Glacial reduction of AMOC strength and long term transition in weathering inputs into the Southern Ocean since the Mid Miocene: Evidence from radiogenic Nd and Hf isotopes

Combined seawater radiogenic hafnium (Hf) and neodymium (Nd) isotope compositions were extracted from bulk sediment leachates and foraminifera of Site 1088, ODP Leg 177, 2082 m water depth on the Agulhas Ridge. The new data provide a continuous reconstruction of long and short-term changes in ocean circulation and continental weathering inputs since the Mid-Miocene. Due to its intermediate water depth the sediments of this core sensitively recorded changes in admixture of North Atlantic Deep Water (NADW) to the Antarctic Circumpolar Current (ACC) as a function of the strength of the Atlantic Meridional Overturning Circulation (AMOC). Nd isotope compositions (εNd) range from -7 to -11 with glacial values generally 1 to 3 units more radiogenic than during the interglacials of the Quaternary. The data reveal episodes of significantly increased AMOC strength during late Miocene and Pliocene warm periods whereas peak radiogenic εNd values mark a strongly diminished AMOC during the major intensification of Northern Hemisphere Glaciation near 2.8 Ma and in the Pleistocene after 1.5 Ma. In contrast, the Hf isotope compositions (εHf) show an essentially continuous evolution from highly radiogenic values of up to +11 during the Miocene to less radiogenic present day values (+2 to +4) during the late Quaternary. The data document a long-term transition in dominant weathering inputs, where inputs from the South America are replaced by those from Southern Africa. Moreover, radiogenic peaks provide evidence for the supply of radiogenic Hf originating from Patagonian rocks to the Atlantic sector of the Southern Ocean via dust inputs

Peak Last Glacial weathering intensity on the North American continent recorded by the authigenic Hf isotope composition of North Atlantic deep-sea sediments

We have retrieved radiogenic hafnium (Hf) isotope compositions (ɛHf) from authigenic Fe–Mn oxyhydroxides of deep northwest Atlantic sediments deposited over the past 26 ka to investigate the oceanic evidence of changes in dissolved weathering inputs from NE America during the last deglaciation. The extraction of seawater-derived Hf isotopic compositions from Fe–Mn oxyhydroxides is not a standard procedure. Comparisons between the Al/Hf ratios and Hf isotopic compositions of the chemically extracted authigenic phase on the one hand, and those of the corresponding detrital fractions on the other, provide evidence that the composition of past seawater has been reliably obtained for most sampled depths with our leaching procedures. This is endorsed most strongly by data for a sediment core from 4250 m water depth at the deeper Blake Ridge, for which consistent replicates were produced throughout. The Hf isotopic composition of the most recent sample in this core also closely matches that of nearby present day central North Atlantic seawater. Comparison with previously published seawater Nd and Pb isotope compositions obtained on the same cores shows that both Hf and Pb were released incongruently during incipient chemical weathering, but responded differently to the deglacial retreat of the Laurentide Ice Sheet. Hafnium was released more congruently during peak glacial conditions of the Last Glacial Maximum (LGM) and changed to typical incongruent interglacial ɛHf signatures either during or shortly after the LGM. This indicates that some zircon-derived Hf was released to seawater during the LGM. Conversely, there is no clear evidence for an increase in the influence of weathering of Lu-rich mineral phases during deglaciation, possibly since relatively unradiogenic Hf contributions from feldspar weathering were superimposed. While the authigenic Pb isotope signal in the same marine sediment samples traced peak chemical weathering rates on continental North America during the transition to the Holocene a similar incongruent excursion is notably absent in the Hf isotope record. The early change towards more radiogenic ɛHf in relation to the LGM may provide direct evidence for the transition from a cold-based to a warm-based Laurentide Ice Sheet on the Atlantic sector of North America

Die Bodenseeregion - eine Wachstumsregion im Verborgenen

Die Bodenseeregion ist eine Grenzregion, in der eine vielfältige Zusammenarbeit zwischen den vier Anrainerstaaten Deutschland, Österreich, Schweiz und Liechtenstein stattfindet. Es handelt sich um eine Region ohne ein eigentliches städtisches Zentrum, die durch eine polyzentrische Siedlungsstruktur mit mehren Oberzentren geprägt ist. Trotz ihrer peripheren Lage zwischen den Metropolräumen hat sich die Region wirtschaftlich gesehen über lange Zeit sehr positiv entwickelt. Dies gilt vor allem für den produzierenden Sektor, der in der Region eine dominierende Rolle spielt und durch stark regional verankerte, aber global tätige Unternehmen geprägt ist. In der Außenwahrnehmung spiegelt sich dies aber nicht und wird die Region vor allem mit dem Tourismus in Verbindung gebracht, der aber ökonomisch mit einem Anteil von rd. 3% an der Wertschöpfung eine untergeordnete Rolle spielt. Eine gemeinsame Wirtschaftsförderpolitik für die Gesamtregion existiert bislang nicht. Zwar gibt es derzeit Ansätze für ein gemeinsames bodenseeweites Standortmarketing, inwieweit sich dieses aber aufgrund der unterschiedlichen Wirtschaftsförderungspolitik in den einzelnen Ländern durchsetzen kann, wird sich zeigen. Gemeinsam mit Fragen einer nachhaltigen Raumnutzung liegen hier die größten Herausforderungen für die künftige Entwicklung der Region.The Lake Constance region is a border region in which there are many diverse forms of cooperation between the four neighbouring countries of Germany, Austria, Switzerland and Liechtenstein. The region has no real urban centre but is characterised by a polycentric settlement structure with a number of major regional centres. Despite its peripheral location between metropolitan regions the area has displayed very positive economic development over a long period of time. This is particularly true for the manufacturing sector, which plays a dominating role in the region and is characterised by regionally rooted companies that are also globally active. External perceptions of the region do not reflect this situation but tend to associate the region with tourism, which with about 3% value added only plays a subsidiary role in economic terms. A joint economic promotion policy for the entire region does not yet exist but joint location marketing for the whole of the Lake Constance area is currently being introduced. However, owing to the different economic promotion policies of the individual countries, it is as yet unclear to what extent this initiative can be enforced. Together with questions related to the sustainable use of space this issue presents the greatest challenges for the future development of the region

Using bi-spectral imaging technology for simulated online-weed control in winter wheat and maize

In spring 2011, two field trials on site-specific weed control in winter wheat and maize were carried out at Ihinger Hof research station of the University of Hohenheim. For the image acquisition, bi-spectral cameras were mounted on a vehicle. These cameras are able to take images free from disturbances by soil, mulch and stones. Images and the corresponding GPS-data were stored on-the-go. Afterwards, the images were analyzed by a weed recognition software. Weed infestation was mapped in consideration of weed species and weeds grouped according to their herbicide sensitivity. In order to simulate an online herbicide application, a onesided moving average of order five was used for the weed mapping. This kind of rearward calculation uses only the data of weed infestation which were already assessed behind or directly in the current position of the vehicle. The calculated weed distribution maps were checked by visual grid sampling. Herbicide application maps were generated by applying weed thresholds on the weed distribution maps. The herbicide application based on the maps was conducted by a multiple sprayer which allows the application of up to three herbicides independently from each other in a single pass across the field. Later on, the performance of the herbicide application was controlled again by visual grid sampling. Compared to a uniform herbicide application, the sitespecific weed control saved 83 % and 58 % herbicides respectively in winter wheat and 66 % in maize. The average efficacy of the site-specific herbicide application system in winter wheat was 70 % of the conventional herbicide application. Keywords: Bi-spectral cameras, herbicide application, image analysis, site-specific, weed controlSimulation einer online Unkrautkontrolle in Winterweizen und Mais unter Verwendung von BispektralkamerasIm Frühjahr 2011 wurden auf der Versuchsstation Ihinger Hof der Universität Hohenheim Feldversuche zur teilschlagspezifischen online-Unkrautkontrolle in den Kulturen Winterweizen und Mais durchgeführt. Die Bildaufnahme für die Erfassung der Verunkrautung mit Hilfe von digitaler Bildverarbeitung erfolgte mit einem Kamerafahrzeug, auf welchem Bispektralkameras montiert waren. Die Verwendung dieser Kameras gewährleistet die Aufnahme von Bildern, die von Boden, Steinen und Mulch weitestgehend ungestört sind. Zusammen mit den Bildern wurden die korrespondierenden Geokoordinaten gespeichert. Nach der anschließenden Bildauswertung unter Verwendung digitaler Bildauswerteverfahren erfolgte eine Kartierung der ermittelten Verunkrautung nach Unkrautarten bzw. Unkräuter gruppiert gemäß der Herbizidempfindlichkeit. Für die Kartierung wurden einseitig gleitende Mittelwerte der fünften Ordnung berechnet. Die Bestimmung des Mittelwertes erfolgte jeweils mit den vier Messwerten die zeitlich gesehen hinter dem aktuellen Messwert lagen und dem aktuellen Messwert. Durch diese rückwärtsgewandte Mittelwertbildung wurde die online Bildverarbeitung simuliert. Zur Überprüfung der Plausibilität der berechneten Unkrautverteilungskarten wurden die aus einer visuellen Rasterbonitur stammenden Daten herangezogen.Unter Verwendung von Schadschwellen wurden die auf der Basis der Bildanalyse erstellten Unkrautverteilungskarten für die Berechnung von Applikationskarten benutzt. Die Umsetzung der Applikationskarten erfolgte mit einer Dreikammerspritze, welche eine simultane Applikation von bis zu drei Herbiziden unabhängig voneinander erlaubt. Eine Erfolgskontrolle der durchgeführten Herbizidapplikation erfolgte im zeitlichen Abstand wiederum anhand einer visuellen Rasterbonitur. Im Vergleich zur betriebsüblichen Variante wurde durch die teilschlagspezifische Herbizidapplikation im Winterweizen eine Herbizideinsparung von 83 % bzw. 58 % und im Mais von 66 % realisiert. Die durchschnittliche Wirksamkeit der teilschlagspezifischen Herbizidmaßnahme im Winterweizen betrug 70 % der betriebsüblichen Variante. Stichwörter: Bildverarbeitung, Bispektralkameras, Herbizidapplikation, teilschlagspezifisch, Unkrautkontroll

Northern Sourced Water dominated the Atlantic Ocean during the Last Glacial Maximum

Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO2 concentrations. Remineralized carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here, we present new sediment-derived bottom-water neodymium isotope records that allow fingerprinting of water masses and provide a more complete picture of the Atlantic Meridional Overturning Circulation geometry during the Last Glacial Maximum. These results suggest that the vertical and meridional structure of the Atlantic water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern-sourced water substantially expanding to shallower depths and farther into the Northern Hemisphere than today, which had been previously inferred from stable carbon isotope (δ13C) reconstructions. We argue that depleted δ13C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern-sourced water. Instead, these values may represent a northern-sourced water mass with lower than modern preformed δ13C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation, corroborating previous evidence

A boundary exchange influence on deglacial neodymium isotope records from the deep western Indian Ocean

The use of neodymium (Nd) isotopes to reconstruct past water mass mixing relies upon the quasi-conservative behaviour of this tracer, whereas recent studies in the modern oceans have suggested that boundary exchange, involving the addition of Nd from ocean margin sediments, may be an important process in the Nd cycle. Here we suggest that the relative importance of water mass advection versus boundary exchange can be assessed where the deep western boundary current in the Indian Ocean flows past the Madagascan continental margin; a potential source of highly unradiogenic Nd. Foraminiferal coatings and bulk sediment reductive leachates are used to reconstruct bottom water Nd isotopic composition (εNd) in 8 Holocene age coretops, with excellent agreement between the two methods. These data record spatial variability of ∼4 εNd units along the flow path of Circumpolar Deep Water; εNd≈−8.8 in the deep southern inflow upstream of Madagascar, which evolves towards εNd≈−11.5 offshore northern Madagascar, whereas εNd≈−7.3 where deep water re-circulates in the eastern Mascarene Basin. This variability is attributed to boundary exchange and, together with measurements of detrital sediment εNd, an isotope mass balance suggests a deep water residence time for Nd of ≤400 yr along the Madagascan margin. Considering deglacial changes, a core in the deep inflow upstream of Madagascar records εNd changes that agree with previous reconstructions of the Circumpolar Deep Water composition in the Southern Ocean, consistent with a control by water mass advection and perhaps indicating a longer residence time for Nd in the open ocean away from local sediment inputs. In contrast, sites along the Madagascan margin record offset εNd values and reduced glacial–interglacial variability, underlining the importance of detecting boundary exchange before inferring water mass source changes from Nd isotope records. The extent of Madagascan boundary exchange appears to be unchanged between the Holocene and Late Glacial periods, while a consistent shift towards more radiogenic εNd values at all sites in the Late Glacial compared to the Holocene may represent a muted signal of a change in water mass source or composition

Reactivity of neodymium carriers in deep sea sediments: Implications for boundary exchange and paleoceanography

The dissolved neodymium (Nd) isotopic distribution in the deep oceans is determined by continental weathering inputs, water mass advection, and boundary exchange between particulate and dissolved fractions. Reconstructions of past Nd isotopic variability may therefore provide evidence on temporal changes in continental weathering inputs and/or ocean circulation patterns over a range of timescales. However, such an approach is limited by uncertainty in the mechanisms and importance of the boundary exchange process, and the challenge in reliably recovering past seawater Nd isotopic composition (εNd) from deep sea sediments. This study addresses these questions by investigating the processes involved in particulate–solution interactions and their impact on Nd isotopes. A better understanding of boundary exchange also has wider implications for the oceanic cycling and budgets of other particle-reactive elements. Sequential acid-reductive leaching experiments at pH ∼2–5 on deep sea sediments from the western Indian Ocean enable us to investigate natural boundary exchange processes over a timescale appropriate to laboratory experiments. We provide evidence that both the dissolution of solid phases and exchange processes influence the εNd of leachates, which suggests that both processes may contribute to boundary exchange. We use major element and rare earth element (REE) data to investigate the pools of Nd that are accessed and demonstrate that sediment leachate εNd values cannot always be explained by admixture between an authigenic component and the bulk detrital component. For example, in core WIND 24B, acid-reductive leaching generates εNd values between −11 and −6 as a function of solution/solid ratios and leaching times, whereas the authigenic components have εNd ≈ −11 and the bulk detrital component has εNd ≈ −15. We infer that leaching in the Mascarene Basin accesses authigenic components and a minor radiogenic volcanic component that is more reactive than Madagascan-derived clays. The preferential mobilisation of such a minor component demonstrates that the Nd released by boundary exchange could often have a significantly different εNd composition than the bulk detrital sediment. These experiments further demonstrate certain limitations on the use of acid-reductive leaching to extract the εNd composition of the authigenic fraction of bulk deep sea sediments. For example, the detrital component may contain a reactive fraction which is also acid-extractible, while the incongruent nature of this dissolution suggests that it is often inappropriate to use the bulk detrital sediment elemental chemistry and/or εNd composition when assessing possible detrital contamination of leachates. Based on the highly systematic controls observed, and evidence from REE patterns on the phases extracted, we suggest two approaches that lead to the most reliable extraction of the authigenic εNd component and good agreement with foraminiferal-based approaches; either (i) leaching of sediments without a prior decarbonation step, or (ii) the use of short leaching times and low solution/solid ratios throughout

Late activation of the 9-oxylipin pathway during arbuscular mycorrhiza formation in tomato and its regulation by jasmonate signalling

The establishment of an arbuscular mycorrhizal (AM) symbiotic interaction is a successful strategy for the promotion of substantial plant growth, development, and fitness. Numerous studies have supported the hypothesis that plant hormones play an important role in the establishment of functional AM symbiosis. Particular attention has been devoted to jasmonic acid (JA) and its derivates, which are believed to play a major role in AM symbiosis. Jasmonates belong to a diverse class of lipid metabolites known as oxylipins that include other biologically active molecules. Recent transcriptional analyses revealed up-regulation of the oxylipin pathway during AM symbiosis in mycorrhizal tomato roots and indicate a key regulatory role for oxylipins during AM symbiosis in tomato, particularly those derived from the action of 9-lipoxygenases (9-LOXs). Continuing with the tomato as a model, the spatial and temporal expression pattern of genes involved in the 9-LOX pathway during the different stages of AM formation in tomato was analysed. The effects of JA signalling pathway changes on AM fungal colonization were assessed and correlated with the modifications in the transcriptional profiles of 9-LOX genes. The up-regulation of the 9-LOX oxylipin pathway in mycorrhizal wild-type roots seems to depend on a particular degree of AM fungal colonization and is restricted to the colonized part of the roots, suggesting that these genes could play a role in controlling fungal spread in roots. In addition, the results suggest that this strategy of the plant to control AM fungi development within the roots is at least partly dependent on JA pathway activation

Influence of the Amazon River on the Nd isotope composition of deep water in the western equatorial Atlantic during the Oligocene–Miocene transition

Dissolved and particulate neodymium (Nd) are mainly supplied to the oceans via rivers, dust, and release from marine sediments along continental margins. This process, together with the short oceanic residence time of Nd, gives rise to pronounced spatial gradients in oceanic 143Nd/144Nd ratios (εNd). However, we do not yet have a good understanding of the extent to which the influence of riverine point-source Nd supply can be distinguished from changes in mixing between different water masses in the marine geological record. This gap in knowledge is important to fill because there is growing awareness that major global climate transitions may be associated not only with changes in large-scale ocean water mass mixing, but also with important changes in continental hydroclimate and weathering. Here we present εNd data for fossilised fish teeth, planktonic foraminifera, and the Fe–Mn oxyhydroxide and detrital fractions of sediments recovered from Ocean Drilling Project (ODP) Site 926 on Ceara Rise, situated approximately 800 km from the mouth of the River Amazon. Our records span the Mi-1 glaciation event during the Oligocene–Miocene transition (OMT; ∼23 Ma). We compare our εNd records with data for ambient deep Atlantic northern and southern component waters to assess the influence of particulate input from the Amazon River on Nd in ancient deep waters at this site. εNd values for all of our fish teeth, foraminifera, and Fe–Mn oxyhydroxide samples are extremely unradiogenic (εNd ≈ −15); much lower than the εNd for deep waters of modern or Oligocene–Miocene age from the North Atlantic (εNd ≈ −10) and South Atlantic (εNd ≈ −8). This finding suggests that partial dissolution of detrital particulate material from the Amazon (εNd ≈ −18) strongly influences the εNd values of deep waters at Ceara Rise across the OMT. We conclude that terrestrially derived inputs of Nd can affect εNd values of deep water many hundreds of kilometres from source. Our results both underscore the need for care in reconstructing changes in large-scale oceanic water-mass mixing using sites proximal to major rivers, and highlight the potential of these marine archives for tracing changes in continental hydroclimate and weathering