7. Climate

7.1. Climate from the Palaeogene to the Anthropocene – bridging timescales and approaches

                       ORAL PRESENTATIONS                    

Miocene glacial events and their influence on lithology distribution within the Danish North Sea area

Karen Dybkjær¹, Erik Skovbjerg Rasmussen¹ and Emma Sheldon^1
1The Geological Survey of Denmark and Greenland (GEUS)
During the Miocene, episodes of global cooling caused repeated, rapid, eustatic sea-level falls in the order of 25-50 m. In proximal settings within the North Sea Basin (onshore Denmark) these sea-level variations affected the distribution of lithologies with deposition of well-sorted delta sand or basin floor fans during the glacial events. These sand deposits form important subsurface aquifers in the western part of Denmark (Jylland).

Based on the dinocyst zonation of Dybkjær & Piasecki (2010) it has been possible to correlate three successive, prograding, fluvio-deltaic sand bodies with the early Miocene glacial events; Mi-1a, Mi-1b and Mi-2 of Miller et al. (1991). In more distal areas (offshore Denmark), the glacial events did not have any (significant) effect on the lithology, but can be recognised by increased abundances of freshwater algae and diatoms.

New data from the uppermost Miocene (upper Tortonian and Messinian) have led to the recognition of some of the climatic events known from this time-interval – and to related sand deposits. A Messinian glacial event, probably correlatable with the Mediterranean “Messinian salinity crisis”, was recently recognised in the Nora-1 well. This event correlates with a prograding depositional system and incision, indicating a sea-level fall of 70-80m (Møller et al. 2009).

Identification and correlation of the Miocene glacial events are important for understanding lithology distribution and can be further used for prediction of potential reservoir sands.

References

Dybkjær, K., Piasecki, S. 2010: Neogene dinocyst zonation in the eastern North Sea Basin, Denmark. Review of Palaeobotany and Palynology 161, 1–29.

Miller, K.G., Wright, J.D. & Fairbanks, R.G. 1991: Unlocking the Ice House: Oligocene–Miocene oxygen istotopes eustacy and margin erosion. Journal of Geophysical Research 96, 6829–6848.

Møller, L.K., Rasmussen & E.S., Clausen, O.R. 2009: Clinoform migration patterns of a Late Miocene delta complex in the Danish Central Graben; implications for relative sea-level changes. In: Henriksen, S. et al. (eds.): Special Issue – Trajectory Analysis in Stratigraphy. Basin Research 21, 704–720.

Eocene bryozoan biota vs climatic events (Seymour Island, West Antarctica)

Urszula Hara^1
1Polish Geological Institute-National Research Institute
The earliest Antarctic late early Eocene bryozoans of the La Meseta Fm., Seymour Island are connected with the major phase of cheilostome evolution; clear preponderance of cerioporoidean cyclostomes along with numerous microporoideans. The internal moulds of the loose, small zooecia in the lowermost part of this formation, includes the cheilostomes of Beanidae, Catenicellidae, Savignyellidae, which nowdays are widely distributed in the tropical-warm, temperate latitudes in the shallow-water settings (Hara 2015). 90% of taxa reveal the multilamellar growth-form connected with a short-term episode in the lower part of Telm1, during their long in situ evolution. The bryozoans from the (Telm4-5) are the microporoideans and the first lunulitiform (free-living) bryozoans of Lunulites and Otionellina, ever reported from Antarctica. Their disc-shaped colonies are today indicative of tropics and subtropics but skeletal mineralogy is also important in view of the transition of such bryozoans from calcitic to bimineralic to aragonitic on the K/T boundary. Recent, free-living lunulitiforms occur in warm, shallow-shelf conditions, in temperatures of 10-29˚ C, on coarse, sandy to muddy bottom with low to moderate deposition in fairly high velocity currents. Contrary to that, the bryozoans recognized in the upper part of the formation (Telm7) are composed of the impoverished bryozoan biota of scarse lepraliomorphs and fragmented cyclostomes, which are accompanied by the crinoids and brachiopods, gadiform fish remains, penguin bones and whales. The well-documented distribution of the bryozoans in the stratigraphical profile of the La Meseta Formation illustrates the climatic changes connected with the EECO, MECO as well as the EOT.

References
Hara U. Polish Polar Research, 36, 25-49 (2015).

Tracers of sea ice, primary production and meltwater inputs: distribution of biogenic proxies in a High Arctic fjord system, Northeast Greenland

Maija Heikkilä¹, Kaarina Weckström¹, Mikael Sejr², Petra Tallberg¹, Guillaume Massé³, Audrey Limoges⁴ and Sofia Ribeiro^5
1University of Helsinki, ²Aarhus University, ³Université Laval, ⁴University of New Brunswick, ⁵GEUS
The coastal ecosystems of Northeast Greenland are vulnerable to the enhanced melt of continental and sea ice as a result climate warming, however little is known of past ecosystem changes in the region. We present the distribution of an array biogenic proxies (dinoflagellate cysts, pollen, diatoms, biogenic silica, C/N and their isotopes, IP25, HBI III) from a transect of 13 surface-sediment samples from Young Sound-Tyrolerfjord, NE Greenland (74°N), in order to assess their relevance as tracers of past changes in sea ice, primary production and terrigenous inputs. The Greenland Ecosystem Monitoring program provides a unique High Arctic time-series of hydrological, atmospheric and biological measurements from the fjord since the mid-1990s, against which the sediment signatures can be compared. The proxy data show an overall good agreement with the monitoring data. Organic carbon contents, diatom production, HBI III and heterotrophic dinoflagellate cyst abundance were higher in the outer fjord, where turbidity is lower, salinity higher and waters more nutrient-rich compared to the inner fjord. Conversely, in the inner fjord, these production proxies follow an opposite pattern. The seasonal sea-ice proxy IP25 and sea-ice-dwelling taxa are present in varying abundances, which reflects the seasonal character of the sea-ice cycle together with species-specific habitat preferences of these taxa. Our results support the notion that future warming and freshening will likely have a negative impact on primary productivity and organic matter sequestration. This implication may be assessed by reconstructing changes during past warm periods using the new sediment core records from the area.

Investigating phase-relationships between ice margin instabilities and oceanographic conditions in Baffin Bay during the last deglaciation and early Holocene

Rebecca Jackson¹, Anne de Vernal², Marit-Solveig Seidenkrantz³, Anders Carlson⁴, Claude Hillaire-Marcel² and Michal Kucera^5
1Geological Survey of Denmark and Greenland (GEUS) and MARUM / Universität Bremen, ²Université du Québec à Montréal, ³Aarhus University, ⁴Oregon State University, ⁵MARUM / Universität Bremen
Freshwater forcing from Northern Hemisphere ice sheets during the last deglaciation likely played an important role in modulating deep-water formation, and thus global climate. The mechanisms of ice margin instabilities and its exact phase relationship with climatic change, such as paleoceanographic variation, are not fully understood.

Baffin Bay represents an important conduit for freshwater transported into the Labrador Sea, released from the Greenland, Innuitian and Laurentide ice sheets. We take advantage of two radiocarbon-dated marine sediment cores from central Baffin Bay that span the last deglaciation and early Holocene (ca. 17-10 kyr BP). These archives provide co-registered records of detrital input from the surrounding ice sheets and sufficient biogenic carbonate for the reconstruction of paleoceanographic conditions.

Two distinct detrital carbonate-rich layers, originating from ice sheets surrounding northern Baffin Bay and dated at 14.2-13.7 kyr BP and 12.7-11 kyr BP, indicate that ice sheet retreat events occurred during both interstadial and stadial periods and were asynchronous with Heinrich events. Despite previous evidence for an oceanic trigger of these events, records here indicate change in deep water properties and stronger inflow of warmer Atlantic water via the West Greenland Current postdated the first event. The second event was not preceded by any major change in oceanographic conditions but likely a response to a combination of a consistently stronger West Greenland Current as well as climatic forcing. Results suggest that there were different mechanisms responsible for ice margin instability events in Baffin Bay during the last deglaciation and early Holocene.

Paleoclimate and paleoceanography data based on isotope ¹³C and ¹⁸O measurements with the new measurement tool

Magda Mandic^1
1ThermoFisher Scientific, Bremen, Germany
The contents of stable carbon and oxygen isotopes, 13C and 18O, in secondary precipitated carbonates and sediments can provide important information about paleoclimate conditions of the area. Environmental factors like temperature, concentration of atmospheric CO2, chemical composition of water, isotopic composition of water, CO2 and deposited are influence the isotopic composition. For many decades different instrumental methods involving generations of the isotope ratio mass spectrometers with different periphery units for sample preparation, have provided scientifically required high precision, and high throughput of samples for variety of different applications in paleoclimate reconstructions.

In this work we will present measurements of δ¹³C and δ¹⁸O from solid carbonate samples, DIC and δ¹⁸O of water with new laser technology, with case study where Delta Ray was in the field (Karstic cave) performing for more than a year collecting high frequency data on δ¹³C and δ¹⁸O .

We have demonstrated usage of a Thermo Scientific™ Delta Ray™ IRIS with URI Connect on certified reference materials and confirmed the high achievable accuracy and a precision better then <0.1‰ for both δ¹³C and δ¹⁸O, in the laboratory or the field with same precision and throughput of samples. With equilibration method for determination of δ¹⁸O in water samples, which we present in this work, achieved repeatability and accuracy are 0.12‰ and 0.68‰ respectively.

Applying new methods for measurement of the samples important for paleoclimate investigation one can come to the results already in the field.

Deglacial – Holocene paleoceanography of Herald Canyon, Chukchi Sea

Christof Pearce¹, Matt O’Regan², Jayne Rattray³, David Hutchinson², Tom Cronin⁴, Natalia Barrientos², Helen Coxall², Igor Semiletov⁵ and Martin Jakobsson^2
1Department of Geoscience, Aarhus University, ²Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm Unversity, Stockh, ³Energy Bioengineering and Geomicrobiology Research Group, University of Calgary, Calgary, Alberta, C, ⁴U.S. Geological Survey, Reston VA, USA, ⁵Tomsk National Research Polytechnic University, Tomsk, Russia
The Herald Canyon is a local depression across the Chukchi Sea shelf, and acts as one of the main pathways for Pacific Water to the Arctic Ocean after entering through the Bering Strait. We analyzed sediment samples of two piston cores from Herald Canyon, collected during the 2014 SWERUS-C3 Arctic Ocean Expedition. Core 2-PC1 from the shallow (57 mwd) flank contains the late Holocene at high resolution (> 2m/kyr), while Core 4-PC1 from the central canyon (120 mwd) extends back in time to ~13 ka. The lower part of 4-PC1 contains an abrupt increase in biogenic silica and a carbon isotopic shift towards more marine values, which are interpreted as the signal of the Bering Land Bridge flooding and water exchange through the Bering Strait (Jakobsson et al., 2017). This major oceanic event is dated to ~11ka and thus occurs in the very early Holocene, contrary to most previous earlier estimates suggesting a Younger Dryas age for the opening of the gateway. The chronology of Core 2-PC1 is based on 17 radiocarbon dates and the 3.6 ka Aniakchak CFE II tephra, which is used as an absolute age marker to calculate the marine radiocarbon reservoir age (Pearce et al., 2017). Analysis of sea ice biomarkers and phytosterols indicate relatively stable sea ice conditions throughout the entire late Holocene, however ending with an abrupt increase of phytoplankton sterols in the very top of both sediment sequences which corresponds to the rapid ice retreat observed in recent decades.

References
Jakobsson, M., Pearce, C., Cronin, T. M., Backman, J., Anderson, L. G., Barrientos, N., Björk, G., Coxall, H., de Boer, A., Mayer, L. A., Mörth, C.-M., Nilsson, J., Rattray, J. E., Stranne, C., Semiletov, I. and O’Regan, M.: Post-glacial flooding of the Bering Land Bridge dated to 11 cal ka BP based on new geophysical and sediment records, Clim Past, 13(8), 991–1005, doi:10.5194/cp-13-991-2017, 2017.

Pearce, C., Varhelyi, A., Wastegård, S., Muschitiello, F., Barrientos, N., O’Regan, M., Cronin, T. M., Gemery, L., Semiletov, I., Backman, J. and Jakobsson, M.: The 3.6 ka Aniakchak tephra in the Arctic Ocean: a constraint on the Holocene radiocarbon reservoir age in the Chukchi Sea, Clim Past, 13(4), 303–316, doi:10.5194/cp-13-303-2017, 2017.

Sea ice, marine productivity, and human settlement dynamics in the North Water Polynya-Qaanaaq region (NW Greenland) during the late Holocene

Sofia Ribeiro¹, Audrey Limoges², Martin Nissen³, Steffen Olsen⁴, Naja Mikkelsen¹ and Guillaume Massé^5
1Geological Survey of Denmark and Greenland, ²University of New Brunswick, Canada, ³Danish Geodata Agency, ⁴Danish Meteorological Institute, ⁵TAKUVIK, Laval University, Canada
The North Water (NOW) is the largest polynya in the Arctic, a large extension of recurrent open waters surrounded by sea ice, in northern Baffin Bay. This polynya is the most productive ecosystem north of the polar circle, and its living resources have sustained human settlements in both Arctic Canada and Greenland for millennia. Within the framework of the ICE-ARC project: Ice, Climate and Economics – Arctic Research on Change (EU FP7, http://www.ice-arc.eu/), we aim to reconstruct changes in climate, sea ice, and marine resources in the NOW region using an integrated approach combining proxy records from marine sediment cores, remote sensing of sea ice, and historical data. We will present the latest results from a multi-proxy investigation of sediment core records from the high Arctic Inglefield fjord (Qaanaaq) and from a new 5,4 m high-resolution sediment core from the NOW, spanning the last ca. 3500 years. Our proxy results will be discussed in the light of historical and archaeological sources in order to identify possible links between past changes in climate and marine resource availability in this high arctic “oasis” with known cultural transitions in Greenland.

Holocene temperature trends in the Northern Hemisphere high latitudes – model-data comparisons

Heikki Seppä¹, Yurui Zhang¹, Hans Renssen² and Paul J. Valdes^3
1Department of Geosciences and Geography, University of Helsinki, Finland, ²Department of Natural Sciences and Environmental Studies, University College of Southeast Norway, ³School of Geographical Sciences, University of Bristol, UK
Regional differences in Holocene climate trends in the Northern Hemisphere high latitudes are primarily determined by orbital-scale insolation variations and melting ice sheets. Previous inter-model comparisons have revealed that multi-simulation consistencies vary spatially. We compared multiple model results with proxy-based reconstructions in Fennoscandia, Greenland, north Canada, Alaska and Siberia. Our model-data comparisons reveal that data and models generally agree in Fennoscandia, Greenland and Canada, with the early-Holocene warming and subsequent gradual decrease to 0 ka BP. In Fennoscandia, simulations and pollen data suggest a 2.0°C warming by 8 ka, but this is less expressed in chironomid data. In Canada, a strong early-Holocene warming is suggested by both the simulations and pollen results. In Greenland, the magnitude of early-Holocene warming ranges from 6.0°C in simulations to 8.0°C in δ¹⁸O-based temperature reconstructions. Simulated and reconstructed temperatures are mismatched in Alaska. Pollen data suggest a strong early-Holocene warming, while the simulations indicate constant Holocene cooling, and chironomid data show a stable trend. Meanwhile, a high frequency of Alaskan peatland initiation before 9 ka can reflect either high temperature, high soil moisture or large seasonality. In high-latitude Siberia, the simulations and proxy data depict high Holocene temperatures, but the signals are noisy owing to a large spread in the simulations and between pollen and chironomid results. On the whole, the Holocene climate trends in most regions (Fennoscandia, Greenland and Canada) are well established and understood, but important questions regarding the Holocene temperature change and mechanisms remain for Alaska and Siberia.

An evaluation of IRD as a proxy for glacier change: results from Upernavik Isfjord.

Flor Vermassen¹, David Wangner¹, Laurence Dyke¹, Amalie Cordua², Sabine Schmidt³, Kurt Kjær⁴ and Camilla Andresen^1
1Geological Survey of Denmark and Greenland, København K, Denmark, ²Institüt für Geologie, University of Hamburg, Hamburg, Germany, ³EPOC, UMR5805, University of Bordeaux, Pessac, France, ⁴Natural History Museum of Denmark, København K, Denmark
The sudden increase of mass loss of the Greenland ice sheet at the onset of this century has spurred investigations regarding ice-discharge at marine terminating glaciers, a process that is thought to contribute up to 50% of Greenland’s total mass loss. To evaluate whether this recent increase of mass loss was an outstanding event or occurs, centennial or millennial timescales, sediment cores in fjords with marine-terminating glaciers can be investigated since they constitute high-resolution sedimentological records that reflect past changes in glacier stability.

In glacimarine fjords, sand-sized sediment is predominantly transported and deposited by melting of sediment-laden icebergs. Therefore, ice-rafting can be reconstructed by quantifying the downcore variations in sand content. Even though the interpretation of IRD as a proxy for glacier stability (iceberg production) is common, many glaciological and sedimentological complexities are involved in interpreting IRD records. A better understanding of those complexities can be achieved by investigating the relationship between IRD variability and recent observations of climatic and glaciological changes.

In this study, we quantify the IRD variability of four short cores (~2 m) from Upernavik Isfjord, West Greenland. Ice-rafting is reconstructed back to 1930 and compared to climatic measurements and a record of glacier terminus position changes, derived from historical expeditions and satellite imagery. We discuss spatial trends of ice-rafting and the different processes that modulate its variability. This information aids the general understanding and interpretation of IRD in paleoceanographic research.

A 2000-year record of ocean influence on Jakobshavn Isbræ calving activity, based on marine sediment cores

David J. Wangner¹, Anne Jennings², Flor Vermassen¹, Laurence Dyke¹, Kelly A. Hogan³, Kurt H. Kjær⁴ and Camilla S.Andresen^1
1GEUS – Geological survey of Greenland and Denmark

²INSTRAAR – Institute of Arctic and Alpine Research, Boulder, Colorado

³British Antarctic Survey, Cambridge, United Kingdom

⁴Natural History Museum of Denmark, Copenhagen, Denmark

The Greenland Ice Sheet has experienced significant mass loss in recent years. A substantial component of this is attributable to the retreat of marine-terminating outlet glaciers, which lost mass through increased calving and meltwater discharge. Jakobshavn Isbræ is the most productive marine-terminating glacier in Greenland, yet relatively little is known about its history before the first instrumental observations of local climatic conditions ~140 years ago.

Three marine sediment cores were collected from locations north-west to the mouth of Jakobshavn Isfjord in Disko Bay. These cores were analyzed to reconstruct changes in glacier behavior in response to past climatic and oceanographic changes; this provides context against which to assess the significance of recent changes. The sediments deposited at this site reflect oceanographic and climatic changes as well as the discharge of ice rafted debris from Jakobshavn Isbræ.

Radiocarbon dates of plant material combined with a 210Pb profile indicates that the cores cover a time span of ~2000 years. X-Ray images and a high-resolution grain size analyses reveal clear changes in the sedimentation regimes over time. The influence of ocean water temperature derived from benthic foraminifera record as well as the impact of a floating glacier tongue on the sediment output of Jakobshavn Isbræ is discussed.

                       POSTER PRESENTATIONS                    

Holocene oceanographic variability in coastal southeast Greenland

Laurence M. Dyke¹, Camilla S. Andresen¹, Marit-Solveig Seidenkrantz², David J. Wangner¹ and Flor Vermassen^1
1GEUS, Department of Glaciology and Climate, Øster Voldgade 10, DK-1350, København K, Denmark., ²Centre for Past Climate Studies, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000, Aarhus C, Denma
The coastal waters of southeast Greenland are the interface between the Atlantic Ocean and the vast Greenland Ice Sheet. Oceanographic processes have been implicated in the recent loss of ice from marine-terminating glaciers across the region. Ocean processes here are also important as they modulate global thermohaline circulation; this occurs both through the influx of meltwater from the ice sheet, and through mixing of water masses on the continental shelf. Understanding how these processes have varied in the past is crucial for predicting future behavior.

We present two complementary sediment core records of oceanographic variability from the continental shelf of central southeast Greenland. Radiocarbon and lead-210 dating demonstrates that these cores cover the last 5000 and 9000 years respectively. We analysed benthic and planktonic foraminifera to reconstruct variability in water masses at both the surface and seabed. We use independent, but complimentary, measurements of sortable silt to reconstruct the strength of ocean circulation at the sea bed and build a holistic picture of oceanographic conditions from the mid-Holocene to the present.

Combining our new results with records from further north in the region yields a unique resource with which to assess the variability of oceanic currents at a regional scale. We use this to examine the factors that have driven the oceanographic development of the region. We then identify how oceanographic changes in southeast Greenland have influenced oceanic and climatic conditions across the wider North Atlantic region.

Late Holocene paleoclimatic and palaeoceanographic development of the eastern Baffin Bay area

Katrine Elnegaard Hansen¹, Isabelle Billy², Pierre Francus³, Eleanor Georgiadis², Jacques Giraudeau², Philippe Martinez², Guillaume St. Onge⁴, Guillaume Massé⁵ and Marit-Solveig Seidenkrantz^1
1Aarhus University, ²University of Bordeaux, ³Institut National de la Recherche Scientifique, ⁴Université du Québec à Rimouski, ⁵Université Laval
A 738 m long marine sediment core, AMD14-204 CasqC, was retrieved from the eastern Baffin Bay during a research cruise on board CCGS Amundsen in 2014. The study of benthic foraminiferal assemblages, XRF core scan data and CT-scans supported by radiocarbon dating of this core allows the reconstruction of the palaeoceanography and palaeoclimate of the eastern Baffin Bay during the last ~4800 cal. BP. Several major changes in oceanographic conditions and climate are reconstructed during this time interval in the eastern Baffin Bay area, which also influenced the nearby Upernavik Isstrøm glacier. Our study reveals that relatively warmer subsurface waters prevailed during the final phase of the warmer ‘Holocene Thermal Maximum’, linked to the entrainment of relatively warm Irminger Current (IC) water into the West Greenland Current (WGC). This relatively strong advection of IC may also have resulted in relatively strong melting of the Upernavik Isstrøm glacier, causing influx of meltwater to the area. However, at ~3100 cal. BP, the onset of the Neoglaciation, the area experienced an abrupt transition to dominantly agglutinated benthic species, indicating enhanced carbonate dissolution. This was likely in part caused by a reduction of the influx of IC water and increased entrainment of the East Greenland Current into the WGC. The reduction of IC water influx also allowed increased influx of the cold, corrosive Baffin Bay Deep Water. These cold subsurface water conditions persisted throughout the late Holocene, only interrupted by short-lived climate fluctuations superimposed on this cooling trend.

Spatiotemporal differences in varve structure and preservation over the last 200 years in Lake Lehmilampi, Eastern Finland

Sarianna Salminen¹, Eeva Haltia¹ and Timo Saarinen^1
1University of Turku
A wide variety of studies considering varved lake sediments as a climate proxy have been performed in Finnish lakes. Nevertheless, none of them is considering spatial distribution of varves within an entire lake, although it is essential to acquire data not only from the deepest point of a lake but also from more shallow areas. The distribution of varves within the entire lake has only been studied in a few lakes in Europe (Jenny et al. 2013).

In previous work the changes in the presence of varves within the whole lake during the past 200 years, arriving at a conclusion in changes in hypolimnetic hypoxia (2mg/l (Roberts et al. 2009)), were investigated. As a result the extent of hypolimnetic hypoxia has clearly changed during the past 200 years in the lake due to climate.

In this study the differences in sediment composition in varved and non-varved sections are studied with SEM (scanning electron microscopy), μXRF (X-ray fluorescence) and X-ray radiography to investigate the factors influencing varve formation in the lake. The aim of this study is to investigate spatiotemporal differences in varve structure, formation and preservation within the whole lake.

References
Giguet-Covex, C., Arnaud, F., Poulenard, J., Enters, D., reyss, J.-L., Millet, L., Lazzaroto, J. & Vidal, O. 2010. Sedimentological and geochemical records of past trophic state and hypolimnetic anoxia in large, hard-water Lake Bourget, French Alps. J Paleolimnol 43: 171.

Jenny, J-P. et al. 2013. A spatiotemporal investigation of varved sediments highlights the dynamics of hypolimnetic hypoxia in a large hard-water lake over the last 150 years. Limnol. Oceanogr., 58(4), 2013, 1395–1408.

Roberts, J., Höök, T., Ludsin, S., Pothoven, S., Vanderploeg, H. & Brandt,S. 2009. Effects of hypolimnetic hypoxia on foraging and distributions of Lake Erie yellow perch. Journal of Experimental Marine Biology and Ecology. S132–S142.