Christoph Vogt

The Last Deglaciation Event in the Eastern Central Arctic Ocean

Oxygen isotope records of cores from the central Arctic Ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15.7 thousand years ago (16,650 calendar years B.C.). The almost parallel trends of the isotope records from the Arctic Ocean, the Fram Strait, and the east Greenland continental margin suggest contemporaneous variations of the Eurasian Arctic and Greenland (Laurentide) ice sheets or increased export of low-saline waters from the Arctic within the East Greenland Current during the last deglaciation. On the basis of isotope and carbon data, the modern surface- and deep-water characteristics and seasonally open-ice conditions with increased surface-water productivity were established in the central Arctic at the end of Termination lb about 7.2 thousand years ago or 6,000 calendar years B.C.).

A multiproxy approach to reconstruct the environmental changes along the Eurasian continental margin over the last 150 000 years

Abstract Sediment cores located along the Eurasian continental margin (Arctic Ocean) have been studied to reconstruct the environmental changes in terms of waxing and waning of the Barents/Kara Sea ice-sheets, Atlantic water inflow, and sea-ice distribution over the last 150 kyr. The stratigraphy of the cores is based on stable oxygen isotopes, AMS 14 C , and paleomagnetic data. We studied variations in marine and terrigenous input by a multiproxy approach, involving direct comparison of sedimentological and organo-geochemical data. Extensive episodes of northern Barents Sea ice-sheet growth during marine isotope stages (MIS) 6 and 2 have been supported by, at least, subsurface Atlantic water inflow, moisture-bearing storms, low summer insolation, and minimal calving of ice. Ice advance during MIS 4 was probably restricted to the shallow shelf. Between MIS 4 and MIS 2, large ice-sheet fluctuations correspond to contemporary Laurentide surging events and indicate short-term climatic changes in the Arctic Ocean as has been recorded in lower latitudes. In contrast, in low precipitation areas in eastern Eurasia, glacial activity was rather limited. Only distinct ice-rafted debris (IRD) input during Termination II and early MIS 3 reflects severe glaciations on the northern Severnaya Semlya margin during MIS 6 and MIS 4. We conclude that (1) oscillations of ice-sheets are less frequent along the eastern Eurasian margin than in areas with continuous moisture supply like the western Eurasian margins and that (2) major fluctuations of the Kara Sea ice-sheet during the last 150 kyr apparently followed the major interglacial/glacial MIS 5/4 and MIS 7/6 transitions rather than the precession (23 kyr) and the tilt (41 kyr) cyclicity of the Earths orbit as observed for the Scandinavian (SIS) and the Svalbard ice-sheets, respectively [Mangerud, J., Jansen, E., Landvik, J.Y., 1996. Late Cenozoic history of the Scandinavian and Barents Sea ice-sheets. In: Solheim, A., Riis, F., Elverhoi, A., Faleide, J.J., Jensen, L.N., Cloetingh, S. (Eds.), Impact of Glaciations on Basin Evolution: Data and Models from the Norwegian Margins and Adjacent Basins. Global and Planetary Chance, Special Issue 12, pp. 11-26.]. Surface and/or subsurface Atlantic water masses coupled with seasonally ice-free conditions penetrated continuously to at least the Franz Victoria Trough during the last 150 kyr. However, sustained periods of open water were largely restricted to substages 5.5, 5.1, and the Holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter (MOM). Signals of periodic open-water conditions along the northern margin of Severnaya Semlya are of less importance. Higher production of foraminifera, probably due to Atlantic water inflow occurred between 38 and 12 14 C kyr and corresponds to periodic Atlantic water advection penetrating into the Arctic Ocean. However, marine organic proxies indicate a continuous decrease of surface-water productivity from the western to the eastern Eurasian continental margin due to a more extensive sea-ice cover over the last 150 kyr.

Stable isotope stratigraphy, sedimentation rates, and salinity changes in the Latest Pleistocene to Holocene eastern central Arctic Ocean

A high-resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents, has been performed on undisturbed near-surface (0–40 cm) sediment sequences taken in the eastern Arctic Ocean during the international Arctic 91 Expedition. Based on the oxygen stable isotope records measured on Neogloboquadrina pachyderma (sin.) and AMS 14C dating, the upper 10 to 20 cm of the sediment sequences represent isotope stage 1, and the base of Termination I (15.7 ka) can be identified very well. Stage 1 sedimentation rates vary between 0.4 and >2.0 cm/kyr. In general, glacial stage 2 sedimentation rates are probably lower and vary between 0.4 and 0.7 cm/kyr. The glacial-interglacial shifts in δ18O values of N. pachyderma sin. may reach values of 1.3 to 2.5‰ indicating (1) that, in addition to the glacial-interglacial global ice-volume signal, changes in surface-water salinity have effected the isotope records and (2) that these salinity changes have varied laterally. Glacial-interglacial differences in salinity were small in the Lomonosov Ridge area (0–0.4‰) and relatively high in the Morris-Jesup-Rise area (up to 1.4‰). This implies that the supply of low-saline waters onto the Eurasian shelves and its further transport into the central Arctic Ocean via the Transpolar Drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central Arctic. On the Morris-Jesup-Rise, on the other hand, the glacial low-saline-water signal at that time was strongly reduced in comparison to the modern situation. At the glacial-interglacial stage 12 boundary, a strong meltwater signal is recorded in a sharp depletion in δ18O as well as δ13C. This central Arctic Ocean meltwater event can be correlated from the Makarov Basin through the Lomonosov Ridge and Amundsen Basin to the eastern Gakkel Ridge. The beginning of this event is AMS 14C dated at 15.7 ka, i.e., significantly older than the major decrease in the global ice-volume signal which occurs between 9 and 13.5 ka. Large amounts of freshwater/meltwater were probably supplied from the Eurasian continent due to the decay of the Barents-Sea-Ice-Sheet, causing this distinct early meltwater anomaly in the central Arctic Ocean. The extension of a well-oxygenated surface-near water mass in the Arctic Ocean and (at least seasonal) open-ice conditions and some increased bioproductivity were probably established at the end of Termination I, as indicated by the increase in δ13C to modern values as well as increased carbonate (i.e., foraminifers, coccoliths, ostracodes) and total organic carbon contents.

Detailed mineralogical evidence for two nearly identical glacial/deglacial cycles and Atlantic water advection to the Arctic Ocean during the last 90,000 years

Abstract Three cores recovered off the northwest of Svalbard were studied with respect to glacial/interglacial changes of clay and bulk mineralogy, lithology and organic geochemistry. The cores cover the Late Quaternary Marine Isotope Stages (MIS) 6–1 (ca. 170,000 years) and are located in the vicinity of the Polar Front which separates the warm Atlantic water of the Westspitsbergen Current and the cold Polar Water of the Transpolar Drift. Globally driven changes in the paleoenvironment like the variable advection of warm Atlantic water into the Arctic Ocean can be distinguished from regional events by means of source mineral signatures and organic geochemistry data. In particular, a combination of high organic carbon and low carbonate contents, high C/N-ratios, a particular lithology and a distinct bulk and clay mineral assemblage can be related to Svalbard ice sheet developments between 23,000 and 19,500 14 C years. This complex sediment pattern has been traced to the northwest of Spitsbergen as far north as 82°N. Additionally, the same signature has been recognized in detail in upper MIS 5 sediments. The striking similarity of the history of the Svalbard/Barents Sea Ice Sheet during the late and early/middle Weichselian is elaborated. Both sediment horizons are intercalated between biogenic calcite rich core sequences which contain the so-called “High Productivity Zones” or “Nordway Events” related to the increased advection of warm Atlantic water to the Arctic Ocean. This study provides further evidence that the meridional circulation pattern has been present during most of the Weichselian and that the ice cover was often reduced in the northeastern Fram Strait and above the Yermak Plateau. Our findings contradict the widely used reconstructions in modelling of the last glaciation cycle and reveal a much more dynamic system in the Fram Strait and southwestern Eurasian Basin of the Arctic Ocean.

A shift in heavy and clay mineral provenance indicates a middle Miocene onset of a perennial sea-ice cover in the Arctic Ocean

During the Arctic Coring Expedition (ACEX), a 428-m-thick sequence of Upper Cretaceous to Quaternary sediments was penetrated. The mineralogical composition of the upper 300 m of this sequence is presented here for the first time. Heavy and clay mineral associations indicate a major and consistent shift in provenance, from the Barents-Kara–western Laptev Sea region, characterized by presence of common clinopyroxene, to the eastern Laptev-East Siberian seas in the upper part of the section, characterized by common hornblende (amphibole). Sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the ACEX drill site, if considering modern sea ice trajectories and velocities. This shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the Arctic Ocean, which occurred at about 13 Ma, thus suggesting a coeval freeze in the Arctic and Antarctic regions.

INVESTIGATION OF THE CLAY FRACTION (<2 μm) OF THE CLAY MINERALS SOCIETY REFERENCE CLAYS

We studied a set of 15 reference clays from The Clay Minerals Society (CMS) Source Clays repository. Our aim was to use them as reference materials in our version of the QUAX mineral database. The QUAX software (Quantitative Phase-Analysis with X-ray Powder Diffraction) has been used successfully at the KTB site (German Continental Deep Drillling) to determine mineral assemblages quickly, in an automatic fashion, on a large number of samples (∼40,000). It was also applied to Quaternary marine sediments of the Japan Sea. Our current research focuses on marine and lacrustrine sediments from the Arctic Ocean and Siberia.QUAX is a full-pattern method using a reference materials database. The quality of a particular quantification depends on the availability of the relevant mineral phases in the database. Our aim is to extend and improve the database continuously with new data from our current projects, particularly from clay and feldspar minerals.A reference material in the QUAX software must be monomineralic. Before X-ray diffraction (XRD) patterns of CMS clays could be added to the database, quantification of any impurities was necessary. After measuring the bulk material by XRD, the <2 µm fraction was separated because we assumed it would contain the smallest amount of impurities. Here we present grain-size data, XRD data and X-ray fluorescence (XRF) data for this clay-sized fraction. The results of chemical and mineralogical preparation techniques and (elemental) analysis methods were combined. For XRD, random and oriented clay-aggregate samples as well as pressed pellets for QUAX analysis were prepared. Semi-quantitative clay mineral determinations were run for comparison.

Pliocene palaeoceanography of the Arctic Ocean and subarctic seas

The Pliocene is important in the geological evolution of the high northern latitudes. It marks the transition from restricted local- to extensive regional-scale glaciations on the circum-Arctic continents between 3.6 and 2.4 Ma. Since the Arctic Ocean is an almost land-locked basin, tectonic activity and sea-level fluctuations controlled the geometry of ocean gateways and continental drainage systems, and exerted a major influence on the formation of continental ice sheets, the distribution of river run-off, and the circulation and water mass characteristics in the Arctic Ocean. The effect of a water mass exchange restricted to the Bering and Fram Straits on the oceanography is unknown, but modelling experiments suggest that this must have influenced the Atlantic meridional overturning circulation. Cold conditions associated with perennial sea-ice cover might have prevailed in the central Arctic Ocean throughout the Pliocene, whereas colder periods alternated with warmer seasonally ice-free periods in the marginal areas. The most pronounced oceanographic change occurred in the Mid-Pliocene when the circulation through the Bering Strait reversed and low-salinity waters increasingly flowed from the North Pacific into the Arctic Ocean. The excess freshwater supply might have facilitated sea-ice formation and contributed to a decrease in the Atlantic overturning circulation.

Effects of Arctic freshwater forcing on thermohaline circulation during the Pleistocene

In this paper, we make use of calcium carbonate-bearing sediment sequences in the Arctic-Atlantic gateway to produce a standard reference climate record for the Arctic Ocean. We present a continuous and exceptionally well-dated marine sediment record documenting the strong imprint of Arctic freshwater pulses on Earths climate system throughout the past 0.8 m.y. Planktic foraminiferal oxygen and carbon isotope data reveal that freshwater plumes released from collapsing circum-Arctic ice sheets and ice-dammed lakes were advected to the Arctic Ocean gateway on sub-Milankovitch time scales. Given the close correspondence of Arctic freshwater pulses and strength of North Atlantic Deep Water formation as inferred from carbon isotope data, we conclude that freshening of the Arctic Ocean influenced thermohaline circulation more frequently than previously recognized. Our data show that it is critical for coupled atmosphere-ice-ocean general circulation models aimed at unraveling climate forcing factors during the Pleistocene to consider Arctic freshwater as a crucial forcing factor.

Spatial and temporal influence of glaciers and rivers on the sedimentary environment in Sassenfjorden and Tempelfjorden, Spitsbergen

Abstract Multiproxy analyses including hydrographical, geochemical, foraminferal, lithological and geophysical data reveal variable influences of the glaciers Tunabreen and von Postbreen as well as the river Sassenelva on the sedimentary environment in two Spitsbergen fjords during the Late Weichselian and the Holocene. Grounded ice covered the study area during the last glacial. The glacier fronts retreated stepwise during the latest Weichselian/earliest Holocene, and the glaciers were probably small during the early Holocene. A growth of Tunabreen occurred between 6 and 4 cal ka BP. Reduced input from Tunabreen from c. 3.7 cal ka BP was probably a result of suppressed iceberg rafting related to the enhanced formation of sea ice and/or reduced meltwater runoff. During the past two millennia, the glacier fronts advanced and retreated several times. The maximum Holocene glacier extent was reached at the end of a surge of von Postbreen in AD 1870. Characteristics of the modern glaciomarine environment include: (1) different colours and bulk-mineral assemblages of the turbid waters emanating from the main sediment sources; (2) variable locations of the turbid-water plumes as a consequence of wind forcing and the Coriolis effect; (3) stratified water masses during summers with interannual variations; (4) increasing productivity with increasing distance from the glacier fronts; (5) foraminifera-faunal assemblages typical for glacierproximal settings; and (6) periodical mass-transport activity.

Late Weichselian and Holocene sedimentary environments and glacial activity in Billefjorden, Svalbard

Abstract Swath bathymetry data and one sediment core were used to improve the understanding of the Late Weichselian and Holocene glacier activity in Billefjorden, Svalbard. Grounded ice existed in Billefjorden prior to 11.23 cal ka BP (calendar years before present), depositing a basal till and producing glacial lineations. The glacier front retreated from the central parts to the inner parts of the fjord between c. 11.23 and 11.2 cal ka BP. Annual recessional moraines suggest that this retreat occurred at a rate of up to 170 m a−1. During the early Holocene, the glacier Nordenskiöldbreen was comparatively small and sediment supply to central Billefjorden occurred mainly from the fjord sides. An increase in ice rafting around 7930 cal a BP is ascribed to enhanced sea-ice formation. The activity of Nordenskiöldbreen increased around 5470 cal a BP. Ice rafting was generally low during the past c. 3230 a. This was most likely related to the formation of a more permanent sea-ice cover. Nordenskiöldbreen reached its maximum Holocene extent around AD 1900, generating glacial lineations and depositing a terminal moraine in the inner fjord. Annual recessional moraines were formed during its subsequent retreat. Icebergs from Nordenskiöldbreen generated iceberg ploughmarks during the late Holocene.