The potential of dust detection by means of µXRF scanning in Eifel maar lake sediments

Mittels kontinuierlicher und hochauflösender μXRF-Geochemieanalysen wird die Variabilität äolischer Sedimente der letzten 60.000 Jahre rekonstruiert. Dazu werden zwei Sedimentbohrkerne jeweils aus einem Maarsee und einem Trockenenmaar (Eifel, Deutschland) untersucht. Beide Kerne umfassen das letzte Glazial, einschließlich des MIS-3, des LGM und MIS-2, Transition I als auch das Holozän. Die energiedispersive RFA-Messungen der Eagle III μXRF wird direkt an Harz imprägnierten Proben angewendet. Diese sogenannten Tränklinge bilden die Grundlage für die Herstellung von petrographischen Dünnschliffen und somit können die Messergebnisse direkt mit einer Mikrofaziesanalyse verglichen werden. Anhand eines Sedimentkerns wird gezeigt, dass eine Quantifizierung der μXRF-Ergebnisse mittels der undamentalparametermethode geeignete ist. Eine Überprüfung der Ergebnisse findet dabei mit wellenlängen-dispersiven RFA-Messungen an diskreten Proben statt. Die Ergebnisse zeigen, dass sich jedes einzelne Maar in der lithologischen Zusammensetzung und damit auch geochemisch unterscheidet. Deshalb wird auf die grundlegenden Prozesse der Elementdeposition in die Seen eingegangen, die mit der Ablagerung von Sedimenten, der Variabilität der chemischen Verwitterung oder der Wasserzirkulation in Zusammenhang stehen. Mittels Hauptkomponentenanalysen standardisierter Variablen ist darüber hinaus die objektive Ableitung eines äolischen Sedimentsignals möglich. Es wird gezeigt, dass dieser Ansatz verlässliche Ergebnisse für alle untersuchten Zeitabschnitte liefert, solange für die Interpretation weitere Kenntnisse über die Lithologie und Paläoökologie zur Verfügung stehen. Das auffälligste Element zur Charakterisierung von Staub ist in beiden untersuchten Kernen Kalzium. Die höchsten Werte (>5 Gew.-%) werden während vollglazialer Bedingungen erreicht. Kalzium hat einen wesentlichen Einfluss auf den Staubfaktor der Hauptkomponentenanalyse. Eine zusätzliche Kombination der Kalziumgehalte mit dem Staubfaktor der Hauptkomponentenanalyse sowie Grauwertmessungen verbessert den Nachweis äolischen Staubs in laminierten Seesedimenten zusätzlich. In beiden Kernen konnten Sedimente mit erhöhten Staubkonzentrationen geochemisch nachgewiesen werden: Während des MIS-3 sind das vor allem das größte Heinrich-Ereignis H4 sowie der Anstieg des atmosphärischen Staubgehalts während der Wiedervereisung der Inlandsgletscher. Weiterhin ist das gesamte MIS-2 einschließlich LGM und der Jüngeren Dryas von starker Staubdeposition charakterisiert. Eine erhöhte Staubkonzentration ist ebenfalls ab dem Subboreal nachgewiesen und wird als anthropogene Aktivität gedeutet.researc

Terrigenous plant wax inputs to the Arabian Sea : implications for the reconstruction of winds associated with the Indian Monsoon

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 69 (2005): 2547-2558, doi:10.1016/j.gca.2005.01.001.We have determined the accumulation rates and carbon isotopic compositions (δ13C) of long-chain (C24–C32) terrigenous plant wax fatty acids in 19 surface sediment samples geographically distributed throughout the Arabian Sea in order to assess the relationship between plant wax inputs and the surrounding monsoon wind systems. Both the accumulation rate data and the δ13C data show that there are three primary eolian sources of plant waxes to the Arabian Sea: Africa, Asia, and the Arabian Peninsula. These sources correspond to the three major wind systems in this region: the summer (Southwest) monsoon, the winter (Northeast) monsoon, and the summer northwesterlies that blow over the Arabian Peninsula. In addition, plant waxes are fluvially supplied to the Gulf of Oman and the Eastern African margin by nearby rivers. Plant wax δ13C values reflect the vegetation types of the continental source regions. Greater than 75% of the waxes from Africa and Asia are derived from C4 plants. Waxes delivered by northwesterly winds reflect a greater influence (25–40%) of C3 vegetation, likely derived from the Mesopotamian region. These data agree well with previously published studies of eolian dust deposition, particularly of dolomite derived from the Arabian Peninsula and the Mesopotamian region, in surface sediments of the Arabian Sea. The west-to-east gradient of plant wax δ13C and dolomite accumulation rates are separately useful indicators of the relationship between the northwesterly winds and the winds of the Southwest monsoon. Combined, however, these two proxies could provide a powerful tool for the reconstruction of both southwest monsoon strength as well as Mesopotamian aridity.This work was supported by a SGER grant from the National Science Foundation to D.O. and a Schlanger Ocean Drilling Fellowship to K.D

Faecal Steroids and n-Alkanes in Lake Sediments

Lake sediments are used as archives for climate and environmental reconstructions. This study investigated if biomarker analyses in lake sediments can be used to reconstruct anthropogenic landscape modifications during Holocene. In contrast to the mineral matrix of sediments and e.g. pollen, plant macro remains and charcoal particles, biomarkers can be more easily translocated within soil profiles before erosion and deposition. Furthermore, a translocation can also occur in lake sediments. Therefore, we tested if biomarker concentrations and patterns correlated with pollen patterns and further paleo environmental proxies in sediments of two maar lakes in the Eifel region. Five core sections of Lake Holzmaar and two core sections of Lake Ulmener Maar were sampled. The analysed core sections contain ca. 10 000 years and a number of data existed from previous analyses (ELSA project). As example for biomarkers for the reconstruction of vegetation changes, n-alkanes were analysed. Steroids incl. bile acids were used as proxies for the deposition of faeces of animals (animal husbandry). Patterns of n-alkanes correlated with pollen data. Parts of the core that show characteristics of dense forest in the catchment area had relatively low amounts of faecal steroids and the steroid patterns indicated the presence of several different animals. In parts of the core that show characteristics for grassland and agricultural fields, faecal steroids showed the presence of animal husbandry. The correlation of biomarker concentrations with pollen data and other data showed that it possible to detect changes in vegetation and land use with biomarker analyses within the catchment area of the two maar lakes

Sea surface temperature pattern reconstructions in the Arabian Sea

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA1014, doi:10.1029/2005PA001162.Sea surface temperature (SST) and seawater δ18O (δ18Ow) were reconstructed in a suite of sediment cores from throughout the Arabian Sea for four distinct time intervals (0 ka, 8 ka, 15 ka, and 20 ka) with the aim of understanding the history of the Indian Monsoon and the climate of the Arabian Sea region. This was accomplished through the use of paired Mg/Ca and δ18O measurements of the planktonic foraminifer Globigerinoides ruber. By analyzing basin-wide changes and changes in cross-basinal gradients, we assess both monsoonal and regional-scale climate changes. SST was colder than present for the majority of sites within all three paleotime slices. Furthermore, both the Indian Monsoon and the regional Arabian Sea mean climate have varied substantially over the past 20 kyr. The 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2.5°–3.5°C attributable, in part, to the influences of glacial atmospheric CO2 concentrations and large continental ice sheets. The elimination of the cross-basinal SST gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength. Changes in δ18Ow that are smaller than the δ18O signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing. SSTs throughout the Arabian Sea were still cooler than present by an average of 1.4°C in the 8 ka time slice. These cool SSTs, along with lower δ18Ow throughout the basin, are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation. The results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling.Analyses were funded by a SGER grant from the NSF (OCE03–34598). Funding was also provided by a Schlanger Ocean Drilling Program Fellowship (to K.A.D.) and NSF Grant OCE02–20776 (to D.W.O.). 1

IRSL Signals from Maar Lake Sediments Stimulated at Various Temperatures

Optisch stimulierte Lumineszenz (OSL) und infrarot stimulierte Lumineszenz (IRSL) wurden an sieben Feinkorn Proben von Kern JW3 aus dem Trockenmaar Jungfernweiher gemessen. Zwei verschiedene post-IR IRSL Messprotokolle (blaue Detektion) wurden an den polymineralischen Feinkörnern (4–11 μm) angewandt. Diese Protokolle beinhalten eine Stimulation mit IR bei 50°C für bis zu 200 s vor einer weiteren IR Stimulation bei erhöhten Temperaturen bei 225°C für 100 s oder 290°C für 200 s. Die OSL von Quarz sättigt bei Dosen von 260–300 Gy und die De-Werte, die mit IRSL bei 50°C (IR50) erhalten werden, nehmen mit der Tiefe nicht zu. Dies weist darauf hin, dass auch dieses Signal bei ~500 Gy in Sättigung geht. De-Werte des post-IR IRSL Signals bei 225°C (pIRIR225) und 290°C (pIRIR290) nehmen jedoch mit der Tiefe von ~800 Gy bis ~1400 Gy zu, und zeigen ein korrigiertes Minimalalter von ~200 ka für die jüngsten Sedimente an. Die durchschnittlichen im Labor gemessene Fadingraten liegen für IR50 bei 4.09 ± 0.02%/decade und für pIRIR225 bei 2.55 ± 0.14%/decade. Für Probe JWS1 wurde für pIRIR290 ein g-value von 0.52 ± 1.12%/decade gemessen. Sowohl fading korrigierte pIRIR225 als auch unkorrigierte pIRIR290 De-Werte der jüngsten Probe (~16 m unterhalb der heutigen Erdoberfläche) weisen auf ein Alter von ~250 ka für die oberste Probe hin. Für die ältesten Proben, die in ~94 m unterhalb der heutigen Erdoberfläche genommen wurden, wurden Alter von bis zu ~400 ka gemessen.researc

Coupled sea surface temperature-seawater delta O-18 reconstructions in the Arabian Sea at the millennial scale for the last 35 ka

Two sediment cores from the western (905; 10.46°9′N, 51.56°4′E, water depth 1586 m) and eastern (SK17; 15°15′N, 72°58′E, water depth 840 m) Arabian Sea were used to study past sea surface temperatures (SST) and seawater δ 18O (δ 18Ow) variations for the past 35 ka. We used coupled Mg/Ca-δ 18O calcite variability in two planktonic foraminiferal species: Globigerinoides ruber, which thrives throughout the year, and Globigerina bulloides, which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing. SSTs in both areas based on Mg/Ca in G. ruber were ∼3 to 4°C lower during the Last Glacial Maximum (LGM; ∼21 ka) than today and the Holocene period. The SST records based on G. bulloides also indicate general cooling, down to 18°C in both areas. SSTs in the western Arabian Sea based on G. bulloides were always lower than those based on G. ruber, indicating the presence of strong seasonal temperature contrast during the Holocene and LGM. We interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling (SW monsoon) and winter convective mixing (NE monsoon) in the western Arabian Sea. In the eastern Arabian Sea, G. bulloides-based SSTs were slightly lower (about 1°C) than G. ruber-based SSTs during the Holocene, indicating the almost absence of a seasonal temperature gradient, similar to today. However, a large seasonal temperature contrast occurred during the LGM which favors the assumption that strong NE monsoon winds forced winter upwelling or convective mixing offshore Goa. SST and δ 18Ow reconstructions reveal evidence of millennial-scale cycles, particularly in the eastern Arabian Sea. Here, the stadial periods (Northern Hemisphere cold periods such as Younger Dryas and Heinrich events) are marked by increasing SSTs and salty sea surface conditions relative to those during the interstadial periods. Indeed, the δ 18Ow record shows evidence of low-saline surface waters during interstadial periods, indicating increased freshwater runoff from the Western Ghats as a consequence of enhanced SW monsoon intensity

Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea : influence of global sea level change on hydrography

Stable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive δ18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53‰ and 55‰ are inferred from pteropod and benthic foraminifera δ18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic δ18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates

Processes controlling the geochemical composition of the South China Sea sediments during the last climatic cycle

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 257 (2008): 240-246, doi:10.1016/j.chemgeo.2008.10.002.Sediments of the upper 28.2 meters of Ocean Drilling Program (ODP) Site 1145 from the northern South China Sea (SCS) were analyzed for their geochemical composition. Most of the major and trace elements exhibit significant fluctuations at glacial-interglacial scales, implying a close relation with regional and global climate change. Al-normalized elemental ratios can be subdivided into three principal components (PC). PC1 (e.g., Ca/Al, Ba/Al, Sr/Al) displays significant glacial-interglacial variation and is related to paleoproductivity in the northern SCS. PC2 (e.g., K/Al, Mg/Al, Rb/Al) is associated with the degree of chemical weathering in the source regions and shows little glacial-interglacial variation. PC3 (e.g., Ti/Al, Zr/Al) reflects the relative contribution of coarse- and fine-grained materials in the terrigenous components of the SCS sediments, likely associated with changes in sea level and monsoon-induced fluvial input. Spectral analyses indicate that paleoproductivity (i.e., Ba/Al) in the South China Sea lags Hulu/Sanbao speleothem δ18O record (a indicator of annual average meteoric precipitation) by 102° and Indian summer monsoon (multi-proxy stack) by 23° at the precession band, indicating a close relationship with the Indian summer monsoon. However, the chemical weathering degree in the source area (PC2) is not sensitive to monsoon-related changes at the precession band during the last climatic cycle.This study was supported by the NSFC to Y.B. Sun and the US NSF to D.W. Oppo (OCE 0502960) and S.C. Clemens (OCE 0352215)

Tectonic and climatic controls on rift escarpments: Erosion and flexural rebound of the Dhofar passive margin (Gulf of Aden, Oman)

International audienceWe investigate the respective roles of climatic parameters and the flexural rigidity of the lithosphere in the erosion history and behavior of two adjacent rift escarpments along the northern coast of the Gulf of Aden, in Oman. At this 25 Myr old passive margin, we define a type 1 scarp, which is high, sharp-crested and has retreated 25-30 km inland from its master fault, and a type 2 scarp, which exhibits a more rounded profile, lower relief, and still coincides with its mapped normal fault trace. Since about 15 Ma, the margin has been seasonally affected by monsoon precipitation but with contrasting effects at the type 1 and type 2 escarpments depending on the position of the Intertropical Convergence Zone in the geologic past: during peak monsoon conditions, both scarps experienced heavy rainfall and runoff, whereas during monsoon-starved conditions (such as today), the type 2 scarp experienced a foggy, moist climate while the type 1 scarp remained much drier. In order to assess the relative effects of climate and flexural parameters on the present-day morphology of the Dhofar margin, we present onedimensional numerical models of erosion and flexure along two profiles representative of the type 1 and type 2 scarps. Unlike most surface process models previously published, where present-day topography is the only criterion by which to evaluate the quality of model outputs, model behavior here is additionally constrained by independent estimates of denudation provided by geological cross sections, well-defined fault traces, and other stratigraphic markers. The best fitting models indicate that the type 1 escarpment formed under relatively arid climatic conditions and was affected by significant erosion, recession and flexural uplift due to a low (7 km) effective elastic thickness. In contrast, the morphology of the type 2 fault scarp was smoothed by a more humid climate, but a high effective elastic thickness ( 15 km) prevented it from uplifting or receding. In addition, we show that the sedimentary load acting at the foot of the escarpments exerts significant influence on their morphological evolution, though this parameter is often neglected in other scarp evolution models