Geochronology, geochemistry and Nd, Sr and Pb isotopes of syn-orogenic granodiorites and granites (Damara orogen, Namibia) – arc-related plutonism or melting of mafic crustal sources?

Highlights • Geochemical data from high-T granodiorites and granites imply lower crustal amphibolite melting. • New U-Pb zircon ages imply syn-orogenic intrusion • New Sr-Nd-Pb isotope data imply ancient crustal sources and constrain AFC processes Abstract: The Gawib pluton (Damara Belt, Namibia) consists of two main intrusive rock types; magnesian, calc-alkaline, mostly metaluminous hornblende- and titanite-bearing granodiorites and magnesian to ferroan, metaluminous to slightly peraluminous calc-alkaline granites. Uranium-Pb zircon data obtained on the granodiorites gave concordant ages of 548.5 ± 5.6 Ma indicating that the pluton belongs to the early syn-orogenic magmatism in the Damara orogen. Major and trace element variations indicate that fractional crystallization was the major rock-forming mechanism for the granodiorites. In the absence of high-precision geochronological data, the granites may represent more advanced fractionation products of the granodiorites although distinct Ba-Sr-Rb relationships preclude a direct derivation of the granites from the exposed granodiorites. If the granites originated by extensive fractional crystallization from similar granodiorites, they can only be derived from high-Ba, high-Sr, low-Rb granodiorites. Crustal contamination was also important in the petrogenesis of both rock types (granodiorites: ε Nd(init.): -7 to -13; 87Sr/86Sr(init.): 0.708-0.713; granites: ε Nd(init): -14 to -18; 87Sr/86Sr(init.): 0.712-0.726). In contrast to the granodiorites, the granites show more radiogenic 87Sr/86Sr ratios and less radiogenic ε Nd values indicating different contaminants for both rock types. ε Nd vs. MgO relationships imply some genetic link to isotopically unevolved quartz diorites similar to those observed at the Palmental complex. This pluton, however, is located c. 80 km NE from the Gawib pluton and probably cannot be viewed as the direct source of the Gawib granodiorites. If such a relationship is allowed, the granodiorites must be viewed as hybrid rocks containing a juvenile component because they were derived from unevolved quartz diorites by fractional crystallization. In addition, AFC processe have also played a role implying that the granodiorites contain also a reprocessed crustal component. Alternatively, comparison with experimentally derived melts imply that the granodiorites are generated by dehydration melting of a mafic, amphibole-bearing lower crustal source. Chemical parameters of the granodiorites compared to experimental results indicate high temperatures of c. 1040 °C. Zirconium saturation temperatures obtained on the most primitive samples gave c. 830 °C whereas apatite saturation temperatures obtained on the same samples give temperatures of c. 960-980 °C; the latter seems to be a more reliable temperature estimate. Interpretation of geochemical and isotope data from the complex suggest that the early synorogenic Pan-African igneous activity in this part of the Damara Belt was a high-temperature intra-crustal event. In contrast to igneous processes along active continental margins that produce also intermediate plutons with calc-alkaline affinities, this igneous event was not a major crust-forming episode and the granodiorites represent mostly reprocessed crustal material

A Novel Synthetic Yeast for Enzymatic Biodigester Pretreatment

Lignin, a complex organic polymer, is a major roadblock to the efficiency of biofuel conversion as it both physically blocks carbohydrate substrates and poisons biomass degrading enzymes, even if broken down to monomer units. A pretreatment process is often applied to separate the lignin from biomass prior to biofuel conversion. However, contemporary methods of pretreatment require large amounts of energy, which may be economically uncompelling or unfeasible. Taking inspiration from several genes that have been isolated from termites and fungi which translate to enzymes that degrade lignin, we want to establish a novel “enzymatic pretreatment” system where microbes secrete these enzymes to degrade lignocellulosic biomass. We incorporated the following genes into yeast vectors: laccase, lignin peroxidase, and alpha-keto-reductase from Reticulitermes flavipes; versatile peroxidase from Colletotrichum fioriniae PJ7; manganese peroxide from Heterobasidion irregulare TC 32-1; and tyrosinase from Agaricus bisporus. These vectors code for fusion proteins with yeast secretion tags at the end of each enzyme gene, fluorescent protein tags at the beginning, as well as standardized restriction sites for synthetic biology manipulation. Furthermore, we designed an additional vector to contain our genetically modified yeast using an oxygen-repressed killswitch. We expect that transformants with our construct will be able to secrete said enzymes and contribute to lignin degradation if added to a biomass slurry. Future studies may focus on constructing a prototype bioreactor system and optimizing which combination of enzymes lead to the most efficient biofuel production

From pole to pole : 33 years of physical oceanography onboard R/V Polarstern

Measuring temperature and salinity profiles in the world's oceans is crucial to understanding ocean dynamics and its influence on the heat budget, the water cycle, the marine environment and on our climate. Since 1983 the German research vessel and icebreaker Polarstern has been the platform of numerous CTD (conductivity, temperature, depth instrument) deployments in the Arctic and the Antarctic. We report on a unique data collection spanning 33 years of polar CTD data. In total 131 data sets (1 data set per cruise leg) containing data from 10 063 CTD casts are now freely available at doi: 10.1594/PANGAEA.860066. During this long period five CTD types with different characteristics and accuracies have been used. Therefore the instruments and processing procedures (sensor calibration, data validation, etc.) are described in detail. This compilation is special not only with regard to the quantity but also the quality of the data -the latter indicated for each data set using defined quality codes. The complete data collection includes a number of repeated sections for which the quality code can be used to investigate and evaluate long-term changes. Beginning with 2010, the salinity measurements presented here are of the highest quality possible in this field owing to the introduction of the OPTIMARE Precision Salinometer.Peer reviewe

Direct measurements of volume transports through Fram Strait

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 106 m3s?1). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates

Observed and modelled stability of overflow across the Greenland-Scotland ridge

Across the Greenland - Scotland ridge there is a continuous flow of cold dense water, termed 'overflow', from the Nordic seas to the Atlantic Ocean(1). This is a main contributor to the production of North Atlantic Deep Water(2) that feeds the lower limb of the Atlantic meridional overturning circulation, which has been predicted to weaken as a consequence of climate change(3,4). The two main overflow branches pass the Denmark Strait and the Faroe Bank channel. Here we combine results from direct current measurements in the Faroe Bank channel(5) for 1995 - 2005 with an ensemble hindcast experiment(6) for 1948 - 2005 using an ocean general circulation model. For the overlapping period we find a convincing agreement between model simulations and observations on monthly to interannual timescales. Both observations and model data show no significant trend in volume transport. In addition, for the whole 1948 - 2005 period, the model indicates no persistent trend in the Faroe Bank channel overflow or in the total overflow transport, in agreement with the few available historical observations. Deepening isopycnals in the Norwegian Sea have tended to decrease the pressure difference across the Greenland - Scotland ridge(7), but this has been compensated for by the effect of changes in sea level. In contrast with earlier studies(7,8), we therefore conclude that the Faroe Bank channel overflow, and also the total overflow, did not decrease consistently from 1950 to 2005, although the model does show a weakening total Atlantic meridional overturning circulation as a result of changes south of the Greenland - Scotland ridge

Abyssal warming in the Nordic Seas

Since Greenland Sea Deep Water (GSDW) is the coldest of the three local Deep Waters, Meincke & Rudels (1995) concluded that the sustained warming in the deep Greenland Sea from the early 1970s to the present was due to a progressive shift from vertical exchange (with the cool surface layers) to horizontal exchange [with the relatively warm Arctic Ocean Deep Water (AODW) through Fram Strait], and the accompanying changes in silicate and oxygen were consistent with that view. Dickson & Østerhus (2007) later explained the parallel warming of Norwegian Sea Deep Water at 2000m beneath OWS M as being due to the spread of this warming GSDW through the Jan Mayen Channel (sill 2000m). Here we follow the warming signal northwards from OWS M through the Lofoten Basin to the Fram Strait, where we conclude that it may explain the steady rise in temperature observed close to the seabed over the last ten years in the deepest part of the water column (2500m) at the HAUSGARTEN-centre site. Since sea-floor temperature is a known control on the dissociation of gas hydrates from sediments in this area, it is important to develop an understanding of the cause of such a sustained warming trend. If our conclusion is correct, the observed warming there may be just the recent expression of a longer trend involving changes in the exchange of deep waters between three ocean basins (Eurasian, Greenland and Norwegian) over a period of 4 decades. And at OWS M and Fram Strait, the deep warming continues