Mud volcanoes and gas hydrates in the Anaximander mountains (Eastern Mediterranean Sea)

Detailed multibeam, sedimentological, and geophysical surveys provide ample new data to confirm that the Anaximander Mountains (Eastern Mediterranean) are an important area for active mud volcanism and gas hydrate formation. More than 3000 km of multibeam track length was acquired during two recent missions and 80 gravity and box cores were recovered. Morphology and backscatter data of the study area have better resolution than previous surveys, and very detailed morphology maps have been made of the known targeted mud volcanoes (Amsterdam, Kazan and Kula), especially the Amsterdam “crater” and the related mud breccia flows. Gas hydrates collected repeatedly from a large area of Amsterdam mud volcano at a sub-bottom depth of around 0.3–1.5 m resemble compacted snow and have a rather flaky form. New gas hydrate sites were found at Amsterdam mud volcano, including the mud flow sloping off to the south. Gas hydrates sampled for the first time at Kazan mud volcano are dispersed throughout the core samples deeper than 0.3 m and display a ‘rice’-like appearance. Relative chronology and AMS dating of interbedded pelagic sediments (Late Holocene hemipelagic, sapropel layer S1 and ash layers) within the mud flows indicate that successive eruptions of Kula mud volcano have a periodicity of about 5–10 kyrs. New mud volcanoes identified on the basis of multibeam backscatter intensity were sampled, documented as active and named “Athina” and “Thessaloniki”. Gas hydrates were sampled also in Thessaloniki mud volcano, the shallowest (1264 m) among all the active Mediterranean sites, at the boundary of the gas hydrate stability zone. Biostratigraphical analyses of mud breccia clasts indicated that the source of the subsurface sedimentary sequences consists of Late Cretaceous limestones, Paleocene siliciclastic rocks, Eocene biogenic limestones and Miocene mudstones. Rough estimations of the total capacity of the Anaximander mud volcanoes in methane gas are 2.56–6.40 km³.     

Differential UVB‐sensitivities of five New Zealand freshwater zooplankton species

Abstract

The ultraviolet (UV) sensitivity of five species of freshwater zooplankton (three Cladocera, two Copepoda) were investigated. The animals were exposed to varying levels of UV‐radiation in a sunshine‐simulator and the UV doses for 10 and 50% mortality (LD₁₀, LD₅₀) were estimated using a dose‐response model. To place these doses in context they were compared with modelled clear‐sky surface UV irradiances in New Zealand. The cladocerans Daphnia carinata and Ceriodaphnia dubia were sensitive to levels of UVB irradiance of LD₁₀ = 18–25 kJ m^?2 and LD₅₀ = 35–37 kJ m^?2. These sensitivities are consistent with published values for other cladocera. In contrast a third cladoceran, Bosmina meridionalis, exhibited no higher mortality over the full range of the cumulative UVB‐doses used (3–40 kJ m^?2) than controls receiving no UV exposure. The copepod Boeckella delicata showed the highest UV‐sensitivity of all organisms tested (LD10 = 7 kJ m^?2, LD50 = 33 kJ m^?2) whereas for Boeckella triarticulata, which was more heavily pigmented than B. delicata, no UV‐induced mortality was observed. Under natural conditions UV irradiances of up to 100 kJ m^?2 day^?1 can fall on the surface of New Zealand lakes. Although this is attenuated in natural waters, these data suggest that UVB irradiance may be a significant ecological variable to some zooplankton species.     

Stellungnahme zu den „Anmerkungen“

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Lead-isotope inhomogeneity in Precambrian igneous K-feldspars

Stepwise Pb-removal experiments, using both vacuum volatilization and HF-leaching techniques, on acid-washed K-feldspar concentrates from Precambrian igneous rocks show that all contain some unsupported radiogenic Pb. Two types of radiogenic Pb were recognized. One has a “normal” isotopic composition, with relative abundances of ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb consistent with the age and U-Th contents of the rocks. The other type of unsupported radiogenic lead in the feldspars is apparently pure ²⁰⁶Pb, derived from long-term migration and accumulation of radioactive daughter(s) of ²³⁸U. This “pure ²⁰⁶pb” lead occupies different sites from the “normal” radiogenic lead, and tends to show a release maximum during vacuum volatilization at about 1150°C.The usefulness of stepwise vacuum volatilization may be limited by the tendency of a small amount of radiogenic lead to concentrate in the least volatile fraction. Stepwise partial HF attacks appear to give at least as good separation of radiogenic from original feldspar lead, and are recommended as a routine procedure for isotopic analyses of Precambrian feldspars. The fact that most of the five K-feldspars examined contained unsupported radiogenic lead implies that caution must be used in applying total-sample lead analyses of Precambrian feldspars to problems of lead-isotope evolution in crustal rocks.