Description: The Carrington Event of 1859 is considered to be among the largest space weather events of the last 150 years. We show that only one out of 14 well-resolved ice core records from Greenland and Antarctica has a nitrate spike dated to 1859. No sharp spikes are observed in the Antarctic cores studied here. In Greenland numerous spikes are observed in the 40 years surrounding 1859, but where other chemistry was measured, all large spikes have the unequivocal signal, including co-located spikes in ammonium, formate, black carbon and vanillic acid, of biomass burning plumes. It seems certain that most spikes in an earlier core, including that claimed for 1859, are also due to biomass burning plumes, and not to solar energetic particle (SEP) events. We conclude that an event as large as the Carrington Event did not leave an observable, widespread imprint in nitrate in polar ice. Nitrate spikes cannot be used to derive the statistics of SEPs.

Description: High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference (Δage) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP Δdepth (5.49 to 5.85 m) and Δage (498 to 601 yr) at the warming onset of GI-21 as well as the Δage range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the δ15N proxy) increases before CH4 concentration by no more than a few decades.

Description: Atmospheric circulation patterns and chemical concentrations in firn cores are highly related to each other. Atmospheric winds transport aerosols like sea salt and mineral dust over the globe and redistribute them. Because of this, it is possible to reconstruct atmospheric circulation bringing aerosol to Antarctica by analyzing chemical impurities in firn and ice. With these analyses, the gap caused by sparse atmospheric measurements can be filled and this knowledge can then be used to improve the understanding of local and global circulation patterns.Due to a very high accumulation rate (~600 kg/m²*a), coastal Dronning Maud Land (CDML) is a perfect site to conduct these studies.Here, the upper 6m of two firn cores drilled on Halvfaryggen and Sörasen (covering the time interval from 2002- 2007) were analyzed on ionic concentrations. This data was then contrasted to measurements from the air chemistry laboratories at Neumayer (NM) and Kohnenstation (KS), and synoptic measurements from automatic weather stations (distributed in CDML and at NM).The analyses show very different results: Sea salt ions (e.g. Na+) are higher correlated to ions measured in aerosol samples at the air chemistry laboratory at KS than to the one located at NM. In contrast, ions representing mineral dust (e.g. nss-Ca2+) only have a weak correlation over the whole area and time period. Accordingly, the deposition of aerosol is highly dependent on its origin and the topography in coastal Antarctica suggesting different transport pathways for sea level and higher altitude sites.

Description: Insoluble Aerosol particles deposited on the Greenland ice sheet have been identified to originate mainly from East Asian deserts. Information on atmospheric transport times and source strengths can be deduced from thetotal mass concentration and the size distribution of these aerosols in ice ores. On glacial-interglacial timescales the lognormal mode of the size istribution has been shown to vary between 1.2 and 1.7 µm in diameter and the concentrations can vary up to a factor 100.Existing Greenland ice cores have the potential of giving this information for the last 120.000 years continuously, when an in-situ analyzer is coupled to a continuous flow analysis (CFA) system. A CFA system consists of a melt head on which the core is uniformly melted and the melt water from the uncontaminated inner part is distributed to be analyzed for various impurities, such as insoluble dust and ionic species. The attempts made so far to obtain high-resolution insoluble aerosol profiles from ice cores using CFA applied a laser particle counter that used the light attenuation caused by particles flowing through the beam. For this study, a Flow Cytometer has been running in parallel to a laser particle counter on sections from the NEEM ice core that is currently drilled in Northwestern Greenland. Flow Cytometers are widely applied in biological and medical applications and compared to laser particle counters they have the advantage that they are single particle counters. Each hydrosol is focussed into the focal point of a laser by a sheath fluid and the side scatter and widening of the beam are detected. It is investigated to what extend the Flow Cytometer can add information on insoluble aerosols and circumvent the disadvantages of the laser particle counter, which are the detection limit close to the lognormal mode and the high sample consumption.

Description: Using high resolution chemical impurity and dielectric profiling data annual layers have been counted on the EPICA ice core from Dronning Maud Land (EDML), Antarctica spanning the past 16700 years. The methodology used for counting Greenland ice cores and creating the Greenland Ice Core Chronology 2005 (GICC05) [Rasmussen et al., 2006] has also been implemented for the EDML counting. The estimated maximum counting error for the EDML counting is approx. 5%, but a preliminary volcanic matching with Greenland ice core records suggest differences of 1% or less during the Holocene between the EDML counting and GICC05. A comparison of cosmogenic isotope records from EDML and Greenland also suggests differences of less than 1% between the two annual layer counted chronologies. Reference: Rasmussen, S.O., Andersen, K.K., Svensson, A., Steffensen, J.P., Vinther, B.M., Clausen, H.B., Andersen, M.L.S., Johnsen, S.J., Larsen, L.B., Dahl-Jensen, D., Bigler, M., Röthlisberger R., Fischer H., Goto-Azuma K., Hansson M.E., Ruth U, A new Greenland ice core chronology for the last glacial termination, Journal of Geophysical Research Vol. 111, D06102, doi:10.1029/2005JD006079. 2006.

Description: The Greenland NGRIP ice core continuously covers the period from present day back to 123 ka before present, which includes several thousand years of ice from the previous interglacial period, MIS 5e or the Eemian. In the glacial part of the core, annual layers can be identified from impurity records and visual stratigraphy, and stratigraphic layer counting has been performed back to 60 ka. In the deepest part of the core, however, the ice is close to the pressure melting point, the visual stratigraphy is dominated by crystal boundaries, and annual layering is not visible to the naked eye. In this study, we apply a newly developed setup for high-resolution ice core impurity analysis to produce continuous records of dust, sodium and ammonium concentrations as well as conductivity of melt water. We analyzed three 2.2 m sections of ice from the Eemian and the glacial inception. In all of the analyzed ice, annual layers can clearly be recognized, most prominently in the dust and conductivity profiles. Part of the samples is, however, contaminated in dust, most likely from drill liquid. It is interesting that the annual layering is preserved despite a very active crystal growth and grain boundary migration in the deep and warm NGRIP ice. Based on annual layer counting of the new records, we determine a mean annual layer thickness close to 11 mm for all three sections, which, to first order, confirms the modeled NGRIP time scale (ss09sea). The counting does, however, suggest a longer duration of the climatically warmest part of the NGRIP record (MIS5e) of up to 1 ka as compared to the model estimate. Our results suggest that stratigraphic layer counting is possible basically throughout the entire NGRIP ice core, provided sufficiently highly-resolved profiles become available.

Description: The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia, where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra and on accurately dated European stalagmites, the Toba event is known to occur between the onsets of Greenland interstadials (GI) 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP) and Antarctic (EDML) ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 ka BP) before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM-19/20 and includes nine acidity peaks that are recognized in both ice cores. The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. The bipolar linking gives no support for a long-term global cooling caused by the Toba eruption as Antarctica experiences a major warming shortly after the event. Furthermore, our bipolar match provides a way to place palaeo-environmental records other than ice cores into a precise climatic context.

Description: Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.