Space Sciences

Giant hydrogen sulfide plume in the oxygen minimum zone off peru supports chemolithoautotrophy

T.Kalvelage , G.Lavik , S.Contreras , C.R. , A.Paulmier , M.M. , H.Schunck , D.K. , T.Grosskopf , H.Siegel , M.Holtappels , P.Rosenstiel , M.B. , M.Graco , R.A. , J.Laroche


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In Eastern Boundary Upwelling Systems nutrient-rich waters are transported to the ocean surface, fuelling high photoautotrophic primary production. Subsequent heterotrophic decomposition of the produced biomass increases the oxygen-depletion at intermediate water depths, which can result in the formation of oxygen minimum zones. OMZs can sporadically accumulate hydrogen sulfide , which is toxic to most multicellular organisms and has been implicated in massive fish kills. During a cruise to the OMZ off Peru in January 2009 we found a sulfidic plume in continental shelf waters, covering an area >5500 km , which contained similar to 2. 2 x 10 tons of H2S. This was the first time that H2S was measured in the Peruvian OMZ and with similar to 440 km the largest plume ever reported for oceanic waters. We assessed the phylogenetic and functional diversity of the inhabiting microbial community by high-throughput sequencing of DNA and RNA, while its metabolic activity was determined with rate measurements of carbon fixation and nitrogen transformation processes. The waters were dominated by several distinct gamma-, delta-and epsilon-proteobacterial taxa associated with either sulfur oxidation or sulfate reduction. Our results suggest that these chemolithoautotrophic bacteria utilized several oxidants to detoxify the sulfidic waters well below the oxic surface. The chemolithoautotrophic activity at our sampling site led to high rates of dark carbon fixation. Assuming that these chemolithoautotrophic rates were maintained throughout the sulfidic waters, they could be representing as much as similar to 30% of the photoautotrophic carbon fixation. Postulated changes such as eutrophication and global warming, which lead to an expansion and intensification of OMZs, might also increase the frequency of sulfidic waters. We suggest that the chemolithoautotrophically fixed carbon may be involved in a negative feedback loop that could fuel further sulfate reduction and potentially stabilize the sulfidic OMZ waters.

A Comparison of Lower Thermospheric Winds Derived From Range Spread and Specular Meteor Trail Echoes

L.G. , H.L. , R.I. , C.Y.H. , N.B.Q. , D.B.


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Extent: 12p.Interferometry measurements of range spread meteor trail echoes (RSTEs; also known as nonspecular echoes) have provided new insights into both the irregularity structures in meteor trails and lower-thermospheric winds (LTWs). In this study, we used trail echoes observed with the newly installed Sanya (18.4°N, 109.6°E) 47.5 MHz VHF coherent radar and the Sanya all-sky meteor radar to estimate instantaneous zonal and hourly averaged meridional winds from RSTEs and hourly averaged zonal and meridional winds from large numbers of specular meteor echoes. The mean height variations in both the zonal and meridional winds estimated from the RSTEs were generally consistent with those estimated from specular meteor echoes below 96 km. This gives validity to the technique proposed recently by Oppenheim et al. (2009) and suggests that RSTE measurements made with a small radar can be used to investigate LTWs, whereas this had previously been limited to larger radars such as the Jicamarca radar. However, some observations show significant differences in wind magnitude at individual heights at times. The results of RSTE measurements show the presence of an intense westward wind with a speed near 100 ms−1. In contrast, the specular meteor zonal winds were generally less than 50 ms−1. On the other hand, the meridional drift of RSTEs derived from the meridional Doppler velocity at higher altitudes shows a very poor correlation with the specular meteor meridional wind. Potential causes for the discrepancy in wind estimates obtained from RSTE and specular meteor trail echoes are discussed.Guozhu Li, Baiqi Ning, Lianhuan Hu, Yen-Hsyang Chu, I. M. Reid and B. K. Dolma

Estimation of the dynamics and yields of cereals in a semi-arid area using remote sensing and the safy growth model

M.Zribi , G.Boulet , B.Mougenot , Z.Lili-Chabaane , A.Chahbi , B.Duchemin , M.Shabou


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In semi-arid areas, a strongly variable climate represents a major risk for food safety. An operational grain yield forecasting system, which could help decision-makers to make early assessments and plan annual imports, is thus needed. It can be challenging to monitor the crop canopy and production capacity of plants, especially cereals. In this context, the aim of the present study is to analyse the characteristics of two types of irrigated and non-irrigated cereals: barley and wheat. Through the use of a rich database, acquired over a period of two years for more than 30 test fields, and from 20 optical satellite SPOT/HRV images, two research approaches are considered. First, statistical analysis is used to characterize the vegetation's dynamics and grain yield, based on remotely sensed normalized difference vegetation index measurements. A relationship is established between the NDVI and LAI. Different robust relationships are established between the satellite NDVI index acquired from SPOT/HRV images, just before the time of maximum growth , and grain and straw, for barley and wheat vegetation covers. Following validation of the proposed empirical approaches, yield maps are produced for the studied site. The second approach is based on the application of a Simple Algorithm for Yield Estimation growth model, developed to simulate the dynamics of the LAI and the grain yield. An inter-comparison between ground yield measurements and SAFY model simulations reveals that yields are underestimated by this model. Finally, the combination of multi-temporal satellite measurements with the SAFY model estimations is also proposed for the purposes of yield mapping. Although the results produced by the SAFY model are found to be reasonably well correlated with those determined by satellite measurements , the grain yields are nevertheless underestimated.

Stability of rift axis magma reservoirs: spatial and temporal evolution of magma supply in the dabbahu rift segment (afar, ethiopia) over the past 30 kyr

I.Schimmelpfennig , L.Benedetti , S.Medynski , R.Pik , P.Burnard , L.France , C.Vye-Brown , K.Whaler , N.Johnson , D.Ayelew , G.Yirgu


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Unravelling the volcanic history of the Dabbahu/Manda Hararo rift segment in the Afar depression using a combination of cosmogenic surface exposure dating of basaltic lava-flows, field observations, geological mapping and geochemistry, we show in this paper that magmatic activity in this rift segment alternates between two distinct magma chambers. Recent activity in the Dabbahu rift has been fed by a seismically well-identified magma reservoir within the rift axis, and we show here that this magma body has been active over the last 30 kyr. However, in addition to this axial magma reservoir, we highlight in this paper the importance of a second, distinct magma reservoir, located 15 km west of the current axis, which has been the principal focus of magma accumulation from 15 ka to the subrecent. Magma supply to the axial reservoir substantially decreased between 20 ka and the present day, while the flank reservoir appears to have been regularly supplied with magma since 15 ka ago, resulting in less variably differentiated lavas. The trace element characteristics of magmas from both reservoirs were generated by variable degrees of partial melting of a single homogeneous mantle source, but their respective magmas evolved separately in distinct crustal plumbing systems. Magmatism in the Dabbahu/Manda Hararo rift segment is not focussed within the current axial depression but instead is spread out over at least 15 km on the western flank. This is consistent with magneto-telluric observations which show that two magma bodies are present below the segment, with the main accumulation of magma currently located below the western flank, precisely where the most voluminous recent flank volcanism is observed at the surface. Applying these observations to slow spreading mid-ocean ridges indicates that magma bodies likely have a lifetime of a least 20 ka, and that the continuity of magmatic activity is maintained by a system of separate relaying reservoirs, which could in return control the location of spreading. This long term alternation between distinct crustal reservoirs located broadly at the same location relative to the segment appears to be a key feature for organizing and maintaining active spreading centres over stable soft points in the mantle.

Recent mechanical weakening of the arctic sea ice cover as revealed from larger inertial oscillations

N.C. , J.Weiss , F.Gimbert , D.Marsan , B.Barnier


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We present a simple and analytical ocean boundary layer-sea ice coupled dynamical model that we apply to the modeling of Arctic sea ice motion in the frequency domain, and particularly in the inertial range. This study further complements our related work in an unpublished paper where the sea ice cover response to the Coriolis forcing has been studied. This analytical model allows interpretation of the spatial, seasonal and pluriannual dependence of the magnitude of the inertial oscillations detailed in terms of mechanical behavior of the ice cover. In this model, the sea ice mechanical response is simplified through the introduction of a linear internal friction term K. A dependence of K allows us to explain the associated dependence of the seasonal and regional Arctic sea ice inertial motion. In addition, a significant decrease of K, i. e. , a mechanical weakening of the sea ice cover, is observed for the period 2002-2008 compared to 1979-2001, for the entire Arctic in both seasons. These results show that the regional, seasonal and pluriannual variations of sea ice inertial motion are not only the trivial consequence of simultaneous variations of thickness and concentration. Instead, the shrinking and thinning of the Arctic sea ice cover over the last few decades has induced a mechanical weakening, which in turns has favored sea ice fracturing and deformation.

Rv SONNE Fahrtbericht / Cruise Report\ud SO234/1 SPACES : Science or the Assessment\ud of Complex Earth System Processes, 22.06. 06.07.2014, Walvis Bay / Namibia - Durban / South Africa


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SO-234/1 was a training and capacity building cruise for students from southern Africa and\ud Germany in the framework of the BMBF-funded SPACES program (Science for the Assessment of Complex Earth System Processes), a cooperative research project initiated by the relevant ministries in Namibia, South Africa, Angola and Germany. Scientifically, SO-234/1 continued geological studies regarding the temporal and geochemical evolution of the Walvis Ridge (Southeast Atlantic) conducted on the precursor SO-233 expedition, and was broadened by biological studies by University of Tübingen scientists, which aimed to get a better understanding of the adaptations of visual systems in mesopelagic animals to bioluminescence. The educational aspects on SO-234/1 comprised fully integration of the\ud students into all scientific work on board and various lectures and courses given by the senior\ud scientists during transit times.\ud The working area of SO-234/1 included several seamounts, such as the Ewing Seamount, and\ud a section of the southeastern margin of the Walvis Ridge. Due to the fair weather conditions\ud and the excellent support from the master and crew, SO-234/1 completed 18 sampling stations within only four working days. Rock sampling has been conducted using chain bag dredges. The seven SO-234/1 dredge hauls recovered in situ rocks from up to 3,500 m water depth, among them fairly fresh lava fragments and volcaniclastic rocks suitable for volcanological, geochemical, and geochronological analyses. Additionally, a TV-grab station has been conducted at Ewing Seamount but the grab failed to return hard rocks. The group of biologists conducted ten trawls at depths between 400 and 1,000 m using a rectangular midwater Tucker Trawl with an opening of 16 square meters. All trawls were successful and brought numerous animals from the junction of the meso- and bathypelagic habitats including, apart from fishes, several cephalopods, crustaceans, deep-sea jellyfish, ctenophors and many salp colonies

Atmospheric Response to Mesoscale Sea Surface Temperature Anomalies: Assessment of Mechanisms and Coupling Strength in a High-Resolution Coupled Model Over the South Atlantic

G.Nicolas , B.David , P.Lukas , F.Ivy , M.Matthias


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Many aspects of the coupling between the ocean and atmosphere at the mesoscale (on the order of 20–100 km) remain unknown. While recent observations from the Southern Ocean revealed that circular fronts associated with oceanic mesoscale eddies leave a distinct imprint on the overlying wind, cloud coverage, and rain, the mechanisms responsible for explaining these atmospheric changes are not well established. Here the atmospheric response above mesoscale ocean eddies is investigated utilizing a newly developed coupled atmosphere–ocean regional model [Consortium for Small-Scale Modeling–Regional Ocean Modelling System (COSMO-ROMS)] configured at a horizontal resolution of ~10 km for the South Atlantic and run for a 3-month period during austral winter of 2004. The model-simulated changes in surface wind, cloud fraction, and rain above the oceanic eddies are very consistent with the relationships inferred from satellite observations for the same region and time. From diagnosing the model’s momentum balance, it is shown that the atmospheric imprint of the oceanic eddies are driven by the modification of vertical mixing in the atmospheric boundary layer, rather than secondary flows driven by horizontal pressure gradients. This is largely due to the very limited ability of the atmosphere to adjust its temperature over the time scale it takes for an air parcel to pass over these mesoscale oceanic features. This results in locally enhanced vertical gradients between the ocean surface and the overlying air and thus a rapid change in turbulent mixing in the atmospheric boundary layer and an associated change in the vertical momentum flux
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