Late Quaternary Changes in Silicate Utilisation and Upwelling Intensity off Peru – Insights from Silicon and Neodymium Isotopes

The Peruvian coastal upwelling region is characterised by one of the most pronounced oxygen minimum zones in the worlds ocean. The extension and strength of bottom water oxygen depletion has varied in the past as a function of surface water primary productivity and changes in circulation and upwelling intensity. So far, it has proven difficult to disentangle these influences. In this study the stable silicon isotope composition of diatoms (δ30Si) is used to reconstruct surface water silicic acid (Si(OH)4) utilisation during primary productivity. Radiogenic neodymium isotopes (εNd) from Fe-Mn coatings and benthic foraminifers were measured to trace water masses and their mixing, and the detrital fraction was analysed to provide information about sediment provenance, weathering inputs and their transport pathways. Besides the utilisation and water mass mixing effect, other processes such as remineralisation of the diatoms in the water column and in the sediment, influence the signal that is preserved. Here, the first systematic study of the dissolved δ30Si in the water column (δ30SiSi(OH)4) and in diatoms (δ30Siopal) from the underlying sediments in a coastal upwelling region is carried out to shed light onto the importance of these processes. The results show that the δ30SiSi(OH)4 signature strongly depends on upwelling strength, i.e. supply of new nutrients. Surface waters in the realm of intense upwelling are only weakly fractionated with respect to the subsurface source water signatures, whereas surface waters are more strongly fractionated where upwelling is less pronounced due to higher utilisation of the smaller amounts of available Si(OH)4. The δ30Siopal values of picked diatoms in the underlying sediments vary within the order of the expected fractionation between surface waters and diatoms and thus serve as a basis for the reliable use of the δ30Siopal as a proxy for past upwelling conditions. The sediments were also analysed for their εNd and compared to water column measurements from the same area. In general, all phases (seawater, Fe-Mn coatings, benthic foraminifers and detrital material) display a trend from more radiogenic values in the north towards less radiogenic values in the south. This is in agreement with the distribution of the signatures of the Andean hinterland rocks. This is most likely due to extensive exchange between sediments and the water column, which makes it difficult to use the εNd signatures obtained from Fe-Mn coatings or from benthic foraminiferal carbonate as a water mass tracer. Paleo-reconstructions show, that diatom-related productivity along the Peruvian upwelling area has varied greatly during the past 20 kyr. It was characterised by low fluxes of diatom opal during the last glacial and much higher values thereafter, in particular during the early and the latest Holocene. The combined approach of δ30Siopal and the radiogenic isotope composition (Nd, Sr) of Fe-Mn coatings of sediment particles and the detrital material itself reveal that this variability has been related to changes in Si(OH)4 utilisation, mostly controlled by the supply of iron and phosphate released from the shelf sediments via upwelling. During the glacial strong upwelling of subsurface waters with an overall low nutrient content significantly diminished primary productivity. During the early and late Holocene oceanographic conditions along the shelf were alternating between stronger and weaker upwelling. Especially the last 2,500 years were characterised by the largest variability of the system of the past 20,000 years, which coincided with the onset of modern El Nino-Southern Oscillation conditions in the Pacific. The late Holocene was also disrupted by major climatic anomalies, such as the Little Ice Age (LIA). Off Peru, a permanent mean southward migration of the Intertropical Convergence Zone (ITCZ) during the LIA strongly affected the trade wind-driven strength of the upwelling causing permanent El Nino-like conditions. The δ30Siopal show that productivity and nutrient utilisation were weak. The detrital sediment fraction was dominated by local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. At the end of the LIA, the ITCZ shifted northward, which resulted in a pronounced increase in the strength of upwelling off Peru. Especially Si(OH)4 and Fe remineralisation from the shelf sediments was enhanced causing higher nutrient supply and diatom productivity. The radiogenic isotope record of the detrital shelf sediments indicates increased dust transport due to drier conditions under more persistent non-El Nino conditions. Comparison between δ30Siopal and bulk δ15N of organic matter suggests that surface water utilisation has been the predominant factor influencing both signals. The δ15N signature recorded in the sediment was not, as previously assumed, mainly influenced by subsurface water nitrate reduction processes

Silicon isotopes as a tracer for silicate utilization in the Peruvian upwelling

EGU2011-6081 Natural stable isotopes are a powerful tool in marine sciences to investigate biological processes, such as present and past nutrient utilization. In this study we present the first dissolved silicon isotope data in the upwelling area off Peru, where one of the world’s largest Oxygen Minimum Zones (OMZ) is located. Silicon is the most important component required for phytoplankton (diatom) growth, which dominates primary productivity in this region. Stable Si isotopes are fractionated during diatom growth in that the lighter Si isotopes are preferentially incorporated into diatoms with a fractionation factor of -1.1 promille. The Si isotope composition of dissolved silicic acid of the corresponding surface waters is therefore left isotopically heavier. The Si isotope composition, 30Si/28Si, is expressed as δ30Si values, which stand forh deviations from a given standard (NBS28). Investigation of the dissolved seawater Si isotope composition thus provides a measure for the utilization and, combined with information on the Si isotope composition of the water masses upwelling off Peru, it is a measure for the supply pathways of Si to the coastal upwelling centres. Surface waters on the shelf off Peru are mainly fed by the Equatorial Undercurrent, which mainly consists of waters originating from the western and Central Pacific and which has a characteristic δ30Si of +1.5 promille. In areas and during phases of intense upwelling the fractionation of Si isotopes was observed to be weaker due to upwelling-driven supply of less fractionated Si (δ30Si = 1.7 promille, from water depths of around 100-150 m, whereas under weak upwelling conditions fractionation is higher (δ30Si ~3 promille due to a more complete utilization of the available dissolved silicate. The distribution of dissolved δ30Si correlates strongly with particulate biogenic silicate (opal) concentrations in that highest opal concentrations in the surface waters show the lowest δ30Si values thus strongest upwelling intensity. The most extreme δ30Si values in surface waters (δ30Si = 4.5 promille are observed offshore where silicic acid concentrations are nearly zero. Furthermore we compare the δ30Si data with the dissolved nitrogen isotope distribution, which in addition to nitrate utilization is mainly influenced by denitrification and annamox processes in the OMZ. Combined silicon and nitrogen isotope compositions can thus help to disentangle different fractionation processes within the nitrogen cycle

HM1.24 gerichtete bispezifische single-chain-Fv Antikörper zur Therapie des Multiplen Myeloms

Das Multiple Myelom ist eine maligne Erkrankung, dessen Prognose durch die aktuellen therapeutischen Möglichkeiten deutlich gebessert, aber in der Regel weiterhin nicht heilbar ist. Die Entwicklung zusätzlicher immuntherapeutischer Strategien könnten ein möglicher Weg sein, um eine minimale Resterkrankung zu eliminieren und damit Langzeitremissionen zu erreichen. Ein vielversprechender Weg ist der Einsatz von Antikörpern. Bei der Therapie des Multiplen Myeloms spielten Antikörper bisher keine größere Rolle, da für Myelomzellen nur wenig geeignete Zielmoleküle definiert sind. HM1.24 wurde als ein Oberflächenmolekül identifiziert, welches auf terminal differenzierten B-Zellen hochexpremiert wird und auf Myelomzellen überexprimiert wird. Fc-Rezeptor-vermittelte Mechanismen wie ADCC spielen eine wichtige Rolle für die Antitumoraktivität von therapeutischen Antikörpern. Durch gezieltes Ansteuern aktivierender Fc-Rezeptoren lässt sich die therapeutische Effizienz von Antikörpern steigern. Eine Möglichkeit zur Verbesserung der Effektorzellrekrutierung bieten bispezifische Antikörper, die mit hoher Affinität an den jeweiligen aktivierenden Fc-Rezeptor binden. Die Effektorzell-vermittelte Lyse über HM1.24 kann möglicherweise durch Verwendung eines bispezifischen Antikörpers erhöht werden. In dieser Arbeit wurde ein rekombinanter bispezifischer single-chain Fv HM1.24xCD16 Antikörper (Tandem-Format) entwickelt, der die gezielte Rekrutierung von CD16-positiven Zellen ermöglicht. Ein bispezischer single-chain Fv HM1.24 x CD16 ist durch seine beiden Antigenbindungstellen in der Lage, HM1.24-positive Myelomzellen und CD16-positive Effektorzellen in räumliche Nähe zu bringen, und über die Aktivierung von diesen Effektorzellen, wie NK-Zellen und Makrophagen, eine zytotoxische Immunantwort mittels ADCC zu induzieren. Zur Herstellung des bsscFv HM1.24xCD16 wurde das scFv Fragment von einem monoklonalen HM1.24 mit dem scFv Fragment gegen CD16 kloniert und rekombinant in 293T exprimiert. Anschließend erfolgte eine zweistufige Proteinaufreinigung mittels Affinitätschromatographie über den Hexahistidin-Tag und Strep-Tag. Durch Western-Blots und Coomassie wurde kontrolliert, ob die Expression sowie die Aufreinigung erfolgreich waren. Dabei wurde eine Bande bei ca 60-65kDa detektiert, was dem erwarteten Molekulargewicht des bsscFv entspricht. Die spezifische Bindung der aufgereinigten Proteine an ihre Zielantigene, HM1.24 und CD16, wurde mittels Immunfluoreszenzanalysen an Antigen-positiven Zellen als auch an Antigen-negativen Zellen untersucht. Als nächstes wurde der bispezifischen HM1.24xCD16 auf seine Fähigkeit untersucht, die spezifische Lyse HM1.24-positiver Zellen zu induzieren durch Rekrutierung von Effektorzellen. Der Antikörper wurde für Zytotoxizitätsuntersuchungen in Form eines 51Cr-Release-Assay eingesetzt. Die Tests wurden mit frisch isolierten, unstimulierten mononukleären Zellen (MNC) aus verschiedenen gesunden Spendern und verschiedenen B-Zell-Linien/Myelomlinien sowie an primären humanen Tumorzellen durchgeführt. In vitro weist der bsscFv HM1.24xCD16 an verschiedenen Zelllinien (ARH-77, RPMI 8226, INA-6, U266, primäre humane Tumorzellen) eine höhere Lyserate auf im Vergleich zum monoklonalen HM1.24. Auch in Untersuchungen, die in Abhängigkeit der eingesetzten Antikörperkonzentrationen sowie in Abhängigkeit des Effektor-zu-Target Verhältnisses durchgeführt wurden, zeigte sich der bsscFc dem monoklonalen Antikörper überlegen. Entsprechende Kontroll-Experimente mit blockierenden Antikörpern zeigen, dass die Lyse spezifisch über den bsscFv HM1.24xCD16 induziert wird. Es wurde gezeigt, dass der rekombinante bsscFv HM1.24xCD16 NK-Zellen an Myelomzellen rekrutiert und durch zelluläre Zytotoxizität Tumorzelllyse induziert

Gender differences in the choice of field of study and the relevance of income information: Insights from a field experiment

Research consistently reports pronounced earnings differences between men and women, even among the highly educated. This article investigates whether students' responsiveness to information on income returns relates to gender differences in major choices, which might contribute to the persistent gender wage gap. We use field-experimental panel data on students in Berlin (Germany), starting one year before high school graduation. Our intervention comprised information on major-specific returns to college and was provided to students in randomly selected schools. By comparing the major-specific application decisions of "treated" and "untreated" high school seniors, we examine whether, and why, male and female students respond differently to this information. As potential mechanisms behind a gender-specific treatment effect, we analyze the role of gender stereotypes and roles associated with certain job attributes. We find that providing income information on college majors only influences the major choices of male (not female) students with college intention: treated male students on average applied to majors associated with higher mean income. Further analyses suggest that this gender difference in the treatment effect cannot be explained by differential distributions or effects of preferred job attributes

Applying to college: do information deficits lower the likelihood of college-eligible students from less-privileged families to pursue their college intentions? Evidence from a field experiment

Information deficits are considered an important source of why students from less-privileged families do not enroll in college, even when they are college-eligible and intend to go to college. In this paper, we examine whether correct and detailed information on the costs of and returns to higher education increases the likelihood of college applications of less-privileged high school graduates who expressed college intentions in their junior high school year. We employ an experimental design with a randomly assigned 25-minute information treatment about funding opportunities for, and returns to, higher education given at Berlin schools awarding university entrance qualifications. Our analyses show that our information treatment indeed substantially increases the likelihood of treated less-privileged students to apply to college. Our study indicates that our low-cost provision of financial information not only increased their college knowledge but also substantially changed their college application behavior, despite other existing barriers, like economic constraints

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to Late Pliocene/Early Pleistocene climate cooling

The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilisation in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Late Pliocene/Early Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to Late Pliocene/Early Pleistocene cooling

Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age

For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (δ30Siopal) and nitrogen (δ15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (εNd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, δ15Nsed values of ~ +5‰ and intermediate δ30Siopal values of ~+0.97‰. At the same time the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were caused by permanent El Niño-like conditions characterized by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, δ30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by δ15Nsed of up to ~ +7‰, and by the highest degree of silicate utilisation with δ30Siopal reaching values of +1.1‰. At the same time detrital εNd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA indicating significantly increased nutrient availability. Comparison between the δ30Siopal and δ15Nsed signatures suggests that during the past 650 years the δ15Nsed signature in the Peruvian Upwelling area has most likely primarily been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column

Changes in diatom productivity and upwelling intensity off Peru since the Last Glacial Maximum: Response to basin-scale atmospheric and oceanic forcing

New records of stable silicon isotope signatures (δ30Si) together with concentrations of biogenic opal and organic carbon from the central (9° S) and northern (5° S) Peruvian margin reveal changes in diatom productivity and nutrient utilization during the past 20,000 years. The findings are based on a new approach using the difference between the δ30Si signatures of small (11-32μm) and large (>150μm) diatom fractions (Δ30Sicoscino-bSi) in combination with the variance in diatom assemblages for reconstruction of past upwelling intensity. Combination of our records with two previously published records from the southern upwelling area off Peru (12-15° S) shows a general decoupling of the environmental conditions at the central and southern shelf mainly caused by a northward shift of the main upwelling cell from its modern position (12-15° S) towards 9° S during Termination 1. At this time only moderate upwelling intensity and productivity levels prevailed between 9° S and 12° S interpreted by a more northerly position of Southern Westerly Winds and the South Pacific Subtropical High. Furthermore, a marked decrease in productivity at 12-15° S during Heinrich Stadial 1 coincided with enhanced biogenic opal production in the Eastern Equatorial Pacific, which was induced by a southward shift of the Intertropical Convergence zone and enhanced northeasterly trade winds. Modern conditions were only established at the onset of the Holocene. Past changes in preformed δ30Si signatures of subsurface waters reaching the Peruvian Upwelling System did not significantly affect the preserved δ30Si signatures