the AMOC using a new paleoclimate model with late Eocene boundary conditions. The control simulation reproduces Eocene observations of low Arctic salinities. Subsequent closure of the Arctic-Atlantic gateway triggers the AMOC by blocking freshwater inflow from the Arctic. Salt advection feedbacks then lead to cessation of overturning in the North Pacific. These circulation changes imply major warming of the North Atlantic Ocean, and simultaneous cooling of the North Pacific, but no interhemispheric change in temperatures.

How to cite: Hutchinson, D., Coxall, H., O'Regan, M., Nilsson, J., Caballero, R., and de Boer, A.: Arctic closure as a trigger for Atlantic overturning at the Eocene-Oligocene Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7493, https://doi.org/10.5194/egusphere-egu2020-7493, 2020.

Retreating marine terminating glaciers influence the rate at which larger ice mass is lost, and thus the rate at which global sea levels rise. About 90% of the circa 240 glaciers terminating in fjords along the West-Antarctic Peninsula coastline are retreating. This happens at variable rates as these fjords have internal feedback mechanisms with e.g. the oceanographic make-up of the bay and the geology / geomorphology of the local hinterland. The NERC-CONICYT funded “ICEBERGS” project is a UK-Chile research collaboration to assess the effects of ice loss and deglaciation on benthic marine ecosystems in Antarctica. Three West-Antarctic fjords where glaciers have been consistently retreating in the last few decades were investigated: Marian Cove (King George Island), Börgen Bay (Anvers Island) and Ryder Bay (Adelaide Island). As part of this project, we monitored the changes in seabed bathymetry and backscatter intensity as a signature of past and on-going ice flow and ice retreat. Together with sediment analyses, the data provide insights in glacial landscape development and on sediment accumulation / seabed erosion rates. We also managed to insonify parts of the changing glacier ice fronts, detailing the grounding zones at the seabed. At the time of abstract submission, the third of three surveys was just underway. In this presentation we will explore the preliminary search for spatial and temporal relationships between grounded ice advance and retreat, undercutting of the grounded glacier terminus, sediment discharge, ice berg scouring, glacial landscape development and mass waste deposits. Our direct time-lapse observations of the seabed and glacier fronts of different fjord systems will help us understand how the local fjord environments define the dynamics of the retreating glaciers they host, whilst the results help elucidate the impact of that deglaciation on the newly emerged seabed and the fast-growing ecosystem it supports. Understanding the ice-filled fjord dynamics in the present-day and in the recent past will also help interpretations made from data representing these environments in the distant past.

How to cite: Van Landeghem, K., Retallick, K., Howard, F., Barnes, D., Jenkins, S., Sands, C., Muñoz-Ramirez, C., and Scourse, J.: Relating changes in seabed properties and retreating glacier fronts in West-Antarctic fjords., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7943, https://doi.org/10.5194/egusphere-egu2020-7943, 2020.

Large sections of the Greenland Ice Sheet (GrIS) drain directly to the ocean through tidewater glaciers and are, therefore, sensitive to changes in ocean circulation through time. Recent research has identified the dynamic response of many tidewater glaciers draining the GrIS showing thinning, flow acceleration and, in many cases, the break-up and retreat of fringing ice shelves and calving margins. This instability has been linked to incursion of relatively warm Atlantic Water as well as increased air temperatures and sea-ice loss.

The Northeast Greenland Ice Stream (NEGIS) is one of the largest ice streams draining approximately 15% of the GrIS with a sea level equivalent of ~ 1.4 m. Recent observations have identified ice shelf loss and grounding line retreat of Zachariae Isstrom, the southern arm of the NEGIS, post 2010 suggesting this sector of the GrIS might be starting to respond to climate forcing. The primary aim of the ‘NEGIS’ project is to reconstruct the history of NEGIS since the Last Glacial Maximum (LGM) to improve our understanding of the interaction between NEGIS and climate (specifically ocean circulation). A series of sediment cores were collected along with bathymetric and sub-bottom profiler data concentrating on the Westwind and Norske Trough systems, two cross-shelf troughs originating from the present day margin of NEGIS. The data were collected through collaboration with the Alfred Wegener Institute as part of the GRIFF project supported by two cruises of the RV Polarstern in 2016 and 2017.

This presentation will focus on the deglaciation and palaeoceanographic evolution of the inner section of Norske Trough (inner continental shelf) investigating the interaction between ocean circulation and the dynamics of the tidewater margins of NEGIS. We present multiproxy results from a spliced box core and 10 m long gravity core collected from the same location covering the last 11,000 cal years. We use the benthic foraminiferal fauna and stable isotope signature to investigate variability in ocean circulation, specifically the relative strength of the Atlantic Water inflow along Norske Trough to the present day ice margin. We also investigate surface water conditions (including sea ice concentration) based on diatoms, dinoflagellates, IP₂₅ and planktic foraminiferal stable isotopes. Our benthic foraminiferal assemblages record the variability in strength of Atlantic Water flow since deglaciation indicating relatively strong Atlantic Water flux during deglaciation reaching a peak during the early Holocene. Surface water proxies indicate variability in meltwater flux and sea ice concentration from the early Holocene. These results provide the first evidence for a variable ocean circulation with the potential to influence ice margin dynamics during deglaciation and through the Holocene.

How to cite: Lloyd, J., Callard, L., O'Cofaigh, C., Roberts, D., Weckstrom, K., and Ribeiro, S.: Deglaciation of the Northeast Greenland ice stream and interaction with ocean circulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9948, https://doi.org/10.5194/egusphere-egu2020-9948, 2020.

The timing and extent of early glaciations in Greenland, and their co-evolution with the underlying landscape remain elusive. In this study, we explore the timing of fjord erosion in Northeast and North Greenland between Scoresby Sund (70°N) and Independence Fjord (82°N). By determining the timing of fjord formation, we can improve our understanding of the early history of the Greenland Ice Sheet in these regions.

We use the concept of geophysical relief to estimate fjord erosion and calculate the subsequent flexural isostatic response to erosional unloading. The timing of erosion and isostatic uplift is constrained by marine sediments of late Pliocene-early Pleistocene age that are now exposed on land between ~24 and 230 m a.s.l.

We find that the northern Independence Fjord system must have formed by glacial erosion at average rates of ~0.5-1 mm/yr since ~2.5 Ma, in order to explain the current elevation of the marine Kap København Formation by erosion-induced isostatic uplift. In contrast, fjord formation in the outer parts of southward Scoresby Sund commenced before the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene by fjord formation progressing inland. Our results suggest that the inception of the Greenland Ice Sheet began in the central parts of Northeast Greenland before the Pleistocene and spread to North Greenland only at the onset of the Pleistocene.  

How to cite: Pedersen, V. K., Krog Larsen, N., and Lundbek Egholm, D.: The timing of fjord formation and early glaciations in North and Northeast Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10880, https://doi.org/10.5194/egusphere-egu2020-10880, 2020.

The Greenland ice sheet’s response to anthropogenic warming will have major consequences for global sea levels but its behavior and stability during past warm intervals is poorly known. To elucidate the long-term behavior of the Greenland ice sheet, high-resolution marine records in ice proximal settings are required. Here we report the first results of a study of a deep-water contourite system on the north-east slope Baffin Bay based on geophysical and shallow core data obtained during two marine expeditions in 2017 and 2019. The contourite drift is incised by channels extending from the slope that is build up by prograding ice stream deposits (Melville Bugt trough-mouth fan). As a result, the contourite system presents a complex architecture. While the mechanisms for deposition and erosion are not yet clear, it is likely that the drift accumulated as a result of interactions between a deep contour current and downslope transport of sediments, presumably of glacigenic origin and therefore constitutes an example of an intertwined contourite-turbidite system. A preliminary age-depth model of the trough-mouth fan evolution indicates that the contourite system began to form during the late Early Pleistocene, possibly around 1 million years ago. The contourite drift is a key target for IODP proposal 909, aimed at unravelling the late Cenozoic evolution of the northern Greenland ice sheet and associated changes in Arctic paleoclimate. Shallow sediment cores from this target area have been retrieved and will be analyzed to generate high-resolution multi-proxy records of ocean circulation and sea-surface conditions including sea ice and paleoproductivity for the late Quaternary-Holocene.

How to cite: Knutz, P. C., Andresen, K. J., Hopper, J. R., Perez, L. F., Campbell, C., Dorschel, B., Bennike, O., Detlef, H., Hansen, K. E., Jackson, R., Jennings, A., Larsen, N. K., Nørgaard-Pedersen, N., Pearce, C., Røy, H., and Ribeiro, S.: A contourite drift succession in north-east Baffin Bay: a high-resolution Pleistocene archive of Greenland ice sheet and ocean variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19301, https://doi.org/10.5194/egusphere-egu2020-19301, 2020.

Deriving paleo-perspectives on polar systems in so-called “last ice” regions of North Greenland and the High Canadian Arctic have been traditionally challenged by logistical/accessibility issues and paleo proxy (including chronology) limitations. Sea-ice retreat and proxy development are changing this paradigm, allowing the region to be mapped, materials collected, and paleo-records developed that provide new insights on the evolution of the region.  Here we report on continued progress from the joint US/Swedish 2015 Petermann Expedition to North Greenland and the joint US/Canadian 2012 Sawtooth Lake Expedition to Ellesmere Island, where new developments in physical properties and chronology are changing our understanding of the region. Computed tomography, X-Ray fluorescence, ice-rafted debris counts, and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources providing info on glacial retreat and advance and other environmental changes. While an improved understanding of the geomagnetic field supported by radiocarbon dating enables regional magnetic synchronization allowing Holocene ice sheet and environmental dynamics to be placed in the context of High Arctic climate evolution.

How to cite: Stoner, J., Reilly, B., Mix, A., Jakobsson, M., Walczak, M., Abbott, M., Lapointe, F., Francus, P., Balascio, N., Jennings, A., Hogan, K., and Mayer, L.: Deriving paleo-perspectives on polar systems: Continued results from the 2012 Sawtooth Lake (Ellesmere Island) and 2015 Petermann (North Greenland) Expeditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12484, https://doi.org/10.5194/egusphere-egu2020-12484, 2020.

Available sea surface temperature (SST) records from the subantarctic SE Pacific reveal large amplitude changes at orbital time-scales. High sedimentation rates along the southern Chilean margin provided higher resolution records back to ~70 ka showing millennial-scale SST variations paralleling temperatures reconstructed in Antarctic ice-cores.

Here we present high-resolution millennial-scale SST and subsurface temperature records based on core MR16-09 PC03 covering a complete glacial/interglacial cycle back to Marine Isotope Stage 6, including a high-resolution record of the Eemian. Located on the Chilean margin at the bifurcation of the Antarctic Circumpolar Current into the Peru-Chile Current to the North and the Cape Horn Current to the South, core MR16-09 PC03 is in an ideal position to study the continent-ocean interactions, including changes in water masses, ice sheet formation, precipitation and vegetation.

We used alkenones and GDGTs to determine SST (U^K’₃₇) and subsurface temperatures (TEX^H₈₆; 0 - 200 m), and integrated these results with XRF core scanner and planktic δ¹⁸O data (G. bulloides). During the Eemian, SSTs and subsurface temperatures were ~2° C and ~4° C, higher than during the Holocene, respectively. The high Eemian temperatures at our site are roughly consistent with the few available subantarctic SST records. The large temperature difference in the subsurface water masses between the Eemian and the Holocene could be explained by a deeper thermocline during the Eemian. During the last glacial period, the strongly fluctuating temperatures averaged ~8° C at the surface and ~6° C in the subsurface. The relative amount of C_37:4 alkenone (%C_37:4) show a drastic increase during the glacial period, especially in Marine Isotope Stage 3 in concentration. High %C_37:4 values suggest increased freshwater supply, which could be related to fluctuations of the Patagonian Ice sheet and/ or precipitation on the adjacent land. The sedimentation rate and other terrigenous proxies, e.g. Titanium, BIT, Iron and Alkanes, confirm such increased and highly variable terrestrial inputs.

How to cite: Hagemann, J. R., Lamy, F., Nagashima, K., Harada, N., Iwasaki, S., Martínez-Garcia, A., Kaiser, J., Arz, H. W., Nowaczyk, N., Lange, C., and Tiedemann, R.: Southern Chilean continent-ocean interaction over the last glacial cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-768, https://doi.org/10.5194/egusphere-egu2020-768, 2020.

A high-resolution marine sediment core NP16-Kro1-MCB from Krossfjorden, Western Svalbard is studied to investigate changes in sea surface conditions in the fjord during the last 60 years (1953-2014). The diatom-based reconstruction of August sea surface temperature (aSST) demonstrates a clear warming trend of 0.6 °C through the record. As inferred from Marginal Ice Zone (MIZ) diatoms, surface warming occurs in parallel with a decline in sea ice extent (SIE) during recent decades. Factor analysis identified variations in diatom assemblages representing different water masses, showing a dominance of Arctic water diatoms throughout the period and decadal variations in the sea ice assemblage during periods of peak sea ice extent. The strong dominance of Arctic water diatoms along with increasing aSST suggest prolonged open water conditions and increased sea ice melting in the region throughout the observed period. The reconstructed ocean surface changes are in line with the background warming occurring over the Arctic region. A comparison with instrumental records from neighboring regions supports the quality of the reconstructions, including the average reconstructed aSST and the magnitude of the warming trend. We suggest that increased CO₂ forcing together with ocean-atmospheric interaction have caused the increasing SST trend and decreasing sea ice presence in Krossfjorden rather than an increasing influence from Atlantic Water, which has amplified changes in many regions of Svalbard. 

How to cite: Guruvayoorappan, H., Miettinen, A., Divine, D., Moros, M., Orme, L., and Mohan, R.: Ocean surface warming in Krossfjorden, Svalbard, during the last 60 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-782, https://doi.org/10.5194/egusphere-egu2020-782, 2020.

The Pliocene saw multiple advances and retreats of the ice-sheet margin in East Antarctica. Amery Ice Shelf (AIS) is the largest ice shelf in East Antarctica and also the largest single ice stream draining from the Antarctic Plateau. It buttresses the Lambert Glacier drainage system, and accounts for 14% of the outflow from the East Antarctic Ice Sheet (EAIS). However, evidence for the state of the EAIS during the Pliocene is sparse and difficult to interpret unequivocally. Marine geological-geophysical data collected from the continental shelf in Prydz Bay, Antarctica, including seismic-reflection data, bathymetry, core records from ODP drilling and gravity coring sites, reveal a complex paleo-subglacial drainage system linked to an offshore depositional regime dominated on a trough mouth fan (TMF). Detailed seismic stratigraphic and facies analysis reveals the glacial evolution of Prydz Bay shelf and its TMF, including several glacial expansions across the shelf indicated by erosional surfaces and stratal bodies with chaotic acoustic character. The geometry of seismic sequences suggests that the glaciers and their associated TMF developed after a major episode of shelf and slope erosion during the Pliocene-Pleistocene.

 The shelf in Prydz Bay is dominated by a wide, south-north trending glacially-eroded trough (the Prydz Channel: -500~-1000 m depth) and shallower banks (-500~0 m depth). Well preserved grounding zone wedges areevidenced by prograding foreset deposits. Evidence for erosion of the wedges and/or lineations that extend across their upper surfaces indifferent water depths ranging from 200 m to 800 m imply their formation during multiple glacial stages or cycles.  Stacked erosional surfaces reveal major cross-shelf glacial expansions and the development of deep channel systems (up to -500 m depth) associated with extensive subglacial meltwater in Prydz Bay. These glacial related features provide good constraints for reconstructing the stability of the Pliocene EAIS.

How to cite: Huang, X., Leitchenkov, G., Bernhardt, A., Eagles, G., Gohl, K., and Gao, J.: Dynamics of Pliocene East Antarctic Ice Sheet from depositional signatures of the Prydz Bay shelf and Trough Mouth Fan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7552, https://doi.org/10.5194/egusphere-egu2020-7552, 2020.

Present-day warming is most pronounced at high latitudes, raising concern for the stability of modern ice caps such as the ones overlying the Svalbard archipelago. Palaeo-records give us opportunity to understand past behavior of these systems, including the ice retreat from the continental shelf at the end of the last glaciation. In order to evaluate and reconstruct this in a robust way, it is essential that we acquire high-quality data sets covering key areas in the Arctic.

New multi-beam bathymetric data was acquired in July 2019 from the Woodfjorden Trough; an up to 60 km long and 40 km wide transverse trough on the northwestern part of the Svalbard continental shelf. Previous investigations have shown that this trough was occupied by a major ice stream draining the Svalbard Ice Sheet during the last glacial, but the deglacial dynamics of this sector of the Svalbard Ice Sheet are presently not well constrained.

The new data reveal a complex seabed morphology including larger (2 km wide, 50 m high) and smaller (100 m wide, 3 m high) ridges, as well as sediment wedges (1 to 2 km wide, 30 m high), partly showing crosscutting relationships. These ridges and wedges are discontinuous in the outer part of the trough, where they are partly superposed by glacial lineations and small- to larger sized iceberg ploughmarks (up to 1500 m wide and 30 m deep). In the middle part of the trough, more continuous ridges dominate.

The ridges and wedges are interpreted to be glacial landforms formed by grounded ice within the Woodfjorden Trough. Their crosscutting relationships testify to a complex deglaciation, including several advances and still stands of the ice front during overall ice retreat, and their size could indicate that the glacier front was stable for some time. Smaller ridges may be retreat moraines formed during shorter (annual?) still stands of the glacier front. Based on their discontinuous characteristics, the ridges and wedges in the outer part of the trough may pre-date the final Late Weichselian deglaciation, i.e. they may have been overridden by a grounded glacier. The more continuous character of the ridges in the middle part of the trough indicate that these likely date from the Late Weichselian deglaciation.

The glacial landforms identified here are rather atypical for glacial troughs, commonly dominated by mega-scale glacial lineations superposed by one or a few grounding zone wedges and/or smaller retreat moraines. The abundant morainal systems and glacial lineations of the Woodfjorden Trough, instead, testify to highly dynamic grounded ice occupying the trough, and a retreat which was characterized by several periods of ice margin stability, interrupted by readvances. This fits with recent studies from onshore areas, showing that the deglaciation of northern Svalbard was at least partly characterized by glacial readvances during the overall ice retreat.

How to cite: Rydningen, T. A., Lasabuda, A., Laberg, J. S., Kollsgård, C. T., Olsen, S. B., Forwick, M., Winsborrow, M., and Ingólfsson, Ó.: New results on the dynamics of the NW part of the Svalbard Ice Sheet during the deglaciation of the Woodfjorden Trough, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10921, https://doi.org/10.5194/egusphere-egu2020-10921, 2020.

Each summer, surface melting of the margin of the Greenland Ice Sheet exposes a distinctive visible stratigraphy that is related to past variability in subaerial dust deposition across the accumulation zone and subsequent ice flow toward the margin. Here we map this surface stratigraphy along the northern margin of the ice sheet using mosaicked Sentinel-2 multispectral satellite imagery from the end of the 2019 melt season and finer-resolution WorldView-2/3 imagery for smaller regions of interest. We trace three distinct transitions in apparent dust concentration and the top of a darker basal layer. The three dust transitions have been identified previously as representing late-Pleistocene climatic transitions, allowing us to develop a coarse margin chronostratigraphy for northern Greenland. Substantial folding of late-Pleistocene stratigraphy is observed but uncommon. The oldest conformal surface-exposed ice in northern Greenland is likely located adjacent to Warming Land and may be up to ~55 thousand years old. Basal ice is commonly exposed hundreds of meters from the ice margin and may indicate a widespread frozen basal thermal state. We conclude that the ice margin across northern Greenland offers multiple compelling opportunities to recover paleoclimatically valuable ice relative to previously studied regions in southwestern Greenland.

How to cite: MacGregor, J., Fahnestock, M., Colgan, W., Larsen, N., Kjeldsen, K., and Welker, J.: The age of surface-exposed ice along the northern margin of the Greenland Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10963, https://doi.org/10.5194/egusphere-egu2020-10963, 2020.

The Ross Ice Shelf is the Antarctic region that over the last deglaciation experienced the greatest change in areal ice cover. Today, cold, dense and saline water masses (brines) produced in the Ross Sea polynya, flow from the shelf to the deep ocean providing a significant contribution to the propelling of the global ocean circulation regulating the climate. In particular, the Hillary Canyon in the Eastern Ross Sea is the main conduit through which brines descend the slope to reach the deeper ocean and is thus one of the greatest regions of cold, dense water export in the world.

A Contourite Depositional System (the ODYSSEA CDS) on the western flank of the Hillary Canyon is inferred to have been generated through several hundred-thousand years by along-slope, contour currents that transported and accumulated the sediments brought down the Hillary Canyon by means of brines. A multi-proxy investigation was conducted on the shallowest part of the ODYSSEA CDS depositional sequences, which we expect to contain i) the record of the brine formation, ii) the indication on contour current strength through time, and iii) their interplay and modulation associated to climate change.

Six gravity cores, collected in both the proximal and distal area of the ODYSSEA CDS, were studied through multi-proxy analyses including sediment physical properties (texture, structures, water content, wet bulk density), compositional characteristics (XRF, geochemistry and detrital apatite, zircon, and rutile U-Pb on ice-rafted debris) (Lucchi et al., 2019; Neofitu et al., 2020) and microfossil content (planktonic and benthic foraminifera, calcareous nannofossils and diatoms). An age model has been reconstructed combining palaeomagnetic record, biostratigraphic content, tephrochronology and AMS radiocarbon dating on planktonic foraminifera tests.

Inferred variations in dense water formation, contour current strength and ice sheet dynamics are discussed in the light of our data interpretation.

Lucchi, R.G., Caburlotto, A., Miserocchi, S., Liu, Y., Morigi, C., Persico, D., Villa, G., Langone, L., Colizza, E., Macrì, P., Sagnotti, L., Conte, R., Rebesco, M., 2019. The depositional record of the Odyssea drift (Ross Sea, Antarctica). Geophysical Research Abstracts, Vol. 21, EGU2019-10409-1, 2019. EGU General Assembly, Vienna (Austria), 7–12, April, 2019 (POSTER).

Neofitu, R., Mark, C., Rebesco, M., Lucchi, R.G., Douss, N., Morigi, C., Kelley, S., Daly, J.S., 2020. Tracking Late Quaternary ice sheet dynamics by multi-proxy detrital mineral U-Pb analysis: A case study from the Odyssea contourite, Ross Sea, Antarctica. Geophysical Research Abstracts. EGU General Assembly, Vienna (Austria), 3–8, May, 2020 (POSTER for session CL1.11).

How to cite: Rebesco, M., Lucchi, R. G., Caburlotto, A., Miserocchi, S., Langone, L., Liu, Y., Morigi, C., Macrì, P., Winkler, A., Di Roberto, A., Del Carlo, P., Colizza, E., Persico, D., Villa, G., Conte, R., Douss, N., Neofitu, R., and Mark, C.: Multi-proxy analysis of Late Quaternary ODYSSEA Contourite Depositional System (Ross Sea, Antarctica) and the depositional record of contour current and cold, dense waters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12940, https://doi.org/10.5194/egusphere-egu2020-12940, 2020.

Reconstructions of sea ice conditions proximal to the Antarctic coast are often hampered by a limited preservation potential of diatoms in these areas. While silica frustules are affected by opal dissolution, specific organic molecules, highly branched isoprenoids (HBIs) produced by diatoms, are well preserved in continental margin and shelf sediments and may help to overcome this gap. Here, we present biomarker and geochemical data obtained from a very well ¹⁴C-dated gravity core from the continental slope off Atka Bay in the northeastern part of the Weddell Sea. HBIs, the HBI-based PIPSO₂₅ index (Vorrath et al., 2019), glycerol dialkyl glycerol tetraether (GDGT) proxies and phytosterols reveal highly variable sea ice conditions and water temperatures as well as primary productivity changes over the last deglacial. These biomarker records are compared to ice core data and further complemented by physical property and XRF scanning data to estimate potential linkages between oceanic forcing and ice-shelf dynamics.

References

Vorrath, M.E., Müller, J., Esper, O., Mollenhauer, G., Haas, C., Schefuß, E., and Fahl, K., 2019. Highly branched isoprenoids for Southern Ocean sea ice reconstructions: a pilot study from the Western Antarctic Peninsula. Biogeosciences, v. 16, no. 15, p. 2961-2981.

How to cite: Müller, J., Gebhardt, C., Mollenhauer, G., and Tiedemann, R.: Deglacial sea ice variability at the continental margin off western Dronning Maud Land, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13950, https://doi.org/10.5194/egusphere-egu2020-13950, 2020.

The Southern Hemisphere`s westerly winds play a critical role in regulating Earth`s climate by shielding Antarctica from low-latitude heat, driving global ocean circulation and regulate the uptake of CO2 in the Southern Ocean. Both strength and position of this globally significant atmospheric pattern are rapidly shifting in the face of ongoing global warming. A string of recent studies links these developments to dramatic coupled changes in temperature, precipitation, sea-ice coverage and glacier extent that unfold across the Southern Ocean region. Critically, a lack of baseline information restricts our ability to understand the causes and patterns of these shifts and represent them robustly in the future projections that underpin climate policies. To help do so, we utilize the sensitivity of glaciers to atmospheric climate change and the potential of glacier-fed lake sediments to record this signal through time. For this purpose, we integrate emerging sedimentological, geochemical and glacier modelling tools in a new method framework to reconstruct changes in glacier extent, temperature and precipitation on human-relevant timescales. To do so, we rely on a number of novel sedimentological and geochemical approaches. These include biomarker-based temperature reconstructions, exposure dating of moraines and the use emerging non-destructive scanning techniques (e.g. Computed Tomography – CT) to fingerprint depositional pathways. Our study area in this cross-disciplinary project is the poorly investigated sub-Antarctic Kerguelen Archipelago, well-situated in the core southern westerly wind belt. During an extensive 2019 field campaign, we collected 130 meters of sediment cores from six lakes, 110 rock samples for exposure dating and numerous catchment samples. 

How to cite: Bakke, J., Arnaud, F., Deline, P., Guiguet-Covex, C., Linge, H., Ravanel, L., Støren, E., and van der Bilt, W.: Late glacial and Holocene glacier fluctuations at the Sub-Antarctic Island Kerguelen in the Southern Indian Ocean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17953, https://doi.org/10.5194/egusphere-egu2020-17953, 2020.

As the melting of the Greenland Ice Sheet (GrIS) accelerates, it is critical to improve our knowledge of its Pleistocene history in order to better understand its sensitivity to different climate states. The study of sediment from the base of the ice sheet offers valuable insights, since this material holds useful information about its history and origin. Here, we present various mineralogical and geochemical analysis from basal sediments of the NEEM ice core from northwestern Greenland (NEEM community, 2013), a complement to the first analysis of the basal ice made by Goossens et al. (2016).

In an effort to specify the provenance and characterize the sediments in the basal ice of the NEEM ice core, strontium and neodymium isotopic ratios were measured in 7 bulk till samples located into the deepest part of the core. Laser granulometry and shape characterization by SEB images of the grains suggest a mixed origin of this material. The deepest sample yield in situ cosmogenic ¹⁰Be and ²⁶Al concentrations lower than 10⁴ at.g^-1 and ²¹Ne concentration in the 10⁷-10⁸ at.g^-1 range. These preliminary cosmogenic nuclides data suggest that several cycles of waning and waxing of the GrIS had occurred over the last 10 million years. Additional sample material is being processed to reduce the uncertainty of ²⁶Al and ¹⁰Be measurements and refine this chronology.

To better characterize the origin of the basal sediment and the duration of pre-burial exposure, measurements of meteoric cosmogenic ¹⁰Be in 7 samples distributed along the basal part of the core are currently in progress. These data will be combined with the measurement of total organic carbon and nitrogen in the same samples. C and N concentrations and isotopes bring useful information about the type of soil and till material in these basal sediments (Bierman et al., 2016).

Bierman, P.R., Shakun, J.D., Corbett, L.B., Zimmerman, S.R., Rood, D.H., 2016. A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years. Nature 540, 256–260. https://doi.org/10.1038/nature20147

Goossens, T., Sapart, C.J., Dahl-Jensen, D., Popp, T., El Amri, S., Tison, J.-L., 2016. A comprehensive interpretation of the NEEM basal ice build-up using a multi-parametric approach. The Cryosphere 10, 553–567. https://doi.org/10.5194/tc-10-553-2016

NEEM community, 2013. Eemian interglacial reconstructed from a Greenland folded ice core. Nature, 493. doi:10.1038/nature11789

How to cite: Protin, M., Blard, P.-H., Tison, J.-L., Dahl-Jensen, D., Steffensen, J., Debaille, V., Fripiat, F., Claeys, P., Caffee, M., Bierman, P., Corbett, L., and Christ, A.: Geological, geochemical and cosmogenic nuclides constraints from the NEEM core basal sediments, Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18143, https://doi.org/10.5194/egusphere-egu2020-18143, 2020.

The super greenhouse climate of the middle Cretaceous represents an analogue for an extreme CO₂ induced (run-away) climate system. In order to improve the understanding of how the high northern latitudes responded to the escalating middle Cretaceous warmth we analysed dinocysts, palynofacies, δ¹³C and various biomarker proxies through a unique mid Cretaceous succession from the northern Baffin Bay. Our study is based on a several sites that were cored during the IODP Expedition 344S.
The composite section represents a nearly complete Albian - Turonian succession deposited during the syn-rift phase separating Greenland from Canada/North America. Depositional environments range from anoxic outer shelf and pro-delta fringe to oxygen-restricted lower delta front. The organic geochemical proxies are focusing on the OAE 2 and will investigate changes in the sea surface temperature and water column oxygenation related with this event.

How to cite: Sliwinska, K. K., Bojesen-Koefoed, J., Naafs, D., Nøhr-Gansen, H., Krarup Pedersen, G., Hovikovski, J., and Knutz, P. C.: Stratigraphy, environment and climate of the mid Cretaceous succession from the Arctic region (Baffin Bay), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18455, https://doi.org/10.5194/egusphere-egu2020-18455, 2020.

Glendonites often used as paleoclimate indicator of cold near-bottom temperature, as these are calcite pseudomorphs of ikaite, a metastable calcium carbonate hexahydrate, precipitates mostly under low temperature (mainly from 0-4^oC) and may be stabilized by high phosphate concentrations that occurs due to anaerobic oxidation of methane and/or organic matter; dissolved organic carbon, sulfates and amino acid may contribute ikaite formation as well.  Therefore, glendonites-bearing host rocks frequently include glacial deposits that make them useful as a paleoclimate indicator of near-freezing temperature.

Our study is based on material collected from five wells drilled in eastern Barents Sea: Severo-Murmanskaya, Ledovaya – 1,2; Ludlovskaya – 1,2. The studied glendonites, mainly represented by relatively small rhombohedral pseudomorphs (0,5-2 cm) and rarely by stellate aggregates, collected from Middle Jurassic to Lower Cretaceous shallow marine clastic deposits. They scattered distributed throughout succession. Totally 18 samples of glendonites were studied. The age of host-bearing rocks were defined by fossils: bivalves or ammonites, microfossils or dinoflagellate. Bajocian-Bathonian glendonites were collected from Ledovaya – 1 and Ludlovskaya – 1 and 2 wells; in addition to these occurrences Middle Jurassic glendonites are known also in boreholes drilled at Shtockmanovskoe field. Numerous ‘jarrowite-like’ glendonites of the Middle Volgian (~ latest early Tithonian) age were sampled from Severo-Murmanskaya well. Unique Late Barremian glendonites were found in Ledovaya – 2 well.

δ¹⁸O values of Middle Jurassic glendonite concretions range from – 5.4 to –1.7 ‰ Vienna Pee Dee Belemnite (VPDB); for Upper Jurassic – Lower Cretaceous δ¹⁸O values range from – 4.3 to –1.6 ‰ VPDB; for Lower Cretaceous - δ¹⁸O values range from – 4.5 to –3.4 ‰ VPDB. Carbon isotope composition for Middle Jurassic glendonite concretions δ¹³C values range from – 33.3 to –22.6 ‰ VPDB; for Upper Jurassic – Lower Cretaceous δ¹³C values range from – 25.1 to –18.4 ‰ VPDB; for Lower Cretaceous - δ¹³C values range from – 30.1 to –25.6 ‰ VPDB.

Based on δ¹⁸O data we supposed that seawater had a strong influence on ikaite-derived calcite precipitation. Received data coincide with δ¹⁸O values reported from other Mesozoic glendonites and Quaternary glendonites formed in cold environments. Values of δ¹³C of glendonites are close to bacterial sulfate reduction and/or anaerobic oxidation of methane or organic matter. Glendonites consist of carbonates forming a number of phases which different in phosphorus and magnesium content. Mg-bearing calcium carbonate and dolomite both include framboidal pyrite, which can indicate (1) lack of strong rock transformations activity and (2) presence of sulfate-reduction bacteria in sediments.

To conclude, Mesozoic climate was generally warm and studied concretions indicate cold climate excursion in Middle Jurassic, Upper Jurassic-Early Cretaceous and Early Cretaceous.

The study was supported by RFBR, project number 20-35-70012.

How to cite: Mikhailova, K., Ershova, V., Rogov, M., Pokrovsky, B., and Vereshchagin, O.: Glendonites from Mesozoic succession of eastern Barents sea: distribution, genesis and paleoclimatic implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19076, https://doi.org/10.5194/egusphere-egu2020-19076, 2020.

The Arctic is warming twice as fast as the global average, and the melting of mountain glaciers and ice caps has accelerated over the last two decades accompanied by reduced sea ice in the Arctic Ocean. Here we combine sedimentological and geochemical approaches to reconstruct changes in glacier extent at the marine terminating glacier Kongsbreen in order to put present-day climate changes into a longer time perspective. Glaciers are highly sensitive climate indicators as they rapidly respond to variations in summer temperature and precipitation, two parameters that are closely linked to atmospheric dynamics. This climate response is recorded by variations in glacier extent and moraine formation and by variations in glacial erosion and hence sedimentation rates in distal glacier-fed lakes. Lake Sarsvatnet is a threshold-lake that only receive glacial derived sediments when the surface of Kongsbreen crosses a local threshold. When the catchment is ice-free, lake sedimentation rate is lower and dominated by material weathered from the immediate proximity and organic-rich sediments. Based on seismic surveying seven coring sites were selected in three different sub-basins in lake Sarsvatnet. Laboratory analyses, including geochemical measurement by XRF scanning and XRD, CT scanning, grain size and measurements of magnetic proxies, were preformed in order to fingerprint the inorganic sediments. Chronological control is based on radiometric dating (¹⁴C, ²¹⁰Pb, and ¹⁰Be). Erratics (n=3, 125-306 m a.s.l.) indicate ice-free conditions since 13.0±1.1 ka (2σ), overlapping with the oldest organic material found in the lake which is 11 860±80 cal. yr BP. Until around 7400 cal. yr BP lake Sarsvatnet is dominated by organic sedimentation. From around 7400 – 6900 cal. yr BP there is evidence for glacial input into the lake indicating the expansion of Kongsbreen and corresponding to the decline in temperature after the HTM. In the following millennia, and entering the Neoglacial period, there is evidence for mulitiple (~20) decadal to centennial-scale periods of glacier expansion, the most recent dated to AD 1650 marking the onset of glacier build-up towards the LIA maximum. This indicate that the Kongsbreen glacier had short lived expansion periods reaching LIA-like extension already during the middle Holocene, as well as multiple times during the Neoglacial.

How to cite: Støren, E. W. N., Brun Bjerkås, A., Bakke, J., Linge, H., D`Andrea, W., van der Bilt, W., Røthe, T., Balascio, N. L., Bradley, R. S., Grant, O., Fabel, D., and Xu, S.: Reconstruction of Holocene glacier fluctuations at Kongsbreen based on sediments deposited in lake Sarsvatnet, Ossian Sarsfjellet, Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19216, https://doi.org/10.5194/egusphere-egu2020-19216, 2020.

In this work we use high-resolution seismic reflection surveys collected across the northeast Baffin Bay region to investigate the glacigenic Melville Bugt Trough Mouth Fan (MB-TMF). The MB-TMF stratigraphy is characterised by over 100 km of progradation since ~2.7 Ma and the heterogeneous truncation or subsidence of topset strata. Variation in topset character is thought to relate to the waxing and waning of the northwest sector of the Greenland Ice Sheet across the shelf since ~2.7 Ma. 3D seismic reflection data reveal the preservation of multiple sets of mega-scale glacial lineations, suggesting that grounded ice extended across the shelf a number of times since the onset of the Middle Pleistocene Transition. Seismic geomorphology and facies analysis of the prograding clinoforms show repeated observations of debrites and gully systems. These features, when considered with other evidence of adjacent glacial landforms and strata, are taken to infer gravity-driven processes and the presence of meltwater-related hyperpycnal flows in areas proximal to the ice sheet on the outer shelf. Bottomset contourites at the base of the continental slope also provide insights into the evolution of the West Greenland Current in Baffin Bay through the Pleistocene, with deposition estimated to have started in the latest Calabrian, based on the current age model. Regional stratigraphic mapping shows that the MB-TMF can be summarised into four stages that were primarily controlled by variations in ice sheet erosion patterns, topographic forcing of ice flow, and changes in accommodation that are related to glacigenic deposition and tectonic subsidence. 

How to cite: Newton, A., Cox, D., Huuse, M., and Knutz, P.: Plio-Pleistocene glacial history of the Melville Bugt Ice Stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19312, https://doi.org/10.5194/egusphere-egu2020-19312, 2020.

The Camp Century Ice core, NW Greenland, recovered a 4.5 m basal section consisting of frozen sediments and debris-rich ice. This material was recently re-discovered in Danish ice core storage and visually logged. As part of a multi-disciplinary effort to unlock the climatic and paleo-environmental signal of this unique record, we have analysed detrital mineral composition and metamorphic ages. Bulk mineral analyses were performed at the Geological Survey of Denmark and Greenland on grain mounts from 2 core intervals using a SEM automated quantitative mineralogy (AQM) approach coupled to laser ablation ICP-MS analyses. This setup allows us to gain a full mineral description together with single-grain U-Pb dates for a large population of metamorphic components, e.g. apatite, rutile, titanite and zircon. In addition, amphibole grains were picked for ⁴⁰Ar-³⁹Ar dating performed at the LDEO Argon Isotope Lab. Mineralogical characterization was completed by X-Ray diffraction analysis of the fine fraction to determine the presence and nature of potential clay weathering products, and single-crystal X-ray diffraction was utilized to characterize the atomic arrangements of minerals that occur in solid solutions. The AQM results indicate that metamorphic minerals are present in sufficient amounts (100’s) for gaining statistically valid provenance data. Preliminary results show ages in the 1900 – 1700 Ma range (amphibole, rutile) and around 2700 Ma (zircon). This, along with the presence of swelling clays in the sediments, is consistent with weathering of the local bedrock, and/or sediments transported from the Inglefield orogenic belt north of the site. To gain information on the youngest thermal events of sediment sources, potentially revealing deep glacial incision, (U-Th-Sm)/He dating of single apatite grains is underway. Preliminary work on the 125-250 µm size fraction yield abundant subhedral-to-subrounded, euhedral apatite suitable for thermochronology. Here we report the results from the different methods and discuss the implications for understanding erosional processes and potential transport pathways of the Camp Century basal ice sediments. 

How to cite: Thomsen, T. B., Knutz, P. C., Fosdick, J. C., Hemming, S. R., Christ, A., Bierman, P. R., Perdrial, N., Hughes, J., Schaefer, J., Tison, J.-L., Blard, P.-H., Protin, M., Dahl-Jensen, D., and Steffensen, J. P.: Detrital mineral composition and provenance of the Camp Century basal ice sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21591, https://doi.org/10.5194/egusphere-egu2020-21591, 2020.