1000 m long gas blow-out pipes

This study presents seismic observation of pipe anomalies from offshore Nigeria, outcrops of blow-out pipes from Rhodes, Greece, and geophysical modelling of an acoustic pipe. The studies give insight into how pipes form, their internal structure, the seismic image and geophysical artefacts related to the pipes. Over one hundred seafloor craters, 100 m-700 m wide and up to 30 m deep, have been observed on the seafloor offshore Nigeria. They are underlain by interpreted cones and seismic pipe anomalies that can be traced down to reservoir zones at 1000 m-1300 m below the seafloor. The seismic pipe anomalies are 50 m-150 m wide and almost vertical. They are interpreted as up-scaled pipes found in outcrops on Rhodes, Greece. The outcrops show pipe-related structures at three levels. Lowest, the reservoir rock contains metre-sized cavities which are filled with a mixture of clay derived from the overlying cap rock. In the middle, several circular to oval structures in plane view of pipes are observed in the lowest part of the cap rock. Highest, 15 m into the clay cap rock, strongly sheared country rock forms circular structures with a core of structureless clay. Based on outcrop observation on Rhodes we constructed an acoustic model of a 50 m wide and 1000 m long pipe. Seismic modelling proves that such pipes would be expressed in seismic data, that they are similar to the seismic pipe anomalies offshore Nigeria but this study also revealed that prominent intra-pipe reflections are artefacts. A formation model for the pipes is suggested: High fluid overpressure in the reservoir generated hydro fractures from the reservoir to seafloor where a mixture of gas and fluid flowed at high speed to form pipes, cones and seafloor craters. After hours to weeks of gas and fluid flow through the pipe the pore pressure in the reservoir dropped and the blow-out terminated. Muddy slurry fell back and plugged the cavity in the reservoir and the pipe.     

On the potential for CO2 mineral storage in continental flood basalts – PHREEQC batch- and 1D diffusion–reaction simulations

Continental flood basalts (CFB) are considered as potential CO₂ storage sites because of their high reactivity and abundant divalent metal ions that can potentially trap carbon for geological timescales. Moreover, laterally extensive CFB are found in many place in the world within reasonable distances from major CO₂ point emission sources. Based on the mineral and glass composition of the Columbia River Basalt (CRB) we estimated the potential of CFB to store CO₂ in secondary carbonates. We simulated the system using kinetic dependent dissolution of primary basalt-minerals (pyroxene, feldspar and glass) and the local equilibrium assumption for secondary phases (weathering products). The simulations were divided into closed-system batch simulations at a constant CO₂ pressure of 100?bar with sensitivity studies of temperature and reactive surface area, an evaluation of the reactivity of H₂O in scCO₂, and finally 1D reactive diffusion simulations giving reactivity at CO₂ pressures varying from 0 to 100?bar. Although the uncertainty in reactive surface area and corresponding reaction rates are large, we have estimated the potential for CO₂ mineral storage and identified factors that control the maximum extent of carbonation. The simulations showed that formation of carbonates from basalt at 40?C may be limited to the formation of siderite and possibly FeMg carbonates. Calcium was largely consumed by zeolite and oxide instead of forming carbonates. At higher temperatures (60 ?C 100?C), magnesite is suggested to form together with siderite and ankerite. The maximum potential of CO₂ stored as solid carbonates, if CO₂ is supplied to the reactions unlimited, is shown to depend on the availability of pore space as the hydration and carbonation reactions increase the solid volume and clog the pore space. For systems such as in the scCO₂ phase with limited amount of water, the total carbonation potential is limited by the amount of water present for hydration of basalt.     

Disinfection by-products and ecotoxicity of ballast water after oxidative treatment – Results and experiences from seven years of full-scale testing of ballast water management systems

Since 2005, five different ballast water management systems (BWMSs) based on chlorination treatment have been tested by Norwegian Institute for Water Research (NIVA) according to guidelines from the International Maritime Organization (IMO). 25% and >50% of all the tested discharge samples exhibited acute and chronic toxic effects on algae, respectively. In most cases this toxicity was plausibly caused by a high free residual oxidant (FRO) level (>0.08 mg Cl/l). Of the 22 disinfection by-products (DBPs) that were identified in treated water at discharge, four compounds were at times found at concentrations that may pose a risk to the local aquatic environment. However, there seemed to be no clear indication that the measured DBP concentrations contributed to the observed algal toxicity. The addition of methylcellulose instead of lignin in the test water to comply with IMO requirements seemed to limit the formation of DBP.     

Diagnostic lipid biomarker and stable carbon isotope signatures of microbial communities mediating the anaerobic oxidation of methane with sulphate

The anaerobic oxidation of methane (AOM) with sulphate is the most important sink for methane in marine environments. This process is mediated by a consortium of methanotrophic archaea and sulphate reducing bacteria. So far, three groups of anaerobic methane oxidisers (ANME-1, -2 and -3) related to the methanogenic Methanosarcinales and Methanomicrobiales were discovered. The sulphate reducing partner of ANME-1 and -2 are two different eco-types of SRB related to the Desulfosarcina/Desulfococcus cluster (Seep-SRB1), whereas ANME-3 is associated with Desulfobulbus spp. (DBB). In this article, we reviewed literature data to assign statistically significant lipid biomarker signatures for a chemotaxonomic identification of the three known AOM communities. The lipid signatures of ANME-2/Seep-SRB1 and ANME-3/DBB are intriguingly similar, whereas ANME-1/Seep-SRB1 shows substantial differences to these AOM communities. ANME-1 can be distinguished from ANME-2 and -3 by a low ratio of the isoprenoidal dialkyl glycerol diethers sn2-hydroxyarchaeol and archaeol combined with a comparably low stable carbon isotope difference of archaeol relative to the source methane. Furthermore, only ANME-1 contains substantial amounts of isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs), however, with the probable exception of the ANME-2c sub-cluster. In contrast to the ANME-1 archaea, the tail to tail linked hydrocarbon tetramethylhexadecane (crocetane) is unique to ANME-2, whereas pentamethylicosenes (PMIs) with 4 and 5 double bonds without any higher saturated homologues were only found in ANME-3. The sulphate reducing partner of ANME-1 can be discerned from those of ANME-2 and -3 by a low ratio of the fatty acids (FAs) C_16:1ω5 relative to i-C_15:0 and, although to a lesser degree, by a high abundance of ai-C_15:0 relative to i-C_15:0. Furthermore, substantial amounts of ¹³C depleted non-isoprenoidal monoalkyl glycerol ethers (MAGEs) were only found in the sulphate reducing partners of ANME-2 and -3. A differentiation of these SRB is possible based on the characteristic presence of the FAs cy-C_17:0ω5,6 and C_17:1ω6, respectively. Generally, the data analysed here show overlaps between the different AOM communities, which highlights the need to use multiple lipid signatures for a robust identification of the dominating microbes involved.     

一个淡水扰动试验中垂直混合对于北大西洋经圈环流的影响

It has been reported recently that the simulated Atlantic meridional overturning circulation(AMOC) using the coupled Bergen climate model(BCM) showed initial intensity declines followed by gradual recoveries over a 150-year enhanced freshwater input experiment.Stratification-dependent oceanic diapycnal mixing has been hypothesized as a reason for the simulated recovery of the AMOC.This study investigated the role of diapycnal mixing in transient responses of simulated AMOCs.Our results showed that stratification-dependent diapycnal mixing can cause stronger upwelling of deep water in the tropical Atlantic than that produced under conditions of fixed diapycnal mixing.Moreover,simulated AMOCs were more sensitive to active stratification-dependent diapycnal mixing than fixed mixing.However,stratification-dependent diapycnal mixing cannot be conclusively singled out as the critical cause of the recoveries of simulated AMOCs under enhanced-freshwater inputs.     

Variability in terrigenous sedimentation processes off northwest Africa and its relation to climate changes: Inferences from grain-size distributions of a Holocene marine sediment record

Variations in deposition of terrigenous fine sediments and their grain-size distributions from a high-resolution marine sediment record offshore northwest Africa (30°51.0′N; 10°16.1′W) document climate changes on the African continent during the Holocene. End-member grain-size distributions of the terrigenous silt fraction, which are related to fluvial and aeolian dust transport, indicate millennial-scale variability in the dominant transport processes at the investigation site off northwest Africa as well as recurring periods of dry conditions in northwest Africa during the Holocene. The terrigenous record from the subtropical North Atlantic reflects generally humid conditions before the Younger Dryas, during the early to mid-Holocene, as well as after 1.3 kyr BP. By contrast, continental runoff was reduced and arid conditions were prevalent at the beginning of the Younger Dryas and during the mid- and late Holocene. A comparison with high- and low-latitude Holocene climate records reveals a strong link between northwest African climate and Northern Hemisphere atmospheric circulation throughout the Holocene. Due to its proximal position, close to an ephemeral river system draining the Atlas Mountains as well as the adjacent Saharan desert, this detailed marine sediment record, which has a temporal resolution between 15 and 120 years, is ideally suited to enhance our understanding of ocean-continent-atmosphere interactions in African climates and the hydrological cycle of northern Africa after the last deglaciation.     

北大西洋年际变率的海气耦合模式模拟Ⅰ：局地海气相互作用

检验了一个全球海气耦合模式对北大西洋年际气候变率的模拟,讨论了导致这种年际变率型的物理机制,并分析了其对年代际变率的可能影响。北大西洋冬季SST的主导变率模态,在经向上表现为三核型,自北而南出现“- -”的带状距平型;最大距平中心位于副极地大洋、中纬度大洋的西部以及热带海域,耦合模式较为真实地再现了这一特征。与三核型SST异常相对应的大气环流型表现为北大西洋涛动,具有显著的正压结构。上述异常型主要发生在年际尺度,具有3—4年的谱峰;在次年代际尺度上,也存在谱峰。分析表明,模式中三核型SST异常的产生,主要来自大气的强迫,NAO增强,中纬度大洋上的西风减弱,海洋感热和潜热通量损失减少,中纬度大洋得到的净热通量增加,导致SST出现正距平;在包括Labrador海在内的副极地大洋,NAO增强、冰岛低压加深,气旋性环流增强,来自高纬度的冷空气吹过洋面,海气温差加大,大洋的感热通量损失增加,SST降低。热带地区东风的增强,也是导致那里SST降低的重要机制。三核型SST异常对大气的反馈作用较弱,文中没有证据表明它能够影响到北大西洋地区的年代际气候变率。     

The poor cluster of galaxies S639

We have studied the poor southern cluster of galaxies S639. Based on new Strömgren photometry of stars in the direction of the cluster, we confirm that the Galactic extinction affecting the cluster is large. We find the extinction in Johnson B to be A_B =0.75±0.03. We have obtained new photometry in Gunn r for E and S0 galaxies in the cluster. If the Fundamental Plane is used for determination of the relative distance and the peculiar velocity of the cluster, we find a distance, in velocity units, of (5706±350) km s⁻¹, and a substantial peculiar velocity, (839±350) km s⁻¹. However, the colours and the absorption line indices of the E and S0 galaxies indicate that the stellar populations in these galaxies are different from those in similar galaxies in the two rich clusters Coma and Hydra I. This difference may severely affect the distance determination and the derived peculiar velocity. The data are consistent with a non-significant peculiar velocity for S639 and the galaxies in the cluster being on average 0.2 dex younger than similar galaxies in Coma and Hydra I. The results for S639 caution that some large peculiar velocities may be spurious and caused by unusual stellar populations.     

A possible feedback mechanism involving the Arctic freshwater, the Arctic sea ice, and the North Atlantic Drift

Model studies point to enhanced warming and to increased freshwater fluxes to high northern latitudes in response to global warming. In order to address possible feedbacks in the ice-ocean system in response to such changes, the combined effect of increased freshwater input to the Arctic Ocean and Arctic warming--the latter manifested as a gradual melting of the Arctic sea ice--is examined using a 3-D isopycnic coordinate ocean general circulation model. A suite of three idealized experiments is carried out: one control integration, one integration with a doubling of the modern Arctic river runoff, and a third more extreme case, where the river runoff is five times the modern value. In the two freshwater cases, the sea ice thickness is reduced by 1.5-2 m in the central Arctic Ocean over a 50-year period. The modelled ocean response is qualitatively the same for both perturbation experiments: freshwater propagates into the Atlantic Ocean and the Nordic Seas, leading to an initial weakening of the North Atlantic Drift.Furthermore, changes in the geostrophic currents in the central Arctic and melting of the Arctic sea ice lead to an intensified Beaufort Gyre, which in turn increases the southward volume transport through the Canadian Archipelago. To compensate for this southward transport of mass, more warm and saline Atlantic water is carried northward with the North Atlantic Drift. It is found that the increased transport of salt into the northern North Atlantic and the Nordic Seas tends to counteract the impact of the increased freshwater originating from the Arctic, leading to a stabilization of the North Atlantic Drift.