Cloud radiative forcing of subtropical low level clouds in global models

Simulations of subtropical marine low clouds and their radiative properties by nine coupled ocean-atmosphere climate models participating in the fourth assesment report (AR4) of the intergovernmental panel on climate change (IPCC) are analyzed. Satellite observations of cloudiness and radiative fluxes at the top of the atmosphere (TOA) are utilized for comparison. The analysis is confined to the marine subtropics in an attempt to isolate low cloudiness from tropical convective systems. All analyzed models have a negative bias in the low cloud fraction (model mean bias of −15%). On the other hand, the models show an excess of cloud radiative cooling in the region (model mean excess of 13 W m⁻²). The latter bias is shown to mainly originate from too much shortwave reflection by the models clouds rather than biases in the clear-sky fluxes. These results confirm earlier studies, thus no major progress in simulating the marine subtropical clouds is noted. As a consequence of the combination of these two biases, this study suggests that all investigated models are likely to overestimate the radiative response to changes in low level subtropical cloudiness.     

The Uppsala urban meteorology project

An extensive urban meteorology project in Uppsala, Sweden, is described. The city itself is considered suitable as a kind of model city, being almost circular, having sharp urban/rural boundaries and being situated in a relatively flat area. The project incorporates numerous measurements. A main station with a 100-m mast is situated at the NE urban/rural border. Its instrumentation consists of a slow-response (profile) system and a turbulence system. The profile instrumentation is described in detail. In addition to the main station, the project comprises: measurements from two 14-m masts, one on the top of a centrally located building, the other mobile; pilot balloon ascents; tethered balloon soundings, car-borne temperature traverses etc. Some preliminary results are presented: analyses of wind profiles from the mast and three-dimensional heat island studies.     

New biocide-free anti-fouling paints are toxic

A number of new anti-fouling paints claimed to be more friendly to the environment, have entered the market since prohibition of biocide containing paints have been enforced in many areas. Leakage waters from five new anti-fouling paints were tested for toxic effects to the macro algae Ceramium tenuicorne and Ceramium strictum and to the crustacean Nitocra spinipes. A banned copper and irgarol 1051 containing anti-fouling paint was used as reference. Five of the six paints tested were toxic to all or some of the organisms after two weeks of leakage with EC50 ranging from 0.08 to around 2% leakage water and LC50 ranging from 1.1% to 88%. The toxicity of leakage water from these paints was still high after 16 weeks. We conclude that these paints contain substances toxic to common organisms in the coastal Baltic ecosystem. A silicone based paint did not exhibit toxic effects to the two organisms. We recommend that biological tests should be used to identify the most harmful products before they are released on the market.     

Petrology of iron-rich magmatic segregations associated with strongly peraluminous trondhjemite in the Cornucopia stock, northeastern Oregon

The Middle Cretaceous Cornucopia stock in the Blue Mountains of northeastern Oregon is a small composite intrusion consisting of hornblende biotite tonalite, biotite trondhjemite, and three cordierite two mica trondhjemite units. Unusual magnetite + biotite-rich tonalitic rocks are associated with the Crater Lake cordierite trondhjemite, the youngest of the intrusions. Oxide-rich tonalites are characterized by high Fe (~47-68 wt% total Fe as FeO), low SiO₂ (<36 wt%), and enrichments in HFSE and REE (La_(N)=361-903). Oxide-rich tonalites appear in a variety of forms, including composite dikes and sheets, in which they are associated with leucocratic tonalite. Leucotonalite is lower in SiO₂ (60-72 wt%) than Crater Lake trondhjemite, and generally has DREE contents and Eu anomalies intermediate between the oxide-rich tonalite and Crater Lake compositions. Oxide-rich tonalites crosscut, and are crosscut by, shear zones in the host trondhjemite, indicating their emplacement late in the pluton's crystallization history. Granitic dikes crosscut the composite dikes in all localities. Geochemical considerations and sedimentary-like structures, such as load casts and bedding of magnetite-rich assemblages in the composite dikes and sheets, are suggestive of crystal settling from an Fe-rich parental magma. The Fe-rich liquid parental to the oxide-rich tonalite-leucotonalite pairs formed by extensive, in-situ, plagioclase + quartz-dominated crystallization of strongly peraluminous trondhjemite. Early magnetite saturation in the trondhjemite was suppressed, either because the parental trondhjemitic magma had a lower initial total Fe content or because it had a lower ferric-ferrous ratio, possibly reflecting a lower oxygen fugacity. Accumulation of magnetite from Fe-rich residual magma is a viable mechanism for the concentration of iron, and the subsequent formation of Fe-rich rocks, in calcic siliceous intrusions. Apparently, Fe-enrichment can occur locally in calcic magmas, and is not restricted to rocks of mafic tholeiitic or anorthositic affinity.     

The 1996 and 1998 subglacial eruptions beneath the Vatnajökull ice sheet in Iceland: contrasting geochemical and geophysical inferences on magma migration

87 Sr/⁸⁶Sr (0.70322) and δ ¹⁸O ( ∼2.9‰), whereas significantly lower and higher values, respectively, are found in samples from the Bárdarbunga volcanic system (0.70307 and 3.8‰). These results strongly indicate that the Gjálp magma originated from the Grímsv?tn magma system. The 1996 magma is of an intermediate composition, representing a basaltic icelandite formed by 50% fractional crystallization of a tholeiite magma similar in composition to that expelled by the 1998 Grímsv?tn eruption. The differentiation that produced the Gjálp magma may have taken place in a subsidiary magma chamber that last erupted in 1938 and would be located directly beneath the 1996 eruption site. This chamber was ruptured when a tectonic fracture propagated southward from Bárdarbunga central volcano, as indicated by the seismicity that preceded the eruption. Our geochemical results are therefore not in agreement with lateral magma migration feeding the 1996 Gjálp eruption. Moreover, the results clearly demonstrate that isotope ratios are excellent tracers for deciphering pathways of magma migration and permit a clear delineation of the volcanic systems beneath Vatnaj?kull ice sheet. Received: 1 April 1998 / Accepted: 17 August 1999     

Phosphorus release from coastal Baltic Sea sediments as estimated from sediment profiles

We used the decline in total phosphorus (P) concentration with depth in sediment profiles from the North-western Baltic Proper coastal zone to calculate the site-specific amount of sediment P eventually to be released to the water column: The potentially mobile P. P fractionation revealed that iron bound P dominated the potentially mobile P at sites with oxic surface sediment layers. Organic P forms were also a major constituent of the potentially mobile P pool. We determined that 1–7 g P/m² were potentially mobile at our sites, and the turnover time of this P pool was considered short, i.e., less than a decade. To determine long-term average P fluxes to and from the surface sediment layer, we first multiplied the constant and relatively low P concentration in deeper sediment layers with the sediment accumulation rate to gain the P burial rate. Then the average total P concentration in settling matter was multiplied with the sediment accumulation rate to estimate the depositional P flux at each site. The difference between the depositional and burial rates represents the long-term average release rate of sediment P and varied between 1.0 and 2.7 g P/m² yr among our sites. These rates are at the same order of magnitude as values reported from other areas of the Baltic Sea, and constitute a major source of P to the water column.     

Interferometric space missions for the search for terrestrial exoplanets: Requirements on the rejection ratio

The requirements on space missions designed to study Terrestrial exoplanets are discussed. We then investigate whether the design of such a mission, specifically the Darwin nulling interferometer, can be carried out in a simplified scenario. The key element here is accepting somewhat higher levels of stellar leakage. We establish detailed requirements resulting from the scientific rationale for the mission, and calculate detailed parameters for the stellar suppression required to achieve those requirements. We do this utilizing the Darwin input catalogue. The dominating noise source for most targets in this sample is essentially constant for all targets, while the leakage diminishes with the square of the distance. This means that the stellar leakage has an effect on the integration time only for the nearby stars, while for the more distant targets its influence decreases significantly. We assess the impact of different array configurations and nulling profiles and identify the stars for which the detection efficiency can be maximized.