ALBERT

Beschreibung: We present a new interface between the geochemical simulator PHREEQC and the open source language R. It represents a tool to flexibly and efficiently program and automate every aspect of geochemical modelling. The interface helps particularly to setup and run large numbers of simulations and visualise the results. Also profiting of numberless high-quality R extension packages, performing sensitivity analysis or Monte Carlo simulations becomes straightforward. Further, an algorithm to speedup reactive transport simulations starting from homogeneous or zone- homogeneous state is programmed and successfully evaluated through the interface. It proved effective and could therefore be included in any reactive transport simulator.

Beschreibung: We studied 40 artesian wells (AWs) in the Amu Darya Delta. These wells include high-salinity (∼ 52 g/l) and saline (5 – 24 g/l) waters but are mostly low-salinity waters (1.3 – 2.9 g/l). The low-salinity AWs cluster into three types, reflecting the variable mixing of different end-member solutes: (residual) brines and solutes deriving from silicate alteration, dissolution of limestone and dissolution of gypsum. The solutes are all undersaturated in calcite and gypsum, contain a substantial cation excess against dissolved inorganic carbon and are characterised by low Ca/SO4 ratios. On the basis of the hydrochemical mass budgets of model cases, we demonstrate that Na-rich Cl-brines (45-48%) and a Na2SO4-brine (30-47%) are the dominant solute components. The solutes derived from aluminium silicate alteration are minor components (7.3 – 19.4%). Even less important are solutes from limestone or gypsum dissolution (0.05 – 3.7%). These waters are unlikely to have originated from sediments hosting gypsum. The low-salinity AWs must have acquired their dominant hydrochemical signatures under non-equilibrium conditions between their remote (unknown) seepage areas and their discharge locations. This acquisition may have begun during the early hydrochemical groundwater evolution when meteoric or surface water passed the critical zone under an arid climate regime. Warmer saline AWs (∼40°C) hosted in deeper Cretaceous formations contain a high portion of NaCl-rich brine (85%) and some are saturated in gypsum. These waters were derived from fluids rising along faults from pre-Cretaceous strata. The high-salinity and relatively cold AWs discharge close to the retreating Aral Sea south of its western basin. These AWs are suboxic, and Si concentrations are very low. The AW hydrochemical signatures reflect the dissolution of halite and gypsum. We observed positive correlations between temperature, Br, B and Si. The temperature correlation with bromide likely documents the transformation of organically bound Br. The silica concentrations in low-salinity AWs southeast of the Aral Sea (eastern basin) are close to quartz saturation and define a chemical Si-geothermometer.

Beschreibung: We applied scaled physical analogue experiments to investigate the early development of salt diapirs induced by differential sedimentary loading in an intra-continental basin realm (e.g. the North German Basin). During the experiments, deformation in a salt-analogue viscous layer was initiated by variations in the thickness of an overlying brittle material and subsequent accumulation of the brittle material further sustained deformation. A 2D optical image correlation system was used to monitor the strain evolution in the salt analogue material. Our models indicate that the formation of salt pillow structures can be achieved by minimum variations in the overburden loading. The increase of differential loading by adding synkinematic layers in the subsided areas causes not only an active piercing of the viscous layer through the brittle overburden but also an additional uplift in the adjacent areas. These elevations, named “secondary structures”, act as origins for a successive generation of diapirs. Consequently, an initial perturbation of the salt–sediment-interface can lead to a lateral propagation temporally shifted diapirs. The linkage between primary and secondary structures is reflected in the synkinematic overburden layers such as overlapping peripheral sinks in the transition zone between two diapirs. These sinks, in turn, are a frequently observable phenomenon around salt structures of the North German basin indicating that “secondary diapirism” is an underestimated process – besides regional tectonic stresses – influencing the evolution of salt structures.

Beschreibung: We study opportunities for CO2 sequestration in geological formations of the state North Rhine Westphalia in Germany. Simulations are performed for evaluating a potential site within the Bunter sandstone formation near the town of Minden in a depth of around 3,000 m using the numerical simulator TOUGHREACT. Our focus is on three CO2 storage mechanisms: (1) hydrodynamic trapping, (2) dissolution trapping, and (3) mineral trapping. The results show that due to buoyancy the injected CO2 phase initially migrates towards the top of the reservoir and is hydrodynamically trapped beneath the confining layer of the cap rock. Then, the CO2 spreads laterally and dissolves partially in the formation water. The dissolution of CO2 results in an increase of the density of the brine causing a downward migration until it settles after 10,000 years at the bottom of the reservoir. The simulations indicate that after 10,000 years, 15% (17 Mt) from a total of 114 Mt injected CO2 are trapped hydrodynamically, 20% (23 Mt) are trapped by dissolution, and 65% (74 Mt) are fixed in newly formed carbonates such as dawsonite, ankerite, and siderite. Within our study pressure increases near the injection well by a factor of 1.1 which is lower than the upper limit usually accepted in gas storage operations. The mineral reactions cause a net decrease of porosity and in turn a decrease of permeability down to 9% of the initial value in parts of the reservoir.

Beschreibung: On 12 September 2007, an Mw 8.4 earthquake occurred within the southern section of the Mentawai segment of the Sumatra subduction zone, where the subduction thrust had previously ruptured in 1833 and 1797. Traveltime data obtained from a temporary local seismic network, deployed between December 2007 and October 2008 to record the aftershocks of the 2007 event, was used to determine two-dimensional (2-D) and three-dimensional (3-D) velocity models of the Mentawai segment. The seismicity distribution reveals significant activity along the subduction interface and within two clusters in the overriding plate either side of the forearc basin. The downgoing slab is clearly distinguished by a dipping region of high Vp (8.0 km/s), which can be a traced to ∼50 km depth, with an increased Vp/Vs ratio (1.75 to 1.90) beneath the islands and the western side of the forearc basin, suggesting hydrated oceanic crust. Above the slab, a shallow continental Moho of less than 30 km depth can be inferred, suggesting that the intersection of the continental mantle with the subducting slab is much shallower than the downdip limit of the seismogenic zone despite localized serpentinization being present at the toe of the mantle wedge. The outer arc islands are characterized by low Vp (4.5–5.8 km/s) and high Vp/Vs (greater than 2.0), suggesting that they consist of fluid saturated sediments. The very low rigidity of the outer forearc contributed to the slow rupture of the Mw 7.7 Mentawai tsunami earthquake on 25 October 2010.

Beschreibung: Sub-diurnal variations in Earth rotation parameters as obtained from time-series of space geodetic observations contain substantial variability even after correcting for the effects of oceanic tides. These residuals are in particular apparent at frequencies of 1, 2 and 3 cycles per solar day, where atmospheric tides, principally excited by water vapor absorption and ozone heating in the middle atmosphere, are known to occur. By means of hourly data of the chemistry-climate model WACCM, the potential of atmospheric tides on the excitation of UT1 variations is re-assessed. Tidal signals are separated into migrating and non-migrating zonal waves for individual height levels. Only standing waves of wavenumber zero are found to be effective in exciting UT1 variations, which are subsequently discussed in terms of their characteristic surface pressure and vertically varying wind amplitudes.

Beschreibung: Regional ocean models are extraordinarily useful tools as complements to global models, since they work at higher spatial and temporal resolutions and parameters can be adapted to the particular conditions in the region of interest. These advantages are bought with new potential issues at the boundaries of the modelled region. At open boundaries, a global model has to provide boundary conditions such as velocity, temperature, and salinity, necessarily obtained at coarser resolution and with less accuracy. The region we focus on is the surroundings of South Africa, comprising parts of the Southern Atlantic and Southern Indian Ocean as well as the Southern Ocean down to the ice shelves of Antarctica.We attempt to better understand the dynamics of the Agulhas Current, which has been shown to have far-reaching impacts also on the Meridional Overturning Circulation and, thereby, on the world’s climate. With our study region expanded southwards, including a fraction of the Antarctic Circumpolar Current (ACC), we investigate the local current-current interactions which are conveyed by small-scale turbulences. In our analysis, we focus on sea surface height and ocean bottom pressure and the different forcing terms that influence these two variables. We configure a version of the Regional Ocean Modelling System (ROMS) to simulate ocean dynamics around South Africa, forced with ERA-Interim atmospheric data, and explore the sensitivity to various choices of boundary conditions. The horizontal resolution of 0.25 degrees - 0.25 degrees at 32 vertical levels is supposed to resolve mesoscale eddies as well as the climatologically important shedding of Agulhas rings. To show the capabilities of our model, we compare the output in terms of sea-surface heights to altimetric measurements provided by AVISO. In-situ data of ocean bottom pressure measured in the ACC path adds to the observational database. The study area is especially promising as, additionally, we can show whether the simulations of an integrated ocean bottom pressure signal correspond to the residuals in measurements of the Superconducting Gravimeter in Sutherland, South Africa.

Beschreibung: Oil-producing sills are commonly considered atypical reservoirs, although they can hold significant exploration potential. The need for a better understanding of fracture properties and petroleum system characteristics for this and similar igneous rock plays is the main motivation of our study. We explore the evolution of this play type by an analysis of the Los Cavaos oil field, located in the Malargue fold belt of the Neuquen Basin, Argentina, integrating multiscale fracture data from outcrops and subsurface. The field was created by a combination of intrusions and mild Miocene-Pliocene inversion. Production stems from thick cavity zones in naturally fractured andesitic sills emplaced in Upper Jurassic shale source rocks. Orientation patterns, fracture spacing, and length of fracture sets in the sill are consistent over several orders of magnitude. Large multiply connected and weakly cemented fractures are responsible for excellent interconnectedness in the reservoir. Fracture density is correlated with fault proximity, indicating a cogenetic evolution during active deformation. Abundant fractures in core with strike-slip to oblique striations support transpressional overprint during and after fracture formation. Although it is challenging to separate cooling from tectonic fractures, we propose two phases of fracturing, marked by a coexistence of subvertical and oblique fractures together with transpressional striae. Petrographic evidence suggests initial local oil expulsion and migration through microfractures, with opening displacements of 0.01 to 1 mm, followed by subsequent charging of the evolving intrasill cavity system as well as the bulk fracture system during cooling and mild deformation. We suggest that the observed patterns may be extrapolated to sills in similar geotectonic settings.

Beschreibung: On 2012 May 20 and 29, two damaging earthquakes with magnitudes Mw 6.1 and 5.9, respectively, struck the Emilia-Romagna region in the sedimentary Po Plain, Northern Italy, causing 26 fatalities, significant damage to historical buildings and substantial impact to the economy of the region. The earthquake sequence included four more aftershocks with Mw ≥ 5.0, all at shallow depths (about 7–9 km), with similar WNW–ESE striking reverse mechanism. The timeline of the sequence suggests significant static stress interaction between the largest events. We perform here a detailed source inversion, first adopting a point source approximation and considering pure double couple and full moment tensor source models. We compare different extended source inversion approaches for the two largest events, and find that the rupture occurred in both cases along a subhorizontal plane, dipping towards SSW. Directivity is well detected for the May 20 main shock, indicating that the rupture propagated unilaterally towards SE. Based on the focal mechanism solution, we further estimate the co-seismic static stress change induced by the May 20 event. By using the rate-and-state model and a Poissonian earthquake occurrence, we infer that the second largest event of May 29 was induced with a probability in the range 0.2–0.4. This suggests that the segment of fault was already prone to rupture. Finally, we estimate peak ground accelerations for the two main events as occurred separately or simultaneously. For the scenario involving hypothetical rupture areas of both main events, we estimate Mw = 6.3 and an increase of ground acceleration by 50 per cent. The approach we propose may help to quantify rapidly which regions are invested by a significant increase of the hazard, bearing the potential for large aftershocks or even a second main shock.

Beschreibung: We present regional-scale mass balances for 25 drainage basins of the Antarctic Ice Sheet (AIS) from satellite observations of the Gravity and Climate Experiment (GRACE) for the years 2002–2011. Satellite gravimetry estimates of the AIS mass balance are strongly influenced by mass movement in the Earth interior caused by ice advance and retreat during the last glacial cycle. Here, we develop an improved glacial-isostatic adjustment (GIA) estimate for Antarctica using newly available GPS uplift rates, allowing us to more accurately separate GIA-induced trends in the GRACE gravity fields from those caused by current imbalances of the AIS. Our revised GIA estimate is considerably lower than previous predictions, yielding an (upper) estimate of apparent mass change of 48 ± 18 Gt yr−1. Therefore, our AIS mass balance of −103 ± 23 Gt yr−1 is considerably less negative than previous GRACE estimates. The Northern Antarctic Peninsula and the Amundsen Sea Sector exhibit the largest mass loss (−25 ± 6 Gt yr−1 and −126 ± 11 Gt yr−1, respectively). In contrast, East Antarctica exhibits a slightly positive mass balance (19 ± 16 Gt yr−1), which is, however, mostly the consequence of compensating mass anomalies in Dronning Maud and Enderby Land (positive) and Wilkes and George V Land (negative) due to interannual accumulation variations. In total, 7% of the area constitute more than half of the AIS imbalance (53%), contributing −151 ± 9 Gt yr−1 to global mean sea-level change. Most of this imbalance is caused by long-term ice-dynamic speed up expected to prevail in the future.

Beschreibung: The Athabasca region of northern Alberta, Canada, is home to deposits of oil sands containing vast amounts (~ 173 billion barrels) of heavily biodegraded petroleum. Oil sands are recovered by surface mining or by in situ steam injection. The extraction of bitumen from oil sands by caustic hot water processing results in large volumes of fluid tailings, which are stored in on-site settling basins. There the tailings undergo a compaction and dewatering process, producing a slowly densifying suspension. The released water is recycled for extraction. The fine tailings will be reclaimed as either dry or wet landscapes. [1] To produce 1 barrel of crude oil, 2 tons of oil sand and 2 - 3 tons of water (including recycled water) are required. [2] Open pit mining and the extraction of the bitumen from the oil sands create large and intense disturbances of different landscapes. The area currently disturbed by mining operations covers about 530 km2 and the area of tailing ponds surpasses 130 km2. An issue of increasing importance is the land remediation and reclamation of oil sand areas in Canada and the reconstruction of these disturbed landscapes back to working ecosystems similar to those existing prior to mining operations. An important issue in this context is the identification of oil sand-derived organic compounds in the tailings, their environmental behaviour and the resulting chances and limitations with respect to land reclamation. Furthermore the biodegradation processes that occur in the tailings and that could lead to a decrease in hazardous organic compounds are important challenges, which need to be investigated. This presentation will give a detailed overview of our compositional and quantitative characterisation of the organic matter in oil sand, unprocessed and processed mature fine tailings samples as well as in tailings sands used as part of land reclamation. The analytical characterisation is based on the extraction of the soluble organic matter, its subsequent separation into asphaltenes, aliphatic hydrocarbons, aromatic hydrocarbons, neutral nitrogen, sulphur, oxygen (NSO) compounds and carboxylic acids. The asphaltene fractions are analysed using pyrolysis-GC, all other fractions are analysed by GC-MS. Additionally Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) is used to study the chemical composition of the samples on the molecular level using different ionisation methods.

Beschreibung: Observations of the ocean-induced magnetic field by the CHAMP magnetic space mission have the potential to be used as a constraint when examining ocean dynamics. This has initiated theoretical studies on the prediction of the poloidal magnetic field induced by the horizontal ocean-circulation flow. This study deals with the computation and analysis of the toroidal magnetic field induced by the tidal ocean-circulation flow on the background of the main Earth’s geomagnetic field. Since the induced toroidal magnetic field cannot be modelled by the single-layer approximation model used to predict the poloidal magnetic field, we treat the ocean as a spherical layer of a finite thickness and compute the toroidal magnetic field by a matrix-propagator technique with a source of electric currents in the ocean layer. Our numerical simulations based on the OMCT tidal ocean velocities show that the induced toroidal magnetic field is extremely sensitive to the vertical gradient of horizontal ocean flow. The larger this gradient, the stronger the induced toroidal magnetic field. Specifically, its magnitudes vary from 10−2 nT for barotropic flow to several nT for baroclinic flow. We show that the induced toroidal magnetic field generated by M2 tidal forcing is comparable in amplitude to the induced poloidal part of the field. The induced toroidal and poloidal magnetic fields differ, however, in their spatial behaviour.

Beschreibung: The weathering and erosion processes that produce and destroy regolith are widely recognized to be positively correlated across diverse landscapes. However, conceptual and numerical models predict some limits to this relationship that remain largely untested. Using new global data compilations of soil production and weathering rates from cosmogenic nuclides and silicate weathering fluxes from global rivers, we show that the weathering-erosion relationship is capped by certain ‘speed limits’. We estimate a soil production speed limit of between 320 to 450 t km−2 yr−1 and the associated weathering rate speed limit of roughly 150 t km−2 yr−1. These limits appear to be valid for a range of lithologies, and also extend to mountain belts, where soil cover is not continuous and erosion rates outpace soil production. We argue that the presence of soil and regolith is a requirement for high weathering fluxes from a landscape, and that rapidly eroding, active mountain belts are not the most efficient sites for weathering.

Beschreibung: In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests.

Beschreibung: 3000 m of ice sheet thickness has ensured that central Greenland has kept it geothermal heat flow (GHF) distribution enigmatic. Some few direct ice temperature measurements from deep ice cores reveal a GHF of 50 to 60 mW/m2 in the Summit region and this is noticeably above what would be expected for the underlying Early Proterozoic lithosphere. In addition, indirect estimates from zones of rapid basal melting suggest extreme anomalies 15 to 30 times continental background. Subglacial topography indicates caldera like topographic features in the zones hinting at possible volcanic activity in the past [1], and all of these observations combined hint at an anomalous lithospheric structure. Further supporting this comes from new high-resolution P-wave tomography, which shows a strong thermal anomaly in the lithosphere crossing Greenland from east to west [2]. Rock outcrops at the eastern and western end of this zone indicate significant former magmatic activity, older in the east and younger in the west. Additionally, plate modelling studies suggest that the Greenland plate passed over the mantle plume that is currently under Iceland from late Cretaceous to Neogene times, consistent with the evidence from age of magmatism. Evidence of rapid basal melt revealed by ice penetrating radar along the hypocentre of the putative plume track indicates that it continues to affect the Greenland continental geotherm today. We analyse plume-induced thermal disturbance of the present-day lithosphere and their effects on the central Greenland ice sheet by using a novel evolutionary model of the climate-ice-lithosphere-upper mantle system. Our results indicate that mantle plume-induced erosion of the lithosphere has occurred, explaining caldera-type volcanic structures, the GHF anomaly, and requiring dyke intrusion into the crust during the early Cenozoic. The residual thermo-mechanical effect of the mantle plume has raised deep-sourced heat flow by over 25 mW/m2 since 60 Ma and explains the high basal melting rates of the Greenland ice sheet observed in the study area. [1] Fahnestock, M., Abdalati, W., Joughin, I., Brozena, J., Gogineni, P., 2001. High geothermal heat flow, Basal melt, and the origin of rapid ice flow in central Greenland. Science (New York, N.Y.). 294, 2338–2342. [2] Jakovlev, A.V., Bushenkova, N.A., Koulakov, I.Y., Dobretsov, N.L., 2012. Structure of the upper mantle in the Circum-Arctic region from regional seismic tomography. Russian Geology and Geophysics. 53, 963–971.

Beschreibung: We present in a statistical study a comparison of thermospheric mass density enhancements (ρrel) with electron temperature (Te), small-scale field-aligned currents (SSFACs), and vertical ion velocity (Vz) at high latitudes around noon magnetic local time (MLT). Satellite data from CHAMP (CHAllenging Minisatellite Payload) and DMSP (Defense Meteorological Satellite Program) sampling the Northern Hemisphere during the years 2002–2005 are used. In a first step we investigate the distribution of the measured quantities in a magnetic latitude (MLat) versus MLT frame. All considered variables exhibit prominent peak amplitudes in the cusp region. A superposed epoch analysis was performed to examine causal relationship between the quantities. The occurrence of a thermospheric relative mass density anomaly, ρrel 〉1.2, in the cusp region is defining an event. The location of the density peak is taken as a reference latitude (Δ MLat = 0°). Interestingly, all the considered quantities, SSFACs, Te, and Vz are co-located with the density anomaly. The amplitudes of the peaks exhibit different characters of seasonal variation. The average relative density enhancement of the more prominent density peaks considered in this study amounts to 1.33 during all seasons. As expected, SSFACs are largest in summer with average amplitudes equal to 2.56 μA m−2, decaying to 2.00 μA m−2 in winter. The event related enhancements of Te and Vz are both largest in winter (Δ Te =730 K, Vz =136 m s−1) and smallest in summer (Δ Te = 377 K, Vz = 57 m s−1. Based on the similarity of the seasonal behaviour we suggest a close relationship between these two quantities. A correlation analysis supports a linear relation with a high coefficient greater than or equal to 0.93, irrespective of season. Our preferred explanation is that dayside reconnection fuels Joule heating of the thermosphere causing air upwelling and at the same time heating of the electron gas that pulls up ions along affected flux tubes.

Beschreibung: We document Quaternary fluvial incision driven by fault-controlled surface deformation in the inverted intermontane Gökırmak Basin in the Central Pontide mountains along the northern margin of the Central Anatolian Plateau. In-situ-produced 10Be, 21Ne, and 36Cl concentrations from gravel-covered fluvial terraces and pediment surfaces along the trunk stream of the basin (the Gökırmak River) yield model exposure ages ranging from 7 ± 1 ka to 346 ± 45 ka and average fluvial incision rates over the past ~350 ka of 0.28 ± 0.01 mm a-1. Similarities between river incision rates and coastal uplift rates at the Black Sea coast suggest that regional uplift is responsible for the river incision. Model exposure ages of deformed pediment surfaces along tributaries of the trunk stream range from 60 ± 5 ka to 110 ± 10 ka, demonstrating that the thrust faults responsible for pediment deformation were active after those times and were likely active earlier as well as explaining the topographic relief of the region. Together, our data demonstrate cumulative incision that is linked to active internal shortening and uplift of ~0.3 mm a-1 in the Central Pontide orogenic wedge, which may ultimately contribute to the lateral growth of the northern Anatolian Plateau.

Beschreibung: Conventional radar and laser altimeters offer high altimetric accuracy but with insufficient spatial and temporal resolution. Global Navigation Satellite System-Reflectometry (GNSS-R) reveals new perspectives for Earth observations. Earthreflected signals from GNSS systems show high reflection characteristics to some surfaces like water, ice and wet soil. The main advantage of GNSS-R is the large number of available GNSS signals and their dense global coverage so that multiple simultaneous height measurements within a wide field of view are possible. The subject of the following paper is to introduce GNSS-R and to summarize some of the activities done at GFZ. In addition, preliminary results from ongoing work will be presented.

Beschreibung: Aging in trees implies a progressive reduction in the growth rate, related to a shortening of the growing period and changes in the photosynthetic capability and efficiency. These changes may continue during the old-growth life stages following the juvenile phase and are reflected in tree-ring properties such as growth increment, density or stable isotopes. We studied possible climate age effects in time series of several tree-ring parameters (ring width, wood density and stable carbon and oxygen isotopes) of mature individuals from two age groups of Pinus uncinata and P. nigra at two locations in Spain. The aim was to test whether age differences in trees in the old-growth life stages could lead to diverging climate responses. The results show some differences in response to climate between age groups at a monthly level, but most of these divergences are not significant for seasonal climate variables. Regardless of the age group, the main limiting climate factors constrained tree growth equally. Although our findings do not support the idea of an age-dependent response to climate that may lead to inaccurate climate reconstructions, further studies using tree-ring density and stable isotope series are urgently needed to verify the current results.

Beschreibung: Plinian and Ignimbrite deposits represent explosive activity (ca. 17-19 cal ka) within the predominantly effusive and mildly explosive (Strombolian) volcanic history of Mount Etna (Italy). Proximal glasses from the Biancavilla Ignimbrites and Unit D Plinian fall deposits are characterised. Fall deposits recorded at Acireale (D1b and D2b) and Giarre (D1a and D2a) are geochemically distinct confirming they relate to different eruptions. The Acireale Plinian fall (D1b and D2b) deposits compositionally overlap with the Biancavilla Ignimbrite deposits. These explosive eruptions from Etna are considered responsible for widespread ash dispersals throughout the central Mediterranean region, producing the marker tephra layers (Y-1/Et-1) recorded in marine and lacustrine sedimentary archives. Stratigraphically these distal tephras occur at or close to the onset of the last deglaciation (Termination 1) within their respective palaeoenvironmental records, therefore making them potentially crucial tephrostratigraphic markers. This study investigates distal tephra deposits thought to be from Etna recorded in the Ionian Sea (Y-1), Lago Grande di Monticchio (LGdM, Italy; tephras TM-11 and TM-12-1), Lago di Mezzano (Italy) and the Haua Fteah cave (Libya). The glass chemistry of Y-1 tephras recorded in the Ionian Sea and at Haua Fteah are consistent with the Biancavilla Ignimbrites (16,965-17,670 cal yrs BP) and the upper Acireale Plinian fall (D2b). The LGdM record indicates that explosive activity on Etna associated with Unit D spans a minimum of 1540 ± 80 varve years. TM-12-1 (19,200-19,804 cal yrs BP) in LGdM appears to represent the oldest distal counterpart of Etna Unit D explosive activity and is associated with the lower Acireale (D1b) Plinian eruption. The proximally undefined TM-11 (17,640-18,324 cal yrs BP) and distal correlatives are geochemically distinct from the Ionian Sea Y-1 tephra. Such significant compositional differences seen between distal tephra layers are not observed within individual proximal units and are likely to indicate that the distal tephras relate to separate eruptive phases. Until proximal relationships can be established, the TM-11 type Y-1 equivalents should be termed TM-11. Great care should be exercised when using these distal ash layers to synchronise sedimentary records during a crucial period of environmental change.