Microparticles and crystal microstructure in polar ice sheets

The pollution input in polar ice sheets in Greenland and Antarctica is of atmospheric aeolian origin, just as all natural non-ice impurities as well. They thus provide potential information on the evolution of the atmospheric share of pollutants in the ocean. Aerosols found in ice are transported with atmospheric circulation and wind patterns and are deposited e.g. with precipitating snow. The impurity content in this so-called meteoric ice is relatively low compared to many other natural materials such as rocks (ppb to ppm range). The reason is that most aerosols in the atmosphere have been removed by fall-out or precipitation during transport from the impurities’ sources to the remote ice sheet. Non-ice constituents in polar ice cores have been studied in the last decades mainly for reconstructions of past atmospheric aerosol concentrations, with respect to questions conceding the global climate change. The fastest and easiest analytical way is chemical analysis of the melted water from ice cores. However despite the tiny concentrations, the interactions with and effects of impurities in the solid ice influence the physical properties of the material as a whole: e.g. electric as well as dielectric response and, in particular, mechanical behaviour thus “softness” of the material seems to be strongly controlled by impurities. Smaller concentrations of impurities (up to a few ‰) do soften the material as a whole, while larger concentrations of particles harden it, depending on the type of impurities of course. The underlying processes are partly hypothesised for decades, but not yet proven or understood satisfactorily as the quest for ppb to ppm concentrations in solid matrix material is a search for a “needle in a haystack”. To improve the data basis regarding the in-situ form of incorporation and spatial distribution of impurities in ice we used micro-cryo-Raman spectroscopy to identify the location, phase and composition of micrometer-sized inclusions in natural ice samples (NEEM ice core from Greenland and EPICA-DML ice core from Antarctica). The combination of Raman results with ice-microsctructure measurements and complementary impurity data provided by the standard analytical methods (IC, CFA, and DEP) allows for a more interdisciplinary approach interconnecting ice core chemistry and ice core physics. While the samples originating from interglacial times were dominated by sulfate salts—mainly gypsum, sodium sulfate (possibly thenardite) and iron–potassium sulfate (likely jarosite)—the glacial ice contained high numbers of mineral dust particles—in particular quartz, mica, feldspar, anatase, hematite and carbonaceous particles (black carbon). We cannot confirm cumulation of impurities in the grain boundary network as reported by other studies, neither micro-particles being dragged by migrating grain boundaries nor in form of liquid veins in triple junctions. We argue that mixing of impurities on the millimeter scale and chemical reactions are facilitated by the deforming ice matrix. Refs.: doi: 10.5194/tc-11-1075-2017 doi: 10.3389/feart.2019.00020 https://www.humboldt-foundation.de/web/trilateral-jagfos-2019.html http://www.nasonline.org/programs/kavli-frontiers-of-science/past-symposia/2019-jagfos.html Invited poster

Impurity Analysis and Microstructure Along the Climatic Transition From MIS 6 Into 5e in the EDML Ice Core Using Cryo-Raman Microscopy

Impurities in polar ice cores have been studied so far mainly for the purpose of reconstructions of past atmospheric aerosol concentrations. However, impurities also critically influence physical properties of the ice matrix itself. To improve the data basis regarding the in-situ form of incorporation and spatial distribution of impurities in ice we used micro-cryo-Raman spectroscopy to identify the location, phase and composition of micrometer-sized inclusions in natural ice samples around the transition from marine isotope stage (MIS) 6 into 5e in the EDML ice core. The combination of Raman results with ice-microsctructure measurements and complementary impurity data provided by the standard analytical methods (IC, CFA, and DEP) allows for a more interdisciplinary approach interconnecting ice core chemistry and ice core physics. While the interglacial samples were dominated by sulfate salts—mainly gypsum, sodium sulfate (possibly thenardite) and iron–potassium sulfate (likely jarosite)—the glacial ice contained high numbers of mineral dust particles—in particular quartz, mica, feldspar, anatase, hematite and carbonaceous particles (black carbon). We cannot confirm cumulation of impurities in the grain boundary network as reported by other studies, neither micro-particles being dragged by migrating grain boundaries nor in form of liquid veins in triple junctions. We argue that mixing of impurities on millimeter scale and chemical reactions are facilitated by the deforming ice matrix. We review possible effects of impurities on physical properties of ice, however the ultimate identification of the deformation agent and the mechanism behind remains challenging

RESPIC - Paleoclimatic changes in the global carbon cycle

The goal of RESPIC is the quantification of changes in the global carbon cycle (GCC) in the past. To this end relevant boundary conditions for the GCC have been reconstructed from the new EPICA ice cores and changes in carbon fluxes have been quantified using the new GCC-model BICYCLE. Ice core aerosol records show substantial changes in mineral dust, thus iron input, to the Southern Ocean (SO) parallel to changes in sea level. In contrast, changes in marine biogenic sulfur do not point to a substantial increase in marine sulfur productivity in parallel to a potential iron fertilisation. Sea ice coverage as revealed in sea salt aerosol doubles for glacial conditions connected to higher SO stratification and reduced gas exchange. In line, BICYCLE reveals a strong effect of SO mixing and carbonate sedimentation/dissolution on atmospheric CO2 while the influence of iron fertilisation is limited to about 20 ppmv. New quantitative information on carbon fluxes can be derived from novell high-precision d13CO2 measurements developed within RESPIC which show 0.5 o/oo higher levels during warm marine isotope stage (MIS) 5.5 compared to the penultimate glacial

Analyses of firn cores of a pre-IPICS-campaign on its ionic and dust concentration

Dust is a substance which can have a great influence on the energy balance of the climate system. Those influences depend on different conditions like the dust concentration, the vertical allocation, and its particle size distribution. These criterions can cause either a warming or a cooling of the atmosphere. Due to the fact that the Antarctic continent is nearly totally covered with snow, there are scarcely natural dust origins on the continent itself. As a conclusion, the dust measured in Antarctica must have another origin and hence gets there via a long range transport. Another advantage of measuring aerosols in Antarctica is an environment without the impact of human being. The concentration of dust in the last years can be measured by analysing firn cores. This analysis has the purpose to make a pre site survey for the IPICS- campaign, so a possible timescale and aerosol distribution for the different positions of a deeper drilling can be seen. Results of the measurement can be compared to the measurement of an over-snow laboratory located near the Neumayer station and the atmospheric conditions in Antarctica. Firn cores were taken from two positions near Neumayer station (Antarctica), one in 6.7°W 71.6°S the other one in 9.9°W 71.4°S. In the cold-room laboratory of the Alfred-Wegener-Institute in Bremerhaven, the firn cores are processed. Due to the high accumulation rate a high temporal resolution of the sample can be obtained. Particle size distribution and the ion concentration are analysed

Chemical profiles accross the last glacial termination: First results from the EPICA-DML ice core

The European Project of Ice Coring in Antarctica (EPICA) aims at reconstructing past climate andenvironmental conditions from two deep ice cores in Antarctica. The two cores are drilled in theDome C area (at 75°06' S, 123° 21'E, 3233m a.s.l.) and in Droning Maud Land (DML, at 75°00'S;00°04'E, 2892 m.a.s.l). Here we will present chemical data from the first approx. 1550 m of theDML core.Continuous ice core melting was employed for sample preparation and decontamination.Continuous profiles were measured on-line for Na, Ca and NH4 soluble ion concentrations bycontinuous flow analysis (CFA) methods as well as for insoluble microparticle concentrationstarting at 113m depth. These profiles will be presented at low resolution (1.0 m) together withsections of high resolution data exemplary for mid-Holocene, Preboreal and the last Glacialperiods.From the high resolution data the annual layer thickness will be derived and the possibilities ofcounting annual layers will be explored during the different periods mentioned. If possible, also theseasonal phasing and shifts thereof will be investigated for the measured species. The lowresolution data will provide an overview of the last glacial termination. The measured componentswill be discussed in terms of degree of relative change and of timing differences. Furthermore, thecontributions of the two main sources for Ca (crustal matter and sea salt aerosol) will be discussed.Presenting Author:Dr. Urs Ruth / Alfre-Wegener-Institute / 27568 Bremerhaven / Columbusstraße / Germany /+4947148311173 / [email protected] Reference No.: ABS-4150-0009