Holocene climatic variations and postglacial sea-level rise geochemically recorded in the sediments of the brackish karst lake An Loch Mor, western Ireland     

GEORG SCHETTLER  ROLF L. ROMER  MICHAEL O'CONNELL  KAREN MOLLOY 《Boreas: An International Journal of Quaternary Research》2006,35(4):674-693

Palaeohydrology of the brackish karst lake An Loch Mór (Inis Oirr) was reconstructed based on its 11 600 year sedimentation record. Low calcareous early Holocene sediments, characterized by high TOC contents and deposited at generally low accumulation rates, show a gradual decrease upwards in the concentration of the siliciclastic sediment until c . 7000 cal. yr BP. From c . 9000 cal. yr BP, sediment accumulation became increasingly dominated by the deposition of autochthonous calcite and organic matter. The deposition of autochthonous calcite and its chemical composition (Ca/Sr, Ca/Mg) are determined by the subsurface inflow of freshwater from the catchment of the lake and by the balance between freshwater and seawater influx. During the early Holocene, the lake mainly received input of sea salt by sea-spray. The sediments document the further development from seasonal towards the onset of diurnal infiltration of seawater at c . 5100 cal. yr BP. At that time, the relative sea level must have risen nearly to its present level in Galway Bay. Diurnal seawater infiltration during high tides was controlled by freshwater input. Freshwater inflow from the catchment gradually increased with human impact on local vegetation (EVPT decrease). Permanent diurnal seawater infiltration in concert with this general freshwater increase made the geochemical sedimentation record highly sensitive to changes in annual precipitation. We use information from the palynological record to interpret geochemically inferred freshwater inflow variations in terms of dry and wet climatic periods and document distinct century-scale successions between wet and dry climatic episodes for western Ireland.  相似文献   

Lipid composition of phytoplankton from the Barents Sea and environmental influences on the distribution pattern of carbon among photosynthetic end products     

R. JAMES HENDERSON  ROLF E. OLSEN  HANS C. EILERTSEN 《Polar research》1991,10(1):229-238

The colonial algae Phaeocystis pouchetii and Dinobryon pellucidum dominated the phytoplankton crop at three stations in the Polar Front area of the Barents Sea.
Lipid extracted from the seawater containing the phytoplankton was dominated by neutral lipid classes, particularly triacylglycerols, and phospholipids were more abundant than galactolipids at all stations. Polyunsaturated fatty acids comprised between 15 and 26% of fatty acids of total lipid.
Of the carbon assimilated into lipid over 24 hours, 40% was located in the neutral lipid fraction. Phospholipids contained a smaller proportion of fixed carbon than galactolipids.
No defiinte relationships were observed between the distribution of fixed carbon in photosynthetic end products and the temperature or irradiance at which the phytoplankton was incubated. At a constant irradiance of 8.5 μmol m⁻²s⁻¹, the highest proportion of fixed carbon was recovered in protein at 4.5°C, but at −1.5°C most radioactivity was present in low molecular weight compounds. Regardless of incubation conditions, lipid always contained less than 30% of total assimilated carbon.  相似文献   

The 'common vole' in Svalbard identified as Microtus epiroticus by chromosome analysis     

KARL FREDGA  MAARIT JAAROLA  ROLF ANKER IMS  HARALD STEEN  NIGEL G. YOCCOZ 《Polar research》1990,8(2):283-290

The chromosomes were studied in six individuals from a population of Microtus from Grumantbyen, Svalbard, and in six Microtur arualis (Pallas 1778) from Lauwersee, Holland. It was shown that the voles from Svalbard did not belong, as earlier supposed, to the species M. arualis (2n = 46) but to M . epiroticus (Ondrias, 1966) (2n = 54). We suggest that the Svalbard voles were introduced by man between 1920 and 1960 together with hay on Russian ships from the vicinity of Leningrad, USSR.  相似文献   

Intercomparison of fog water samplers     

DIETER SCHELL  HANS-WALTER GEORGII  ROLF MASER  WOLFGANG JAESCHKE  BEATE G. ARENDS  GERARD P. A. KOS  PETER WINKLER  THOMAS SCHNEIDER  AXEL BERNER  CHRISTIAN KRUISZ 《Tellus. Series B, Chemical and physical meteorology》1992,44(5):612-631

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Genesis of Ultramafic Lamprophyres and Carbonatites at Aillik Bay, Labrador: a Consequence of Incipient Lithospheric Thinning beneath the North Atlantic Craton   总被引：7，自引：0，他引：7  

TAPPE  SEBASTIAN; FOLEY  STEPHEN F.; JENNER  GEORGE A.; HEAMAN  LARRY M.; KJARSGAARD  BRUCE A.; ROMER  ROLF L.; STRACKE  ANDREAS; JOYCE  NANCY; HOEFS  JOCHEN 《Journal of Petrology》2006,47(7):1261-1315

Numerous dykes of ultramafic lamprophyre (aillikite, mela-aillikite,damtjernite) and subordinate dolomite-bearing carbonatite withU–Pb perovskite emplacement ages of 590–555 Ma occurin the vicinity of Aillik Bay, coastal Labrador. The ultramaficlamprophyres principally consist of olivine and phlogopite phenocrystsin a carbonate- or clinopyroxene-dominated groundmass. Ti-richprimary garnet (kimzeyite and Ti-andradite) typically occursat the aillikite type locality and is considered diagnosticfor ultramafic lamprophyre–carbonatite suites. Titanianaluminous phlogopite and clinopyroxene, as well as comparativelyAl-enriched but Cr–Mg-poor spinel (Cr-number < 0.85),are compositionally distinct from analogous minerals in kimberlites,orangeites and olivine lamproites, indicating different magmageneses. The Aillik Bay ultramafic lamprophyres and carbonatiteshave variable but overlapping ⁸⁷Sr/⁸⁶Sr_i ratios (0·70369–0·70662)and show a narrow range in initial _Nd (+0·1 to +1·9)implying that they are related to a common type of parentalmagma with variable isotopic characteristics. Aillikite is closestto this primary magma composition in terms of MgO (15–20wt %) and Ni (200–574 ppm) content; the abundant groundmasscarbonate has ¹³C_PDB between –5·7 and –5,similar to primary mantle-derived carbonates, and ¹⁸O_SMOW from9·4 to 11·6. Extensive melting of a garnet peridotitesource region containing carbonate- and phlogopite-rich veinsat 4–7 GPa triggered by enhanced lithospheric extensioncan account for the volatile-bearing, potassic, incompatibleelement enriched and MgO-rich nature of the proto-aillikitemagma. It is argued that low-degree potassic silicate to carbonatiticmelts from upwelling asthenosphere infiltrated the cold baseof the stretched lithosphere and solidified as veins, therebycrystallizing calcite and phlogopite that were not in equilibriumwith peridotite. Continued Late Neoproterozoic lithosphericthinning, with progressive upwelling of the asthenosphere beneatha developing rift branch in this part of the North Atlanticcraton, caused further veining and successive remelting of veinsplus volatile-fluxed melting of the host fertile garnet peridotite,giving rise to long-lasting hybrid ultramafic lamprophyre magmaproduction in conjunction with the break-up of the Rodinia supercontinent.Proto-aillikite magma reached the surface only after coatingthe uppermost mantle conduits with glimmeritic material, whichcaused minor alkali loss. At intrusion level, carbonate separationfrom this aillikite magma resulted in fractionated dolomite-bearingcarbonatites (¹³C_PDB –3·7 to –2·7)and carbonate-poor mela-aillikite residues. Damtjernites maybe explained by liquid exsolution from alkali-rich proto-aillikitemagma batches that moved through previously reaction-lined conduitsat uppermost mantle depths. KEY WORDS: liquid immiscibility; mantle-derived magmas; metasomatism, Sr–Nd isotopes; U–Pb geochronology  相似文献   

Dolomite formation within microbial mats in the coastal sabkha of Abu Dhabi (United Arab Emirates)   总被引：1，自引：0，他引：1  

TOMASO R. R. BONTOGNALI  CRISÓGONO VASCONCELOS  ROLF J. WARTHMANN  STEFANO M. BERNASCONI  CHRISTOPHE DUPRAZ  CHRISTIAN J. STROHMENGER  JUDITH A. McKENZIE 《Sedimentology》2010,57(3):824-844

Microbial mediation is the only demonstrated mechanism to precipitate dolomite under Earth surface conditions. A link between microbial activity and dolomite formation in the sabkha of Abu Dhabi has, until now, not been evaluated, even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences. Such an evaluation is the purpose of this study, which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of Abu Dhabi, along a transect from the intertidal to the supratidal zone. This investigation revealed a close association between microbial mats and dolomite, suggesting that microbes are involved in the mineralization process. Observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats. In current models, microbial dolomite precipitation is linked to an active microbial activity that sustains high pH and alkalinity and decreased sulphate concentrations in pore waters. Such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone. By contrast, these models cannot be applied to the supratidal zone, where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity. As no abiotic mechanism is known to form dolomite at Earth surface conditions, two different hypotheses can reconcile this result. In a first scenario, all of the dolomite present in the supratidal zone formed in the past, when the mats were active at the surface. In a second scenario, dolomite formation continues within the buried and inactive mats. In order to explain dolomite formation in the absence of active microbial metabolisms, a revised microbial model is proposed in which the mineral‐template properties of exopolymeric substances play a crucial role.  相似文献   

Observations and modelling of the global distribution and long-term trend of atmospheric ¹⁴CO₂     

By INGEBORG LEVIN †  TOBIAS NAEGLER †  BERND KROMER  MORITZ DIEHL ‡  ROGER J. FRANCEY  ANGEL J. GOMEZ-PELAEZ  L. PAUL STEELE  DIETMAR WAGENBACH  ROLF WELLER  DOUGLAS E. WORTHY 《Tellus. Series B, Chemical and physical meteorology》2010,62(1):26-46

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Petrological, Geochemical and Isotopic Constraints on the Origin of the Harzburg Intrusion, Germany   总被引：1，自引：0，他引：1  

SANO  SAKAE; OBERHANSLI  ROLAND; ROMER  ROLF L.; VINX  ROLAND 《Journal of Petrology》2002,43(8):1529-1549

We present mineralogical, petrological and geochemical datato constrain the origin of the Harzburg mafic–ultramaficintrusion. The intrusion is composed mainly of mafic rocks rangingfrom gabbronorite to quartz diorite. Ultramafic rocks are veryrare in surface outcrops. Dunite is observed only in deepersections of the Flora I drill core. Microgranitic (fine-grainedquartz-feldspathic) veins found in the mafic and ultramaficrocks result from contamination of the ultramafic magmas bycrustal melts. In ultramafic and mafic compositions cumulatetextures are widespread and filter pressing phenomena are obvious.The order of crystallization is olivine pargasite, phlogopite,spinel plagioclase, orthopyroxene plagioclase, clinopyroxene.Hydrous minerals such as phlogopite and pargasite are essentialconstituents of the ultramafic cumulates. The most primitiveolivine composition is Fo_89·5 with 0·4 wt % NiO,which indicates that the olivine may have been in equilibriumwith primitive mantle melts. Coexisting melt compositions estimatedfrom this olivine have mg-number = 71. The chemical varietyof the rocks constituting the intrusion and the mg-number ofthe most primitive melt allow an estimation of the approximatecomposition of the mantle-derived primary magma. The geochemicalcharacteristics of the estimated magma are similar to thoseof an island-arc tholeiite, characterized by low TiO₂ and alkalisand high Al₂O₃. Geochemical and Pb, Sr and Nd isotope data demonstratethat even the most primitive rocks have assimilated crustalmaterial. The decoupling of Sr from Nd in some samples demonstratesthe influence of a fluid that transported radiogenic Sr. Leadof crustal origin from two isotopically distinct reservoirsdominates the Pb of all samples. The ultramafic rocks and thecumulates best reflect the initial isotopic and geochemicalsignature of the parent magma. Magma that crystallized in theupper part of the chamber was more strongly affected by assimilatedmaterial. Petrographic, geochemical and isotope evidence demonstratesthat during a late stage of crystallization, hybrid rocks formedthrough the mechanical mixing of early cumulates and melts withstrong crustal contamination from the upper levels of the magmachamber. KEY WORDS: Harzburg mafic–ultramafic intrusion; Sr–Nd–Pb isotopes; magma evolution; crustal contamination  相似文献   

P-T-t Evolution of Ultrahigh-Temperature Granulites from the Saxon Granulite Massif, Germany. Part II: Geochronology     

ROMER  ROLF L.; ROTZLER  JOCHEN 《Journal of Petrology》2001,42(11):2015-2032

Granulite-facies metamorphism in the structurally lower partof the Saxon Granulite Massif culminated at 1010–1060°Cand  相似文献   

Six-year record of atmospheric carbon dioxide and methane at a high-altitude mountain site in Poland   总被引：2，自引：0，他引：2  

JAROSLAW NECKI  MARTINA SCHMIDT  KAZIMIERZ ROZANSKI  MIROSLAW ZIMNOCH  ADAM KORUS  JAN LASA  ROLF GRAUL  INGEBORG LEVIN 《Tellus. Series B, Chemical and physical meteorology》2003,55(2):94-104

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