Ole Stecher

• Cand Scient 1982, DEA 1977
• Principal Investigator at Geotop Denmark

Growing season conditions are widely recognized as the main driver for tundra shrub radial growth, but the effects of winter warming and snow remain an open question. Here, we present a more than 100 years long Betula nana ring-width chronology from Disko Island in western Greenland that demonstrates a highly significant and positive growth respons...

Recent warming is expected to dramatically modify the arctic terrestrial ecosystem and woody plants growth. Many studies dealing with Arctic shrubs growth responses to temperature usually base their estimations on biomass measurements of only the above-ground segments neglecting the below-ground growth. In this context, the study of shrub-rings can...

Air fallout volcanic ash layers are important in time scale studies because they provide widespread, essentially instantaneous, time markers in sedimentary sequences, including ice cores. Tephrochronology offers the possibility of tying together terrestrial and marine records for a better understanding of past climatic and ocean circulation systems...

The climate record covering the past 70 my shows that global temperatures peaked during the Early Eocene around ˜54 to 52 Ma; the Early Eocene Climatic Optimum (EECO) (1). Preceding and during the EECO were three ephemeral global warming events, each with approximately half the intensity of its predecessor: the Paleocene Eocene Thermal Maximum (PET...

Tektites of the Australasian strewn field cover an area from SE-Asia, through the Southwestern part of the Pacific Ocean and parts of the Indian Ocean, down to Australia. The impact crater has until now not been positively located, but it is generally assumed to be located somewhere in Indochina, where tektites also are more abundant and larger. 40...

Fluorine in 22 international reference samples has been determined with an ion selective electrode following fusion with a Na2bCO3-ZnO mixture. To eliminate the effect of fluorine complexes in the solutions, the results presented are means of fluoride determinations from a standard calibration curve and from the method of standard addition. Togethe...

The recent availability of commercial multi-collector noble gas mass spectrometers provides new opportunities for improved precision in 40Ar/39Ar dating, particularly for young Quaternary aged samples, where precise measurement of the 40Ar/36Ar ratio is critical. Multicollection reduces the errors introduced through signal decay and sequential meas...

Recent data for the Sm isotopic composition of meteorites indicate that the excess in ^{142}Nd seen for the terrestrial upper mantle is not caused by nucleosynthetic effects and support the hypothesis of an early terrestrial fractionation event creating the upper mantle as the depleted counterpart to an enriched reservoir. The coupling of the short...

40Ar/39Ar dating has identified a succession of middle Miocene (14-13 Ma) basaltic lavas in East Greenland that overlie Eocene flood basalts that were erupted during continental breakup ca. 56-55 Ma. The long postbreakup magmatic history (∼40 m.y.) of the East Greenland margin precludes a simple relationship between this later igneous activity and...

RECEIVED SEPTEMBER 4, 2000; ACCEPTED MAY 26, 2003 Dykes of the East Greenland Tertiary dyke swarm can be divided into pre-and syn-break-up tholeiitic dykes, and post-break-up transitional dykes. Of the pre-and syn-break-up dykes, the most abundant group (Tholeiitic Series; TS) has major element compositions similar to the main part of the East Gree...

After continental break-up in the presence of the Iceland mantle plume, nephelinite and melilitite lavas were erupted in NE Greenland in the early Eocene. The lavas are interpreted to represent melts derived directly from recycled oceanic lithosphere. High FeOtot (to>16wt.%), MgO and low SiO_2 Al_2O_3 and CaO suggest that they were derived by low d...

We present new Pb isotope data on 21 samples of break-up-related flood basalts (56–54 Ma) from the Blosseville Kyst region of East Greenland. These samples show a considerable range in isotopic composition (206Pb/204Pb 17.6 to 19.3) that broadly correlates with compositional type. The ‘low-Ti’ type is characterised by the lowest 206Pb/204Pb (17.6 t...

We report high-precision Pb-isotope data for > 120 neovolcanic lavas from Iceland that were analysed on an Axiom double focusing MC-ICP-MS, using a 207Pb-204Pb double spike to correct for instrumental mass bias. The external reproducibility of Pb isotope ratios determined for the standard SRM981 was +/-100 ppm (DS corrected) and replicate analyses...

Alkaline ultramafic lavas in north East Greenland were contemporaneous with Tertiary tholeiitic flood basalts in East Greenland. The alkaline lavas are enriched in light rare earth elements (REEs) and Ti and Nb, but depleted in Rb, Ba, K, Th, and P. The flood basalts have trace element profiles similar to those of the alkaline lavas. These features...

Pb stepwise leaching (PbSL) determinations on two magnetite-enriched fractions of a BIF sample from the northeastern part of the Isua supracrustal belt (West Greenland) yield an isochron of 3691 ± 22 Ma (MSWD = 0.4). In combination with previously published geochronological constraints for a minimum deposition age of ∼3.71 Ga for volcanic sequences...

Torfajökull is the largest silicic center in Iceland and is located on the eastern branch of Iceland's neovolcanic zone. Torfajökull's location on the Iceland volcanic crust is unique because (1) it is situated behind the tip of a propagating ridge, and (2) several ridge jumps made it possible for lavas to extrude through relatively old basaltic cr...

A new analytical procedure has been established in order to determine low fluorine concentrations (30–100 ppm F) in igneous rocks, and the method has also proven successful for higher concentrations (100–4000 ppm F). Fluorine has been measured in a series of olivine tholeiites from the Reykjanes Peninsula, a tholeiite to rhyolitic rock series from...

Metamorphosed anorthositic and gabbro-anorthositic rocks are found as scattered occurrences in the basement gneisses of the Caledonian fold belt of North-East Greenland. A Tm-MD-nd model age determined on a gabbro- anorthositic sample yields a value of 2146 Ma. This model age is in agreement with the general age of crust formation in the region. Th...

Marine geological investigations including shallow seismic, sedimentological and stratigraphical studies were carried out in Fakse Bay, southwestern Baltic. Seismic sequence analytical methods were used, supplemented by detailed lithological descriptions, pollen analysis and 14C dating of core material. Detailed correlations between sediment facies...

The Sr and Nd isotopic composition was analyzed for samples from the Late Eocene tektite material from DSDP site 612 off the New Jersey coast, to determine whether these tektites may be assigned to the North-American-tektite group. It was found that the ranges of the Sr-87/Sr-86 and the Nd-143/Nd-144 ratios were much wider than in the 612-tectite m...

A series of komatiite flows from Munro Township, Ontario, have Re and Os concentrations that range from 0.545 to 1.27 ppb and 1.00 to 2.20 ppb, respectively. The187Re/186Os in the suite range from 14.05 to 52.37 and the187Os/186Os range from 1.49 to 3.22, giving a crystallization age of2726 ± 93Ma and an of initial187Os/186Os of0.873 ± 0.035. This...

Precambrian and Eocambrian ultramafic and ultrapotassic dike rocks from the Sisimiut (Holsteinsborg) area of West Greenland can be grouped into three main types each showing characteristic mineral parageneses. Micaceous kimberlites contain macrocrysts and phenocrysts of olivine and phlogopite set in a groundmass of olivine, phlogopite, diopside, pe...

Field work for the Isukasia map sheet north of Godthåbsfjord, started in 1981 (Allaart et al., 1982), was continued in 1982. A tent base camp was set up at the fjord Kangiussaq both summers. In 1982 seventeen fjeld teams and the glaciological station Qamanârssup sermia were supplied from the base by the GGU cutter J. F. Johnstrup and by a Jet Range...

During the summer of 1981 mapping of the two geological map sheets Ivisartoq 64 V.2 N and Isukasia 65 V.2 S was begun, and mapping continued on the sheet Fiskefjord 64 V.1 N. The map areas are situated between 64°30/ and 65°30/ N (fig. 15). A tent base camp was established at the fjord Kangiussaq in the eastern part of the Godthåb area. Thirteen ge...

Different sources of counting loss are described and the relation Rt = Rm exp (Rt τ) is considered valid for most commercial XRF counting devices. Based on a series of Kα/Kβ measurements and an initial estimate of the Rt (Kα)/Rt (Kβ) value, corresponding τ values can be computed. If the chosen Rt (Kα)/Rt (Kβ) value differs from the correct one, the...

The 1979 field work was the last of a series of three GGU reconnaissance mapping expeditions in the Søndre Upernavik - Kuvdlorssuaq region. The investigations aimed at the production of the 1:500 000 geological map sheet of the Marmorilik - Melville Bugt region. However, at the end of the 1979 field season it became clear that enough field data had...

A geological reconnaissance of the region between 72°15' and 74°15'N was made by Escher & Pulvertaft (1968) during the summer of 1967. In 1977 the region was revisited by J. E. and O. S. and the geological survey was extended as far north as Steenstrup Gletscher (75°15'N) (fig. 7). Both investigations aimed at the production of a 1:500000 geologica...