SSP2.12

EDI
Polar climate and environmental change throughout geological time

Polar regions are particularly sensitive to climate variability and play a key role in global climate and environmental conditions through various feedback mechanisms. In this session we invite contributions dealing with all aspects of Phanerozoic (i.e. Cambrian to Holocene) geology from high latitude regions: stratigraphy, paleoenvironment, paleoclimate, and modelling.

Co-organized by CL1
Convener: Madeleine VickersECSECS | Co-conveners: Jennifer M. Galloway, Kasia K. Sliwinska
vPICO presentations
| Wed, 28 Apr, 15:30–17:00 (CEST)

vPICO presentations: Wed, 28 Apr

Chairpersons: Madeleine Vickers, Kasia K. Sliwinska, Jennifer M. Galloway
15:30–15:35
Mesozoic and Palaeogene
15:35–15:37
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EGU21-10659
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ECS
Iben W. Hougård, Madeleine L. Vickers, Peter Alsen, Mads E. Jelby, Clemens V. Ullmann, and Christoph Korte

Keywords: Late Jurassic; palaeoclimate; Greenland; carbon cycling; Viking Corridor; belemnite stable isotopes

The “polar amplification” effect, whereby the poles experience greater changes in temperature compared to the low latitudes for a given global average temperature change, makes high-latitude isotope records ideally suited to investigate fluctuations in palaeoclimate. The present study investigates palaeoclimatic and oceanographic changes along the Viking Corridor – the narrow seaway that connected the Tethys to the Arctic Boreal Realm during the Middle and Late Jurassic.

Stable-isotope data obtained from belemnites from East Greenland, originating from along the western margin of the Viking Corridor, show a M. Bathonian warming trend, which may indicate the reopening of the corridor after North Sea doming. We also discuss various controls on the carbon-isotope record that may dampen or amplify global signals. Changes in local depositional settings caused partial overprinting of the δ13C record during the Late Jurassic VOICE event.

How to cite: Hougård, I. W., Vickers, M. L., Alsen, P., Jelby, M. E., Ullmann, C. V., and Korte, C.:  Middle and Late Jurassic climatic, oceanographic and environmental trends along the Viking Corridor, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10659, https://doi.org/10.5194/egusphere-egu21-10659, 2021.

15:37–15:39
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EGU21-5021
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ECS
Kseniya Mikhailova, Victoria Ershova, and Mikhail Rogov

In the middle of 20th century glendonites were purposed as an indicator of cold climate. There is no doubt that unique morphology and sizes of pseudomorphs occurring through Precambrian to Quaternary succession indicate uncommon geochemical environment. Here, we present an overview of Early Cretaceous glendonites distribution across Arctic which widely distributed here despite generally greenhouse climate conditions in Early Cretaceous.

Late Berriasian pseudomorphs are known on northeastern Siberia and Arctic Canada. Valanginian glendonites are the widest ones are described from the Northern and Western Siberia, Spitsbergen and the Arctic Canada. Late Hauterivian concretions were studied on Svalbard. Barremian and lower Aptian glendonites are unknown in this area due to wide distributed continental succession, but late Barremian glendonites were reported from the wells drilled on the Barents Sea shelf. Middle and Upper Aptian glendonites are found on Svalbard,  North Greenland, the Arctic Canada and North-East Russia. Lower Albian glendonites are found on Svalbard, islands of Arctic Canada and the Koryak Uplands.

Nowadays it is reliable known that the precursor of glendonites is an ikaite - metastable calcium carbonate hexahydrate, forming in a narrow temperature range from 0-4oC, mainly in near-bottom conditions. Besides low temperature, high phosphate concentrations that occurs due to anaerobic oxidation of methane and/or organic matter; dissolved organic carbon, sulfates and amino acid may favor to ikaite formation as well. However, glendonites associated with terrigenious rocks, often including glacial deposits, that allow to use them as a paleoclimate indicator.

Glendonites show a wide variability in form and size: from single crystal blades to stellate aggregates and rosettes, usually ranged from a few mm to dozens of cm. Mineralogical composition of pseudomorph is represented mainly by three calcite phases determining by CL-light. Both δ18O and δ13C of glendonites are characterized by a broad range of values. Oxygen isotope composition ranges from -14 to -0 ‰ Vienna Pee Dee Belemnite (VPDB), whilst  carbon isotope composition ranges from -52.4 to – 14 ‰ Vienna Pee Dee Belemnite (VPDB).

Based on received data we suggest that δ18O reflects the complex processes involved in ikaite-glendonite transformation, supposing mixing depleted fluids with seawater. Nevertheless, received data coincide with δ18O values reported from Paleozoic-Quaternary glendonites formed in near-freezing environments. Values of δ13C of glendonites is the result of both mixing seawater inorganic carbon and sedimentary organic diagenesis and close to bacterial sulfate reduction and/or anaerobic oxidation of methane or organic matter.

To conclude,  Early Cretaceous climate was warm generally, however studied pseudomorphs point to cold episodes in Late Berriasian, Valanginian, Late Hauterivian, Middle-Late Aptian and Early Albian.

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

How to cite: Mikhailova, K., Ershova, V., and Rogov, M.: Early Cretaceous glendonites of Arctic realm: distributions and their paleoclimate implication, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5021, https://doi.org/10.5194/egusphere-egu21-5021, 2021.

15:39–15:41
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EGU21-9571
Stephane Bodin, Carlette Blok, Jon Ineson, Kresten Anderskouv, Alicia Fantasia, Emma Sheldon, Nicolas Thibault, and Thierry Adatte
Our understanding of the climatic evolution during the early Cretaceous in general, and the Oceanic Anoxic Event 1a (OAE-1a) in peculiar, is widely derived from the investigation of Tethyan localities, leaving large uncertainties about their significance on a global scale. In this study, we have performed high-resolution clay-mineral assemblage analyses in the upper Hauterivian to lower Aptian of the North Jens-1 core, located in the Danish central graben that was part of the Boreal realm. High amount of detrital Kaolinite is observed throughout the core, indicating the presence of a local, kaolinite-rich source. A long-term decline in Kaolinite content is occurring from the lower Hauterivian to the lowermost, pre-OAE-1a Aptian, followed by a sharp rise within the OAE-1a. This trend is similar to the one observed in the Tethyan realm, indicating a supra-regional climatic evolution from humid conditions in the late Hauterivian toward drier conditions in the latest Barremian – earliest Aptian, followed by renewed humid conditions during the unfolding of OAE-1a. Precise timing of climate change during the OAE-1a differs however in between the Tethyan and Boreal realm. Shift toward humid conditions coincides hence with the onset of OAE-1a (segment C3) in the Tethyan realm, followed by a return to drier conditions in the second half of OAE-1a. In the Boreal realm, the onset of OAE-1a is characterized by a relatively dry climate, followed by the installation of humid climate during the mid-OAE-1a (segments C4-C5) that persists through the remainder of the early Aptian. Across latitudinal belts, there is thus a non-linear change in precipitation pattern during the unfolding of OAE-1a. Similar observations have been made for other OAEs, suggesting more complex weathering feedback mechanism during hyperthermal events than generally assumed.

How to cite: Bodin, S., Blok, C., Ineson, J., Anderskouv, K., Fantasia, A., Sheldon, E., Thibault, N., and Adatte, T.: Climate changes across Oceanic Anoxic Event 1a: new data from the Boreal realm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9571, https://doi.org/10.5194/egusphere-egu21-9571, 2021.

15:41–15:43
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EGU21-8196
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ECS
Wolf Dummann, Claudia Schröder-Adams, Peter Hofmann, Janet Rethemeyer, and Jens O. Herrle

Oceanic anoxic event (OAE) 1a documents a major perturbation of the Early Cretaceous global carbon cycle with severe consequences for the ocean-climate-biosphere system. While numerous studies over the past decades have provided a relatively detailed picture of the environmental repercussions of OAE 1a at low and mid-latitudes, studies from high latitudes, in particular the High Arctic, are limited. In this study, we present a high-resolution carbon isotopic and sequence stratigraphic framework for the lower to lower upper Aptian interval of the Isachsen Formation of the High Arctic Sverdrup Basin (Canada). These data enable us to precisely locate the stratigraphic position of OAE 1a in a deltaic sedimentary environment. The carbon isotope record allows, for the first time, identification of the different carbon isotope segments (CISs) of OAE 1a in the Sverdrup Basin and thereby correlation of the High Arctic record with sections from lower latitudes. Based on this improved chemostratigraphy, we revise the age of upper Paterson Island, Rondon, and Walker Island Members, important regional lithostratigraphic marker units. Whole-rock geochemical data record two episodes of marine incursion into the Sverdrup Basin during OAE 1a (CISs Ap3 and Ap6), which are interpreted as regional maximum flooding surfaces. This information is used in conjunction with detailed sedimentological logs and geochemical grain-size proxies to refine the sequence stratigraphic framework for the upper Isachsen Formation. We propose that transgressive-regressive cycles in the Sverdrup Basin were mainly controlled by the combined effects of eustatic sea-level changes and regional tectonic uplift, potentially related to the emplacement of Alpha Ridge, which culminated at ca. 122 Ma during CIS Ap9.

How to cite: Dummann, W., Schröder-Adams, C., Hofmann, P., Rethemeyer, J., and Herrle, J. O.: Carbon isotope and sequence stratigraphy of the upper Isachsen Formation on Axel Heiberg Island (Nunavut, Canada): High Arctic expression of oceanic anoxic event 1a in a deltaic environment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8196, https://doi.org/10.5194/egusphere-egu21-8196, 2021.

15:43–15:45
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EGU21-10923
Maria Rose Petrizzo, David K. Watkins, Kenneth G. MacLeod, Takashi Hasegawa, Brian T. Huber, Sietske J. Batenburg, and Tomonori Kato

Planktonic foraminiferal population dynamics and stable isotope data are presented to interpret environmental changes across the Cenomanian-Turonian boundary interval at Integrated Ocean Discovery Program (IODP) Expedition 369 Site U1516 in the Mentelle Basin (Indian Ocean, SW Australia). Site U1516 was located at 60°-62°S paleolatitude and it is the first high latitude locality in the Southern Hemisphere where planktonic foraminifera are consistently recorded across the Oceanic Anoxic Event 2 (OAE 2) interval and its associated positive δ13C excursion. Planktonic foraminifera and calcareous nannofossil biostratigraphy and stable isotopic results indicate the presence of a hiatus in the upper Cenomanian that spans the base of the δ13C excursion, thus the record of the onset of OAE 2 is not preserved. Nevertheless, correlation between the δ13C and δ18O profiles at Site U1516 and the European reference section at Eastbourne (England) allow identification of the Carbon Isotopic Excursion and, tentatively, of correlative local cooling consistent with the expression of the Plenus Cold Event at low latitudes.

Absolute abundances of planktonic and benthic foraminifera, and radiolaria combined with δ13C and δ18O measurements of both bulk carbonate and planktonic and benthic foraminifera provide clues concerning the paleoceanographic changes across OAE 2. In the lower part of OAE 2 and coinciding with the trough in the δ13C profile, the planktonic foraminiferal assemblages are dominated by small-sized (125-38 μm) opportunistic species and radiolaria indicating a dominantly eutrophic regime. An increase in benthic foraminiferal abundance may indicate a local increase of oxygenation during the interval of the Plenus Cold Event associated with high δ18O values, as observed at low latitudes. At Site U1516, the middle part of OAE 2 corresponding to the plateau phase of the δ13C profile is masked by absence of carbonate, highest TOC values, and high biogenic silica indicating this interval corresponded to a time of highly stressed eutrophic conditions with possible shoaling of the Carbonate Compensation Depth. Above this interval, bulk isotopic results are characterized by a decrease in δ13C values, CaCO3 increases associated with the abundance of opportunist planktonic species and apparently cyclic fluctuations in the absolute abundance of benthic foraminifera. These observations point to dominantly eutrophic conditions likely affected by upwelling of nutrient-rich and δ13C-depleted intermediate water masses.

Toward the top of OAE 2 across the C-T boundary interval, the planktonic foraminiferal assemblages show changes in composition with an overall increase in species diversity and continued cyclic fluctuations in absolute abundances. These features coupled with the foraminiferal species-specific δ13C and δ18O patterns reveal that Site U1516 occupied a paleoceanographic setting still affected by eutrophy likely related to enhanced input of nutrients. However, the occurrence of species that occupied relatively deep ecological niches indicates there were also episodes of stability with ecological/thermal stratification in the surface waters. This interval also records the highest sea surface water paleotemperatures values estimated as 20°-23°C based on δ18O values of foraminiferal shell and assuming seawater δ18O values of -1‰V-SMOW. Following the OAE 2 event and associated δ13C excursion, stable conditions in the water column were established.

 

 

How to cite: Petrizzo, M. R., Watkins, D. K., MacLeod, K. G., Hasegawa, T., Huber, B. T., Batenburg, S. J., and Kato, T.: Paleoceanographic reconstructions from planktonic foraminifera across the Cenomanian/Turonian boundary and OAE 2 at southern high latitudes (IODP Site U1516, Mentelle Basin, Indian Ocean, SW Australia) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10923, https://doi.org/10.5194/egusphere-egu21-10923, 2021.

15:45–15:47
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EGU21-10917
Peter Bijl, Joost Frieling, Margot J. Cramwinckel, Christine Boschman, Appy Sluijs, and Francien Peterse

Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (sw) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be obscured by contributions of additional isoGDGT sources. We here use current proxy insights to assess the reliability of the isoGDGT-based SST signal in 69 newly analysed and 242 re-analysed samples covering the Maastrichtian to Oligocene from ODP Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques. We then reinterpret the record in context of paleo-environmental and paleoclimatologic reconstructions based on dinoflagellate cysts. Our ~130 kyr-resolution SST record reaffirms previous reconstructions of anomalous warmth in the early Eocene sw Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and temperature-sensitive taxa show a strong response to the local SST evolution, supporting the robustness of the marine biomarker record.  In addition, the long-term isoGDGT and dinocyst records provide further support for an apparent temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs), recorded in the same samples.

Soil-derived branched GDGTs (brGDGTs) stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land through the MBT’5me proxy. General trends in SST and MAAT are similar, except for 1) an enigmatic absence of MAAT rise during the Paleocene-Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and 2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocyst assemblages and brGDGT indices (the isomerization index) suggest a mid-shelf depositional environment with strong river-runoff during the Paleocene-early Eocene, becoming more open marine thereafter. This trend reflects gradual drying and more seasonal precipitation regime in the northward drifting Australian hinterland. The overall correlation between dinocyst assemblages, biodiversity and SST changes suggests that temperature and associated environmental changes exert a strong influence on the surface-water ecosystem.

How to cite: Bijl, P., Frieling, J., Cramwinckel, M. J., Boschman, C., Sluijs, A., and Peterse, F.: Maastrichtian-Rupelian paleoclimates in the southwest Pacific realm – a critical evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10917, https://doi.org/10.5194/egusphere-egu21-10917, 2021.

15:47–15:49
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EGU21-15673
Urszula Hara

The Paleocene-Eocene bryozoans such as microporoideans, umbonulomorphs, lepraliomorphs as well as cerioporoidean cyclostomes are successful biota inhabited the marine and glacio-marine sequences in Antarctica. Changes in their taxonomic composition, associated faunas, colony growth-forms, biodiversity, skeletal mineralogy and geochemistry are important environmental/climatic indicators.

The earliest Cenozoic Antarctic bryozoan fossil records (late early Eocene) are well-documented from the shallow-marine–estuarine clastic succession of the lower part (Telm1-2) of the La Meseta Formation of Seymour Island, where the faunas are represented by massive multilamellar colonies, often spectacular in size and dominated by the cyclostome cerioporids and diverse ascophoran cheilostomes. The distinct free-living lunulitiforms, for the first time reported from Antarctica from the Ypresian/Lutetian of the middle part of the La Meseta Fm. (Telm4-6) are represented by the disc-shaped colonies, which are characteristic for the temperate warm, shallow-shelf environment, with the bottom temperature, which are never lower than 10 to 12°C (Hara et al., 2018). The skeletons of the Lunulites, Otionellina, and Uharella are formed by the intermediate-Mg calcite (IMC) with the 4.5 mol% MgCO3. The use of the X-ray diffraction (XRD) and the Laser Raman spectroscopy (Hara et al., in preparation) shows that they build the bimineralic skeletons (with the traces of aragonite, calcite and strontium apatite), which are indicative for the temperate shelf environment, sandy and often shifting substrate. Biogeographically, the free-living lunulitiforms (Lunulites and Otionellina) are valuable climatic indicators, inhabited in the Recent the circumtropical, tropical-subtropical to warm-temperate Australasian sand environments.

Contrary to that, the bryozoans of the Telm6-7 with a scarce lepraliomorphs tentatively assignated to ?Goodonia and accompanied by crustaceans, brachiopods and gadiform fish remains are known from the temperate environments.

The isotopic analyses of the δ18O of the bryozoan skeletons from the lower part of the La Meseta Fm. show the range of the temperature from 13.4°C to 14.6°C (according to the equation given by Anderson & Arthur 1983).

It is worth pointing that the middle Ypresian/early Lutetian bryozoans, which in the stratigraphical profile of the LMF document the nearly 10 MA evolutionary history of the bryozoans are well-correlated with the MECO event, what is also consisted with the isotopic data based on the macrofaunal marine fossil records (Ivany et al. 2008).

Anderson T.F., and Arthur M.A.1983. Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. SEPM Short Course, 10: 1-151.

Hara U., Mors T., Hagstrom  and Reguero M. A., 2018. Eocene bryozoan assemblages from the La Meseta Formation of Seymour Island. Geological Quarterly, 62: 705-728. 

Hara U., Wrzosek B., and Mors, T. 2020. Calcite and aragonite distribution in the skeletons of bimineralic high-latitude bryozoans in the Raman spectroscopy (in preparation).

Ivany L.C., Lohmann K. C. Hasiuk F., Blake D.B., Glass A., Aronson R.B., and Moody R.M. 2008. Eocene climate record of the high southern latitude continental shelf: Seymour Island, Antarctica. Geological Society of America Bulletin, v. 120, no. 5-6: 659-678.

How to cite: Hara, U.: Environmental/climatic changes during the Eocene: biotic and geochemical evidences based on the bryozoan fauna (Antarctic Peninsula), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15673, https://doi.org/10.5194/egusphere-egu21-15673, 2021.

Neogene and Quaternary
15:49–15:59
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EGU21-12959
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solicited
Vivi Kathrine Pedersen, Nicolaj Krog Larsen, and David Lundbek Egholm

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 formation 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 volumes 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. The late Pliocene-early Pleistocene sediments themselves attest to a time of limited ice cover in Greenland, with temperatures as much as 6-8 °C higher than present (e.g. Bennike et al., 2010).

We find that the northern Independence Fjord system must have formed by glacial erosion since the deposition of the marine late Pliocene-early Pleistocene sediments at ~2.5 Ma, in order to explain the current elevation of the sediments by erosion-induced isostatic uplift. In contrast, fjord formation in the outer parts of southward Scoresby Sund commenced prior to the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene with 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. 

References:

Bennike, O., Knudsen, K.L., Abrahamsen, N., Böcher, J., Cremer, H., and Wagner, B., 2010, Early Pleistocene sediments on Store Koldewey, north­east Greenland: Boreas v. 39, p. 603–619, https://doi.org /10.1111/j.1502-3885.2010.00147.x.

How to cite: Pedersen, V. K., Larsen, N. K., and Egholm, D. L.: The timing of fjord formation and early glaciations in North and Northeast Greenland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12959, https://doi.org/10.5194/egusphere-egu21-12959, 2021.

15:59–16:01
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EGU21-8345
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ECS
Flor Vermassen, Helen K. Coxall, Gabriel West, and Matt O'Regan

Harsh environmental and taphonomic conditions in the central Arctic Ocean make age-modelling for Quaternary palaeoclimate reconstructions challenging. Pleistocene age models in the Arctic have relied heavily on cyclostratigraphy using lithologic variability tied to relatively poorly calibrated foraminifera biostratigraphic events. Recently, the identification of Pseudoemiliania lacunosa in a sediment core from the Lomonosov Ridge, a coccolithophore that went extinct during marine isotope stage (MIS) 12 (478-424 ka), has been used to delineate glacial-interglacial units back to MIS 14 (~500 ka BP). Here we present a comparative study on how this nannofossil biostratigraphy fits with existing foraminifer biohorizons that are recognised in central Arctic Ocean sediments. A new core from the Alpha Ridge is presented, together with its lithologic variability and down-core compositional changes in planktonic and benthic foraminifera. The core exhibits an interval dominated by Turborotalita egelida, a planktonic foraminifer that is increasingly being adopted as a marker for MIS11 in sediment cores from the Amerasian Basin of the Arctic Ocean. We show that the new age-constraints provided by calcareous nannofossils are difficult to reconcile with the proposed MIS 11 age for the T. egelida horizon. Instead, the emerging litho- and coccolith biostratigraphy implies that Amerasian Basin sediments predating MIS5 are older than the egelida-based age models suggest, i.e. that the T. egelida Zone is older than MIS11. These results expose uncertainties regarding the age determination of glacial-interglacial cycles in the Amerasian basin and point out that future work is required to reconcile the micro- and nannofossil biostratigraphy of the Amerasian and Eurasian basin.

How to cite: Vermassen, F., Coxall, H. K., West, G., and O'Regan, M.: Testing the synchronicity of Pleistocene biostratigraphic events in the central Arctic – Do we have a consistent biostratigraphic framework?  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8345, https://doi.org/10.5194/egusphere-egu21-8345, 2021.

16:01–16:03
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EGU21-7522
David Chandler and Petra Langebroek

Proxy records and climate models suggest that the Last Interglacial (LIG, ~130 to 115 thousand years before present) was characterised by high-latitude air and sea surface temperatures (SSTs) slightly warmer than present, and by mean global sea level a few metres higher. Therefore, the LIG is widely used as an analogue for near-future oceanographic/climatic conditions. Of particular interest is the Antarctic Ice Sheet’s contribution to rapid sea level rise and to Southern Ocean surface freshening, in response to warming. In the Southern Ocean, existing LIG temperature reconstructions suffer from very high variance amongst a low number of individual records. Recent syntheses have focused on the LIG climatic optimum, but conditions during the penultimate glacial are also important for forcing transient climate or Antarctic Ice Sheet simulations. Here we use databases of modern core-top sediments to evaluate the strengths of SST proxies available in the Southern Ocean, and consider their likely sources of bias and variance. By selecting only those paleo-temperature reconstructions which we believe are reliable in this region, we then compile a Southern Ocean SST synthesis covering the penultimate glacial and the LIG. This longer temperature time series can be used as a basis for LIG ice sheet simulations or for climate model development.  

How to cite: Chandler, D. and Langebroek, P.: Revised Southern Ocean sea surface temperatures over the last 180 ka, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7522, https://doi.org/10.5194/egusphere-egu21-7522, 2021.

16:03–16:05
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EGU21-1213
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ECS
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Highlight
Matthew Chadwick, Claire Allen, Louise Sime, and Xavier Crosta

Marine Isotope Stage (MIS) 5e marks the peak of the last interglacial (130-116 ka) and is an important ‘process analogue’ for understanding the high latitude climatic feedbacks and forcings active under future anthropogenic warming. Antarctic sea-ice extent is a critical component of the Earth’s climate system through its impact on global albedo and its roles in Southern Hemisphere atmospheric and ocean circulation. Published marine sediment core records are located too far north to accurately constrain the timing and extent of the winter sea-ice (WSI) minimum during MIS 5e (Chadwick et al., 2020) and researchers/models have therefore assumed that this minimum occurs synchronously with the Antarctic peak warming in ice core records (Holloway et al., 2017).

This study presents new reconstructions of Southern Ocean WSI extent for MIS 5e based on the diatom species assemblage records in marine sediment cores. These records have robust age models, which allow for the different timings and patterns of WSI retreat throughout the Southern Ocean to be examined. In particular, the difference between the relatively stable WSI extent in the Pacific sector of the Southern Ocean and the more dynamic WSI extent in the Atlantic sector of the Southern Ocean. Using sediment cores located south of 55 oS creates a novel synthesis for assessing the evidence for the considerable MIS 5e WSI reduction (67% in the Atlantic sector) predicted by model simulations (Holloway et al., 2017).

References

Chadwick M., Allen C.S., Sime L.C., Hillenbrand C-D. (2020). Analysing the timing of peak warming and minimum winter sea-ice extent in the Southern Ocean during MIS 5e. Quaternary Science Reviews, 229: 106134.

Holloway M.D., Sime L.C., Allen C.S., Hillenbrand C-D., Bunch P., Wolff E., Valdes P.J. (2017). The Spatial Structure of the 128 ka Antarctic Sea Ice Minimum. Geophysical Research Letters, 44 (21): 11129-11139.

How to cite: Chadwick, M., Allen, C., Sime, L., and Crosta, X.: Reconstructing Antarctic winter sea-ice extent during Marine Isotope Stage 5e, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1213, https://doi.org/10.5194/egusphere-egu21-1213, 2021.

16:05–16:07
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EGU21-15799
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ECS
Stuart Vyse, Ulrike Herzschuh, Andrei Andreev, Lyudmila Pestryakova, Bernhard Diekmann, Simon Armitage, and Boris Biskaborn

Palaeoenvironmental reconstructions with temporal coverages extending beyond Marine Isotope Stage (MIS) three are scarce within the data sparse region of Chukotka, Far East Russia. The objective of this work was to infer palaeoenvironmental variability from a 10.76 m long, radiocarbon and OSL dated sediment core from Lake Ilirney, Chukotka (67°21´N, 168°19´E). We performed acoustic sub-bottom profiling of the lake basin and analysed high-resolution elements (XRF), organic carbon (TC, TN, TOC), grain-size, mineralogy (XRD) and partly also diatoms and pollen from the core. Our results affirm the application of XRF-based sediment-geochemical proxies as effective tracers of palaeoenvironmental variability within arctic lake systems. Our work reveals that a lake formed during MIS 3 from ca. 51.8 ka BP, following an extensive MIS 4 glaciation in the Ilirney valley. Catchment palaeoenvironmental conditions during this time likely remained cold associated with the continued presence of a catchment glacier until ca. 36.2 ka BP. Partial amelioration reflected by increased diatom, catchment vegetation and lake organic productivity and clastic sediment input from mixed sources from ca. 36.2 ka BP potentially resulted in a lake high-stand ~15 m above the present level and may represent evidence of a more productive palaeoenvironment overlapping in timing with the MIS 3 interstadial optimum. A transitional period of deteriorating palaeoenvironmental conditions occurred ca. 30- 27.9 ka BP and was superseded by periglacial-glacial conditions from ca. 27.9 ka BP, during MIS 2. Deglaciation as marked by sediment-geochemical proxies commenced ca. 20.2 ka BP. Our findings are compared with lacustrine, Yedoma and river-bluff records from across Beringia and potentially yield limited support for a marked Younger Dryas cooling in the study area.

How to cite: Vyse, S., Herzschuh, U., Andreev, A., Pestryakova, L., Diekmann, B., Armitage, S., and Biskaborn, B.: Geochemical and sedimentological responses of Arctic glacial Lake Ilirney, Chukotka (Far East Russia) to palaeoenvironmental change since ~ 51.8 ka BP, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15799, https://doi.org/10.5194/egusphere-egu21-15799, 2021.

16:07–16:09
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EGU21-10823
Emma Ownsworth, David Selby, Jeremy Lloyd, and Sönke Szidat

The advance and retreat of the Greenland, Innuitian and Laurentide ice sheets (GIS, IIS, LIS) which surrounded Baffin Bay (West of Greenland) have been studied using numerous methods to gain insight into past ice sheet and ice stream dynamics. However, the exact timings, movements and relationships to climate events are still somewhat debated. Utilising osmium isotopes (187Os/188Os) as part of a multi-proxy strategy coupled with absolute age models, an enhanced understanding of the palaeoceanography and palaeoglaciology of this region for last ~40 kyrs is presented.

Carbonate-enriched layers recorded in many cores across Baffin Bay (Baffin Bay detrital carbonate - BBDC) are thought to be sourced from Palaeozoic carbonate rich rocks in the north/north-west of the bay which were covered by the IIS and LIS. Age modelling indicates that core JR175 records BBDC 0 and BBDC 1. Coincident with the BBDC events, hydrogenous 187Os/188Os compositions abruptly become more radiogenic. This suggests that alongside the carbonate delivery from the north of the bay, there is also a radiogenic Os source. Radiogenic Os derives from typically older, continental inputs, such as the Archean/Proterozoic terrains of western Greenland and Baffin Island. The seemingly sudden nature (within 1000 years) of the increase in 187Os/188Os would suggest a catastrophic ice sheet break-up and a period of increased iceberg discharge, or a sudden advance of the glacier outlets closer to the core site from the GIS and/or LIS.These events are also coincident with the Younger Dryas (~12.8 ka BP) and the end of the Oldest Dryas/ beginning of the Bølling–Allerød interstadial (~14.7 ka BP).

During periods of low carbonate enrichment, the 187Os/188Os values are less radiogenic. We invoke this to be a baseline during lower continental erosion periods and/or iceberg delivery, and more influence of oceanic Os from the Atlantic. Indeed, during the last 10 kyrs, 187Os/188Os values gradually decrease to compositions similar to the present day North Atlantic Ocean (~1.0).  This could represent increased mixing of marine Atlantic waters into Baffin Bay and/or a decrease in sediment delivery from all ice sheets representing the gradual retreat of the ice sheets through the Holocene.

In summary our data provide further insight into ice sheet advance, retreat, and sediment provenance within Baffin Bay during the past 40 kyrs, suggesting asynchronous behaviour of the surrounding ice sheets during theYounger Dryas and the end of the Oldest Dryas/ beginning of the Bølling–Allerød interstadial.

How to cite: Ownsworth, E., Selby, D., Lloyd, J., and Szidat, S.: Catastrophic ice sheet break-up surrounding Baffin Bay coincident with the Younger Dryas and the Oldest Dryas/ Bølling-Allerød interstadial, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10823, https://doi.org/10.5194/egusphere-egu21-10823, 2021.

16:09–16:11
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EGU21-15494
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ECS
Christine Tømmervik Kollsgård, Jan Sverre Laberg, Tom Arne Rydningen, Matthias Forwick, Katrine Husum, and Amando Lasabuda

The continental margin of the northern Barents Sea is a key area for understanding the behavior and dynamics of the northern Barents Sea Ice Sheet, as well as the Arctic ocean circulation pattern during the Last Glacial Maximum, the deglaciation, and the Holocene.

In this study, we investigate the continental slope north of Kvitøya and Nordaustlandet (Svalbard) by analyzing the seabed morphology of the improved IBCAO 4.0 bathymetric grid (Jakobsson et al., 2020) and high-resolution sub-bottom profiles (CHIRP), one giant piston core and three gravity cores (4.61 to 18 m long). We present results from the multi-proxy analysis of the sediment cores, including lithostratigraphy, physical properties, grain-size distribution, XRF core scanning data, and radiocarbon dates.

The morphology of the Kvitøya Trough-Mouth Fan is generally smooth, with furrows 500 m wide and 200-500 m deep stretching from the shelf edge at around 250 m water depth to at least 3000 m water depth into the Arctic Ocean. The morphology of the continental slope east and west of the trough-mouth fan is smooth in the upper parts, and characterized by 3-5 km wide and 200-500 m deep channels and canyons cutting into the slope from a water depth of around 1000 to 3000 m.

The observations from the bathymetric data show that the trough-mouth fan buries channels and canyons, smoothing the morphology of the continental slope. The furrows are likely erosional features resulting from downslope activity such as debris flows and turbidity currents. In the inter-fan areas to the east and west, we interpret that the uppermost smooth morphology results from suspension fallout of sediments from the ocean currents flowing along-slope, indicating that these accumulations are contourites. The rugged topography further downslope possibly represents channel and canyon systems that are only partially buried, likely due to reduced influence from ocean currents at greater water depths. Analysis of the cores provides insight on the sediment properties of the contourites, debris flows, and turbidites, and radiocarbon dates shed light on the interplay and timing of the ocean current regime and the glacial dynamics.

 

Jakobsson, M., Mayer, L.A., Bringensparr, C. et al. The International Bathymetric Chart of the Arctic Ocean Version 4.0. Sci Data 7, 176 (2020). https://doi.org/10.1038/s41597-020-0520-9

How to cite: Kollsgård, C. T., Laberg, J. S., Rydningen, T. A., Forwick, M., Husum, K., and Lasabuda, A.: Sedimentary processes on the continental slope north of Kvitøya (northern Barents Sea) – preliminary results from regional bathymetry and sediment cores, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15494, https://doi.org/10.5194/egusphere-egu21-15494, 2021.

16:11–16:13
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EGU21-10201
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ECS
Liubov Kireenko, Nina Kozina, and Anna Tikhonova

Holocene and Pleistocene benthic foraminifera assemblage patterns studied from 63 samples in sediment core AMK-5890 collected from Iceland's western slope in the Denmark Strait during the 71th cruise of research vessel"Academic Mstislav Keldysh" in 2018 (Novigatsky A.N, et al., 2018). Core were sampled at 1 cm interval from Holocene and 5 cm from Pleistocene and washed through a 63 micron sieve.

In the first complex of deposits represented by Holocene deposits the total benthic foraminifera abundance reaches highest values 35 000 – 60 000 individuals/g of dry sediment (ind/g of dry sed). In the lower part of the complex, abundance decreases to 10,000 ind/g of dry sed. The species diversity ranges from 25 to 35 species in the sample. Trifarina angulosa is the dominant species (about 60%). The species Cibicides lobatulus is subdominant (25-30%) in the Holocene community which lived in areas with increased hydrodynamic characteristics (Lorenz, 2005). The small group benthic foraminifera (from 2 to 15%) includes Atlantic and boreal species Cassidulina laevigata, Cassidulina neoteretis and Uvigerina peregrina (Sejrup et al, 2004). This database of distribution and ecology of benthic foraminifera indicated that in Holocene favorable living environment (positive bottom temperatures and salinity, close to modern sea), increased productivity and wide influence of Atlantic waters to the north existed. The lower part of complex reflects the epoch of deglaciation.

There are short changes in all measures at the boundary of Holocene and Pleistocene: total benthic foraminifera abundance (1000-400 ind/g of dry sed) and species diversity (<20 species) decreases, and species assemblage is almost completely changes. It allows to identify the second complex that characterizes the transition to glacial deposits. At the top of the glacial complex, the peak of occurrence of Cibicidoides wuellerstorfi (about 25%) associates with a decrease in the influence of meltwater and active hydrodynamics (Struck, 2007). The glacial assemblage consists of two dominant species C. lobatulus (about 35%) and Cassidulina obusta (about 40%). Also, there are Cassidulina reniforme, Elphidium clavatum and Nonion labradoricum, which prefer cold waters and Arctic environmental conditions with the presence of ice cover.

 Acknowledgments: Preparation, processing of samples and micropaleontological analysis was funded by RFBR, project number 20-35-90093. The expedition studies was funded by RPF, project number 14-50-00095, the primary lithological-mineralogical and geochemical studies was funded of the State assignment of the FANO of Russia (№ 0149-2019-0007).

How to cite: Kireenko, L., Kozina, N., and Tikhonova, A.: Distribution and paleoecology of benthic foraminifera of Denmark Strait in Holocene and late Pleistocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10201, https://doi.org/10.5194/egusphere-egu21-10201, 2021.

16:13–16:15
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EGU21-10875
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ECS
Mengli Cao, Jens Hefter, Ralf Tiedemann, Lester Lembke-Jene, and Gesine Mollenhauer

Anthropogenic climate change has profound impacts on Arctic temperatures, with consequences for Arctic ecosystems and landscapes, and the stability of organic-rich permafrost deposits. When mobilized, these permafrost deposits might release vast amounts of greenhouse gases. We use periods of past rapid warming in the high latitudes as analogues to study the ecological changes and effects on permafrost stability under climate change. We used marine sediment cores from the Bering and Okhotsk Sea continental margins, off the mouths of the Yukon and Amur rivers, to study two types of terrigenous biomarkers, which trace different terrestrial organic carbon (OC) components and transport pathways, and cover the early deglaciation to the early Holocene. The Yukon basin remains within the permafrost-affected region today, whereas the Amur basin changed from being subject to complete permafrost cover during the last glacial to permafrost-free conditions today. 

Vascular plant-derived lignin phenols were analyzed and compared to published n-alkane content data. The carbon- and sediment-normalized contents of the vanillyl phenols (V), syringyl phenols (S), and cinnamyl phenols (C) phenols (Λ8 and Σ8) reflect the content of lignin dominantly transported by river runoff. The C/V and S/V ratios serve to distinguish between woody and non-woody tissues of angiosperms and gymnosperms. The acid to aldehyde ratios of V and S phenols ((Ad/Al)V and (Ad/Al)S) indicate the degree of lignin degradation. In addition, the ratio of 3,5-dihydroxybenzoic acid to V (3,5Bd/V) likely reflects the wetland extent, while lignin reflects primarily transportation into the marine sediment via surface runoff. In contrast, the n-alkane contents represent primarily terrigenous organic matter eroded from deeper deposits and a second marker for wetland extent via the Paq index. Lignin and n-alkane mass accumulation rates (MAR) can thus be used to reconstruct the mobilization of different carbon pools and the relative timing of the processes leading to their export to the ocean.

The MAR of biomarkers and the wetland indicators 3,5 Bd/V and Paq start to increase in the Bering Sea sediment during the early deglaciation (19-14.6 ka BP), while no obvious change in lignin MAR in the Okhotsk Sea occurred during this time. We observe distinct peaks of mass accumulation rates, wetland indices and indicators for degradation of lignin (Ad/Al) in both sediment cores during the warm Bølling-Allerød (12.9-14.6 ka BP) and Pre-Boreal (9-11.5 ka BP) intervals, and during the Younger Dryas cold spell (11.5-12.9 ka BP). In contrast, in the Okhotsk Sea, the ratios of S/V and C/V did not change before the Preboreal. 

Our biomarker data suggest that the permafrost in the Yukon basin may have started to be remobilized by inland warming leading to wetland development in the early deglaciation, while the onset of permafrost degradation in the Amur basin occurred during the Preboreal.

How to cite: Cao, M., Hefter, J., Tiedemann, R., Lembke-Jene, L., and Mollenhauer, G.: Deglacial records of terrigenous organic matter accumulation off the Yukon and Amur rivers using lignin phenols and long-chain n-alkanes as biomarkers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10875, https://doi.org/10.5194/egusphere-egu21-10875, 2021.

16:15–16:17
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EGU21-14641
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ECS
Maaike Zwier, Anne Bjune, and Willem van der Bilt

The Southern Hemisphere Westerly Winds play a major role in the global climate system. By driving circulation in the Southern Ocean and its subsequent effect on the upwelling of carbon-rich deep water, the Westerlies affect the oceans ability to take up atmospheric CO2. Furthermore, by impacting temperature conditions and moisture availability, the Westerlies act as a first-order control on local environmental conditions. Uncovering long term natural climatic variability in the sub-Antarctic is therefore crucial to understand how the global system might react under future climate changes. Due to the lack of land mass on the Southern Hemisphere, sub-Antarctic islands are essential for studying climate variability in this region; terrestrial records provide valuable insights into both local and regional surface climate conditions. We use a pollen record from Lake Diamond to provide detailed reconstructions of vegetation and climate on sub-Antarctic South Georgia for the last ~9900 years. Westerly Wind strength and position is inferred from long-distance transport of pollen from South America, Africa, and New Zealand. Additionally, changes in relative pollen abundance of native taxa occupying either upland (cold) or lowland (warm) environments are used to infer local climatic variation, supported by additional sedimentological proxies. On South Georgia we find long-distance transported pollen from several South American taxa, mainly Nothofagus, Ephedra and Asteraceae. They show a general increase in abundance throughout the Holocene, with peak influx between 2800 and 1500 cal yr BP, most likely caused by changes in the strength of the Southern Hemisphere Westerly Winds. In both our record and others, this interval is seen as the end of the Neoglacial period.

How to cite: Zwier, M., Bjune, A., and van der Bilt, W.: Southern Hemisphere Westerly Winds and Holocene climate variability on sub-Antarctic South Georgia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14641, https://doi.org/10.5194/egusphere-egu21-14641, 2021.

16:17–16:19
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EGU21-3651
Syed Azharuddin, Jinho Ahn, Yeongjun Ryu, and Ed Brook

Nitrous oxide (N2O) is an important greenhouse gas with sources that respond to the biogeochemical processes on land and ocean. The major sources of atmospheric N2O are nitrification and denitrification occurring in terrestrial soils and the ocean. Here we present a new high-resolution atmospheric N2O record obtained from South Pole Ice (SPICE) core site covering the Mid- to Late Holocene (since ~5.5 ka). The N2O analysis was performed in a specialised wet extraction facility installed at Seoul National University that used small ice samples (<20 g) to yield a high precision (average standard deviation of ~1ppb) record. The new N2O data agree well with existing records on the millennial scale and reveal new details on the multi-centennial scale. Our results show a progressive increase in atmospheric N2O during 5.5 to 3.2 ka which correlates well with the increase of marine denitrification around the Arabian Sea (AS) and Peru-Chile Margin (PCM) as well as Indian monsoon precipitation around the same period. A local minimum in N2O is observed around 2.8 ka, possibly related to a sudden decrease in Western Tropical South (WTS) Pacific sea surface temperature and increased La-Nina like conditions which may have supressed denitrification along PCM. These conditions may have further influenced the monsoons and reduced denitrification in land soils. Our record also shows a local N2O maximum around 2.2 ka which may correspond to relaxed La-Nina like conditions around WTS Pacific. Subsequently, the N2O further dropped to attain a pronounced minimum around 1.4 ka. Similar N2O minima are also observed in Styx (Antarctica) and  NEEM (Greenland) ice core records, demonstrating the robustness of the signals.

How to cite: Azharuddin, S., Ahn, J., Ryu, Y., and Brook, E.: Climate related variations in atmospheric nitrous oxide concentration during the Mid- to Late Holocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3651, https://doi.org/10.5194/egusphere-egu21-3651, 2021.

16:19–17:00